[PATCH bpf-next 00/17] BPF static linker: support externs

[PATCH bpf-next 00/17] BPF static linker: support externs

[Andrii Nakryiko]

Add BPF static linker support for extern resolution of global variables,
functions, and BTF-defined maps.

This patch set consists of 4 parts:
  - few patches are extending bpftool to simplify working with BTF dump;
  - libbpf object loading logic is extended to support __hidden functions and
    overriden (unused) __weak functions; also BTF-defined map parsing logic is
    refactored to be re-used by linker;
  - the crux of the patch set is BPF static linker logic extension to perform
    extern resolution for three categories: global variables, BPF
    sub-programs, BTF-defined maps;
  - a set of selftests that validate that all the combinations of
    extern/weak/__hidden are working as expected.

See respective patches for more details.

One aspect hasn't been addressed yet and is going to be resolved in the next
patch set, but is worth mentioning. With BPF static linking of multiple .o
files, dealing with static everything becomes more problematic for BPF
skeleton and in general for any by name look up APIs. This is due to static
entities are allowed to have non-unique name. Historically this was never
a problem due to BPF programs were always confined to a single C file. That
changes now and needs to be addressed. The thinking so far is for BPF static
linker to prepend filename to each static variable and static map (which is
currently not supported by libbpf, btw), so that they can be unambiguously
resolved by (mostly) unique name. Mostly, because even filenames can be
duplicated, but that should be rare and easy to address by wiser choice of
filenames by users. Fortunately, static BPF subprograms don't suffer from this
issues, as they are not independent entities and are neither exposed in BPF
skeleton, nor is lookup-able by any of libbpf APIs (and there is little reason
to do that anyways).

This and few other things will be the topic of the next set of patches.

Andrii Nakryiko (17):
  bpftool: support dumping BTF VAR's "extern" linkage
  bpftool: dump more info about DATASEC members
  libbpf: suppress compiler warning when using SEC() macro with externs
  libbpf: mark BPF subprogs with hidden visibility as static for BPF
    verifier
  libbpf: allow gaps in BPF program sections to support overriden weak
    functions
  libbpf: refactor BTF map definition parsing
  libbpf: factor out symtab and relos sanity checks
  libbpf: make few internal helpers available outside of libbpf.c
  libbpf: extend sanity checking ELF symbols with externs validation
  libbpf: tighten BTF type ID rewriting with error checking
  libbpf: add linker extern resolution support for functions and global
    variables
  libbpf: support extern resolution for BTF-defined maps in .maps
    section
  selftests/bpf: use -O0 instead of -Og in selftests builds
  selftests/bpf: omit skeleton generation for multi-linked BPF object
    files
  selftests/bpf: add function linking selftest
  selftests/bpf: add global variables linking selftest
  sleftests/bpf: add map linking selftest

 tools/bpf/bpftool/btf.c                       |   30 +-
 tools/lib/bpf/bpf_helpers.h                   |   19 +-
 tools/lib/bpf/btf.c                           |    5 -
 tools/lib/bpf/libbpf.c                        |  370 +++--
 tools/lib/bpf/libbpf_internal.h               |   45 +
 tools/lib/bpf/linker.c                        | 1292 ++++++++++++++---
 tools/testing/selftests/bpf/Makefile          |   18 +-
 .../selftests/bpf/prog_tests/linked_funcs.c   |   42 +
 .../selftests/bpf/prog_tests/linked_maps.c    |   33 +
 .../selftests/bpf/prog_tests/linked_vars.c    |   43 +
 .../selftests/bpf/progs/linked_funcs1.c       |   73 +
 .../selftests/bpf/progs/linked_funcs2.c       |   73 +
 .../selftests/bpf/progs/linked_maps1.c        |  102 ++
 .../selftests/bpf/progs/linked_maps2.c        |  112 ++
 .../selftests/bpf/progs/linked_vars1.c        |   60 +
 .../selftests/bpf/progs/linked_vars2.c        |   61 +
 16 files changed, 2028 insertions(+), 350 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_funcs.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_maps.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_vars.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs1.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs2.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_maps1.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_maps2.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_vars1.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_vars2.c

-- 
2.30.2

[PATCH bpf-next 01/17] bpftool: support dumping BTF VAR's "extern" linkage

[Andrii Nakryiko]

Add dumping of "extern" linkage for BTF VAR kind. Also shorten
"global-allocated" to "global" to be in line with FUNC's "global".

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/bpf/bpftool/btf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 62953bbf68b4..001749a34899 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -71,7 +71,9 @@ static const char *btf_var_linkage_str(__u32 linkage)
 	case BTF_VAR_STATIC:
 		return "static";
 	case BTF_VAR_GLOBAL_ALLOCATED:
-		return "global-alloc";
+		return "global";
+	case BTF_VAR_GLOBAL_EXTERN:
+		return "extern";
 	default:
 		return "(unknown)";
 	}
-- 
2.30.2

[PATCH bpf-next 02/17] bpftool: dump more info about DATASEC members

[Andrii Nakryiko]

Dump succinct information for each member of DATASEC: its kinds and name. This
is extremely helpful to see at a quick glance what is inside each DATASEC of
a given BTF. Without this, one has to jump around BTF data to just find out
the name of a VAR or FUNC. DATASEC's var_secinfo member is special in that
regard because it doesn't itself contain the name of the member, delegating
that to the referenced VAR and FUNC kinds. Other kinds, like
STRUCT/UNION/FUNC/ENUM, encode member names directly and thus are clearly
identifiable in BTF dump.

The new output looks like this:

[35] DATASEC '.bss' size=0 vlen=6
        type_id=8 offset=0 size=4 (VAR 'input_bss1')
        type_id=13 offset=0 size=4 (VAR 'input_bss_weak')
        type_id=16 offset=0 size=4 (VAR 'output_bss1')
        type_id=17 offset=0 size=4 (VAR 'output_data1')
        type_id=18 offset=0 size=4 (VAR 'output_rodata1')
        type_id=20 offset=0 size=8 (VAR 'output_sink1')
[36] DATASEC '.data' size=0 vlen=2
        type_id=9 offset=0 size=4 (VAR 'input_data1')
        type_id=14 offset=0 size=4 (VAR 'input_data_weak')
[37] DATASEC '.kconfig' size=0 vlen=2
        type_id=25 offset=0 size=4 (VAR 'LINUX_KERNEL_VERSION')
        type_id=28 offset=0 size=1 (VAR 'CONFIG_BPF_SYSCALL')
[38] DATASEC '.ksyms' size=0 vlen=1
        type_id=30 offset=0 size=1 (VAR 'bpf_link_fops')
[39] DATASEC '.rodata' size=0 vlen=2
        type_id=12 offset=0 size=4 (VAR 'input_rodata1')
        type_id=15 offset=0 size=4 (VAR 'input_rodata_weak')
[40] DATASEC 'license' size=0 vlen=1
        type_id=24 offset=0 size=4 (VAR 'LICENSE')

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/bpf/bpftool/btf.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 001749a34899..385d5c955cf3 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -100,26 +100,28 @@ static const char *btf_str(const struct btf *btf, __u32 off)
 	return btf__name_by_offset(btf, off) ? : "(invalid)";
 }
 
+static int btf_kind_safe(int kind)
+{
+	return kind <= BTF_KIND_MAX ? kind : BTF_KIND_UNKN;
+}
+
 static int dump_btf_type(const struct btf *btf, __u32 id,
 			 const struct btf_type *t)
 {
 	json_writer_t *w = json_wtr;
-	int kind, safe_kind;
-
-	kind = BTF_INFO_KIND(t->info);
-	safe_kind = kind <= BTF_KIND_MAX ? kind : BTF_KIND_UNKN;
+	int kind = btf_kind(t);
 
 	if (json_output) {
 		jsonw_start_object(w);
 		jsonw_uint_field(w, "id", id);
-		jsonw_string_field(w, "kind", btf_kind_str[safe_kind]);
+		jsonw_string_field(w, "kind", btf_kind_str[btf_kind_safe(kind)]);
 		jsonw_string_field(w, "name", btf_str(btf, t->name_off));
 	} else {
-		printf("[%u] %s '%s'", id, btf_kind_str[safe_kind],
+		printf("[%u] %s '%s'", id, btf_kind_str[btf_kind_safe(kind)],
 		       btf_str(btf, t->name_off));
 	}
 
-	switch (BTF_INFO_KIND(t->info)) {
+	switch (kind) {
 	case BTF_KIND_INT: {
 		__u32 v = *(__u32 *)(t + 1);
 		const char *enc;
@@ -302,7 +304,8 @@ static int dump_btf_type(const struct btf *btf, __u32 id,
 		break;
 	}
 	case BTF_KIND_DATASEC: {
-		const struct btf_var_secinfo *v = (const void *)(t+1);
+		const struct btf_var_secinfo *v = (const void *)(t + 1);
+		const struct btf_type *vt;
 		__u16 vlen = BTF_INFO_VLEN(t->info);
 		int i;
 
@@ -324,6 +327,13 @@ static int dump_btf_type(const struct btf *btf, __u32 id,
 			} else {
 				printf("\n\ttype_id=%u offset=%u size=%u",
 				       v->type, v->offset, v->size);
+
+				if (v->type <= btf__get_nr_types(btf)) {
+					vt = btf__type_by_id(btf, v->type);
+					printf(" (%s '%s')",
+					       btf_kind_str[btf_kind_safe(btf_kind(vt))],
+					       btf_str(btf, vt->name_off));
+				}
 			}
 		}
 		if (json_output)
-- 
2.30.2

[PATCH bpf-next 03/17] libbpf: suppress compiler warning when using SEC() macro with externs

[Andrii Nakryiko]

When used on externs SEC() macro will trigger compilation warning about
inapplicable `__attribute__((used))`. That's expected for extern declarations,
so suppress it with the corresponding _Pragma.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/bpf_helpers.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index b904128626c2..75c7581b304c 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -25,9 +25,16 @@
 /*
  * Helper macro to place programs, maps, license in
  * different sections in elf_bpf file. Section names
- * are interpreted by elf_bpf loader
+ * are interpreted by libbpf depending on the context (BPF programs, BPF maps,
+ * extern variables, etc).
+ * To allow use of SEC() with externs (e.g., for extern .maps declarations),
+ * make sure __attribute__((unused)) doesn't trigger compilation warning.
  */
-#define SEC(NAME) __attribute__((section(NAME), used))
+#define SEC(name) \
+	_Pragma("GCC diagnostic push")					    \
+	_Pragma("GCC diagnostic ignored \"-Wignored-attributes\"")	    \
+	__attribute__((section(name), used))				    \
+	_Pragma("GCC diagnostic pop")					    \
 
 /* Avoid 'linux/stddef.h' definition of '__always_inline'. */
 #undef __always_inline
-- 
2.30.2

[PATCH bpf-next 04/17] libbpf: mark BPF subprogs with hidden visibility as static for BPF verifier

[Andrii Nakryiko]

Define __hidden helper macro in bpf_helpers.h, which is a short-hand for
__attribute__((visibility("hidden"))). Add libbpf support to mark BPF
subprograms marked with __hidden as static in BTF information to enforce BPF
verifier's static function validation algorithm, which takes more information
(caller's context) into account during a subprogram validation.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/bpf_helpers.h     |  8 ++++++
 tools/lib/bpf/btf.c             |  5 ----
 tools/lib/bpf/libbpf.c          | 45 ++++++++++++++++++++++++++++++++-
 tools/lib/bpf/libbpf_internal.h |  6 +++++
 4 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 75c7581b304c..9720dc0b4605 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -47,6 +47,14 @@
 #define __weak __attribute__((weak))
 #endif
 
+/*
+ * Use __hidden attribute to mark a non-static BPF subprogram effectively
+ * static for BPF verifier's verification algorithm purposes, allowing more
+ * extensive and permissive BPF verification process, taking into account
+ * subprogram's caller context.
+ */
+#define __hidden __attribute__((visibility("hidden")))
+
 /* When utilizing vmlinux.h with BPF CO-RE, user BPF programs can't include
  * any system-level headers (such as stddef.h, linux/version.h, etc), and
  * commonly-used macros like NULL and KERNEL_VERSION aren't available through
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index d30e67e7e1e5..d57e13a13798 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -1605,11 +1605,6 @@ static void *btf_add_type_mem(struct btf *btf, size_t add_sz)
 			      btf->hdr->type_len, UINT_MAX, add_sz);
 }
 
-static __u32 btf_type_info(int kind, int vlen, int kflag)
-{
-	return (kflag << 31) | (kind << 24) | vlen;
-}
-
 static void btf_type_inc_vlen(struct btf_type *t)
 {
 	t->info = btf_type_info(btf_kind(t), btf_vlen(t) + 1, btf_kflag(t));
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ed5586cce227..b6a7f62521a6 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -71,6 +71,7 @@
 static struct bpf_map *bpf_object__add_map(struct bpf_object *obj);
 static const struct btf_type *
 skip_mods_and_typedefs(const struct btf *btf, __u32 id, __u32 *res_id);
+static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog);
 
 static int __base_pr(enum libbpf_print_level level, const char *format,
 		     va_list args)
@@ -275,6 +276,7 @@ struct bpf_program {
 	bpf_program_clear_priv_t clear_priv;
 
 	bool load;
+	bool mark_btf_static;
 	enum bpf_prog_type type;
 	enum bpf_attach_type expected_attach_type;
 	int prog_ifindex;
@@ -699,6 +701,15 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
 		if (err)
 			return err;
 
+		/* if function is a global/weak symbol, but has hidden
+		 * visibility (or any non-default one), mark its BTF FUNC as
+		 * static to enable more permissive BPF verification mode with
+		 * more outside context available to BPF verifier
+		 */
+		if (GELF_ST_BIND(sym.st_info) != STB_LOCAL
+		    && GELF_ST_VISIBILITY(sym.st_other) != STV_DEFAULT)
+			prog->mark_btf_static = true;
+
 		nr_progs++;
 		obj->nr_programs = nr_progs;
 
@@ -2619,7 +2630,7 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
 {
 	struct btf *kern_btf = obj->btf;
 	bool btf_mandatory, sanitize;
-	int err = 0;
+	int i, err = 0;
 
 	if (!obj->btf)
 		return 0;
@@ -2633,6 +2644,38 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
 		return 0;
 	}
 
+	/* Even though some subprogs are global/weak, user might prefer more
+	 * permissive BPF verification process that BPF verifier performs for
+	 * static functions, taking into account more context from the caller
+	 * functions. In such case, they need to mark such subprogs with
+	 * __attribute__((visibility("hidden"))) and libbpf will adjust
+	 * corresponding FUNC BTF type to be marked as static and trigger more
+	 * involved BPF verification process.
+	 */
+	for (i = 0; i < obj->nr_programs; i++) {
+		struct bpf_program *prog = &obj->programs[i];
+		struct btf_type *t;
+		const char *name;
+		int j, n;
+
+		if (!prog->mark_btf_static || !prog_is_subprog(obj, prog))
+			continue;
+
+		n = btf__get_nr_types(obj->btf);
+		for (j = 1; j <= n; j++) {
+			t = btf_type_by_id(obj->btf, j);
+			if (!btf_is_func(t) || btf_func_linkage(t) != BTF_FUNC_GLOBAL)
+				continue;
+
+			name = btf__str_by_offset(obj->btf, t->name_off);
+			if (strcmp(name, prog->name) != 0)
+				continue;
+
+			t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_STATIC, 0);
+			break;
+		}
+	}
+
 	sanitize = btf_needs_sanitization(obj);
 	if (sanitize) {
 		const void *raw_data;
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 6017902c687e..92b7eae10c6d 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -19,6 +19,7 @@
 #pragma GCC poison reallocarray
 
 #include "libbpf.h"
+#include "btf.h"
 
 #ifndef EM_BPF
 #define EM_BPF 247
@@ -132,6 +133,11 @@ struct btf_type;
 
 struct btf_type *btf_type_by_id(struct btf *btf, __u32 type_id);
 
+static inline __u32 btf_type_info(int kind, int vlen, int kflag)
+{
+	return (kflag << 31) | (kind << 24) | vlen;
+}
+
 void *libbpf_add_mem(void **data, size_t *cap_cnt, size_t elem_sz,
 		     size_t cur_cnt, size_t max_cnt, size_t add_cnt);
 int libbpf_ensure_mem(void **data, size_t *cap_cnt, size_t elem_sz, size_t need_cnt);
-- 
2.30.2

[PATCH bpf-next 05/17] libbpf: allow gaps in BPF program sections to support overriden weak functions

[Andrii Nakryiko]

Currently libbpf is very strict about parsing BPF program isnstruction
sections. No gaps are allowed between sequential BPF programs within a given
ELF section. Libbpf enforced that by keeping track of the next section offset
that should start a new BPF (sub)program and cross-checks that by searching for
a corresponding STT_FUNC ELF symbol.

But this is too restrictive once we allow to have weak BPF programs and link
together two or more BPF object files. In such case, some weak BPF programs
might be "overriden" by either non-weak BPF program with the same name and
signature, or even by another weak BPF program that just happened to be linked
first. That, in turn, leaves BPF instructions of the "lost" BPF (sub)program
intact, but there is no corresponding ELF symbol, because no one is going to
be referencing it.

Libbpf already correctly handles such cases in the sense that it won't append
such dead code to actual BPF programs loaded into kernel. So the only change
that needs to be done is to relax the logic of parsing BPF instruction
sections. Instead of assuming next BPF (sub)program section offset, iterate
available STT_FUNC ELF symbols to discover all available BPF subprograms and
programs.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/libbpf.c | 56 ++++++++++++++++--------------------------
 1 file changed, 21 insertions(+), 35 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b6a7f62521a6..38c78195ce57 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -503,8 +503,6 @@ static Elf_Scn *elf_sec_by_name(const struct bpf_object *obj, const char *name);
 static int elf_sec_hdr(const struct bpf_object *obj, Elf_Scn *scn, GElf_Shdr *hdr);
 static const char *elf_sec_name(const struct bpf_object *obj, Elf_Scn *scn);
 static Elf_Data *elf_sec_data(const struct bpf_object *obj, Elf_Scn *scn);
-static int elf_sym_by_sec_off(const struct bpf_object *obj, size_t sec_idx,
-			      size_t off, __u32 sym_type, GElf_Sym *sym);
 
 void bpf_program__unload(struct bpf_program *prog)
 {
@@ -645,10 +643,12 @@ static int
 bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
 			 const char *sec_name, int sec_idx)
 {
+	Elf_Data *symbols = obj->efile.symbols;
 	struct bpf_program *prog, *progs;
 	void *data = sec_data->d_buf;
 	size_t sec_sz = sec_data->d_size, sec_off, prog_sz;
-	int nr_progs, err;
+	size_t n = symbols->d_size / sizeof(GElf_Sym);
+	int nr_progs, err, i;
 	const char *name;
 	GElf_Sym sym;
 
@@ -656,14 +656,16 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
 	nr_progs = obj->nr_programs;
 	sec_off = 0;
 
-	while (sec_off < sec_sz) {
-		if (elf_sym_by_sec_off(obj, sec_idx, sec_off, STT_FUNC, &sym)) {
-			pr_warn("sec '%s': failed to find program symbol at offset %zu\n",
-				sec_name, sec_off);
-			return -LIBBPF_ERRNO__FORMAT;
-		}
+	for (i = 0; i < n; i++) {
+		if (!gelf_getsym(symbols, i, &sym))
+			continue;
+		if (sym.st_shndx != sec_idx)
+			continue;
+		if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
+			continue;
 
 		prog_sz = sym.st_size;
+		sec_off = sym.st_value;
 
 		name = elf_sym_str(obj, sym.st_name);
 		if (!name) {
@@ -712,8 +714,6 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
 
 		nr_progs++;
 		obj->nr_programs = nr_progs;
-
-		sec_off += prog_sz;
 	}
 
 	return 0;
@@ -2826,26 +2826,6 @@ static Elf_Data *elf_sec_data(const struct bpf_object *obj, Elf_Scn *scn)
 	return data;
 }
 
-static int elf_sym_by_sec_off(const struct bpf_object *obj, size_t sec_idx,
-			      size_t off, __u32 sym_type, GElf_Sym *sym)
-{
-	Elf_Data *symbols = obj->efile.symbols;
-	size_t n = symbols->d_size / sizeof(GElf_Sym);
-	int i;
-
-	for (i = 0; i < n; i++) {
-		if (!gelf_getsym(symbols, i, sym))
-			continue;
-		if (sym->st_shndx != sec_idx || sym->st_value != off)
-			continue;
-		if (GELF_ST_TYPE(sym->st_info) != sym_type)
-			continue;
-		return 0;
-	}
-
-	return -ENOENT;
-}
-
 static bool is_sec_name_dwarf(const char *name)
 {
 	/* approximation, but the actual list is too long */
@@ -3726,11 +3706,16 @@ bpf_object__collect_prog_relos(struct bpf_object *obj, GElf_Shdr *shdr, Elf_Data
 	int err, i, nrels;
 	const char *sym_name;
 	__u32 insn_idx;
+	Elf_Scn *scn;
+	Elf_Data *scn_data;
 	GElf_Sym sym;
 	GElf_Rel rel;
 
+	scn = elf_sec_by_idx(obj, sec_idx);
+	scn_data = elf_sec_data(obj, scn);
+
 	relo_sec_name = elf_sec_str(obj, shdr->sh_name);
-	sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, sec_idx));
+	sec_name = elf_sec_name(obj, scn);
 	if (!relo_sec_name || !sec_name)
 		return -EINVAL;
 
@@ -3748,7 +3733,8 @@ bpf_object__collect_prog_relos(struct bpf_object *obj, GElf_Shdr *shdr, Elf_Data
 				relo_sec_name, (size_t)GELF_R_SYM(rel.r_info), i);
 			return -LIBBPF_ERRNO__FORMAT;
 		}
-		if (rel.r_offset % BPF_INSN_SZ) {
+
+		if (rel.r_offset % BPF_INSN_SZ || rel.r_offset >= scn_data->d_size) {
 			pr_warn("sec '%s': invalid offset 0x%zx for relo #%d\n",
 				relo_sec_name, (size_t)GELF_R_SYM(rel.r_info), i);
 			return -LIBBPF_ERRNO__FORMAT;
@@ -3772,9 +3758,9 @@ bpf_object__collect_prog_relos(struct bpf_object *obj, GElf_Shdr *shdr, Elf_Data
 
 		prog = find_prog_by_sec_insn(obj, sec_idx, insn_idx);
 		if (!prog) {
-			pr_warn("sec '%s': relo #%d: program not found in section '%s' for insn #%u\n",
+			pr_debug("sec '%s': relo #%d: couldn't find program in section '%s' for insn #%u, probably overridden weak function, skipping...\n",
 				relo_sec_name, i, sec_name, insn_idx);
-			return -LIBBPF_ERRNO__RELOC;
+			continue;
 		}
 
 		relos = libbpf_reallocarray(prog->reloc_desc,
-- 
2.30.2

[PATCH bpf-next 06/17] libbpf: refactor BTF map definition parsing

[Andrii Nakryiko]

Refactor BTF-defined maps parsing logic to allow it to be nicely reused by BPF
static linker. Further, at least for BPF static linker, it's important to know
which attributes of a BPF map were defined explicitly, so provide a bit set
for each known portion of BTF map definition. This allows BPF static linker to
do a simple check when dealing with extern map declarations.

