From: Yonghong Song <yhs@fb.com>
To: <bpf@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Cong Wang <xiyou.wangcong@gmail.com>,
Daniel Borkmann <daniel@iogearbox.net>, <kernel-team@fb.com>,
Andrii Nakryiko <andrii@kernel.org>
Subject: [PATCH bpf-next v5 09/12] libbpf: support subprog address relocation
Date: Fri, 26 Feb 2021 12:49:30 -0800 [thread overview]
Message-ID: <20210226204930.3885367-1-yhs@fb.com> (raw)
In-Reply-To: <20210226204920.3884074-1-yhs@fb.com>
A new relocation RELO_SUBPROG_ADDR is added to capture
subprog addresses loaded with ld_imm64 insns. Such ld_imm64
insns are marked with BPF_PSEUDO_FUNC and will be passed to
kernel. For bpf_for_each_map_elem() case, kernel will
check that the to-be-used subprog address must be a static
function and replace it with proper actual jited func address.
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
tools/lib/bpf/libbpf.c | 64 ++++++++++++++++++++++++++++++++++++++++--
1 file changed, 61 insertions(+), 3 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 21a3eedf070d..62d9ed56b081 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -188,6 +188,7 @@ enum reloc_type {
RELO_CALL,
RELO_DATA,
RELO_EXTERN,
+ RELO_SUBPROG_ADDR,
};
struct reloc_desc {
@@ -579,6 +580,11 @@ static bool is_ldimm64(struct bpf_insn *insn)
return insn->code == (BPF_LD | BPF_IMM | BPF_DW);
}
+static bool insn_is_pseudo_func(struct bpf_insn *insn)
+{
+ return is_ldimm64(insn) && insn->src_reg == BPF_PSEUDO_FUNC;
+}
+
static int
bpf_object__init_prog(struct bpf_object *obj, struct bpf_program *prog,
const char *name, size_t sec_idx, const char *sec_name,
@@ -2979,6 +2985,23 @@ static bool sym_is_extern(const GElf_Sym *sym)
GELF_ST_TYPE(sym->st_info) == STT_NOTYPE;
}
+static bool sym_is_subprog(const GElf_Sym *sym, int text_shndx)
+{
+ int bind = GELF_ST_BIND(sym->st_info);
+ int type = GELF_ST_TYPE(sym->st_info);
+
+ /* in .text section */
+ if (sym->st_shndx != text_shndx)
+ return false;
+
+ /* local function */
+ if (bind == STB_LOCAL && type == STT_SECTION)
+ return true;
+
+ /* global function */
+ return bind == STB_GLOBAL && type == STT_FUNC;
+}
+
static int find_extern_btf_id(const struct btf *btf, const char *ext_name)
{
const struct btf_type *t;
@@ -3435,6 +3458,23 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
return -LIBBPF_ERRNO__RELOC;
}
+ /* loading subprog addresses */
+ if (sym_is_subprog(sym, obj->efile.text_shndx)) {
+ /* global_func: sym->st_value = offset in the section, insn->imm = 0.
+ * local_func: sym->st_value = 0, insn->imm = offset in the section.
+ */
+ if ((sym->st_value % BPF_INSN_SZ) || (insn->imm % BPF_INSN_SZ)) {
+ pr_warn("prog '%s': bad subprog addr relo against '%s' at offset %zu+%d\n",
+ prog->name, sym_name, (size_t)sym->st_value, insn->imm);
+ return -LIBBPF_ERRNO__RELOC;
+ }
+
+ reloc_desc->type = RELO_SUBPROG_ADDR;
+ reloc_desc->insn_idx = insn_idx;
+ reloc_desc->sym_off = sym->st_value;
+ return 0;
+ }
+
type = bpf_object__section_to_libbpf_map_type(obj, shdr_idx);
sym_sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, shdr_idx));
@@ -6172,6 +6212,10 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
}
relo->processed = true;
break;
+ case RELO_SUBPROG_ADDR:
+ insn[0].src_reg = BPF_PSEUDO_FUNC;
+ /* will be handled as a follow up pass */
+ break;
case RELO_CALL:
/* will be handled as a follow up pass */
break;
@@ -6358,11 +6402,11 @@ bpf_object__reloc_code(struct bpf_object *obj, struct bpf_program *main_prog,
for (insn_idx = 0; insn_idx < prog->sec_insn_cnt; insn_idx++) {
insn = &main_prog->insns[prog->sub_insn_off + insn_idx];
- if (!insn_is_subprog_call(insn))
+ if (!insn_is_subprog_call(insn) && !insn_is_pseudo_func(insn))
continue;
relo = find_prog_insn_relo(prog, insn_idx);
- if (relo && relo->type != RELO_CALL) {
+ if (relo && relo->type != RELO_CALL && relo->type != RELO_SUBPROG_ADDR) {
pr_warn("prog '%s': unexpected relo for insn #%zu, type %d\n",
prog->name, insn_idx, relo->type);
return -LIBBPF_ERRNO__RELOC;
@@ -6374,8 +6418,22 @@ bpf_object__reloc_code(struct bpf_object *obj, struct bpf_program *main_prog,
* call always has imm = -1, but for static functions
* relocation is against STT_SECTION and insn->imm
* points to a start of a static function
+ *
+ * for subprog addr relocation, the relo->sym_off + insn->imm is
+ * the byte offset in the corresponding section.
*/
- sub_insn_idx = relo->sym_off / BPF_INSN_SZ + insn->imm + 1;
+ if (relo->type == RELO_CALL)
+ sub_insn_idx = relo->sym_off / BPF_INSN_SZ + insn->imm + 1;
+ else
+ sub_insn_idx = (relo->sym_off + insn->imm) / BPF_INSN_SZ;
+ } else if (insn_is_pseudo_func(insn)) {
+ /*
+ * RELO_SUBPROG_ADDR relo is always emitted even if both
+ * functions are in the same section, so it shouldn't reach here.
+ */
+ pr_warn("prog '%s': missing subprog addr relo for insn #%zu\n",
+ prog->name, insn_idx);
+ return -LIBBPF_ERRNO__RELOC;
} else {
/* if subprogram call is to a static function within
* the same ELF section, there won't be any relocation
--
2.24.1
next prev parent reply other threads:[~2021-02-26 20:50 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-26 20:49 [PATCH bpf-next v5 00/12] bpf: add bpf_for_each_map_elem() helper Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 01/12] bpf: factor out visit_func_call_insn() in check_cfg() Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 02/12] bpf: factor out verbose_invalid_scalar() Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 03/12] bpf: refactor check_func_call() to allow callback function Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 04/12] bpf: change return value of verifier function add_subprog() Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 05/12] bpf: add bpf_for_each_map_elem() helper Yonghong Song
2021-02-26 21:29 ` Alexei Starovoitov
2021-02-26 20:49 ` [PATCH bpf-next v5 06/12] bpf: add hashtab support for " Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 07/12] bpf: add arraymap " Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 08/12] libbpf: move function is_ldimm64() earlier in libbpf.c Yonghong Song
2021-02-26 20:49 ` Yonghong Song [this message]
2021-02-26 20:49 ` [PATCH bpf-next v5 10/12] bpftool: print subprog address properly Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 11/12] selftests/bpf: add hashmap test for bpf_for_each_map_elem() helper Yonghong Song
2021-02-26 20:49 ` [PATCH bpf-next v5 12/12] selftests/bpf: add arraymap " Yonghong Song
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