* [PATCH 2/3] btf_encoder: Move find_all_percpu_vars in generic collect_symbols
2020-11-04 21:59 [PATCHv3 0/3] pahole/kernel: Workaround dwarf bug for function encoding Jiri Olsa
2020-11-04 21:59 ` [PATCH 1/3] bpf: Move iterator functions into special init section Jiri Olsa
@ 2020-11-04 21:59 ` Jiri Olsa
2020-11-05 19:34 ` Andrii Nakryiko
2020-11-04 21:59 ` [PATCH 3/3] btf_encoder: Change functions check due to broken dwarf Jiri Olsa
2 siblings, 1 reply; 8+ messages in thread
From: Jiri Olsa @ 2020-11-04 21:59 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Hao Luo, dwarves, bpf, Alexei Starovoitov, Andrii Nakryiko,
Yonghong Song, Frank Ch. Eigler, Mark Wielaard
Moving find_all_percpu_vars under generic collect_symbols
function that walks over symbols and calls collect_percpu_var.
We will add another collect function that needs to go through
all the symbols, so it's better we go through them just once.
There's no functional change intended.
Acked-by: Hao Luo <haoluo@google.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
btf_encoder.c | 124 +++++++++++++++++++++++++++-----------------------
1 file changed, 67 insertions(+), 57 deletions(-)
diff --git a/btf_encoder.c b/btf_encoder.c
index 4c92908beab2..1866bb16a8ba 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -250,75 +250,85 @@ static bool percpu_var_exists(uint64_t addr, uint32_t *sz, const char **name)
return true;
}
-static int find_all_percpu_vars(struct btf_elf *btfe)
+static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym)
{
- uint32_t core_id;
- GElf_Sym sym;
+ const char *sym_name;
+ uint64_t addr;
+ uint32_t size;
- /* cache variables' addresses, preparing for searching in symtab. */
- percpu_var_cnt = 0;
+ /* compare a symbol's shndx to determine if it's a percpu variable */
+ if (elf_sym__section(sym) != btfe->percpu_shndx)
+ return 0;
+ if (elf_sym__type(sym) != STT_OBJECT)
+ return 0;
- /* search within symtab for percpu variables */
- elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) {
- const char *sym_name;
- uint64_t addr;
- uint32_t size;
+ addr = elf_sym__value(sym);
+ /*
+ * Store only those symbols that have allocated space in the percpu section.
+ * This excludes the following three types of symbols:
+ *
+ * 1. __ADDRESSABLE(sym), which are forcely emitted as symbols.
+ * 2. __UNIQUE_ID(prefix), which are introduced to generate unique ids.
+ * 3. __exitcall(fn), functions which are labeled as exit calls.
+ *
+ * In addition, the variables defined using DEFINE_PERCPU_FIRST are
+ * also not included, which currently includes:
+ *
+ * 1. fixed_percpu_data
+ */
+ if (!addr)
+ return 0;
- /* compare a symbol's shndx to determine if it's a percpu variable */
- if (elf_sym__section(&sym) != btfe->percpu_shndx)
- continue;
- if (elf_sym__type(&sym) != STT_OBJECT)
- continue;
+ size = elf_sym__size(sym);
+ if (!size)
+ return 0; /* ignore zero-sized symbols */
- addr = elf_sym__value(&sym);
- /*
- * Store only those symbols that have allocated space in the percpu section.
- * This excludes the following three types of symbols:
- *
- * 1. __ADDRESSABLE(sym), which are forcely emitted as symbols.
- * 2. __UNIQUE_ID(prefix), which are introduced to generate unique ids.
- * 3. __exitcall(fn), functions which are labeled as exit calls.