The same capabilities allow to distinguish attributes explicitly set to zero
(e.g., __uint(max_entries, 0)) vs the case of not specifying it at all (no
max_entries attribute at all). Libbpf is currently not utilizing that, but it
could be useful for backwards compatibility reasons later.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/libbpf.c          | 256 ++++++++++++++++++--------------
 tools/lib/bpf/libbpf_internal.h |  32 ++++
 2 files changed, 177 insertions(+), 111 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 38c78195ce57..b0dfe822cb50 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2026,255 +2026,262 @@ static int build_map_pin_path(struct bpf_map *map, const char *path)
 	return bpf_map__set_pin_path(map, buf);
 }
 
-
-static int parse_btf_map_def(struct bpf_object *obj,
-			     struct bpf_map *map,
-			     const struct btf_type *def,
-			     bool strict, bool is_inner,
-			     const char *pin_root_path)
+int parse_btf_map_def(const char *map_name, struct btf *btf,
+		      const struct btf_type *def_t, bool strict,
+		      struct btf_map_def *map_def, struct btf_map_def *inner_def)
 {
 	const struct btf_type *t;
 	const struct btf_member *m;
+	bool is_inner = inner_def == NULL;
 	int vlen, i;
 
-	vlen = btf_vlen(def);
-	m = btf_members(def);
+	vlen = btf_vlen(def_t);
+	m = btf_members(def_t);
 	for (i = 0; i < vlen; i++, m++) {
-		const char *name = btf__name_by_offset(obj->btf, m->name_off);
+		const char *name = btf__name_by_offset(btf, m->name_off);
 
 		if (!name) {
-			pr_warn("map '%s': invalid field #%d.\n", map->name, i);
+			pr_warn("map '%s': invalid field #%d.\n", map_name, i);
 			return -EINVAL;
 		}
 		if (strcmp(name, "type") == 0) {
-			if (!get_map_field_int(map->name, obj->btf, m,
-					       &map->def.type))
+			if (!get_map_field_int(map_name, btf, m, &map_def->map_type))
 				return -EINVAL;
-			pr_debug("map '%s': found type = %u.\n",
-				 map->name, map->def.type);
+			map_def->parts |= MAP_DEF_MAP_TYPE;
 		} else if (strcmp(name, "max_entries") == 0) {
-			if (!get_map_field_int(map->name, obj->btf, m,
-					       &map->def.max_entries))
+			if (!get_map_field_int(map_name, btf, m, &map_def->max_entries))
 				return -EINVAL;
-			pr_debug("map '%s': found max_entries = %u.\n",
-				 map->name, map->def.max_entries);
+			map_def->parts |= MAP_DEF_MAX_ENTRIES;
 		} else if (strcmp(name, "map_flags") == 0) {
-			if (!get_map_field_int(map->name, obj->btf, m,
-					       &map->def.map_flags))
+			if (!get_map_field_int(map_name, btf, m, &map_def->map_flags))
 				return -EINVAL;
-			pr_debug("map '%s': found map_flags = %u.\n",
-				 map->name, map->def.map_flags);
+			map_def->parts |= MAP_DEF_MAP_FLAGS;
 		} else if (strcmp(name, "numa_node") == 0) {
-			if (!get_map_field_int(map->name, obj->btf, m, &map->numa_node))
+			if (!get_map_field_int(map_name, btf, m, &map_def->numa_node))
 				return -EINVAL;
-			pr_debug("map '%s': found numa_node = %u.\n", map->name, map->numa_node);
+			map_def->parts |= MAP_DEF_NUMA_NODE;
 		} else if (strcmp(name, "key_size") == 0) {
 			__u32 sz;
 
-			if (!get_map_field_int(map->name, obj->btf, m, &sz))
+			if (!get_map_field_int(map_name, btf, m, &sz))
 				return -EINVAL;
-			pr_debug("map '%s': found key_size = %u.\n",
-				 map->name, sz);
-			if (map->def.key_size && map->def.key_size != sz) {
+			if (map_def->key_size && map_def->key_size != sz) {
 				pr_warn("map '%s': conflicting key size %u != %u.\n",
-					map->name, map->def.key_size, sz);
+					map_name, map_def->key_size, sz);
 				return -EINVAL;
 			}
-			map->def.key_size = sz;
+			map_def->key_size = sz;
+			map_def->parts |= MAP_DEF_KEY_SIZE;
 		} else if (strcmp(name, "key") == 0) {
 			__s64 sz;
 
-			t = btf__type_by_id(obj->btf, m->type);
+			t = btf__type_by_id(btf, m->type);
 			if (!t) {
 				pr_warn("map '%s': key type [%d] not found.\n",
-					map->name, m->type);
+					map_name, m->type);
 				return -EINVAL;
 			}
 			if (!btf_is_ptr(t)) {
 				pr_warn("map '%s': key spec is not PTR: %s.\n",
-					map->name, btf_kind_str(t));
+					map_name, btf_kind_str(t));
 				return -EINVAL;
 			}
-			sz = btf__resolve_size(obj->btf, t->type);
+			sz = btf__resolve_size(btf, t->type);
 			if (sz < 0) {
 				pr_warn("map '%s': can't determine key size for type [%u]: %zd.\n",
-					map->name, t->type, (ssize_t)sz);
+					map_name, t->type, (ssize_t)sz);
 				return sz;
 			}
-			pr_debug("map '%s': found key [%u], sz = %zd.\n",
-				 map->name, t->type, (ssize_t)sz);
-			if (map->def.key_size && map->def.key_size != sz) {
+			if (map_def->key_size && map_def->key_size != sz) {
 				pr_warn("map '%s': conflicting key size %u != %zd.\n",
-					map->name, map->def.key_size, (ssize_t)sz);
+					map_name, map_def->key_size, (ssize_t)sz);
 				return -EINVAL;
 			}
-			map->def.key_size = sz;
-			map->btf_key_type_id = t->type;
+			map_def->key_size = sz;
+			map_def->key_type_id = t->type;
+			map_def->parts |= MAP_DEF_KEY_SIZE | MAP_DEF_KEY_TYPE;
 		} else if (strcmp(name, "value_size") == 0) {
 			__u32 sz;
 
-			if (!get_map_field_int(map->name, obj->btf, m, &sz))
+			if (!get_map_field_int(map_name, btf, m, &sz))
 				return -EINVAL;
-			pr_debug("map '%s': found value_size = %u.\n",
-				 map->name, sz);
-			if (map->def.value_size && map->def.value_size != sz) {
+			if (map_def->value_size && map_def->value_size != sz) {
 				pr_warn("map '%s': conflicting value size %u != %u.\n",
-					map->name, map->def.value_size, sz);
+					map_name, map_def->value_size, sz);
 				return -EINVAL;
 			}
-			map->def.value_size = sz;
+			map_def->value_size = sz;
+			map_def->parts |= MAP_DEF_VALUE_SIZE;
 		} else if (strcmp(name, "value") == 0) {
 			__s64 sz;
 
-			t = btf__type_by_id(obj->btf, m->type);
+			t = btf__type_by_id(btf, m->type);
 			if (!t) {
 				pr_warn("map '%s': value type [%d] not found.\n",
-					map->name, m->type);
+					map_name, m->type);
 				return -EINVAL;
 			}
 			if (!btf_is_ptr(t)) {
 				pr_warn("map '%s': value spec is not PTR: %s.\n",
-					map->name, btf_kind_str(t));
+					map_name, btf_kind_str(t));
 				return -EINVAL;
 			}
-			sz = btf__resolve_size(obj->btf, t->type);
+			sz = btf__resolve_size(btf, t->type);
 			if (sz < 0) {
 				pr_warn("map '%s': can't determine value size for type [%u]: %zd.\n",
-					map->name, t->type, (ssize_t)sz);
+					map_name, t->type, (ssize_t)sz);
 				return sz;
 			}
-			pr_debug("map '%s': found value [%u], sz = %zd.\n",
-				 map->name, t->type, (ssize_t)sz);
-			if (map->def.value_size && map->def.value_size != sz) {
+			if (map_def->value_size && map_def->value_size != sz) {
 				pr_warn("map '%s': conflicting value size %u != %zd.\n",
-					map->name, map->def.value_size, (ssize_t)sz);
+					map_name, map_def->value_size, (ssize_t)sz);
 				return -EINVAL;
 			}
-			map->def.value_size = sz;
-			map->btf_value_type_id = t->type;
+			map_def->value_size = sz;
+			map_def->value_type_id = t->type;
+			map_def->parts |= MAP_DEF_VALUE_SIZE | MAP_DEF_VALUE_TYPE;
 		}
 		else if (strcmp(name, "values") == 0) {
+			char inner_map_name[128];
 			int err;
 
 			if (is_inner) {
 				pr_warn("map '%s': multi-level inner maps not supported.\n",
-					map->name);
+					map_name);
 				return -ENOTSUP;
 			}
 			if (i != vlen - 1) {
 				pr_warn("map '%s': '%s' member should be last.\n",
-					map->name, name);
+					map_name, name);
 				return -EINVAL;
 			}
-			if (!bpf_map_type__is_map_in_map(map->def.type)) {
+			if (!bpf_map_type__is_map_in_map(map_def->map_type)) {
 				pr_warn("map '%s': should be map-in-map.\n",
-					map->name);
+					map_name);
 				return -ENOTSUP;
 			}
-			if (map->def.value_size && map->def.value_size != 4) {
+			if (map_def->value_size && map_def->value_size != 4) {
 				pr_warn("map '%s': conflicting value size %u != 4.\n",
-					map->name, map->def.value_size);
+					map_name, map_def->value_size);
 				return -EINVAL;
 			}
-			map->def.value_size = 4;
-			t = btf__type_by_id(obj->btf, m->type);
+			map_def->value_size = 4;
+			t = btf__type_by_id(btf, m->type);
 			if (!t) {
 				pr_warn("map '%s': map-in-map inner type [%d] not found.\n",
-					map->name, m->type);
+					map_name, m->type);
 				return -EINVAL;
 			}
 			if (!btf_is_array(t) || btf_array(t)->nelems) {
 				pr_warn("map '%s': map-in-map inner spec is not a zero-sized array.\n",
-					map->name);
+					map_name);
 				return -EINVAL;
 			}
-			t = skip_mods_and_typedefs(obj->btf, btf_array(t)->type,
-						   NULL);
+			t = skip_mods_and_typedefs(btf, btf_array(t)->type, NULL);
 			if (!btf_is_ptr(t)) {
 				pr_warn("map '%s': map-in-map inner def is of unexpected kind %s.\n",
-					map->name, btf_kind_str(t));
+					map_name, btf_kind_str(t));
 				return -EINVAL;
 			}
-			t = skip_mods_and_typedefs(obj->btf, t->type, NULL);
+			t = skip_mods_and_typedefs(btf, t->type, NULL);
 			if (!btf_is_struct(t)) {
 				pr_warn("map '%s': map-in-map inner def is of unexpected kind %s.\n",
-					map->name, btf_kind_str(t));
+					map_name, btf_kind_str(t));
 				return -EINVAL;
 			}
 
-			map->inner_map = calloc(1, sizeof(*map->inner_map));
-			if (!map->inner_map)
-				return -ENOMEM;
-			map->inner_map->fd = -1;
-			map->inner_map->sec_idx = obj->efile.btf_maps_shndx;
-			map->inner_map->name = malloc(strlen(map->name) +
-						      sizeof(".inner") + 1);
-			if (!map->inner_map->name)
-				return -ENOMEM;
-			sprintf(map->inner_map->name, "%s.inner", map->name);
-
-			err = parse_btf_map_def(obj, map->inner_map, t, strict,
-						true /* is_inner */, NULL);
+			snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", map_name);
+			err = parse_btf_map_def(inner_map_name, btf, t, strict, inner_def, NULL);
 			if (err)
 				return err;
+
+			map_def->parts |= MAP_DEF_INNER_MAP;
 		} else if (strcmp(name, "pinning") == 0) {
 			__u32 val;
-			int err;
 
 			if (is_inner) {
-				pr_debug("map '%s': inner def can't be pinned.\n",
-					 map->name);
+				pr_warn("map '%s': inner def can't be pinned.\n", map_name);
 				return -EINVAL;
 			}
-			if (!get_map_field_int(map->name, obj->btf, m, &val))
+			if (!get_map_field_int(map_name, btf, m, &val))
 				return -EINVAL;
-			pr_debug("map '%s': found pinning = %u.\n",
-				 map->name, val);
-
-			if (val != LIBBPF_PIN_NONE &&
-			    val != LIBBPF_PIN_BY_NAME) {
+			if (val != LIBBPF_PIN_NONE && val != LIBBPF_PIN_BY_NAME) {
 				pr_warn("map '%s': invalid pinning value %u.\n",
-					map->name, val);
+					map_name, val);
 				return -EINVAL;
 			}
-			if (val == LIBBPF_PIN_BY_NAME) {
-				err = build_map_pin_path(map, pin_root_path);
-				if (err) {
-					pr_warn("map '%s': couldn't build pin path.\n",
-						map->name);
-					return err;
-				}
-			}
+			map_def->pinning = val;
+			map_def->parts |= MAP_DEF_PINNING;
 		} else {
 			if (strict) {
-				pr_warn("map '%s': unknown field '%s'.\n",
-					map->name, name);
+				pr_warn("map '%s': unknown field '%s'.\n", map_name, name);
 				return -ENOTSUP;
 			}
-			pr_debug("map '%s': ignoring unknown field '%s'.\n",
-				 map->name, name);
+			pr_debug("map '%s': ignoring unknown field '%s'.\n", map_name, name);
 		}
 	}
 
-	if (map->def.type == BPF_MAP_TYPE_UNSPEC) {
-		pr_warn("map '%s': map type isn't specified.\n", map->name);
+	if (map_def->map_type == BPF_MAP_TYPE_UNSPEC) {
+		pr_warn("map '%s': map type isn't specified.\n", map_name);
 		return -EINVAL;
 	}
 
 	return 0;
 }
 
+static void fill_map_from_def(struct bpf_map *map, const struct btf_map_def *def)
+{
+	map->def.type = def->map_type;
+	map->def.key_size = def->key_size;
+	map->def.value_size = def->value_size;
+	map->def.max_entries = def->max_entries;
+	map->def.map_flags = def->map_flags;
+
+	map->numa_node = def->numa_node;
+	map->btf_key_type_id = def->key_type_id;
+	map->btf_value_type_id = def->value_type_id;
+
+	if (def->parts & MAP_DEF_MAP_TYPE)
+		pr_debug("map '%s': found type = %u.\n", map->name, def->map_type);
+
+	if (def->parts & MAP_DEF_KEY_TYPE)
+		pr_debug("map '%s': found key [%u], sz = %u.\n",
+			 map->name, def->key_type_id, def->key_size);
+	else if (def->parts & MAP_DEF_KEY_SIZE)
+		pr_debug("map '%s': found key_size = %u.\n", map->name, def->key_size);
+
+	if (def->parts & MAP_DEF_VALUE_TYPE)
+		pr_debug("map '%s': found value [%u], sz = %u.\n",
+			 map->name, def->value_type_id, def->value_size);
+	else if (def->parts & MAP_DEF_VALUE_SIZE)
+		pr_debug("map '%s': found value_size = %u.\n", map->name, def->value_size);
+
+	if (def->parts & MAP_DEF_MAX_ENTRIES)
+		pr_debug("map '%s': found max_entries = %u.\n", map->name, def->max_entries);
+	if (def->parts & MAP_DEF_MAP_FLAGS)
+		pr_debug("map '%s': found map_flags = %u.\n", map->name, def->map_flags);
+	if (def->parts & MAP_DEF_PINNING)
+		pr_debug("map '%s': found pinning = %u.\n", map->name, def->pinning);
+	if (def->parts & MAP_DEF_NUMA_NODE)
+		pr_debug("map '%s': found numa_node = %u.\n", map->name, def->numa_node);
+
+	if (def->parts & MAP_DEF_INNER_MAP)
+		pr_debug("map '%s': found inner map definition.\n", map->name);
+}
+
 static int bpf_object__init_user_btf_map(struct bpf_object *obj,
 					 const struct btf_type *sec,
 					 int var_idx, int sec_idx,
 					 const Elf_Data *data, bool strict,
 					 const char *pin_root_path)
 {
+	struct btf_map_def map_def = {}, inner_def = {};
 	const struct btf_type *var, *def;
 	const struct btf_var_secinfo *vi;
 	const struct btf_var *var_extra;
 	const char *map_name;
 	struct bpf_map *map;
+	int err;
 
 	vi = btf_var_secinfos(sec) + var_idx;
 	var = btf__type_by_id(obj->btf, vi->type);
@@ -2328,7 +2335,34 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
 	pr_debug("map '%s': at sec_idx %d, offset %zu.\n",
 		 map_name, map->sec_idx, map->sec_offset);
 
-	return parse_btf_map_def(obj, map, def, strict, false, pin_root_path);
+	err = parse_btf_map_def(map->name, obj->btf, def, strict, &map_def, &inner_def);
+	if (err)
+		return err;
+
+	fill_map_from_def(map, &map_def);
+
+	if (map_def.pinning == LIBBPF_PIN_BY_NAME) {
+		err = build_map_pin_path(map, pin_root_path);
+		if (err) {
+			pr_warn("map '%s': couldn't build pin path.\n", map->name);
+			return err;
+		}
+	}
+
+	if (map_def.parts & MAP_DEF_INNER_MAP) {
+		map->inner_map = calloc(1, sizeof(*map->inner_map));
+		if (!map->inner_map)
+			return -ENOMEM;
+		map->inner_map->fd = -1;
+		map->inner_map->name = malloc(strlen(map_name) + sizeof(".inner") + 1);
+		if (!map->inner_map->name)
+			return -ENOMEM;
+		sprintf(map->inner_map->name, "%s.inner", map_name);
+
+		fill_map_from_def(map->inner_map, &inner_def);
+	}
+
+	return 0;
 }
 
 static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 92b7eae10c6d..17883073710c 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -138,6 +138,38 @@ static inline __u32 btf_type_info(int kind, int vlen, int kflag)
 	return (kflag << 31) | (kind << 24) | vlen;
 }
 
+enum map_def_parts {
+	MAP_DEF_MAP_TYPE	= 0x001,
+	MAP_DEF_KEY_TYPE	= 0x002,
+	MAP_DEF_KEY_SIZE	= 0x004,
+	MAP_DEF_VALUE_TYPE	= 0x008,
+	MAP_DEF_VALUE_SIZE	= 0x010,
+	MAP_DEF_MAX_ENTRIES	= 0x020,
+	MAP_DEF_MAP_FLAGS	= 0x040,
+	MAP_DEF_NUMA_NODE	= 0x080,
+	MAP_DEF_PINNING		= 0x100,
+	MAP_DEF_INNER_MAP	= 0x200,
+
+	MAP_DEF_ALL		= 0x3ff, /* combination of all above */
+};
+
+struct btf_map_def {
+	enum map_def_parts parts;
+	__u32 map_type;
+	__u32 key_type_id;
+	__u32 key_size;
+	__u32 value_type_id;
+	__u32 value_size;
+	__u32 max_entries;
+	__u32 map_flags;
+	__u32 numa_node;
+	__u32 pinning;
+};
+
+int parse_btf_map_def(const char *map_name, struct btf *btf,
+		      const struct btf_type *def_t, bool strict,
+		      struct btf_map_def *map_def, struct btf_map_def *inner_def);
+
 void *libbpf_add_mem(void **data, size_t *cap_cnt, size_t elem_sz,
 		     size_t cur_cnt, size_t max_cnt, size_t add_cnt);
 int libbpf_ensure_mem(void **data, size_t *cap_cnt, size_t elem_sz, size_t need_cnt);
-- 
2.30.2

[PATCH bpf-next 07/17] libbpf: factor out symtab and relos sanity checks

[Andrii Nakryiko]

Factor out logic for sanity checking SHT_SYMTAB and SHT_REL sections into
separate sections. They are already quite extensive and are suffering from too
deep indentation. Subsequent changes will extend SYMTAB sanity checking
further, so it's better to factor each into a separate function.

No functional changes are intended.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/linker.c | 233 ++++++++++++++++++++++-------------------
 1 file changed, 127 insertions(+), 106 deletions(-)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 4e08bc07e635..0bb927226370 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -131,6 +131,8 @@ static int init_output_elf(struct bpf_linker *linker, const char *file);
 
 static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, struct src_obj *obj);
 static int linker_sanity_check_elf(struct src_obj *obj);
+static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec);
+static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec);
 static int linker_sanity_check_btf(struct src_obj *obj);
 static int linker_sanity_check_btf_ext(struct src_obj *obj);
 static int linker_fixup_btf(struct src_obj *obj);
@@ -663,8 +665,8 @@ static bool is_pow_of_2(size_t x)
 
 static int linker_sanity_check_elf(struct src_obj *obj)
 {
-	struct src_sec *sec, *link_sec;
-	int i, j, n;
+	struct src_sec *sec;
+	int i, err;
 
 	if (!obj->symtab_sec_idx) {
 		pr_warn("ELF is missing SYMTAB section in %s\n", obj->filename);
@@ -692,43 +694,11 @@ static int linker_sanity_check_elf(struct src_obj *obj)
 			return -EINVAL;
 
 		switch (sec->shdr->sh_type) {
-		case SHT_SYMTAB: {
-			Elf64_Sym *sym;
-
-			if (sec->shdr->sh_entsize != sizeof(Elf64_Sym))
-				return -EINVAL;
-			if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
-				return -EINVAL;
-
-			if (!sec->shdr->sh_link || sec->shdr->sh_link >= obj->sec_cnt) {
-				pr_warn("ELF SYMTAB section #%zu points to missing STRTAB section #%zu in %s\n",
-					sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
-				return -EINVAL;
-			}
-			link_sec = &obj->secs[sec->shdr->sh_link];
-			if (link_sec->shdr->sh_type != SHT_STRTAB) {
-				pr_warn("ELF SYMTAB section #%zu points to invalid STRTAB section #%zu in %s\n",
-					sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
-				return -EINVAL;
-			}
-
-			n = sec->shdr->sh_size / sec->shdr->sh_entsize;
-			sym = sec->data->d_buf;
-			for (j = 0; j < n; j++, sym++) {
-				if (sym->st_shndx
-				    && sym->st_shndx < SHN_LORESERVE
-				    && sym->st_shndx >= obj->sec_cnt) {
-					pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
-						j, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
-					return -EINVAL;
-				}
-				if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) {
-					if (sym->st_value != 0)
-						return -EINVAL;
-				}
-			}
+		case SHT_SYMTAB:
+			err = linker_sanity_check_elf_symtab(obj, sec);
+			if (err)
+				return err;
 			break;
-		}
 		case SHT_STRTAB:
 			break;
 		case SHT_PROGBITS:
@@ -739,87 +709,138 @@ static int linker_sanity_check_elf(struct src_obj *obj)
 			break;
 		case SHT_NOBITS:
 			break;
-		case SHT_REL: {
-			Elf64_Rel *relo;
-			struct src_sec *sym_sec;
+		case SHT_REL:
+			err = linker_sanity_check_elf_relos(obj, sec);
+			if (err)
+				return err;
+			break;
+		case SHT_LLVM_ADDRSIG:
+			break;
+		default:
+			pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n",
+				sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename);
+			return -EINVAL;
+		}
+	}
 
-			if (sec->shdr->sh_entsize != sizeof(Elf64_Rel))
-				return -EINVAL;
-			if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
-				return -EINVAL;
+	return 0;
+}
 
-			/* SHT_REL's sh_link should point to SYMTAB */
-			if (sec->shdr->sh_link != obj->symtab_sec_idx) {
-				pr_warn("ELF relo section #%zu points to invalid SYMTAB section #%zu in %s\n",
-					sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
-				return -EINVAL;
-			}
+static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec)
+{
+	struct src_sec *link_sec;
+	Elf64_Sym *sym;
+	int i, n;
 
-			/* SHT_REL's sh_info points to relocated section */
-			if (!sec->shdr->sh_info || sec->shdr->sh_info >= obj->sec_cnt) {
-				pr_warn("ELF relo section #%zu points to missing section #%zu in %s\n",
-					sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
-				return -EINVAL;
-			}
-			link_sec = &obj->secs[sec->shdr->sh_info];
+	if (sec->shdr->sh_entsize != sizeof(Elf64_Sym))
+		return -EINVAL;
+	if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
+		return -EINVAL;
+
+	if (!sec->shdr->sh_link || sec->shdr->sh_link >= obj->sec_cnt) {
+		pr_warn("ELF SYMTAB section #%zu points to missing STRTAB section #%zu in %s\n",
+			sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
+		return -EINVAL;
+	}
+	link_sec = &obj->secs[sec->shdr->sh_link];
+	if (link_sec->shdr->sh_type != SHT_STRTAB) {
+		pr_warn("ELF SYMTAB section #%zu points to invalid STRTAB section #%zu in %s\n",
+			sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
+		return -EINVAL;
+	}
 
-			/* .rel<secname> -> <secname> pattern is followed */
-			if (strncmp(sec->sec_name, ".rel", sizeof(".rel") - 1) != 0
-			    || strcmp(sec->sec_name + sizeof(".rel") - 1, link_sec->sec_name) != 0) {
-				pr_warn("ELF relo section #%zu name has invalid name in %s\n",
-					sec->sec_idx, obj->filename);
+	n = sec->shdr->sh_size / sec->shdr->sh_entsize;
+	sym = sec->data->d_buf;
+	for (i = 0; i < n; i++, sym++) {
+		if (sym->st_shndx
+		    && sym->st_shndx < SHN_LORESERVE
+		    && sym->st_shndx >= obj->sec_cnt) {
+			pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
+				i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
+			return -EINVAL;
+		}
+		if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) {
+			if (sym->st_value != 0)
 				return -EINVAL;
-			}
+			continue;
+		}
+	}
 
-			/* don't further validate relocations for ignored sections */
-			if (link_sec->skipped)
-				break;
+	return 0;
+}
 
-			/* relocatable section is data or instructions */
-			if (link_sec->shdr->sh_type != SHT_PROGBITS
-			    && link_sec->shdr->sh_type != SHT_NOBITS) {
-				pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n",
-					sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
-				return -EINVAL;
-			}
+static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec)
+{
+	struct src_sec *link_sec, *sym_sec;
+	Elf64_Rel *relo;
+	int i, n;
 
-			/* check sanity of each relocation */
-			n = sec->shdr->sh_size / sec->shdr->sh_entsize;
-			relo = sec->data->d_buf;
-			sym_sec = &obj->secs[obj->symtab_sec_idx];
-			for (j = 0; j < n; j++, relo++) {
-				size_t sym_idx = ELF64_R_SYM(relo->r_info);
-				size_t sym_type = ELF64_R_TYPE(relo->r_info);
-
-				if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32) {
-					pr_warn("ELF relo #%d in section #%zu has unexpected type %zu in %s\n",
-						j, sec->sec_idx, sym_type, obj->filename);
-					return -EINVAL;
-				}
+	if (sec->shdr->sh_entsize != sizeof(Elf64_Rel))
+		return -EINVAL;
+	if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
+		return -EINVAL;
 
-				if (!sym_idx || sym_idx * sizeof(Elf64_Sym) >= sym_sec->shdr->sh_size) {
-					pr_warn("ELF relo #%d in section #%zu points to invalid symbol #%zu in %s\n",
-						j, sec->sec_idx, sym_idx, obj->filename);
-					return -EINVAL;
-				}
+	/* SHT_REL's sh_link should point to SYMTAB */
+	if (sec->shdr->sh_link != obj->symtab_sec_idx) {
+		pr_warn("ELF relo section #%zu points to invalid SYMTAB section #%zu in %s\n",
+			sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
+		return -EINVAL;
+	}
 
-				if (link_sec->shdr->sh_flags & SHF_EXECINSTR) {
-					if (relo->r_offset % sizeof(struct bpf_insn) != 0) {
-						pr_warn("ELF relo #%d in section #%zu points to missing symbol #%zu in %s\n",
-							j, sec->sec_idx, sym_idx, obj->filename);
-						return -EINVAL;
-					}
-				}
-			}
-			break;
+	/* SHT_REL's sh_info points to relocated section */
+	if (!sec->shdr->sh_info || sec->shdr->sh_info >= obj->sec_cnt) {
+		pr_warn("ELF relo section #%zu points to missing section #%zu in %s\n",
+			sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
+		return -EINVAL;
+	}
+	link_sec = &obj->secs[sec->shdr->sh_info];
+
+	/* .rel<secname> -> <secname> pattern is followed */
+	if (strncmp(sec->sec_name, ".rel", sizeof(".rel") - 1) != 0
+	    || strcmp(sec->sec_name + sizeof(".rel") - 1, link_sec->sec_name) != 0) {
+		pr_warn("ELF relo section #%zu name has invalid name in %s\n",
+			sec->sec_idx, obj->filename);
+		return -EINVAL;
+	}
+
+	/* don't further validate relocations for ignored sections */
+	if (link_sec->skipped)
+		return 0;
+
+	/* relocatable section is data or instructions */
+	if (link_sec->shdr->sh_type != SHT_PROGBITS && link_sec->shdr->sh_type != SHT_NOBITS) {
+		pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n",
+			sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
+		return -EINVAL;
+	}
+
+	/* check sanity of each relocation */
+	n = sec->shdr->sh_size / sec->shdr->sh_entsize;
+	relo = sec->data->d_buf;
+	sym_sec = &obj->secs[obj->symtab_sec_idx];
+	for (i = 0; i < n; i++, relo++) {
+		size_t sym_idx = ELF64_R_SYM(relo->r_info);
+		size_t sym_type = ELF64_R_TYPE(relo->r_info);
+
+		if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32) {
+			pr_warn("ELF relo #%d in section #%zu has unexpected type %zu in %s\n",
+				i, sec->sec_idx, sym_type, obj->filename);
+			return -EINVAL;
 		}
-		case SHT_LLVM_ADDRSIG:
-			break;
-		default:
-			pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n",
-				sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename);
+
+		if (!sym_idx || sym_idx * sizeof(Elf64_Sym) >= sym_sec->shdr->sh_size) {
+			pr_warn("ELF relo #%d in section #%zu points to invalid symbol #%zu in %s\n",
+				i, sec->sec_idx, sym_idx, obj->filename);
 			return -EINVAL;
 		}
+
+		if (link_sec->shdr->sh_flags & SHF_EXECINSTR) {
+			if (relo->r_offset % sizeof(struct bpf_insn) != 0) {
+				pr_warn("ELF relo #%d in section #%zu points to missing symbol #%zu in %s\n",
+					i, sec->sec_idx, sym_idx, obj->filename);
+				return -EINVAL;
+			}
+		}
 	}
 
 	return 0;
-- 
2.30.2

[PATCH bpf-next 08/17] libbpf: make few internal helpers available outside of libbpf.c

[Andrii Nakryiko]

Make skip_mods_and_typedefs(), btf_kind_str(), and btf_func_linkage() helpers
available outside of libbpf.c, to be used by static linker code.

Also do few cleanups (error code fixes, comment clean up, etc) that don't
deserve their own commit.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/libbpf.c          | 13 +++----------
 tools/lib/bpf/libbpf_internal.h |  7 +++++++
 tools/lib/bpf/linker.c          |  8 ++++----
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b0dfe822cb50..16fe2065ef7d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -69,8 +69,6 @@
 #define __printf(a, b)	__attribute__((format(printf, a, b)))
 
 static struct bpf_map *bpf_object__add_map(struct bpf_object *obj);
-static const struct btf_type *
-skip_mods_and_typedefs(const struct btf *btf, __u32 id, __u32 *res_id);
 static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog);
 
 static int __base_pr(enum libbpf_print_level level, const char *format,
@@ -1907,7 +1905,7 @@ static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
 	return 0;
 }
 
-static const struct btf_type *
+const struct btf_type *
 skip_mods_and_typedefs(const struct btf *btf, __u32 id, __u32 *res_id)
 {
 	const struct btf_type *t = btf__type_by_id(btf, id);
@@ -1962,16 +1960,11 @@ static const char *__btf_kind_str(__u16 kind)
 	}
 }
 
-static const char *btf_kind_str(const struct btf_type *t)
+const char *btf_kind_str(const struct btf_type *t)
 {
 	return __btf_kind_str(btf_kind(t));
 }
 
-static enum btf_func_linkage btf_func_linkage(const struct btf_type *t)
-{
-	return (enum btf_func_linkage)BTF_INFO_VLEN(t->info);
-}
-
 /*
  * Fetch integer attribute of BTF map definition. Such attributes are
  * represented using a pointer to an array, in which dimensionality of array
@@ -7048,7 +7041,7 @@ static bool insn_is_helper_call(struct bpf_insn *insn, enum bpf_func_id *func_id
 	return false;
 }
 
-static int bpf_object__sanitize_prog(struct bpf_object* obj, struct bpf_program *prog)
+static int bpf_object__sanitize_prog(struct bpf_object *obj, struct bpf_program *prog)
 {
 	struct bpf_insn *insn = prog->insns;
 	enum bpf_func_id func_id;
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 17883073710c..ee426226928f 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -132,6 +132,13 @@ struct btf;
 struct btf_type;
 
 struct btf_type *btf_type_by_id(struct btf *btf, __u32 type_id);
+const char *btf_kind_str(const struct btf_type *t);
+const struct btf_type *skip_mods_and_typedefs(const struct btf *btf, __u32 id, __u32 *res_id);
+
+static inline enum btf_func_linkage btf_func_linkage(const struct btf_type *t)
+{
+	return (enum btf_func_linkage)(int)btf_vlen(t);
+}
 
 static inline __u32 btf_type_info(int kind, int vlen, int kflag)
 {
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 0bb927226370..b23bfa6e7e5f 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -925,13 +925,13 @@ static int init_sec(struct bpf_linker *linker, struct dst_sec *dst_sec, struct s
 
 	scn = elf_newscn(linker->elf);
 	if (!scn)
-		return -1;
+		return -ENOMEM;
 	data = elf_newdata(scn);
 	if (!data)
-		return -1;
+		return -ENOMEM;
 	shdr = elf64_getshdr(scn);
 	if (!shdr)
-		return -1;
+		return -ENOMEM;
 
 	dst_sec->scn = scn;
 	dst_sec->shdr = shdr;
@@ -1221,7 +1221,7 @@ static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *ob
 				return err;
 			}
 		} else if (!secs_match(dst_sec, src_sec)) {
-			pr_warn("Secs %s are not compatible\n", src_sec->sec_name);
+			pr_warn("sections %s are not compatible\n", src_sec->sec_name);
 			return -1;
 		}
 
-- 
2.30.2

[PATCH bpf-next 09/17] libbpf: extend sanity checking ELF symbols with externs validation

[Andrii Nakryiko]

Add logic to validate extern symbols, plus some other minor extra checks, like
ELF symbol #0 validation, general symbol visibility and binding validations.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/linker.c | 43 +++++++++++++++++++++++++++++++++---------
 1 file changed, 34 insertions(+), 9 deletions(-)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index b23bfa6e7e5f..dc202a5d8235 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -752,14 +752,39 @@ static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *s
 	n = sec->shdr->sh_size / sec->shdr->sh_entsize;
 	sym = sec->data->d_buf;
 	for (i = 0; i < n; i++, sym++) {
-		if (sym->st_shndx
-		    && sym->st_shndx < SHN_LORESERVE
-		    && sym->st_shndx >= obj->sec_cnt) {
+		int sym_type = ELF64_ST_TYPE(sym->st_info);
+		int sym_bind = ELF64_ST_BIND(sym->st_info);
+
+		if (i == 0) {
+			if (sym->st_name != 0 || sym->st_info != 0
+			    || sym->st_other != 0 || sym->st_shndx != 0
+			    || sym->st_value != 0 || sym->st_size != 0) {
+				pr_warn("ELF sym #0 is invalid in %s\n", obj->filename);
+				return -EINVAL;
+			}
+			continue;
+		}
+		if (sym_bind != STB_LOCAL && sym_bind != STB_GLOBAL && sym_bind != STB_WEAK) {
+			pr_warn("ELF sym #%d is section #%zu has unsupported symbol binding %d\n",
+				i, sec->sec_idx, sym_bind);
+			return -EINVAL;
+		}
+		if (sym->st_shndx == 0) {
+			if (sym_type != STT_NOTYPE || sym_bind == STB_LOCAL
+			    || sym->st_value != 0 || sym->st_size != 0) {
+				pr_warn("ELF sym #%d is invalid extern symbol in %s\n",
+					i, obj->filename);
+
+				return -EINVAL;
+			}
+			continue;
+		}
+		if (sym->st_shndx < SHN_LORESERVE && sym->st_shndx >= obj->sec_cnt) {
 			pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
 				i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
 			return -EINVAL;
 		}
-		if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) {
+		if (sym_type == STT_SECTION) {
 			if (sym->st_value != 0)
 				return -EINVAL;
 			continue;
@@ -1137,16 +1162,16 @@ static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj
 		size_t dst_sym_idx;
 		int name_off;
 
-		/* we already have all-zero initial symbol */
-		if (sym->st_name == 0 && sym->st_info == 0 &&
-		    sym->st_other == 0 && sym->st_shndx == SHN_UNDEF &&
-		    sym->st_value == 0 && sym->st_size ==0)
+		/* We already validated all-zero symbol #0 and we already
+		 * appended it preventively to the final SYMTAB, so skip it.
+		 */
+		if (i == 0)
 			continue;
 
 		sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
 		if (!sym_name) {
 			pr_warn("can't fetch symbol name for symbol #%d in '%s'\n", i, obj->filename);
-			return -1;
+			return -EINVAL;
 		}
 
 		if (sym->st_shndx && sym->st_shndx < SHN_LORESERVE) {
-- 
2.30.2

[PATCH bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking

[Andrii Nakryiko]

It should never fail, but if it does, it's better to know about this rather
than end up with nonsensical type IDs.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/linker.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index dc202a5d8235..978756889de6 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -1425,6 +1425,15 @@ static int linker_fixup_btf(struct src_obj *obj)
 static int remap_type_id(__u32 *type_id, void *ctx)
 {
 	int *id_map = ctx;
+	int new_id = id_map[*type_id];
+
+	if (*type_id == 0)
+		return 0;
+
+	if (new_id == 0) {
+		pr_warn("failed to find new ID mapping for original BTF type ID %u\n", *type_id);
+		return -EINVAL;
+	}
 
 	*type_id = id_map[*type_id];
 
-- 
2.30.2

[PATCH bpf-next 11/17] libbpf: add linker extern resolution support for functions and global variables

[Andrii Nakryiko]

Add BPF static linker logic to resolve extern variables and functions across
multiple linked together BPF object files.