- *
- * In addition, the variables defined using DEFINE_PERCPU_FIRST are
- * also not included, which currently includes:
- *
- * 1. fixed_percpu_data
- */
- if (!addr)
- continue;
+ sym_name = elf_sym__name(sym, btfe->symtab);
+ if (!btf_name_valid(sym_name)) {
+ dump_invalid_symbol("Found symbol of invalid name when encoding btf",
+ sym_name, btf_elf__verbose, btf_elf__force);
+ if (btf_elf__force)
+ return 0;
+ return -1;
+ }
- size = elf_sym__size(&sym);
- if (!size)
- continue; /* ignore zero-sized symbols */
+ if (btf_elf__verbose)
+ printf("Found per-CPU symbol '%s' at address 0x%lx\n", sym_name, addr);
- sym_name = elf_sym__name(&sym, btfe->symtab);
- if (!btf_name_valid(sym_name)) {
- dump_invalid_symbol("Found symbol of invalid name when encoding btf",
- sym_name, btf_elf__verbose, btf_elf__force);
- if (btf_elf__force)
- continue;
- return -1;
- }
+ if (percpu_var_cnt == MAX_PERCPU_VAR_CNT) {
+ fprintf(stderr, "Reached the limit of per-CPU variables: %d\n",
+ MAX_PERCPU_VAR_CNT);
+ return -1;
+ }
+ percpu_vars[percpu_var_cnt].addr = addr;
+ percpu_vars[percpu_var_cnt].sz = size;
+ percpu_vars[percpu_var_cnt].name = sym_name;
+ percpu_var_cnt++;
- if (btf_elf__verbose)
- printf("Found per-CPU symbol '%s' at address 0x%lx\n", sym_name, addr);
+ return 0;
+}
+
+static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
+{
+ uint32_t core_id;
+ GElf_Sym sym;
- if (percpu_var_cnt == MAX_PERCPU_VAR_CNT) {
- fprintf(stderr, "Reached the limit of per-CPU variables: %d\n",
- MAX_PERCPU_VAR_CNT);
+ /* cache variables' addresses, preparing for searching in symtab. */
+ percpu_var_cnt = 0;
+
+ /* search within symtab for percpu variables */
+ elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) {
+ if (collect_percpu_vars && collect_percpu_var(btfe, &sym))
return -1;
- }
- percpu_vars[percpu_var_cnt].addr = addr;
- percpu_vars[percpu_var_cnt].sz = size;
- percpu_vars[percpu_var_cnt].name = sym_name;
- percpu_var_cnt++;
}
- if (percpu_var_cnt)
- qsort(percpu_vars, percpu_var_cnt, sizeof(percpu_vars[0]), percpu_var_cmp);
+ if (collect_percpu_vars) {
+ if (percpu_var_cnt)
+ qsort(percpu_vars, percpu_var_cnt, sizeof(percpu_vars[0]), percpu_var_cmp);
- if (btf_elf__verbose)
- printf("Found %d per-CPU variables!\n", percpu_var_cnt);
+ if (btf_elf__verbose)
+ printf("Found %d per-CPU variables!\n", percpu_var_cnt);
+ }
return 0;
}
@@ -347,7 +357,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
if (!btfe)
return -1;
- if (!skip_encoding_vars && find_all_percpu_vars(btfe))
+ if (collect_symbols(btfe, !skip_encoding_vars))
goto out;
has_index_type = false;
--
2.26.2
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [PATCH 3/3] btf_encoder: Change functions check due to broken dwarf
2020-11-04 21:59 [PATCHv3 0/3] pahole/kernel: Workaround dwarf bug for function encoding Jiri Olsa
2020-11-04 21:59 ` [PATCH 1/3] bpf: Move iterator functions into special init section Jiri Olsa
2020-11-04 21:59 ` [PATCH 2/3] btf_encoder: Move find_all_percpu_vars in generic collect_symbols Jiri Olsa
@ 2020-11-04 21:59 ` Jiri Olsa
2020-11-05 19:52 ` Andrii Nakryiko
2 siblings, 1 reply; 8+ messages in thread
From: Jiri Olsa @ 2020-11-04 21:59 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: dwarves, bpf, Alexei Starovoitov, Andrii Nakryiko, Yonghong Song,
Hao Luo, Frank Ch. Eigler, Mark Wielaard
We need to generate just single BTF instance for the
function, while DWARF data contains multiple instances
of DW_TAG_subprogram tag.
Unfortunately we can no longer rely on DW_AT_declaration
tag (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97060)
Instead we apply following checks:
- argument names are defined for the function
- there's symbol and address defined for the function
- function is generated only once
Also because we want to follow kernel's ftrace traceable
functions, this patchset is adding extra check that the
function is one of the ftrace's functions.
All ftrace functions addresses are stored in vmlinux
binary within symbols:
__start_mcount_loc
__stop_mcount_loc
During object preparation code we read those addresses,
sort them and use them as filter for all detected dwarf
functions.
We also filter out functions within .init section, ftrace
is doing that in runtime. At the same time we keep functions
from .init.bpf.preserve_type, because they are needed in BTF.
I can still see several differences to ftrace functions in
/sys/kernel/debug/tracing/available_filter_functions file:
- available_filter_functions includes modules
- available_filter_functions includes functions like:
__acpi_match_device.part.0.constprop.0
acpi_ns_check_sorted_list.constprop.0
acpi_os_unmap_generic_address.part.0
acpiphp_check_bridge.part.0
which are not part of dwarf data
- BTF includes multiple functions like:
__clk_register_clkdev
clk_register_clkdev
which share same code so they appear just as single function
in available_filter_functions, but dwarf keeps track of both
of them
With this change I'm getting 38353 BTF functions, which
when added above functions to consideration gives same
amount of functions in available_filter_functions.