For that, linker maintains a separate list of struct glob_sym structures,
which keeps track of few pieces of metadata (is it extern or resolved global,
is it a weak symbol, which ELF section it belongs to, etc) and ties together
BTF type info and ELF symbol information and keeps them in sync.

With adding support for extern variables/funcs, it's now possible for some
sections to contain both extern and non-extern definitions. This means that
some sections may start out as ephemeral (if only externs are present and thus
there is not corresponding ELF section), but will be "upgraded" to actual ELF
section as symbols are resolved or new non-extern definitions are appended.

Additional care is taken to not duplicate extern entries in sections like
.kconfig and .ksyms.

Given libbpf requires BTF type to always be present for .kconfig/.ksym
externs, linker extends this requirement to all the externs, even those that
are supposed to be resolved during static linking and which won't be visible
to libbpf. With BTF information always present, static linker will check not
just ELF symbol matches, but entire BTF type signature match as well. That
logic is stricter that BPF CO-RE checks. It probably should be re-used by
.ksym resolution logic in libbpf as well, but that's left for follow up
patches.

To make it unnecessary to rewrite ELF symbols and minimize BTF type
rewriting/removal, ELF symbols that correspond to externs initially will be
updated in place once they are resolved. Similarly for BTF type info, VAR/FUNC
and var_secinfo's (sec_vars in struct bpf_linker) are staying stable, but
types they point to might get replaced when extern is resolved. This might
leave some left-over types (even though we try to minimize this for common
cases of having extern funcs with not argument names vs concrete function with
names properly specified). That can be addresses later with a generic BTF
garbage collection. That's left for a follow up as well.

Given BTF type appending phase is separate from ELF symbol
appending/resolution, special struct glob_sym->underlying_btf_id variable is
used to communicate resolution and rewrite decisions. 0 means
underlying_btf_id needs to be appended (it's not yet in final linker->btf), <0
values are used for temporary storage of source BTF type ID (not yet
rewritten), so -glob_sym->underlying_btf_id is BTF type id in obj-btf. But by
the end of linker_append_btf() phase, that underlying_btf_id will be remapped
and will always be > 0. This is the uglies part of the whole process, but
keeps the other parts much simpler due to stability of sec_var and VAR/FUNC
types, as well as ELF symbol, so please keep that in mind while reviewing.

BTF-defined maps require some extra custom logic and is addressed separate in
the next patch, so that to keep this one smaller and easier to review.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/linker.c | 846 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 787 insertions(+), 59 deletions(-)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 978756889de6..7f9b91760462 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -22,6 +22,8 @@
 #include "libbpf_internal.h"
 #include "strset.h"
 
+#define BTF_EXTERN_SEC ".extern"
+
 struct src_sec {
 	const char *sec_name;
 	/* positional (not necessarily ELF) index in an array of sections */
@@ -74,11 +76,36 @@ struct btf_ext_sec_data {
 	void *recs;
 };
 
+struct glob_sym {
+	/* ELF symbol index */
+	int sym_idx;
+	/* associated section id for .ksyms, .kconfig, etc, but not .extern */
+	int sec_id;
+	/* extern name offset in STRTAB */
+	int name_off;
+	/* optional associated BTF type ID */
+	int btf_id;
+	/* BTF type ID to which VAR/FUNC type is pointing to; used for
+	 * rewriting types when extern VAR/FUNC is resolved to a concrete
+	 * definition
+	 */
+	int underlying_btf_id;
+	/* sec_var index in the corresponding dst_sec, if exists */
+	int var_idx;
+
+	/* extern or resolved/global symbol */
+	bool is_extern;
+	/* weak or strong symbol, never goes back from strong to weak */
+	bool is_weak;
+};
+
 struct dst_sec {
 	char *sec_name;
 	/* positional (not necessarily ELF) index in an array of sections */
 	int id;
 
+	bool ephemeral;
+
 	/* ELF info */
 	size_t sec_idx;
 	Elf_Scn *scn;
@@ -120,6 +147,10 @@ struct bpf_linker {
 
 	struct btf *btf;
 	struct btf_ext *btf_ext;
+
+	/* global (including extern) ELF symbols */
+	int glob_sym_cnt;
+	struct glob_sym *glob_syms;
 };
 
 #define pr_warn_elf(fmt, ...)									\
@@ -138,6 +169,8 @@ static int linker_sanity_check_btf_ext(struct src_obj *obj);
 static int linker_fixup_btf(struct src_obj *obj);
 static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj);
 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj);
+static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
+				 Elf64_Sym *sym, const char *sym_name, int src_sym_idx);
 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj);
 static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj);
 static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj);
@@ -943,6 +976,7 @@ static int init_sec(struct bpf_linker *linker, struct dst_sec *dst_sec, struct s
 
 	dst_sec->sec_sz = 0;
 	dst_sec->sec_idx = 0;
+	dst_sec->ephemeral = src_sec->ephemeral;
 
 	/* ephemeral sections are just thin section shells lacking most parts */
 	if (src_sec->ephemeral)
@@ -1006,6 +1040,9 @@ static struct dst_sec *find_dst_sec_by_name(struct bpf_linker *linker, const cha
 
 static bool secs_match(struct dst_sec *dst, struct src_sec *src)
 {
+	if (dst->ephemeral || src->ephemeral)
+		return true;
+
 	if (dst->shdr->sh_type != src->shdr->sh_type) {
 		pr_warn("sec %s types mismatch\n", dst->sec_name);
 		return false;
@@ -1031,13 +1068,33 @@ static bool sec_content_is_same(struct dst_sec *dst_sec, struct src_sec *src_sec
 	return true;
 }
 
-static int extend_sec(struct dst_sec *dst, struct src_sec *src)
+static int extend_sec(struct bpf_linker *linker, struct dst_sec *dst, struct src_sec *src)
 {
 	void *tmp;
-	size_t dst_align = dst->shdr->sh_addralign;
-	size_t src_align = src->shdr->sh_addralign;
+	size_t dst_align, src_align;
 	size_t dst_align_sz, dst_final_sz;
+	int err;
+
+	/* Ephemeral source section doesn't contribute anything to ELF
+	 * section data.
+	 */
+	if (src->ephemeral)
+		return 0;
+
+	/* Some sections (like .maps) can contain both externs (and thus be
+	 * ephemeral) and non-externs (map definitions). So it's possible that
+	 * it has to be "upgraded" from ephemeral to non-ephemeral when the
+	 * first non-ephemeral entity appears. In such case, we add ELF
+	 * section, data, etc.
+	 */
+	if (dst->ephemeral) {
+		err = init_sec(linker, dst, src);
+		if (err)
+			return err;
+	}
 
+	dst_align = dst->shdr->sh_addralign;
+	src_align = src->shdr->sh_addralign;
 	if (dst_align == 0)
 		dst_align = 1;
 	if (dst_align < src_align)
@@ -1133,10 +1190,7 @@ static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj
 		/* record mapped section index */
 		src_sec->dst_id = dst_sec->id;
 
-		if (src_sec->ephemeral)
-			continue;
-
-		err = extend_sec(dst_sec, src_sec);
+		err = extend_sec(linker, dst_sec, src_sec);
 		if (err)
 			return err;
 	}
@@ -1147,21 +1201,16 @@ static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj
 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj)
 {
 	struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
-	Elf64_Sym *sym = symtab->data->d_buf, *dst_sym;
-	int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize;
+	Elf64_Sym *sym = symtab->data->d_buf;
+	int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize, err;
 	int str_sec_idx = symtab->shdr->sh_link;
+	const char *sym_name;
 
 	obj->sym_map = calloc(n + 1, sizeof(*obj->sym_map));
 	if (!obj->sym_map)
 		return -ENOMEM;
 
 	for (i = 0; i < n; i++, sym++) {
-		struct src_sec *src_sec = NULL;
-		struct dst_sec *dst_sec = NULL;
-		const char *sym_name;
-		size_t dst_sym_idx;
-		int name_off;
-
 		/* We already validated all-zero symbol #0 and we already
 		 * appended it preventively to the final SYMTAB, so skip it.
 		 */
@@ -1174,41 +1223,625 @@ static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj
 			return -EINVAL;
 		}
 
-		if (sym->st_shndx && sym->st_shndx < SHN_LORESERVE) {
-			src_sec = &obj->secs[sym->st_shndx];
-			if (src_sec->skipped)
+		err = linker_append_elf_sym(linker, obj, sym, sym_name, i);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+static Elf64_Sym *get_sym_by_idx(struct bpf_linker *linker, size_t sym_idx)
+{
+	struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
+	Elf64_Sym *syms = symtab->raw_data;
+
+	return &syms[sym_idx];
+}
+
+static struct glob_sym *find_glob_sym(struct bpf_linker *linker, const char *sym_name)
+{
+	struct glob_sym *glob_sym;
+	const char *name;
+	int i;
+
+	for (i = 0; i < linker->glob_sym_cnt; i++) {
+		glob_sym = &linker->glob_syms[i];
+		name = strset__data(linker->strtab_strs) + glob_sym->name_off;
+
+		if (strcmp(name, sym_name) == 0)
+			return glob_sym;
+	}
+
+	return NULL;
+}
+
+static struct glob_sym *add_glob_sym(struct bpf_linker *linker)
+{
+	struct glob_sym *syms, *sym;
+
+	syms = libbpf_reallocarray(linker->glob_syms, linker->glob_sym_cnt + 1,
+				   sizeof(*linker->glob_syms));
+	if (!syms)
+		return NULL;
+
+	sym = &syms[linker->glob_sym_cnt];
+	memset(sym, 0, sizeof(*sym));
+	sym->var_idx = -1;
+
+	linker->glob_syms = syms;
+	linker->glob_sym_cnt++;
+
+	return sym;
+}
+
+static bool glob_sym_btf_matches(const char *sym_name, bool exact,
+				 const struct btf *btf1, __u32 id1,
+				 const struct btf *btf2, __u32 id2)
+{
+	const struct btf_type *t1, *t2;
+	bool is_static1, is_static2;
+	const char *n1, *n2;
+	int i, n;
+
+recur:
+	n1 = n2 = NULL;
+	t1 = skip_mods_and_typedefs(btf1, id1, &id1);
+	t2 = skip_mods_and_typedefs(btf2, id2, &id2);
+
+	/* check if only one side is FWD, otherwise handle with common logic */
+	if (!exact && btf_is_fwd(t1) != btf_is_fwd(t2)) {
+		n1 = btf__str_by_offset(btf1, t1->name_off);
+		n2 = btf__str_by_offset(btf2, t2->name_off);
+		if (strcmp(n1, n2) != 0) {
+			pr_warn("global '%s': incompatible forward declaration names '%s' and '%s'\n",
+				sym_name, n1, n2);
+			return false;
+		}
+		/* validate if FWD kind matches concrete kind */
+		if (btf_is_fwd(t1)) {
+			if (btf_kflag(t1) && btf_is_union(t2))
+				return true;
+			if (!btf_kflag(t1) && btf_is_struct(t2))
+				return true;
+			pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
+				sym_name, btf_kflag(t1) ? "union" : "struct", btf_kind_str(t2));
+			return false;
+		} else {
+			if (btf_kflag(t2) && btf_is_union(t1))
+				return true;
+			if (!btf_kflag(t2) && btf_is_struct(t1))
+				return true;
+			pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
+				sym_name, btf_kflag(t2) ? "union" : "struct", btf_kind_str(t1));
+			return false;
+		}
+		return false;
+	}
+
+	if (btf_kind(t1) != btf_kind(t2)) {
+		pr_warn("global '%s': incompatible BTF kinds %s and %s\n",
+			sym_name, btf_kind_str(t1), btf_kind_str(t2));
+		return false;
+	}
+
+	switch (btf_kind(t1)) {
+	case BTF_KIND_STRUCT:
+	case BTF_KIND_UNION:
+	case BTF_KIND_ENUM:
+	case BTF_KIND_FWD:
+	case BTF_KIND_FUNC:
+	case BTF_KIND_VAR:
+		n1 = btf__str_by_offset(btf1, t1->name_off);
+		n2 = btf__str_by_offset(btf2, t2->name_off);
+		if (strcmp(n1, n2) != 0) {
+			pr_warn("global '%s': incompatible %s names '%s' and '%s'\n",
+				sym_name, btf_kind_str(t1), n1, n2);
+			return false;
+		}
+		break;
+	default:
+		break;
+	}
+
+	switch (btf_kind(t1)) {
+	case BTF_KIND_UNKN: /* void */
+	case BTF_KIND_FWD:
+		return true;
+	case BTF_KIND_INT:
+	case BTF_KIND_FLOAT:
+	case BTF_KIND_ENUM:
+		/* ignore encoding for int and enum values for enum */
+		if (t1->size != t2->size) {
+			pr_warn("global '%s': incompatible %s '%s' size %u and %u\n",
+				sym_name, btf_kind_str(t1), n1, t1->size, t2->size);
+			return false;
+		}
+		return true;
+	case BTF_KIND_PTR:
+		/* just validate overall shape of the referenced type, so no
+		 * contents comparison for struct/union, and allowd fwd vs
+		 * struct/union
+		 */
+		exact = false;
+		id1 = t1->type;
+		id2 = t2->type;
+		goto recur;
+	case BTF_KIND_ARRAY:
+		/* ignore index type and array size */
+		id1 = btf_array(t1)->type;
+		id2 = btf_array(t2)->type;
+		goto recur;
+	case BTF_KIND_FUNC:
+		/* extern and global linkages are compatible */
+		is_static1 = btf_func_linkage(t1) == BTF_FUNC_STATIC;
+		is_static2 = btf_func_linkage(t2) == BTF_FUNC_STATIC;
+		if (is_static1 != is_static2) {
+			pr_warn("global '%s': incompatible func '%s' linkage\n", sym_name, n1);
+			return false;
+		}
+
+		id1 = t1->type;
+		id2 = t2->type;
+		goto recur;
+	case BTF_KIND_VAR:
+		/* extern and global linkages are compatible */
+		is_static1 = btf_var(t1)->linkage == BTF_VAR_STATIC;
+		is_static2 = btf_var(t2)->linkage == BTF_VAR_STATIC;
+		if (is_static1 != is_static2) {
+			pr_warn("global '%s': incompatible var '%s' linkage\n", sym_name, n1);
+			return false;
+		}
+
+		id1 = t1->type;
+		id2 = t2->type;
+		goto recur;
+	case BTF_KIND_STRUCT:
+	case BTF_KIND_UNION: {
+		const struct btf_member *m1, *m2;
+
+		if (!exact)
+			return true;
+
+		if (btf_vlen(t1) != btf_vlen(t2)) {
+			pr_warn("global '%s': incompatible number of %s fields %u and %u\n",
+				sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
+			return false;
+		}
+
+		n = btf_vlen(t1);
+		m1 = btf_members(t1);
+		m2 = btf_members(t2);
+		for (i = 0; i < n; i++, m1++, m2++) {
+			n1 = btf__str_by_offset(btf1, m1->name_off);
+			n2 = btf__str_by_offset(btf2, m2->name_off);
+			if (strcmp(n1, n2) != 0) {
+				pr_warn("global '%s': incompatible field #%d names '%s' and '%s'\n",
+					sym_name, i, n1, n2);
+				return false;
+			}
+			if (m1->offset != m2->offset) {
+				pr_warn("global '%s': incompatible field #%d ('%s') offsets\n",
+					sym_name, i, n1);
+				return false;
+			}
+			if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
+				return false;
+		}
+
+		return true;
+	}
+	case BTF_KIND_FUNC_PROTO: {
+		const struct btf_param *m1, *m2;
+
+		if (btf_vlen(t1) != btf_vlen(t2)) {
+			pr_warn("global '%s': incompatible number of %s params %u and %u\n",
+				sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
+			return false;
+		}
+
+		n = btf_vlen(t1);
+		m1 = btf_params(t1);
+		m2 = btf_params(t2);
+		for (i = 0; i < n; i++, m1++, m2++) {
+			/* ignore func arg names */
+			if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
+				return false;
+		}
+
+		/* now check return type as well */
+		id1 = t1->type;
+		id2 = t2->type;
+		goto recur;
+	}
+
+	case BTF_KIND_TYPEDEF:
+	case BTF_KIND_VOLATILE:
+	case BTF_KIND_CONST:
+	case BTF_KIND_RESTRICT:
+	case BTF_KIND_DATASEC:
+	default:
+		pr_warn("global '%s': unsupported BTF kind %s\n",
+			sym_name, btf_kind_str(t1));
+		return false;
+	}
+}
+
+static bool glob_syms_match(const char *sym_name,
+			    struct bpf_linker *linker, struct glob_sym *glob_sym,
+			    struct src_obj *obj, Elf64_Sym *sym, size_t sym_idx, int btf_id)
+{
+	const struct btf_type *src_t;
+
+	/* if we are dealing with externs, BTF types describing both global
+	 * and extern VARs/FUNCs should be completely present in all files
+	 */
+	if (!glob_sym->btf_id || !btf_id) {
+		pr_warn("BTF info is missing for global symbol '%s'\n", sym_name);
+		return false;
+	}
+
+	src_t = btf__type_by_id(obj->btf, btf_id);
+	if (!btf_is_var(src_t) && !btf_is_func(src_t)) {
+		pr_warn("only extern variables and functions are supported, but got '%s' for '%s'\n",
+			btf_kind_str(src_t), sym_name);
+		return false;
+	}
+
+	if (!glob_sym_btf_matches(sym_name, true /*exact*/,
+				  linker->btf, glob_sym->btf_id, obj->btf, btf_id))
+		return false;
+
+	return true;
+}
+
+static bool btf_is_non_static(const struct btf_type *t)
+{
+	return (btf_is_var(t) && btf_var(t)->linkage != BTF_VAR_STATIC)
+	       || (btf_is_func(t) && btf_func_linkage(t) != BTF_FUNC_STATIC);
+}
+
+static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name,
+			     int *out_btf_sec_id, int *out_btf_id)
+{
+	int i, j, n = btf__get_nr_types(obj->btf), m, btf_id = 0;
+	const struct btf_type *t;
+	const struct btf_var_secinfo *vi;
+	const char *name;
+
+	for (i = 1; i <= n; i++)
+	{
+		t = btf__type_by_id(obj->btf, i);
+
+		/* some global and extern FUNCs and VARs might not be associated with any
+		 * DATASEC, so try to detect them in the same pass
+		 */
+		if (btf_is_non_static(t)) {
+			name = btf__str_by_offset(obj->btf, t->name_off);
+			if (strcmp(name, sym_name) != 0)
 				continue;
-			dst_sec = &linker->secs[src_sec->dst_id];
 
-			/* allow only one STT_SECTION symbol per section */
-			if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION && dst_sec->sec_sym_idx) {
-				obj->sym_map[i] = dst_sec->sec_sym_idx;
+			/* remember and still try to find DATASEC */
+			btf_id = i;
+			continue;
+		}
+
+		if (!btf_is_datasec(t))
+			continue;
+
+		vi = btf_var_secinfos(t);
+		for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
+			t = btf__type_by_id(obj->btf, vi->type);
+			name = btf__str_by_offset(obj->btf, t->name_off);
+
+			if (strcmp(name, sym_name) != 0)
+				continue;
+			if (btf_is_var(t) && btf_var(t)->linkage == BTF_VAR_STATIC)
 				continue;
+			if (btf_is_func(t) && btf_func_linkage(t) == BTF_FUNC_STATIC)
+				continue;
+
+			if (btf_id && btf_id != vi->type) {
+				pr_warn("global/extern '%s' BTF is ambiguous: both types #%d and #%u match\n",
+					sym_name, btf_id, vi->type);
+				return -EINVAL;
 			}
+
+			*out_btf_sec_id = i;
+			*out_btf_id = vi->type;
+
+			return 0;
 		}
+	}
 
-		name_off = strset__add_str(linker->strtab_strs, sym_name);
-		if (name_off < 0)
-			return name_off;
+	/* free-floating extern or global FUNC */
+	if (btf_id) {
+		*out_btf_sec_id = 0;
+		*out_btf_id = btf_id;
+		return 0;
+	}
 
-		dst_sym = add_new_sym(linker, &dst_sym_idx);
-		if (!dst_sym)
-			return -ENOMEM;
+	pr_warn("failed to find BTF info for global/extern symbol '%s'\n", sym_name);
+	return -ENOENT;
+}
 
-		dst_sym->st_name = name_off;
-		dst_sym->st_info = sym->st_info;
-		dst_sym->st_other = sym->st_other;
-		dst_sym->st_shndx = src_sec ? dst_sec->sec_idx : sym->st_shndx;
-		dst_sym->st_value = (src_sec ? src_sec->dst_off : 0) + sym->st_value;
-		dst_sym->st_size = sym->st_size;
+static struct src_sec *find_src_sec_by_name(struct src_obj *obj, const char *sec_name)
+{
+	struct src_sec *sec;
+	int i;
 
-		obj->sym_map[i] = dst_sym_idx;
+	for (i = 1; i < obj->sec_cnt; i++) {
+		sec = &obj->secs[i];
 
-		if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION && dst_sym) {
-			dst_sec->sec_sym_idx = dst_sym_idx;
-			dst_sym->st_value = 0;
+		if (strcmp(sec->sec_name, sec_name) == 0)
+			return sec;
+	}
+
+	return NULL;
+}
+
+static int complete_extern_btf_info(struct btf *dst_btf, int dst_id,
+				    struct btf *src_btf, int src_id)
+{
+	struct btf_type *dst_t = btf_type_by_id(dst_btf, dst_id);
+	struct btf_type *src_t = btf_type_by_id(src_btf, src_id);
+	struct btf_param *src_p, *dst_p;
+	const char *s;
+	int i, n, off;
+
+	/* We already made sure that source and destination types (FUNC or
+	 * VAR) match in terms of types and argument names.
+	 */
+	if (btf_is_var(dst_t)) {
+		btf_var(dst_t)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
+		return 0;
+	}
+
+	dst_t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_GLOBAL, 0);
+
+	/* now onto FUNC_PROTO types */
+	src_t = btf_type_by_id(src_btf, src_t->type);
+	dst_t = btf_type_by_id(dst_btf, dst_t->type);
+
+	/* Fill in all the argument names, which for extern FUNCs are missing.
+	 * We'll end up with two copies of FUNCs/VARs for externs, but that
+	 * will be taken care of by BTF dedup at the very end.
+	 * It might be that BTF types for extern in one file has less/more BTF
+	 * information (e.g., FWD instead of full STRUCT/UNION information),
+	 * but that should be (in most cases, subject to BTF dedup rules)
+	 * handled and resolved by BTF dedup algorithm as well, so we won't
+	 * worry about it. Our only job is to make sure that argument names
+	 * are populated on both sides, otherwise BTF dedup will pedantically
+	 * consider them different.
+	 */
+	src_p = btf_params(src_t);
+	dst_p = btf_params(dst_t);
+	for (i = 0, n = btf_vlen(dst_t); i < n; i++, src_p++, dst_p++) {
+		if (!src_p->name_off)
+			continue;
+
+		/* src_btf has more complete info, so add name to dst_btf */
+		s = btf__str_by_offset(src_btf, src_p->name_off);
+		off = btf__add_str(dst_btf, s);
+		if (off < 0)
+			return off;
+		dst_p->name_off = off;
+	}
+	return 0;
+}
+
+static void sym_update_bind(Elf64_Sym *sym, int sym_bind)
+{
+	sym->st_info = ELF64_ST_INFO(sym_bind, ELF64_ST_TYPE(sym->st_info));
+}
+
+static void sym_update_type(Elf64_Sym *sym, int sym_type)
+{
+	sym->st_info = ELF64_ST_INFO(ELF64_ST_BIND(sym->st_info), sym_type);
+}
+
+static void sym_update_visibility(Elf64_Sym *sym, int sym_vis)
+{
+	/* libelf doesn't provide setters for ST_VISIBILITY,
+	 * but it is stored in the lower 2 bits of st_other
+	 */
+	sym->st_other &= 0x03;
+	sym->st_other |= sym_vis;
+}
+
+static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
+				 Elf64_Sym *sym, const char *sym_name, int src_sym_idx)
+{
+	struct src_sec *src_sec = NULL;
+	struct dst_sec *dst_sec = NULL;
+	struct glob_sym *glob_sym = NULL;
+	int name_off, sym_type, sym_bind, sym_vis, err;
+	int btf_sec_id = 0, btf_id = 0;
+	size_t dst_sym_idx;
+	Elf64_Sym *dst_sym;
+	bool sym_is_extern;
+
+	sym_type = ELF64_ST_TYPE(sym->st_info);
+	sym_bind = ELF64_ST_BIND(sym->st_info);
+	sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
+	sym_is_extern = sym->st_shndx == SHN_UNDEF;
+
+	if (sym_is_extern) {
+		if (!obj->btf) {
+			pr_warn("externs without BTF info are not supported\n");
+			return -ENOTSUP;
 		}
+	} else if (sym->st_shndx < SHN_LORESERVE) {
+		src_sec = &obj->secs[sym->st_shndx];
+		if (src_sec->skipped)
+			return 0;
+		dst_sec = &linker->secs[src_sec->dst_id];
+
+		/* allow only one STT_SECTION symbol per section */
+		if (sym_type == STT_SECTION && dst_sec->sec_sym_idx) {
+			obj->sym_map[src_sym_idx] = dst_sec->sec_sym_idx;
+			return 0;
+		}
+	}
+
+	if (sym_bind == STB_LOCAL)
+		goto add_sym;
+
+	/* find matching BTF info */
+	err = find_glob_sym_btf(obj, sym, sym_name, &btf_sec_id, &btf_id);
+	if (err)
+		return err;
+
+	if (sym_is_extern && btf_sec_id) {
+		const char *sec_name = NULL;
+		const struct btf_type *t;
+
+		t = btf__type_by_id(obj->btf, btf_sec_id);
+		sec_name = btf__str_by_offset(obj->btf, t->name_off);
 
+		/* Clang puts unannotated extern vars into
+		 * '.extern' BTF DATASEC. Treat them the same
+		 * as unannotated extern funcs (which are
+		 * currently not put into any DATASECs).
+		 * Those don't have associated src_sec/dst_sec.
+		 */
+		if (strcmp(sec_name, BTF_EXTERN_SEC) != 0) {
+			src_sec = find_src_sec_by_name(obj, sec_name);
+			if (!src_sec) {
+				pr_warn("failed to find matching ELF sec '%s'\n", sec_name);
+				return -ENOENT;
+			}
+			dst_sec = &linker->secs[src_sec->dst_id];
+		}
+	}
+
+	glob_sym = find_glob_sym(linker, sym_name);
+	if (glob_sym) {
+		/* Preventively resolve to existing symbol. This is
+		 * needed for further relocation symbol remapping in
+		 * the next step of linking. */
+		obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
+
+		/* If both symbols are non-externs, at least one of
+		 * them has to be STB_WEAK, otherwise they are in
+		 * a conflict with each other.
+		 */
+		if (!sym_is_extern && !glob_sym->is_extern
+		    && !glob_sym->is_weak && sym_bind != STB_WEAK) {
+			pr_warn("conflicting non-weak symbol #%d (%s) definition in '%s'\n",
+				src_sym_idx, sym_name, obj->filename);
+			return -EINVAL;
+		}
+
+		if (!glob_syms_match(sym_name, linker, glob_sym, obj, sym, src_sym_idx, btf_id))
+			return -EINVAL;
+
+		dst_sym = get_sym_by_idx(linker, glob_sym->sym_idx);
+
+		/* If new symbol is strong, then force dst_sym to be strong as
+		 * well; this way a mix of weak and non-weak extern
+		 * definitions will end up being strong.
+		 */
+		if (sym_bind == STB_GLOBAL) {
+			/* We still need to preserve type (NOTYPE or
+			 * OBJECT/FUNC, depending on whether the symbol is
+			 * extern or not)
+			 */
+			sym_update_bind(dst_sym, STB_GLOBAL);
+			glob_sym->is_weak = false;
+		}
+
+		/* Non-default visibility is "contaminating", with stricter
+		 * visibility overwriting more permissive ones, even if more
+		 * permissive visibility comes from just an extern definition
+		 */
+		if (sym_vis > ELF64_ST_VISIBILITY(dst_sym->st_other))
+			sym_update_visibility(dst_sym, sym_vis);
+
+		/* If the new symbol is extern, then regardless if
+		 * existing symbol is extern or resolved global, just
+		 * keep the existing one untouched.
+		 */
+		if (sym_is_extern)
+			return 0;
+
+		/* If existing symbol is a strong resolved symbol, bail out,
+		 * because we lost resolution battle have nothing to
+		 * contribute. We already checked abover that there is no
+		 * strong-strong conflict. We also already tightened binding
+		 * and visibility, so nothing else to contribute at that point.
+		 */
+		if (!glob_sym->is_extern && sym_bind == STB_WEAK)
+			return 0;
+
+		/* At this point, new symbol is strong non-extern,
+		 * so overwrite glob_sym with new symbol information.
+		 * Preserve binding and visibility.
+		 */
+		sym_update_type(dst_sym, sym_type);
+		dst_sym->st_shndx = dst_sec->sec_idx;
+		dst_sym->st_value = src_sec->dst_off + sym->st_value;
+		dst_sym->st_size = sym->st_size;
+
+		/* see comment below about dst_sec->id vs dst_sec->sec_idx */
+		glob_sym->sec_id = dst_sec->id;
+		glob_sym->is_extern = false;
+		/* never relax strong to weak binding */
+		if (sym_bind == STB_GLOBAL)
+			glob_sym->is_weak = false;
+
+		if (complete_extern_btf_info(linker->btf, glob_sym->btf_id,
+					     obj->btf, btf_id))
+			return -EINVAL;
+
+		/* request updating VAR's/FUNC's underlying BTF type when appending BTF type */
+		glob_sym->underlying_btf_id = 0;
+
+		obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
+		return 0;
+	}
+
+add_sym:
+	name_off = strset__add_str(linker->strtab_strs, sym_name);
+	if (name_off < 0)
+		return name_off;
+
+	dst_sym = add_new_sym(linker, &dst_sym_idx);
+	if (!dst_sym)
+		return -ENOMEM;
+
+	dst_sym->st_name = name_off;
+	dst_sym->st_info = sym->st_info;
+	dst_sym->st_other = sym->st_other;
+	dst_sym->st_shndx = dst_sec ? dst_sec->sec_idx : sym->st_shndx;
+	dst_sym->st_value = (src_sec ? src_sec->dst_off : 0) + sym->st_value;
+	dst_sym->st_size = sym->st_size;
+
+	obj->sym_map[src_sym_idx] = dst_sym_idx;
+
+	if (sym_type == STT_SECTION && dst_sym) {
+		dst_sec->sec_sym_idx = dst_sym_idx;
+		dst_sym->st_value = 0;
+	}
+
+	if (sym_bind != STB_LOCAL) {
+		glob_sym = add_glob_sym(linker);
+		if (!glob_sym)
+			return -ENOMEM;
+
+		glob_sym->sym_idx = dst_sym_idx;
+		/* we use dst_sec->id (and not dst_sec->sec_idx), because
+		 * ephemeral sections (.kconfig, .ksyms, etc) don't have
+		 * sec_idx (as they don't have corresponding ELF section), but
+		 * still have id. .extern doesn't have even ephemeral section
+		 * associated with it, so dst_sec->id == dst_sec->sec_idx == 0.
+		 */
+		glob_sym->sec_id = dst_sec ? dst_sec->id : 0;
+		glob_sym->name_off = name_off;
+		/* we will fill btf_id in during BTF merging step */
+		glob_sym->btf_id = 0;
+		glob_sym->is_extern = sym_is_extern;
+		glob_sym->is_weak = sym_bind == STB_WEAK;
 	}
 
 	return 0;
@@ -1258,7 +1891,7 @@ static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *ob
 		dst_sec->shdr->sh_info = dst_linked_sec->sec_idx;
 
 		src_sec->dst_id = dst_sec->id;
-		err = extend_sec(dst_sec, src_sec);
+		err = extend_sec(linker, dst_sec, src_sec);
 		if (err)
 			return err;
 
@@ -1311,21 +1944,6 @@ static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *ob
 	return 0;
 }
 
-static struct src_sec *find_src_sec_by_name(struct src_obj *obj, const char *sec_name)
-{
-	struct src_sec *sec;
-	int i;
-
-	for (i = 1; i < obj->sec_cnt; i++) {
-		sec = &obj->secs[i];
-
-		if (strcmp(sec->sec_name, sec_name) == 0)
-			return sec;
-	}
-
-	return NULL;
-}
-
 static Elf64_Sym *find_sym_by_name(struct src_obj *obj, size_t sec_idx,
 				   int sym_type, const char *sym_name)
 {
@@ -1380,12 +1998,32 @@ static int linker_fixup_btf(struct src_obj *obj)
 				t->size = sec->shdr->sh_size;
 		} else {
 			/* BTF can have some sections that are not represented
-			 * in ELF, e.g., .kconfig and .ksyms, which are used
-			 * for special extern variables.  Here we'll
-			 * pre-create "section shells" for them to be able to
-			 * keep track of extra per-section metadata later
-			 * (e.g., BTF variables).
+			 * in ELF, e.g., .kconfig, .ksyms, .extern, which are used
+			 * for special extern variables.
+			 *
+			 * For all but one such special (ephemeral)
+			 * sections, we pre-create "section shells" to be able
+			 * to keep track of extra per-section metadata later
+			 * (e.g., those BTF extern variables).
+			 *
+			 * .extern is even more special, though, because it
+			 * contains extern variables that need to be resolved
+			 * by static linker, not libbpf and kernel. When such
+			 * externs are resolved, we are going to remove them
+			 * from .extern BTF section and might end up not
+			 * needing it at all. Each resolved extern should have
+			 * matching non-extern VAR/FUNC in other sections.
+			 *
+			 * We do support leaving some of the externs
+			 * unresolved, though, to support cases of building
+			 * libraries, which will later be linked against final
+			 * BPF applications. So if at finalization we still
+			 * see unresolved externs, we'll create .extern
+			 * section on our own.
 			 */
+			if (strcmp(sec_name, BTF_EXTERN_SEC) == 0)
+				continue;
+
 			sec = add_src_sec(obj, sec_name);
 			if (!sec)
 				return -ENOMEM;
@@ -1444,6 +2082,7 @@ static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
 {
 	const struct btf_type *t;
 	int i, j, n, start_id, id;
+	const char *name;
 
 	if (!obj->btf)
 		return 0;
@@ -1456,12 +2095,40 @@ static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
 		return -ENOMEM;
 
 	for (i = 1; i <= n; i++) {
+		struct glob_sym *glob_sym = NULL;
+
 		t = btf__type_by_id(obj->btf, i);
 
 		/* DATASECs are handled specially below */
 		if (btf_kind(t) == BTF_KIND_DATASEC)
 			continue;
 
+		if (btf_is_non_static(t)) {
+			/* there should be glob_sym already */
+			name = btf__str_by_offset(obj->btf, t->name_off);
+			glob_sym = find_glob_sym(linker, name);
+
+			/* VARs without corresponding glob_sym are those that
+			 * belong to skipped/deduplicated sections (i.e.,
+			 * license and version), so just skip them
+			 */
+			if (!glob_sym)
+				continue;
+
+			if (glob_sym->underlying_btf_id == 0)
+				glob_sym->underlying_btf_id = -t->type;
+
+			/* globals from previous object files that match our
+			 * VAR/FUNC already have a corresponding associated
+			 * BTF type, so just make sure to use it
+			 */
+			if (glob_sym->btf_id) {
+				/* reuse existing BTF type for global var/func */
+				obj->btf_type_map[i] = glob_sym->btf_id;
+				continue;
+			}
+		}
+
 		id = btf__add_type(linker->btf, obj->btf, t);
 		if (id < 0) {
 			pr_warn("failed to append BTF type #%d from file '%s'\n", i, obj->filename);
@@ -1469,6 +2136,12 @@ static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
 		}
 
 		obj->btf_type_map[i] = id;
+
+		/* record just appended BTF type for var/func */
+		if (glob_sym) {
+			glob_sym->btf_id = id;
+			glob_sym->underlying_btf_id = -t->type;
+		}
 	}
 
 	/* remap all the types except DATASECs */
@@ -1480,6 +2153,22 @@ static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
 			return -EINVAL;
 	}
 
+	/* Rewrite VAR/FUNC underlying types (i.e., FUNC's FUNC_PROTO and VAR's
+	 * actual type), if necessary
+	 */
+	for (i = 0; i < linker->glob_sym_cnt; i++) {
+		struct glob_sym *glob_sym = &linker->glob_syms[i];
+		struct btf_type *glob_t;
+
+		if (glob_sym->underlying_btf_id >= 0)
+			continue;
+
+		glob_sym->underlying_btf_id = obj->btf_type_map[-glob_sym->underlying_btf_id];
+
+		glob_t = btf_type_by_id(linker->btf, glob_sym->btf_id);
+		glob_t->type = glob_sym->underlying_btf_id;
+	}
+
 	/* append DATASEC info */
 	for (i = 1; i < obj->sec_cnt; i++) {
 		struct src_sec *src_sec;
@@ -1507,6 +2196,42 @@ static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
 		n = btf_vlen(t);
 		for (j = 0; j < n; j++, src_var++) {
 			void *sec_vars = dst_sec->sec_vars;
+			int new_id = obj->btf_type_map[src_var->type];
+			struct glob_sym *glob_sym = NULL;
+
+			t = btf_type_by_id(linker->btf, new_id);
+			if (btf_is_non_static(t)) {
+				name = btf__str_by_offset(linker->btf, t->name_off);
+				glob_sym = find_glob_sym(linker, name);
+				if (glob_sym->sec_id != dst_sec->id) {
+					pr_warn("global '%s': section mismatch %d vs %d\n",
+						name, glob_sym->sec_id, dst_sec->id);
+					return -EINVAL;
+				}
+			}
+
+			/* If there is already a member (VAR or FUNC) mapped
+			 * to the same type, don't add a duplicate entry.
+			 * This will happen when multiple object files define
+			 * the same extern VARs/FUNCs.
+			 */
+			if (glob_sym && glob_sym->var_idx >= 0) {
+				__s64 sz;
+
+				dst_var = &dst_sec->sec_vars[glob_sym->var_idx];
+				/* Because underlying BTF type might have
+				 * changed, so might its size have changed, so
+				 * re-calculate and update it in sec_var.
+				 */
+				sz = btf__resolve_size(linker->btf, glob_sym->underlying_btf_id);
+				if (sz < 0) {
+					pr_warn("global '%s': failed to resolve size of underlying type: %d\n",
+						name, (int)sz);
+					return -EINVAL;
+				}
+				dst_var->size = sz;
+				continue;
+			}
 
 			sec_vars = libbpf_reallocarray(sec_vars,
 						       dst_sec->sec_var_cnt + 1,
@@ -1521,6 +2246,9 @@ static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
 			dst_var->type = obj->btf_type_map[src_var->type];
 			dst_var->size = src_var->size;
 			dst_var->offset = src_sec->dst_off + src_var->offset;
+
+			if (glob_sym)
+				glob_sym->var_idx = dst_sec->sec_var_cnt - 1;
 		}
 	}
 
-- 
2.30.2

[PATCH bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section

[Andrii Nakryiko]

Add extra logic to handle map externs (only BTF-defined maps are supported for
linking). Re-use the map parsing logic used during bpf_object__open(). Map
externs are currently restricted to always and only specify map type, key
type and/or size, and value type and/or size. Nothing extra is allowed. If any
of those attributes are mismatched between extern and actual map definition,
linker will report an error.

The original intent was to allow for extern to specify attributes that matters
(to user) to enforce. E.g., if you specify just key information and omit
value, then any value fits. Similarly, it should have been possible to enforce
map_flags, pinning, and any other possible map attribute. Unfortunately, that
means that multiple externs can be only partially overlapping with each other,
which means linker would need to combine their type definitions to end up with
the most restrictive and fullest map definition. This requires an extra amount
of BTF manipulation which at this time was deemed unnecessary and would
require further extending generic BTF writer APIs. So that is left for future
follow ups, if there will be demand for that. But the idea seems intresting
and useful, so I want to document it here.

Otherwise extern maps behave intuitively, just like extern vars and funcs.
Weak definitions are also supported.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/linker.c | 167 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 167 insertions(+)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 7f9b91760462..9432c125fa43 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -1467,6 +1467,169 @@ static bool glob_sym_btf_matches(const char *sym_name, bool exact,
 	}
 }
 
+static bool map_defs_match(const char *sym_name, bool full_match,
+			   const struct btf *main_btf,
+			   const struct btf_map_def *main_def,
+			   const struct btf_map_def *main_inner_def,
+			   const struct btf *extra_btf,
+			   const struct btf_map_def *extra_def,
+			   const struct btf_map_def *extra_inner_def)
+{
+	const char *reason;
+
+	if (main_def->map_type != extra_def->map_type) {
+		reason = "type";
+		goto mismatch;
+	}
+
+	/* check key type/size match */
+	if (main_def->key_size != extra_def->key_size) {
+		reason = "key_size";
+		goto mismatch;
+	}
+	if (!!main_def->key_type_id != !!extra_def->key_type_id) {
+		reason = "key type";
+		goto mismatch;
+	}
+	if ((main_def->parts & MAP_DEF_KEY_TYPE)
+	     && !glob_sym_btf_matches(sym_name, true /*exact*/,
+				      main_btf, main_def->key_type_id,
+				      extra_btf, extra_def->key_type_id)) {
+		reason = "key type";
+		goto mismatch;
+	}
+
+	/* validate value type/size match */
+	if (main_def->value_size != extra_def->value_size) {
+		reason = "value_size";
+		goto mismatch;
+	}
+	if (!!main_def->value_type_id != !!extra_def->value_type_id) {
+		reason = "value type";
+		goto mismatch;
+	}
+	if ((main_def->parts & MAP_DEF_VALUE_TYPE)
+	     && !glob_sym_btf_matches(sym_name, true /*exact*/,
+				      main_btf, main_def->value_type_id,
+				      extra_btf, extra_def->value_type_id)) {
+		reason = "key type";
+		goto mismatch;
+	}
+
+	/* when having non-extern and extern, we don't compare the rest,
+	 * because externs are currently enforced to only specify map type,
+	 * key, and value info
+	 */
+	if (!full_match)
+		return true;
+
+	if (main_def->max_entries != extra_def->max_entries) {
+		reason = "max_entries";
+		goto mismatch;
+	}
+	if (main_def->map_flags != extra_def->map_flags) {
+		reason = "map_flags";
+		goto mismatch;
+	}
+	if (main_def->numa_node != extra_def->numa_node) {
+		reason = "numa_node";
+		goto mismatch;
+	}
+	if (main_def->pinning != extra_def->pinning) {
+		reason = "pinning";
+		goto mismatch;
+	}
+
+	if ((main_def->parts & MAP_DEF_INNER_MAP) != (extra_def->parts & MAP_DEF_INNER_MAP)) {
+		reason = "inner map";
+		goto mismatch;
+	}
+
+	if (main_def->parts & MAP_DEF_INNER_MAP) {
+		char inner_map_name[128];
+
+		snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", sym_name);
+
+		return map_defs_match(inner_map_name, true /*full_match*/,
+				      main_btf, main_inner_def, NULL,
+				      extra_btf, extra_inner_def, NULL);
+	}
+
+	return true;
+
+mismatch:
+	pr_warn("global '%s': map %s mismatch\n", sym_name, reason);
+	return false;
+}
+
+#define MAP_DEF_EXTERN_PARTS (MAP_DEF_MAP_TYPE				\
+			      | MAP_DEF_KEY_SIZE | MAP_DEF_KEY_TYPE	\
+			      | MAP_DEF_VALUE_SIZE | MAP_DEF_VALUE_TYPE)
+
+static bool glob_map_defs_match(const char *sym_name,
+				struct bpf_linker *linker, struct glob_sym *glob_sym,
+				struct src_obj *obj, Elf64_Sym *sym, int btf_id)
+{
+	bool sym_is_extern = sym->st_shndx == SHN_UNDEF;
+	struct btf_map_def dst_def = {}, dst_inner_def = {};
+	struct btf_map_def src_def = {}, src_inner_def = {};
+	const struct btf_type *t;
+	int err;
+
+	t = btf__type_by_id(obj->btf, btf_id);
+	if (!btf_is_var(t)) {
+		pr_warn("global '%s': invalid map definition type [%d]\n", sym_name, btf_id);
+		return false;
+	}
+	t = skip_mods_and_typedefs(obj->btf, t->type, NULL);
+
+	err = parse_btf_map_def(sym_name, obj->btf, t, true /*strict*/, &src_def, &src_inner_def);
+	if (err) {
+		pr_warn("global '%s': invalid map definition\n", sym_name);
+		return false;
+	}
+
+	/* We restict extern map defs to only specify map type and key/value
+	 * type or size. Inner map definitions are prohibited for now as well.
+	 */
+	if (sym_is_extern && (src_def.parts & ~MAP_DEF_EXTERN_PARTS)) {
+		pr_warn("global '%s': extern map can specify only map type and key/value info\n",
+			sym_name);
+		return false;
+	}
+
+	/* re-parse existing map definition */
+	t = btf__type_by_id(linker->btf, glob_sym->btf_id);
+	t = skip_mods_and_typedefs(linker->btf, t->type, NULL);
+	err = parse_btf_map_def(sym_name, linker->btf, t, true /*strict*/, &dst_def, &dst_inner_def);
+	if (err) {
+		/* this should not happen, because we already validated it */
+		pr_warn("global '%s': invalid dst map definition\n", sym_name);
+		return false;
+	}
+
+	if (glob_sym->is_extern != sym_is_extern) {
+		/* extern map def should be a subset of non-extern one */
+		if (sym_is_extern)
+			/* existing map def is the main one */
+			return map_defs_match(sym_name, false /*full_match*/,
+					      linker->btf, &dst_def, &dst_inner_def,
+					      obj->btf, &src_def, &src_inner_def);
+		else
+			/* new map def is the main one */
+			return map_defs_match(sym_name, false /*full_match*/,
+					      obj->btf, &src_def, &src_inner_def,
+					      linker->btf, &dst_def, &dst_inner_def);
+	} else {
+		/* map defs should match exactly regardless of extern/extern
+		 * or non-extern/non-extern case
+		 */
+		return map_defs_match(sym_name, true /*full_match*/,
+				      linker->btf, &dst_def, &dst_inner_def,
+				      obj->btf, &src_def, &src_inner_def);
+	}
+}
+
 static bool glob_syms_match(const char *sym_name,
 			    struct bpf_linker *linker, struct glob_sym *glob_sym,
 			    struct src_obj *obj, Elf64_Sym *sym, size_t sym_idx, int btf_id)
@@ -1488,6 +1651,10 @@ static bool glob_syms_match(const char *sym_name,
 		return false;
 	}
 
+	/* deal with .maps definitions specially */
+	if (glob_sym->sec_id && strcmp(linker->secs[glob_sym->sec_id].sec_name, MAPS_ELF_SEC) == 0)
+		return glob_map_defs_match(sym_name, linker, glob_sym, obj, sym, btf_id);
+
 	if (!glob_sym_btf_matches(sym_name, true /*exact*/,
 				  linker->btf, glob_sym->btf_id, obj->btf, btf_id))
 		return false;
-- 
2.30.2

[PATCH bpf-next 13/17] selftests/bpf: use -O0 instead of -Og in selftests builds

[Andrii Nakryiko]

While -Og is designed to work well with debugger, it's still inferior to -O0
in terms of debuggability experience. It will cause some variables to still be
inlined, it will also prevent single-stepping some statements and otherwise
interfere with debugging experience. So switch to -O0 which turns off any
optimization and provides the best debugging experience.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/Makefile | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 6448c626498f..22a88580b491 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -21,7 +21,7 @@ endif
 
 BPF_GCC		?= $(shell command -v bpf-gcc;)
 SAN_CFLAGS	?=
-CFLAGS += -g -Og -rdynamic -Wall $(GENFLAGS) $(SAN_CFLAGS)		\
+CFLAGS += -g -O0 -rdynamic -Wall $(GENFLAGS) $(SAN_CFLAGS)		\
 	  -I$(CURDIR) -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)		\
 	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(OUTPUT)			\
 	  -Dbpf_prog_load=bpf_prog_test_load				\
@@ -201,7 +201,7 @@ $(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)    \
 		    $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/bpftool
 	$(Q)$(MAKE) $(submake_extras)  -C $(BPFTOOLDIR)			       \
 		    CC=$(HOSTCC) LD=$(HOSTLD)				       \
-		    EXTRA_CFLAGS='-g -Og'				       \
+		    EXTRA_CFLAGS='-g -O0'				       \
 		    OUTPUT=$(HOST_BUILD_DIR)/bpftool/			       \
 		    prefix= DESTDIR=$(HOST_SCRATCH_DIR)/ install
 
@@ -219,7 +219,7 @@ $(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
 	   ../../../include/uapi/linux/bpf.h                                   \
 	   | $(INCLUDE_DIR) $(BUILD_DIR)/libbpf
 	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
-		    EXTRA_CFLAGS='-g -Og'					       \
+		    EXTRA_CFLAGS='-g -O0'				       \
 		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
 
 ifneq ($(BPFOBJ),$(HOST_BPFOBJ))
@@ -227,7 +227,7 @@ $(HOST_BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)                \
 	   ../../../include/uapi/linux/bpf.h                                   \
 	   | $(INCLUDE_DIR) $(HOST_BUILD_DIR)/libbpf
 	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR)                             \
-		    EXTRA_CFLAGS='-g -Og'					       \
+		    EXTRA_CFLAGS='-g -O0'				       \
 		    OUTPUT=$(HOST_BUILD_DIR)/libbpf/ CC=$(HOSTCC) LD=$(HOSTLD) \
 		    DESTDIR=$(HOST_SCRATCH_DIR)/ prefix= all install_headers
 endif
-- 
2.30.2

[PATCH bpf-next 14/17] selftests/bpf: omit skeleton generation for multi-linked BPF object files

[Andrii Nakryiko]

Skip generating individual BPF skeletons for files that are supposed to be
linked together to form the final BPF object file. Very often such files are
"incomplete" BPF object files, which will fail libbpf bpf_object__open() step,
if used individually, thus failing BPF skeleton generation. This is by design,
so skip individual BPF skeletons and only validate them as part of their
linked final BPF object file and skeleton.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 22a88580b491..cfa3e91c9a49 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -307,6 +307,8 @@ LINKED_SKELS := test_static_linked.skel.h
 
 test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o
 
+LINKED_BPF_SRCS := $(patsubst %.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
+
 # Set up extra TRUNNER_XXX "temporary" variables in the environment (relies on
 # $eval()) and pass control to DEFINE_TEST_RUNNER_RULES.
 # Parameters:
@@ -325,7 +327,7 @@ TRUNNER_TESTS_HDR := $(TRUNNER_TESTS_DIR)/tests.h
 TRUNNER_BPF_SRCS := $$(notdir $$(wildcard $(TRUNNER_BPF_PROGS_DIR)/*.c))
 TRUNNER_BPF_OBJS := $$(patsubst %.c,$$(TRUNNER_OUTPUT)/%.o, $$(TRUNNER_BPF_SRCS))
 TRUNNER_BPF_SKELS := $$(patsubst %.c,$$(TRUNNER_OUTPUT)/%.skel.h,	\
-				 $$(filter-out $(SKEL_BLACKLIST),	\
+				 $$(filter-out $(SKEL_BLACKLIST) $(LINKED_BPF_SRCS),\
 					       $$(TRUNNER_BPF_SRCS)))
 TRUNNER_BPF_SKELS_LINKED := $$(addprefix $$(TRUNNER_OUTPUT)/,$(LINKED_SKELS))
 TEST_GEN_FILES += $$(TRUNNER_BPF_OBJS)
-- 
2.30.2

[PATCH bpf-next 15/17] selftests/bpf: add function linking selftest

[Andrii Nakryiko]

Add selftest validating various aspects of statically linking functions:
  - no conflicts and correct resolution for name-conflicting static funcs;
  - correct resolution of extern functions;
  - correct handling of weak functions, both resolution itself and libbpf's
    handling of unused weak function that "lost" (it leaves gaps in code with
    no ELF symbols);
  - correct handling of hidden visibility to turn global function into
    "static" for the purpose of BPF verification.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/Makefile          |  3 +-
 .../selftests/bpf/prog_tests/linked_funcs.c   | 42 +++++++++++
 .../selftests/bpf/progs/linked_funcs1.c       | 73 +++++++++++++++++++
 .../selftests/bpf/progs/linked_funcs2.c       | 73 +++++++++++++++++++
 4 files changed, 190 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_funcs.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs1.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs2.c

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index cfa3e91c9a49..c5d25aef1074 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -303,9 +303,10 @@ endef
 
 SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
 
-LINKED_SKELS := test_static_linked.skel.h
+LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h
 
 test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o
+linked_funcs.skel.h-deps := linked_funcs1.o linked_funcs2.o
 
 LINKED_BPF_SRCS := $(patsubst %.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
 
diff --git a/tools/testing/selftests/bpf/prog_tests/linked_funcs.c b/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
new file mode 100644
index 000000000000..768166a7c534
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+#include <sys/syscall.h>
+#include "linked_funcs.skel.h"
+
+void test_linked_funcs(void)
+{
+	int err;
+	struct linked_funcs* skel;
+
+	skel = linked_funcs__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	skel->rodata->my_tid = syscall(SYS_gettid);
+	skel->rodata->syscall_id = SYS_getpgid;
+
+	err = linked_funcs__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
+	err = linked_funcs__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto cleanup;
+
+	/* trigger */
+	syscall(SYS_getpgid);
+
+	ASSERT_EQ(skel->bss->output_val1, 2000 + 2000, "output_val1");
+	ASSERT_EQ(skel->bss->output_ctx1, SYS_getpgid, "output_ctx1");
+	ASSERT_EQ(skel->bss->output_weak1, 42, "output_weak1");
+
+	ASSERT_EQ(skel->bss->output_val2, 2 * 1000 + 2 * (2 * 1000), "output_val2");
+	ASSERT_EQ(skel->bss->output_ctx2, SYS_getpgid, "output_ctx2");
+	/* output_weak2 should never be updated */
+	ASSERT_EQ(skel->bss->output_weak2, 0, "output_weak2");
+
+cleanup:
+	linked_funcs__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/linked_funcs1.c b/tools/testing/selftests/bpf/progs/linked_funcs1.c
new file mode 100644
index 000000000000..cc621d4e4d82
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_funcs1.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+/* weak and shared between two files */
+const volatile int my_tid __weak = 0;
+const volatile long syscall_id __weak = 0;
+
+int output_val1 = 0;
+int output_ctx1 = 0;
+int output_weak1 = 0;
+
+/* same "subprog" name in all files, but it's ok because they all are static */
+static __noinline int subprog(int x)
+{
+	/* but different formula */
+	return x * 1;
+}
+
+/* Global functions can't be void */
+int set_output_val1(int x)
+{
+	output_val1 = x + subprog(x);
+	return x;
+}
+
+/* This function can't be verified as global, as it assumes raw_tp/sys_enter
+ * context and accesses syscall id (second argument). So we mark it as
+ * __hidden, so that libbpf will mark it as static in the final object file,
+ * right before verifying it in the kernel.
+ *
+ * But we don't mark it as __hidden here, rather at extern site. __hidden is
+ * "contaminating" visibility, so it will get propagated from either extern or
+ * actual definition (including from the losing __weak definition).
+ */
+void set_output_ctx1(__u64 *ctx)
+{
+	output_ctx1 = ctx[1]; /* long id, same as in BPF_PROG below */
+}
+
+/* this weak instance should win because it's the first one */
+__weak int set_output_weak(int x)
+{
+	output_weak1 = x;
+	return x;
+}
+
+extern int set_output_val2(int x);
+
+/* here we'll force set_output_ctx2() to be __hidden in the final obj file */
+__hidden extern void set_output_ctx2(__u64 *ctx);
+
+SEC("raw_tp/sys_enter")
+int BPF_PROG(handler1, struct pt_regs *regs, long id)
+{
+	if (my_tid != (u32)bpf_get_current_pid_tgid() || id != syscall_id)
+		return 0;
+
+	set_output_val2(1000);
+	set_output_ctx2(ctx); /* ctx definition is hidden in BPF_PROG macro */
+
+	/* keep input value the same across both files to avoid dependency on
+	 * handler call order; differentiate by output_weak1 vs output_weak2.
+	 */
+	set_output_weak(42);
+
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/linked_funcs2.c b/tools/testing/selftests/bpf/progs/linked_funcs2.c
new file mode 100644
index 000000000000..a5a935a4f748
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_funcs2.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+/* weak and shared between both files */
+const volatile int my_tid __weak = 0;
+const volatile long syscall_id __weak = 0;
+
+int output_val2 = 0;
+int output_ctx2 = 0;
+int output_weak2 = 0; /* should stay zero */
+
+/* same "subprog" name in all files, but it's ok because they all are static */
+static __noinline int subprog(int x)
+{
+	/* but different formula */
+	return x * 2;
+}
+
+/* Global functions can't be void */
+int set_output_val2(int x)
+{
+	output_val2 = 2 * x + 2 * subprog(x);
+	return 2 * x;
+}
+
+/* This function can't be verified as global, as it assumes raw_tp/sys_enter
+ * context and accesses syscall id (second argument). So we mark it as
+ * __hidden, so that libbpf will mark it as static in the final object file,
+ * right before verifying it in the kernel.
+ *
+ * But we don't mark it as __hidden here, rather at extern site. __hidden is
+ * "contaminating" visibility, so it will get propagated from either extern or
+ * actual definition (including from the losing __weak definition).
+ */
+void set_output_ctx2(__u64 *ctx)
+{
+	output_ctx2 = ctx[1]; /* long id, same as in BPF_PROG below */
+}
+
+/* this weak instance should lose, because it will be processed second */
+__weak int set_output_weak(int x)
+{
+	output_weak2 = x;
+	return 2 * x;
+}
+
+extern int set_output_val1(int x);
+
+/* here we'll force set_output_ctx1() to be __hidden in the final obj file */
+__hidden extern void set_output_ctx1(__u64 *ctx);
+
+SEC("raw_tp/sys_enter")
+int BPF_PROG(handler2, struct pt_regs *regs, long id)
+{
+	if (my_tid != (u32)bpf_get_current_pid_tgid() || id != syscall_id)
+		return 0;
+
+	set_output_val1(2000);
+	set_output_ctx1(ctx); /* ctx definition is hidden in BPF_PROG macro */
+
+	/* keep input value the same across both files to avoid dependency on
+	 * handler call order; differentiate by output_weak1 vs output_weak2.
+	 */
+	set_output_weak(42);
+
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
-- 
2.30.2

[PATCH bpf-next 16/17] selftests/bpf: add global variables linking selftest

[Andrii Nakryiko]

Add selftest validating various aspects of statically linking global
variables:
  - correct resolution of extern variables across .bss, .data, and .rodata
    sections;
  - correct handling of weak definitions;
  - correct de-duplication of repeating special externs (.kconfig, .ksyms).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/Makefile          |  3 +-
 .../selftests/bpf/prog_tests/linked_vars.c    | 43 +++++++++++++
 .../selftests/bpf/progs/linked_vars1.c        | 60 ++++++++++++++++++
 .../selftests/bpf/progs/linked_vars2.c        | 61 +++++++++++++++++++
 4 files changed, 166 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_vars.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_vars1.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_vars2.c

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index c5d25aef1074..a690fd125c6d 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -303,10 +303,11 @@ endef
 
 SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
 
-LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h
+LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h linked_vars.skel.h
 
 test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o
 linked_funcs.skel.h-deps := linked_funcs1.o linked_funcs2.o
+linked_vars.skel.h-deps := linked_vars1.o linked_vars2.o
 
 LINKED_BPF_SRCS := $(patsubst %.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
 
diff --git a/tools/testing/selftests/bpf/prog_tests/linked_vars.c b/tools/testing/selftests/bpf/prog_tests/linked_vars.c
new file mode 100644
index 000000000000..4122ec330039
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/linked_vars.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+#include <sys/syscall.h>
+#include "linked_vars.skel.h"
+
+void test_linked_vars(void)
+{
+	int err;
+	struct linked_vars* skel;
+
+	skel = linked_vars__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	skel->bss->input_bss1 = 1000;
+	skel->bss->input_bss2 = 2000;
+	skel->bss->input_bss_weak = 3000;
+
+	err = linked_vars__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
+	err = linked_vars__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto cleanup;
+
+	/* trigger */
+	syscall(SYS_getpgid);
+
+	ASSERT_EQ(skel->bss->output_bss1, 1000 + 2000 + 3000, "output_bss1");
+	ASSERT_EQ(skel->bss->output_bss2, 1000 + 2000 + 3000, "output_bss2");
+	/* 10 comes from "winner" input_data_weak in first obj file */
+	ASSERT_EQ(skel->bss->output_data1, 1 + 2 + 10, "output_bss1");
+	ASSERT_EQ(skel->bss->output_data2, 1 + 2 + 10, "output_bss2");
+	/* 10 comes from "winner" input_rodata_weak in first obj file */
+	ASSERT_EQ(skel->bss->output_rodata1, 11 + 22 + 100 , "output_weak1");
+	ASSERT_EQ(skel->bss->output_rodata2, 11 + 22 + 100 , "output_weak2");
+
+cleanup:
+	linked_vars__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/linked_vars1.c b/tools/testing/selftests/bpf/progs/linked_vars1.c
new file mode 100644
index 000000000000..e3865047ed5d
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_vars1.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+extern int LINUX_KERNEL_VERSION __kconfig;
+/* this weak extern will be strict due to the other file's strong extern */
+extern bool CONFIG_BPF_SYSCALL __kconfig __weak;
+extern const void bpf_link_fops __ksym __weak;
+/* make sure special extern funcs are handled as well */
+/* extern int bpf_kfunc_call_test2(struct sock *, __u32, __u32) __ksym; */
+
+/* static name conflicts are not handled by BPF skeleton well yet */
+/* static volatile int input_bss_static = 0; */
+
+int input_bss1 = 0;
+int input_data1 = 1;
+const volatile int input_rodata1 = 11;
+
+int input_bss_weak __weak = 0;
+/* these two definitions should win */
+int input_data_weak __weak = 10;
+const volatile int input_rodata_weak __weak = 100;
+
+extern int input_bss2;
+extern int input_data2;
+extern const int input_rodata2;
+
+int output_bss1 = 0;
+int output_data1 = 0;
+int output_rodata1 = 0;
+
+long output_sink1 = 0;
+
+static __noinline int get_bss_res(void)
+{
+	/* just make sure all the relocations work against .text as well */
+	return /*input_bss_static +*/ input_bss1 + input_bss2 + input_bss_weak;
+}
+
+SEC("raw_tp/sys_enter")
+int BPF_PROG(handler1)
+{
+	output_bss1 = get_bss_res();
+	output_data1 = input_data1 + input_data2 + input_data_weak;
+	output_rodata1 = input_rodata1 + input_rodata2 + input_rodata_weak;
+
+	/* make sure we actually use above special externs, otherwise compiler
+	 * will optimize them out
+	 */
+	output_sink1 = LINUX_KERNEL_VERSION
+		       + CONFIG_BPF_SYSCALL
+		       + (long)&bpf_link_fops;
+		       /* + (long)&bpf_kfunc_call_test2; */
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/linked_vars2.c b/tools/testing/selftests/bpf/progs/linked_vars2.c
new file mode 100644
index 000000000000..18880b54bc29
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_vars2.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+extern int LINUX_KERNEL_VERSION __kconfig;
+/* when an extern is defined as both strong and weak, resulting symbol will be strong */
+extern bool CONFIG_BPF_SYSCALL __kconfig;
+extern const void __start_BTF __ksym;
+/* make sure special extern funcs are handled as well */
+/*extern int bpf_kfunc_call_test2(struct sock *, __u32, __u32) __ksym;*/
+
+/* static naming conflicts are not handled by BPF skeleton yet */
+/* static volatile int input_bss_static = 0; */
+
+int input_bss2 = 0;
+int input_data2 = 2;
+const volatile int input_rodata2 = 22;
+
+int input_bss_weak __weak = 0;
+/* these two weak variables should lose */
+int input_data_weak __weak = 20;
+const volatile int input_rodata_weak __weak = 200;
+
+extern int input_bss1;
+extern int input_data1;
+extern const int input_rodata1;
+
+int output_bss2 = 0;
+int output_data2 = 0;
+int output_rodata2 = 0;
+
+int output_sink2 = 0;
+
+static __noinline int get_data_res(void)
+{
+	/* just make sure all the relocations work against .text as well */
+	return input_data1 + input_data2 + input_data_weak;
+}
+
+SEC("raw_tp/sys_enter")
+int BPF_PROG(handler2)
+{
+	output_bss2 = /*input_bss_static +*/ input_bss1 + input_bss2 + input_bss_weak;
+	output_data2 = get_data_res();
+	output_rodata2 = input_rodata1 + input_rodata2 + input_rodata_weak;
+
+	/* make sure we actually use above special externs, otherwise compiler
+	 * will optimize them out
+	 */
+	output_sink2 = LINUX_KERNEL_VERSION
+		       + CONFIG_BPF_SYSCALL
+		       + (long)&__start_BTF;
+		       /*+ (long)&bpf_kfunc_call_test2;*/
+
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
-- 
2.30.2

[PATCH bpf-next 17/17] sleftests/bpf: add map linking selftest

[Andrii Nakryiko]

Add selftest validating various aspects of statically linking BTF-defined map
definitions. Legacy map definitions do not support extern resolution between
object files. Some of the aspects validated:
  - correct resolution of extern maps against concrete map definitions;
  - extern maps can currently only specify map type and key/value size and/or
    type information;
  - weak concrete map definitions are resolved properly.

Static map definitions are not yet supported by libbpf, so they are not
explicitly tested, though manual testing showes that BPF linker handles them
properly.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/Makefile          |   4 +-
 .../selftests/bpf/prog_tests/linked_maps.c    |  33 ++++++
 .../selftests/bpf/progs/linked_maps1.c        | 102 ++++++++++++++++
 .../selftests/bpf/progs/linked_maps2.c        | 112 ++++++++++++++++++
 4 files changed, 250 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_maps.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_maps1.c
 create mode 100644 tools/testing/selftests/bpf/progs/linked_maps2.c

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index a690fd125c6d..bd6d60644275 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -303,11 +303,13 @@ endef
 
 SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
 
-LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h linked_vars.skel.h
+LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h		\
+		linked_vars.skel.h linked_maps.skel.h
 
 test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o
 linked_funcs.skel.h-deps := linked_funcs1.o linked_funcs2.o
 linked_vars.skel.h-deps := linked_vars1.o linked_vars2.o
+linked_maps.skel.h-deps := linked_maps1.o linked_maps2.o
 
 LINKED_BPF_SRCS := $(patsubst %.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
 
diff --git a/tools/testing/selftests/bpf/prog_tests/linked_maps.c b/tools/testing/selftests/bpf/prog_tests/linked_maps.c
new file mode 100644
index 000000000000..69e0ef34aff2
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/linked_maps.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+#include <sys/syscall.h>
+#include "linked_maps.skel.h"
+
+void test_linked_maps(void)
+{
+	int err;
+	struct linked_maps* skel;
+
+	skel = linked_maps__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	err = linked_maps__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto cleanup;
+
+	/* trigger */
+	syscall(SYS_getpgid);
+
+	ASSERT_EQ(skel->bss->output_first1, 2000, "output_first1");
+	ASSERT_EQ(skel->bss->output_second1, 2, "output_second1");
+	ASSERT_EQ(skel->bss->output_weak1, 2, "output_weak1");
+	/*
+	ASSERT_EQ(skel->bss->output_static1, 2, "output_static1");
+	*/
+
+cleanup:
+	linked_maps__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/linked_maps1.c b/tools/testing/selftests/bpf/progs/linked_maps1.c
new file mode 100644
index 000000000000..6fb853043318
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_maps1.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+struct my_key { long x; };
+struct my_value { long x; };
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, struct my_key);
+	__type(value, struct my_value);
+	__uint(max_entries, 16);
+} map1 SEC(".maps");
+
+extern struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, int);
+	/* no max_entries can be specified in extern map */
+} map2 SEC(".maps");
+
+/* This should be the winning map definition, but we have no way of verifying,
+ * so we just make sure that it links and works without errors
+ */
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, int);
+	__uint(max_entries, 16);
+} map_weak __weak SEC(".maps");
+
+/* Once BPF skeleton can handle static maps with the same name, this map
+ * should be renamed to just map_static in both files. For now we just make
+ * sure that static map definitions work.
+ */
+/*
+static struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, int);
+	__type(value, int);
+	__uint(max_entries, 4);
+} map_static1 SEC(".maps");
+*/
+
+int output_first1 = 0;
+int output_second1 = 0;
+int output_weak1 = 0;
+/*
+int output_static1 = 0;
+*/
+
+SEC("raw_tp/sys_enter")
+int BPF_PROG(handler_enter1)
+{
+	/* update values with key = 1 */
+	int key = 1, val = 1;
+	struct my_key key_struct = { .x = 1 };
+	struct my_value val_struct = { .x = 1000 };
+
+	bpf_map_update_elem(&map1, &key_struct, &val_struct, 0);
+	bpf_map_update_elem(&map2, &key, &val, 0);
+	bpf_map_update_elem(&map_weak, &key, &val, 0);
+	/*
+	bpf_map_update_elem(&map_static1, &key, &val, 0);
+	*/
+
+	return 0;
+}
+
+SEC("raw_tp/sys_exit")
+int BPF_PROG(handler_exit1)
+{
+	/* lookup values with key = 2, set in another file */
+	int key = 2, *val;
+	struct my_key key_struct = { .x = 2 };
+	struct my_value *value_struct;
+
+	value_struct = bpf_map_lookup_elem(&map1, &key_struct);
+	if (value_struct)
+		output_first1 = value_struct->x;
+
+	val = bpf_map_lookup_elem(&map2, &key);
+	if (val)
+		output_second1 = *val;
+
+	val = bpf_map_lookup_elem(&map_weak, &key);
+	if (val)
+		output_weak1 = *val;
+	
+	/*
+	val = bpf_map_lookup_elem(&map_static1, &key);
+	if (val)
+		output_static1 = *val;
+	*/
+
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/linked_maps2.c b/tools/testing/selftests/bpf/progs/linked_maps2.c
new file mode 100644
index 000000000000..93ac7c4f90d2
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/linked_maps2.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+/* modifiers and typedefs are ignored when comparing key/value types */
+typedef struct my_key { long x; } key_type;
+typedef struct my_value { long x; } value_type;
+
+extern struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, key_type);
+	__type(value, value_type);
+	/* no max_entries on extern map definitions */
+} map1 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, int);
+	__uint(max_entries, 8);
+} map2 SEC(".maps");
+
+/* this definition will lose, but it has to exactly match the winner */
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, int);
+	__uint(max_entries, 16);
+} map_weak __weak SEC(".maps");
+
+/* Once BPF skeleton can handle static maps with the same name, this map
+ * should be renamed to just map_static in both files. For now we just make
+ * sure that static map definitions work.
+ */
+/*
+static struct {
+*/
+	/* different type */
+/*
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+*/
+	/* key and value are kept int for convenience, they don't have to
+	 * match with map_static1
+	 */
+/*
+	__type(key, int);
+	__type(value, int);
+*/
+	/* different max_entries */
+/*
+	__uint(max_entries, 20);
+} map_static2 SEC(".maps");
+*/
+
+int output_first2 = 0;
+int output_second2 = 0;
+int output_weak2 = 0;
+/*
+int output_static2 = 0;
+*/
+
+SEC("raw_tp/sys_enter")
+int BPF_PROG(handler_enter2)
+{
+	/* update values with key = 2 */
+	int key = 2, val = 2;
+	key_type key_struct = { .x = 2 };
+	value_type val_struct = { .x = 2000 };
+
+	bpf_map_update_elem(&map1, &key_struct, &val_struct, 0);
+	bpf_map_update_elem(&map2, &key, &val, 0);
+	bpf_map_update_elem(&map_weak, &key, &val, 0);
+	/*
+	bpf_map_update_elem(&map_static2, &key, &val, 0);
+	*/
+
+	return 0;
+}
+
+SEC("raw_tp/sys_exit")
+int BPF_PROG(handler_exit2)
+{
+	/* lookup values with key = 1, set in another file */
+	int key = 1, *val;
+	key_type key_struct = { .x = 1 };
+	value_type *value_struct;
+
+	value_struct = bpf_map_lookup_elem(&map1, &key_struct);
+	if (value_struct)
+		output_first2 = value_struct->x;
+
+	val = bpf_map_lookup_elem(&map2, &key);
+	if (val)
+		output_second2 = *val;
+
+	val = bpf_map_lookup_elem(&map_weak, &key);
+	if (val)
+		output_weak2 = *val;
+	
+	/*
+	val = bpf_map_lookup_elem(&map_static2, &key);
+	if (val)
+		output_static2 = *val;
+	*/
+
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
-- 
2.30.2

Re: [PATCH bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section

[Alexei Starovoitov]

On 4/14/21 1:01 PM, Andrii Nakryiko wrote:
> Add extra logic to handle map externs (only BTF-defined maps are supported for
> linking). Re-use the map parsing logic used during bpf_object__open(). Map
> externs are currently restricted to always and only specify map type, key
> type and/or size, and value type and/or size. Nothing extra is allowed. If any
> of those attributes are mismatched between extern and actual map definition,
> linker will report an error.

I don't get the motivation for this.
It seems cumbersome to force users to do:
+extern struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, key_type);
+	__type(value, value_type);
+	/* no max_entries on extern map definitions */
+} map1 SEC(".maps");

> The original intent was to allow for extern to specify attributes that matters
> (to user) to enforce. E.g., if you specify just key information and omit
> value, then any value fits. Similarly, it should have been possible to enforce
> map_flags, pinning, and any other possible map attribute. Unfortunately, that
> means that multiple externs can be only partially overlapping with each other,
> which means linker would need to combine their type definitions to end up with
> the most restrictive and fullest map definition.

but there is only one such full map definition.
Can all externs to be:
extern struct {} map1 SEC(".maps");

They can be in multiple .o files, but one true global map def
should have all the fields and will take the precedence during
the linking.

The map type, key size, value size, max entries are all irrelevant
during compilation. They're relevant during loading, but libbpf is
not going to load every .o individually. So "extern map" can
have any fields it wouldn't change the end result after linking.
May be enforce that 'extern struct {} map' doesn't have
any fields defined instead?
It seems asking users to copy-paste map defs in one file and in all
of extern is just extra hassle.
The users wouldn't want to copy-paste them for production code,
but will put map def into .h and include in multiple .c,
but adding "extern " in many .c-s and not
adding that "extern " is the main .c is another macro hassle.
Actually forcing "no max_entries in extern" is killing this idea.
So it's mandatory copy-paste or even more macro magic with partial
defs of maps?
What am I missing?

Re: [PATCH bpf-next 13/17] selftests/bpf: use -O0 instead of -Og in selftests builds

[Alexei Starovoitov]

On 4/14/21 1:01 PM, Andrii Nakryiko wrote:
> While -Og is designed to work well with debugger, it's still inferior to -O0
> in terms of debuggability experience. It will cause some variables to still be
> inlined, it will also prevent single-stepping some statements and otherwise
> interfere with debugging experience. So switch to -O0 which turns off any
> optimization and provides the best debugging experience.
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>   tools/testing/selftests/bpf/Makefile | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 6448c626498f..22a88580b491 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -21,7 +21,7 @@ endif
>   
>   BPF_GCC		?= $(shell command -v bpf-gcc;)
>   SAN_CFLAGS	?=
> -CFLAGS += -g -Og -rdynamic -Wall $(GENFLAGS) $(SAN_CFLAGS)		\
> +CFLAGS += -g -O0 -rdynamic -Wall $(GENFLAGS) $(SAN_CFLAGS)		\
>   	  -I$(CURDIR) -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)		\
>   	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(OUTPUT)			\
>   	  -Dbpf_prog_load=bpf_prog_test_load				\
> @@ -201,7 +201,7 @@ $(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)    \
>   		    $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/bpftool
>   	$(Q)$(MAKE) $(submake_extras)  -C $(BPFTOOLDIR)			       \
>   		    CC=$(HOSTCC) LD=$(HOSTLD)				       \
> -		    EXTRA_CFLAGS='-g -Og'				       \
> +		    EXTRA_CFLAGS='-g -O0'				       \

lol. so much for gcc docs :)

RE: [PATCH bpf-next 13/17] selftests/bpf: use -O0 instead of -Og in selftests builds

[David Laight]

From: Andrii Nakryiko
> Sent: 14 April 2021 21:02
> 
> While -Og is designed to work well with debugger, it's still inferior to -O0
> in terms of debuggability experience. It will cause some variables to still be
> inlined, it will also prevent single-stepping some statements and otherwise
> interfere with debugging experience. So switch to -O0 which turns off any
> optimization and provides the best debugging experience.

Surely the selftests need to use the normal compiler options
so the compiler is generating the same type of code.
Otherwise you are likely to miss out some instructions completely.

For normal code I actually prefer using -O2 when dubugging.
If/when you need to look at the generated code you can see
the wood for the trees, with -O0 the code is typically
full of memory read/write to/from the stack.

About the only annoying thing is tail-calls.
They can get confusing.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section

[Andrii Nakryiko]

On Wed, Apr 14, 2021 at 3:00 PM Alexei Starovoitov <ast@fb.com> wrote:
>
> On 4/14/21 1:01 PM, Andrii Nakryiko wrote:
> > Add extra logic to handle map externs (only BTF-defined maps are supported for
> > linking). Re-use the map parsing logic used during bpf_object__open(). Map
> > externs are currently restricted to always and only specify map type, key
> > type and/or size, and value type and/or size. Nothing extra is allowed. If any
> > of those attributes are mismatched between extern and actual map definition,
> > linker will report an error.
>
> I don't get the motivation for this.
> It seems cumbersome to force users to do:
> +extern struct {
> +       __uint(type, BPF_MAP_TYPE_HASH);
> +       __type(key, key_type);
> +       __type(value, value_type);
> +       /* no max_entries on extern map definitions */
> +} map1 SEC(".maps");

The intent was to simulate what you'd have in a language with
generics. E.g., if you were declaring extern for a map in C++:

extern std::map<key_type, value_type> my_map;

You'd want a linker to make sure that actual my_map definition to
conform to your expectations, no?

>
> > The original intent was to allow for extern to specify attributes that matters
> > (to user) to enforce. E.g., if you specify just key information and omit
> > value, then any value fits. Similarly, it should have been possible to enforce
> > map_flags, pinning, and any other possible map attribute. Unfortunately, that
> > means that multiple externs can be only partially overlapping with each other,
> > which means linker would need to combine their type definitions to end up with
> > the most restrictive and fullest map definition.
>
> but there is only one such full map definition.
> Can all externs to be:
> extern struct {} map1 SEC(".maps");

I can certainly modify logic to allow this. But for variables and
funcs we want to enforce type information, right? So I'm not sure why
you think it's bad for maps.

>
> They can be in multiple .o files, but one true global map def
> should have all the fields and will take the precedence during
> the linking.

So if it's just a multi-file application and you don't care which file
declares that map, you can do a single __weak definition in a header
and forget about it.

But imagine a BPF library, maintained separately from some BPF
application that is using it. And imagine that for some reason that
BPF library wants/needs to "export" its map directly. In such case,
I'd imagine BPF library author to provide a header with pre-defined
correct extern definition of that map.

It's the same situation as with extern functions. You are either
copy/pasting exact function signature or providing it through some
common header. BPF map definition is just slightly more verbose.


>
> The map type, key size, value size, max entries are all irrelevant
> during compilation. They're relevant during loading, but libbpf is
> not going to load every .o individually. So "extern map" can
> have any fields it wouldn't change the end result after linking.
> May be enforce that 'extern struct {} map' doesn't have
> any fields defined instead?

It's easy for me to do that as well, it's just a question of what
behavior makes more sense and what are we trying to achieve. Of course
during the compilation itself it doesn't matter that's the type of map
is or what key/value type/size is. But from the programmer's point of
view, when I do lookup/update, I'd like to know that my map
corresponds to my understanding. So if I assume 4-byte key, and
16-byte value and allocate stack variables according to that
understanding, yet something changes about BPF map definition, I'd
rather notice that during linking, than maybe notice during BPF
verification. So that was the only motivation: catch mismatch earlier.
I originally wanted to let users define which attributes matter and
enforce them (as I mention in the commit description), but that
requires some more work on merging BTF. Now that I'm done with all the
rest logic, I guess I can go and address that as well. So that would
support cases from:

extern struct {} my_map SEC(".maps");

to

extern struct {
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __type(key, int);
    __type(value, struct value_type);
    __uint(map_flags, BPF_F_MMAPABLE); /* because I care for whatever reason */
    __uint(pinning, LIBBPF_PIN_BY_NAME); /* because I can */
} my_peculiar_map SEC(".maps");


But basically, if we allow only `extern struct {} my_map
SEC(".maps");`, why do I even bother with BTF in that case?


> It seems asking users to copy-paste map defs in one file and in all
> of extern is just extra hassle.

So see above about __weak. As for the BPF library providers, that felt
unavoidable (and actually desirable), because that's what they would
do with extern func and extern vars anyways. And that's what we do
with C code today, except linker is oblivious to types (because no BTF
in user-space C world).

> The users wouldn't want to copy-paste them for production code,
> but will put map def into .h and include in multiple .c,
> but adding "extern " in many .c-s and not
> adding that "extern " is the main .c is another macro hassle.
> Actually forcing "no max_entries in extern" is killing this idea.

so forcing to type+key+value is to make sure that currently all
externs (if there are many) are exactly the same. Because as soon as I
allow some to specify max_entries and some don't, then depending on
the order in which I see those externs (before actual definition),
I'll need to merge their definitions (worst case), or at least pick
the most complete one. It's doable, but felt unnecessary for the first
iteration.

> So it's mandatory copy-paste or even more macro magic with partial
> defs of maps?
> What am I missing?

Maybe nothing, just there is no single right answer (except the
aspirational implementation I explained above). I'm open to
discussion, btw, not claiming my way is the best way.

Re: [PATCH bpf-next 13/17] selftests/bpf: use -O0 instead of -Og in selftests builds

[Andrii Nakryiko]

On Wed, Apr 14, 2021 at 3:15 PM David Laight <David.Laight@aculab.com> wrote:
>
> From: Andrii Nakryiko
> > Sent: 14 April 2021 21:02
> >
> > While -Og is designed to work well with debugger, it's still inferior to -O0
> > in terms of debuggability experience. It will cause some variables to still be
> > inlined, it will also prevent single-stepping some statements and otherwise
> > interfere with debugging experience. So switch to -O0 which turns off any
> > optimization and provides the best debugging experience.
>
> Surely the selftests need to use the normal compiler options
> so the compiler is generating the same type of code.
> Otherwise you are likely to miss out some instructions completely.
>

I don't know, it's not like I'm trying to validate that GCC is
generating a valid assembly. And there is almost nothing in libbpf and
selftests that relies on delicate timing, so I don't think we should
worry about changing timing characteristics. And there is nothing
performance-critical in libbpf logic itself either, for the most part.
So I don't see much harm in running selftests in debug mode.

> For normal code I actually prefer using -O2 when dubugging.
> If/when you need to look at the generated code you can see
> the wood for the trees, with -O0 the code is typically
> full of memory read/write to/from the stack.

Whenever I try debugging anything in selftest+libbpf+bpftool, if any
of those components are built with -O2, it makes it almost impossible
to figure anything out in debugger. So I always go back and force all
of them to -O0. So that's what this patch is doing, so that I and
others don't have to go through this every single time we need to
debug something.

>
> About the only annoying thing is tail-calls.
> They can get confusing.
>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>

Re: [PATCH bpf-next 00/17] BPF static linker: support externs

[Andrii Nakryiko]

On Wed, Apr 14, 2021 at 1:02 PM Andrii Nakryiko <andrii@kernel.org> wrote:
>
> Add BPF static linker support for extern resolution of global variables,
> functions, and BTF-defined maps.
>
> This patch set consists of 4 parts:
>   - few patches are extending bpftool to simplify working with BTF dump;
>   - libbpf object loading logic is extended to support __hidden functions and
>     overriden (unused) __weak functions; also BTF-defined map parsing logic is
>     refactored to be re-used by linker;
>   - the crux of the patch set is BPF static linker logic extension to perform
>     extern resolution for three categories: global variables, BPF
>     sub-programs, BTF-defined maps;
>   - a set of selftests that validate that all the combinations of
>     extern/weak/__hidden are working as expected.
>
> See respective patches for more details.
>
> One aspect hasn't been addressed yet and is going to be resolved in the next
> patch set, but is worth mentioning. With BPF static linking of multiple .o
> files, dealing with static everything becomes more problematic for BPF
> skeleton and in general for any by name look up APIs. This is due to static
> entities are allowed to have non-unique name. Historically this was never
> a problem due to BPF programs were always confined to a single C file. That
> changes now and needs to be addressed. The thinking so far is for BPF static
> linker to prepend filename to each static variable and static map (which is
> currently not supported by libbpf, btw), so that they can be unambiguously
> resolved by (mostly) unique name. Mostly, because even filenames can be
> duplicated, but that should be rare and easy to address by wiser choice of
> filenames by users. Fortunately, static BPF subprograms don't suffer from this
> issues, as they are not independent entities and are neither exposed in BPF
> skeleton, nor is lookup-able by any of libbpf APIs (and there is little reason
> to do that anyways).
>
> This and few other things will be the topic of the next set of patches.
>

I forgot to mention that selftests are relying on Clang fix [0], which
is not yet in nightly builds, so kernel-patches CI is currently
failing a test. So, when/if testing locally, please make sure to build
Clang from latest main.

  [0] https://reviews.llvm.org/D100362

> Andrii Nakryiko (17):
>   bpftool: support dumping BTF VAR's "extern" linkage
>   bpftool: dump more info about DATASEC members
>   libbpf: suppress compiler warning when using SEC() macro with externs
>   libbpf: mark BPF subprogs with hidden visibility as static for BPF
>     verifier
>   libbpf: allow gaps in BPF program sections to support overriden weak
>     functions
>   libbpf: refactor BTF map definition parsing
>   libbpf: factor out symtab and relos sanity checks
>   libbpf: make few internal helpers available outside of libbpf.c
>   libbpf: extend sanity checking ELF symbols with externs validation
>   libbpf: tighten BTF type ID rewriting with error checking
>   libbpf: add linker extern resolution support for functions and global
>     variables
>   libbpf: support extern resolution for BTF-defined maps in .maps
>     section
>   selftests/bpf: use -O0 instead of -Og in selftests builds
>   selftests/bpf: omit skeleton generation for multi-linked BPF object
>     files
>   selftests/bpf: add function linking selftest
>   selftests/bpf: add global variables linking selftest
>   sleftests/bpf: add map linking selftest
>
>  tools/bpf/bpftool/btf.c                       |   30 +-
>  tools/lib/bpf/bpf_helpers.h                   |   19 +-
>  tools/lib/bpf/btf.c                           |    5 -
>  tools/lib/bpf/libbpf.c                        |  370 +++--
>  tools/lib/bpf/libbpf_internal.h               |   45 +
>  tools/lib/bpf/linker.c                        | 1292 ++++++++++++++---
>  tools/testing/selftests/bpf/Makefile          |   18 +-
>  .../selftests/bpf/prog_tests/linked_funcs.c   |   42 +
>  .../selftests/bpf/prog_tests/linked_maps.c    |   33 +
>  .../selftests/bpf/prog_tests/linked_vars.c    |   43 +
>  .../selftests/bpf/progs/linked_funcs1.c       |   73 +
>  .../selftests/bpf/progs/linked_funcs2.c       |   73 +
>  .../selftests/bpf/progs/linked_maps1.c        |  102 ++
>  .../selftests/bpf/progs/linked_maps2.c        |  112 ++
>  .../selftests/bpf/progs/linked_vars1.c        |   60 +
>  .../selftests/bpf/progs/linked_vars2.c        |   61 +
>  16 files changed, 2028 insertions(+), 350 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_funcs.c
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_maps.c
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_vars.c
>  create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs1.c
>  create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs2.c
>  create mode 100644 tools/testing/selftests/bpf/progs/linked_maps1.c
>  create mode 100644 tools/testing/selftests/bpf/progs/linked_maps2.c
>  create mode 100644 tools/testing/selftests/bpf/progs/linked_vars1.c
>  create mode 100644 tools/testing/selftests/bpf/progs/linked_vars2.c
>
> --
> 2.30.2
>

Re: [PATCH bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section

[Alexei Starovoitov]

On Wed, Apr 14, 2021 at 04:48:25PM -0700, Andrii Nakryiko wrote:
> On Wed, Apr 14, 2021 at 3:00 PM Alexei Starovoitov <ast@fb.com> wrote:
> >
> > On 4/14/21 1:01 PM, Andrii Nakryiko wrote:
> > > Add extra logic to handle map externs (only BTF-defined maps are supported for
> > > linking). Re-use the map parsing logic used during bpf_object__open(). Map
> > > externs are currently restricted to always and only specify map type, key
> > > type and/or size, and value type and/or size. Nothing extra is allowed. If any
> > > of those attributes are mismatched between extern and actual map definition,
> > > linker will report an error.
> >
> > I don't get the motivation for this.
> > It seems cumbersome to force users to do:
> > +extern struct {
> > +       __uint(type, BPF_MAP_TYPE_HASH);
> > +       __type(key, key_type);
> > +       __type(value, value_type);
> > +       /* no max_entries on extern map definitions */
> > +} map1 SEC(".maps");
> 
> The intent was to simulate what you'd have in a language with
> generics. E.g., if you were declaring extern for a map in C++:
> 
> extern std::map<key_type, value_type> my_map;

right, because C++ will mangle types into names.
When llvm bpf backend will support C++ front-end it will do the mangling too.
I think BPF is ready for C++, but it's a separate discussion, of course.

> > but there is only one such full map definition.
> > Can all externs to be:
> > extern struct {} map1 SEC(".maps");
> 
> I can certainly modify logic to allow this. But for variables and
> funcs we want to enforce type information, right? So I'm not sure why
> you think it's bad for maps.

I'm not saying it's bad.
Traditional linker only deals with names, since we're in C domain, so far,
I figured it's an option, but more below.
C++ is good analogy too.

> So if it's just a multi-file application and you don't care which file
> declares that map, you can do a single __weak definition in a header
> and forget about it.
> 
> But imagine a BPF library, maintained separately from some BPF
> application that is using it. And imagine that for some reason that
> BPF library wants/needs to "export" its map directly. In such case,
> I'd imagine BPF library author to provide a header with pre-defined
> correct extern definition of that map.

I'm mainly looking at patch 17 and thinking how that copy paste can be avoided.
In C and C++ world the user would do:
defs.h:
  struct S {
    ...
  };
  extern struct S s;
file.c:
  #include "defs.h"
  struct S s;
and it would work, but afaics it won't work for BPF C in patch 17.
If the user does:
defs.h:
  struct my_map {
          __uint(type, BPF_MAP_TYPE_HASH);
          __type(key, struct my_key);
          __type(value, struct my_value);
          __uint(max_entries, 16);
  };
  extern struct my_map map1 SEC(".maps");
file.c:
  #include "defs.h"
  struct my_map map1;  // do we need SEC here too? probably not?

It won't work for another_filer.c since max_entries are not allowed?
Why, btw?

So how the user suppose to do this? With __weak in .h ?
But if that's the only reasonable choice whe bother supporting extern in the linker?

> I originally wanted to let users define which attributes matter and
> enforce them (as I mention in the commit description), but that
> requires some more work on merging BTF. Now that I'm done with all the
> rest logic, I guess I can go and address that as well.

I think that would be overkill. It won't match neither C style nor C++.
Let's pick one.

> So see above about __weak. As for the BPF library providers, that felt
> unavoidable (and actually desirable), because that's what they would
> do with extern func and extern vars anyways.

As far as supporting __weak for map defs, I think __weak in one file.c
should be weak for all attributes. Another_file.c should be able
to define the same map name without __weak and different types, value/type
sizes. Because why not? Sort-of C++ style of override.

> so forcing to type+key+value is to make sure that currently all
> externs (if there are many) are exactly the same. Because as soon as I
> allow some to specify max_entries and some don't,

I don't get why max_entries is special.
They can be overridden in typical skeleton usage. After open and before load.
So max_entries is a default value in map init. Whether it's part of
extern or not why should that matter?

> Maybe nothing, just there is no single right answer (except the
> aspirational implementation I explained above). I'm open to
> discussion, btw, not claiming my way is the best way.

I'm not suggesting that extern struct {} my_map; is the right answer either.
Mainly looking into how user code will look like and trying to
make it look the most similar to how C, C++ code traditionally looks.
BPF C is reduced and extended C at the same time.
BPF C++ will be similar. Certain features will be supported right away,
some others will take time.
I'm looking at BTF as a language independent concept.
Both C and C++ will rely on it.

To summarize if max_entries can be supported and ingored in extern
when the definition has a different value then it's probably good to enforce
that the rest of map fields are the same. Then my .h/.c example above will work.
In case of __weak probably all map fields can change.
It can be seen as a weak definition of the whole map. Not just weak of the variable.
It's a default for everything that can be overridden.
While non-weak can override max_entries only.

btw for signed progs I'm thinking to allow override of max_entries only,
since this attribute doesn't affect safety, correctness, behavior.
Meaning max_entries will and will not be part of a signature at the same time.
In other words it's necessary to support existing bcc/libbpf-tools.
If we go with 'allow max_entries in extern' that would match that behavior.

Re: [PATCH bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section

[Andrii Nakryiko]

On Wed, Apr 14, 2021 at 7:01 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Apr 14, 2021 at 04:48:25PM -0700, Andrii Nakryiko wrote:
> > On Wed, Apr 14, 2021 at 3:00 PM Alexei Starovoitov <ast@fb.com> wrote:
> > >
> > > On 4/14/21 1:01 PM, Andrii Nakryiko wrote:
> > > > Add extra logic to handle map externs (only BTF-defined maps are supported for
> > > > linking). Re-use the map parsing logic used during bpf_object__open(). Map
> > > > externs are currently restricted to always and only specify map type, key
> > > > type and/or size, and value type and/or size. Nothing extra is allowed. If any
> > > > of those attributes are mismatched between extern and actual map definition,
> > > > linker will report an error.
> > >
> > > I don't get the motivation for this.
> > > It seems cumbersome to force users to do:
> > > +extern struct {
> > > +       __uint(type, BPF_MAP_TYPE_HASH);
> > > +       __type(key, key_type);
> > > +       __type(value, value_type);
> > > +       /* no max_entries on extern map definitions */
> > > +} map1 SEC(".maps");
> >
> > The intent was to simulate what you'd have in a language with
> > generics. E.g., if you were declaring extern for a map in C++:
> >
> > extern std::map<key_type, value_type> my_map;
>
> right, because C++ will mangle types into names.
> When llvm bpf backend will support C++ front-end it will do the mangling too.
> I think BPF is ready for C++, but it's a separate discussion, of course.
>
> > > but there is only one such full map definition.
> > > Can all externs to be:
> > > extern struct {} map1 SEC(".maps");
> >
> > I can certainly modify logic to allow this. But for variables and
> > funcs we want to enforce type information, right? So I'm not sure why
> > you think it's bad for maps.
>
> I'm not saying it's bad.
> Traditional linker only deals with names, since we're in C domain, so far,
> I figured it's an option, but more below.
> C++ is good analogy too.
>
> > So if it's just a multi-file application and you don't care which file
> > declares that map, you can do a single __weak definition in a header
> > and forget about it.
> >
> > But imagine a BPF library, maintained separately from some BPF
> > application that is using it. And imagine that for some reason that
> > BPF library wants/needs to "export" its map directly. In such case,
> > I'd imagine BPF library author to provide a header with pre-defined
> > correct extern definition of that map.
>
> I'm mainly looking at patch 17 and thinking how that copy paste can be avoided.
> In C and C++ world the user would do:
> defs.h:
>   struct S {
>     ...
>   };
>   extern struct S s;
> file.c:
>   #include "defs.h"
>   struct S s;
> and it would work, but afaics it won't work for BPF C in patch 17.

Yes, you are right, there is no clean way to avoid defining extern and
full map definition. Which is the case for functions and variables,
except those type signatures tend to be shorter. E.g., if you had

void my_func(int arg) { ... }

you'd still have to duplicate it as at least:

extern void my_func(int);

I don't think you can use typedef for this either.

> If the user does:
> defs.h:
>   struct my_map {
>           __uint(type, BPF_MAP_TYPE_HASH);
>           __type(key, struct my_key);
>           __type(value, struct my_value);
>           __uint(max_entries, 16);
>   };
>   extern struct my_map map1 SEC(".maps");
> file.c:
>   #include "defs.h"
>   struct my_map map1;  // do we need SEC here too? probably not?

yeah, we do, all map "variables" are designated with .maps section,
otherwise they'll be treated as just a normal global variable (there
is no way to distinguish two, generally speaking).

>
> It won't work for another_filer.c since max_entries are not allowed?
> Why, btw?

So the idea was that for consumers of extern map definition map type
and key/value info was the only thing they should care about and
linker should enforce (at least that's how I thought about this and
what I think the typical use case would be). E.g., caring about exact
max_entries, or numa_node, or pinning, or map_flags, etc, shouldn't be
the concern of the consumer of the map.

>
> So how the user suppose to do this? With __weak in .h ?
> But if that's the only reasonable choice whe bother supporting extern in the linker?
>
> > I originally wanted to let users define which attributes matter and
> > enforce them (as I mention in the commit description), but that
> > requires some more work on merging BTF. Now that I'm done with all the
> > rest logic, I guess I can go and address that as well.
>
> I think that would be overkill. It won't match neither C style nor C++.
> Let's pick one.

So I still think we might want to implement it down the road, but
let's stick to something simpler for now. See below.

>
> > So see above about __weak. As for the BPF library providers, that felt
> > unavoidable (and actually desirable), because that's what they would
> > do with extern func and extern vars anyways.
>
> As far as supporting __weak for map defs, I think __weak in one file.c
> should be weak for all attributes. Another_file.c should be able
> to define the same map name without __weak and different types, value/type
> sizes. Because why not? Sort-of C++ style of override.

That's a significant deviation from semantics of weak variables and
functions, but I can see how it's useful. E.g., we can have some
potentially compiled out big map definition, but a __weak fallback to
a small, but compatible one.

>
> > so forcing to type+key+value is to make sure that currently all
> > externs (if there are many) are exactly the same. Because as soon as I
> > allow some to specify max_entries and some don't,
>
> I don't get why max_entries is special.
> They can be overridden in typical skeleton usage. After open and before load.
> So max_entries is a default value in map init. Whether it's part of
> extern or not why should that matter?

This is just a source code-level contract. You can override any
attribute of the map at runtime from user-space code. You can even
replace one map with an entirely different map (using
bpf_map__reuse_fd()). You can change type, etc, etc. The goal here is
to not prevent the abuse (I don't think it's possible at linking
stage, but at least BPF verifier will stop from something totally
stupid), rather for a typical case to make sure that there is no
accidental mismatch at the C code level.

>
> > Maybe nothing, just there is no single right answer (except the
> > aspirational implementation I explained above). I'm open to
> > discussion, btw, not claiming my way is the best way.
>
> I'm not suggesting that extern struct {} my_map; is the right answer either.
> Mainly looking into how user code will look like and trying to
> make it look the most similar to how C, C++ code traditionally looks.
> BPF C is reduced and extended C at the same time.
> BPF C++ will be similar. Certain features will be supported right away,
> some others will take time.
> I'm looking at BTF as a language independent concept.
> Both C and C++ will rely on it.
>
> To summarize if max_entries can be supported and ingored in extern
> when the definition has a different value then it's probably good to enforce
> that the rest of map fields are the same. Then my .h/.c example above will work.
> In case of __weak probably all map fields can change.
> It can be seen as a weak definition of the whole map. Not just weak of the variable.
> It's a default for everything that can be overridden.
> While non-weak can override max_entries only.

How about we start in the most restrictive way first. Each extern
would need to specify all the attributes that should match the map
definition. That includes max_entries. That way the typedef struct {
... } my_map_t re-use will work right out of the box. Later, if we see
this is not sufficient, we can start relaxing the rules. Ultimately
what I proposed above with selective extern attributes enforcement
would allow to cover any scenario. Granted it's special compared to C
linking style, but given the __weak map definition proposal above also
deviates significantly, we can just treat maps specially, but in a
"makes sense" way.

>
> btw for signed progs I'm thinking to allow override of max_entries only,
> since this attribute doesn't affect safety, correctness, behavior.
> Meaning max_entries will and will not be part of a signature at the same time.
> In other words it's necessary to support existing bcc/libbpf-tools.
> If we go with 'allow max_entries in extern' that would match that behavior.

Ok, unless I misunderstood, allowing and checking all map attributes
as a starting point should work, right?

Re: [PATCH bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section

[Alexei Starovoitov]

On 4/15/21 1:35 PM, Andrii Nakryiko wrote:
> 
> How about we start in the most restrictive way first. Each extern
> would need to specify all the attributes that should match the map
> definition. That includes max_entries. That way the typedef struct {
> ... } my_map_t re-use will work right out of the box. Later, if we see
> this is not sufficient, we can start relaxing the rules.

+1

>>
>> btw for signed progs I'm thinking to allow override of max_entries only,
>> since this attribute doesn't affect safety, correctness, behavior.
>> Meaning max_entries will and will not be part of a signature at the same time.
>> In other words it's necessary to support existing bcc/libbpf-tools.
>> If we go with 'allow max_entries in extern' that would match that behavior.
> 
> Ok, unless I misunderstood, allowing and checking all map attributes
> as a starting point should work, right?

yes. thanks!