The patch still keeps the original function filter condition
(that uses current fn->declaration check) in case the object
does not contain *_mcount_loc symbol -> object is not vmlinux.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
btf_encoder.c | 261 +++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 259 insertions(+), 2 deletions(-)
diff --git a/btf_encoder.c b/btf_encoder.c
index 1866bb16a8ba..df89b4467e4c 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -26,6 +26,174 @@
*/
#define KSYM_NAME_LEN 128
+struct symbols {
+ unsigned long start;
+ unsigned long stop;
+ unsigned long init_begin;
+ unsigned long init_end;
+ unsigned long init_bpf_begin;
+ unsigned long init_bpf_end;
+ unsigned long start_section;
+};
+
+struct elf_function {
+ const char *name;
+ unsigned long addr;
+ bool generated;
+};
+
+static struct elf_function *functions;
+static int functions_alloc;
+static int functions_cnt;
+static int functions_valid;
+
+static int functions_cmp(const void *_a, const void *_b)
+{
+ const struct elf_function *a = _a;
+ const struct elf_function *b = _b;
+
+ return strcmp(a->name, b->name);
+}
+
+static void delete_functions(void)
+{
+ free(functions);
+ functions_alloc = functions_cnt = functions_valid = 0;
+}
+
+#ifndef max
+#define max(x, y) ((x) < (y) ? (y) : (x))
+#endif
+
+static int collect_function(struct btf_elf *btfe, GElf_Sym *sym)
+{
+ struct elf_function *new;
+
+ if (elf_sym__type(sym) != STT_FUNC)
+ return 0;
+ if (!elf_sym__value(sym))
+ return 0;
+
+ if (functions_cnt == functions_alloc) {
+ functions_alloc = max(1000, functions_alloc * 3 / 2);
+ new = realloc(functions, functions_alloc * sizeof(*functions));
+ if (!new) {
+ delete_functions();
+ return -1;
+ }
+ functions = new;
+ }
+
+ functions[functions_cnt].name = elf_sym__name(sym, btfe->symtab);
+ functions[functions_cnt].addr = elf_sym__value(sym);
+ functions[functions_cnt].generated = false;
+ functions_cnt++;
+ return 0;
+}
+
+static int addrs_cmp(const void *_a, const void *_b)
+{
+ const unsigned long *a = _a;
+ const unsigned long *b = _b;
+
+ if (*a == *b)
+ return 0;
+ return *a < *b ? -1 : 1;
+}
+
+static bool is_init(struct symbols *ms, unsigned long addr)
+{
+ return addr >= ms->init_begin && addr < ms->init_end;
+}
+
+static bool is_bpf_init(struct symbols *ms, unsigned long addr)
+{
+ return addr >= ms->init_bpf_begin && addr < ms->init_bpf_end;
+}
+
+static int filter_functions(struct btf_elf *btfe, struct symbols *ms)
+{
+ unsigned long *addrs, count, offset, i;
+ Elf_Data *data;
+ GElf_Shdr shdr;
+ Elf_Scn *sec;
+
+ /*
+ * Find mcount addressed marked by __start_mcount_loc
+ * and __stop_mcount_loc symbols and load them into
+ * sorted array.
+ */
+ sec = elf_getscn(btfe->elf, ms->start_section);
+ if (!sec || !gelf_getshdr(sec, &shdr)) {
+ fprintf(stderr, "Failed to get section(%lu) header.\n",
+ ms->start_section);
+ return -1;
+ }
+
+ offset = ms->start - shdr.sh_addr;
+ count = (ms->stop - ms->start) / 8;
+
+ data = elf_getdata(sec, 0);
+ if (!data) {
+ fprintf(stderr, "Failed to get section(%lu) data.\n",
+ ms->start_section);
+ return -1;
+ }
+
+ addrs = malloc(count * sizeof(addrs[0]));
+ if (!addrs) {
+ fprintf(stderr, "Failed to allocate memory for ftrace addresses.\n");
+ return -1;
+ }
+
+ memcpy(addrs, data->d_buf + offset, count * sizeof(addrs[0]));
+ qsort(addrs, count, sizeof(addrs[0]), addrs_cmp);
+
+ /*
+ * Let's got through all collected functions and filter
+ * out those that are not in ftrace and init code.
+ */
+ for (i = 0; i < functions_cnt; i++) {
+ struct elf_function *func = &functions[i];
+
+ /*
+ * Do not enable .init section functions,
+ * but keep .init.bpf.preserve_type functions.
+ */
+ if (is_init(ms, func->addr) && !is_bpf_init(ms, func->addr))
+ continue;
+
+ /* Make sure function is within ftrace addresses. */
+ if (bsearch(&func->addr, addrs, count, sizeof(addrs[0]), addrs_cmp)) {
+ /*
+ * We iterate over sorted array, so we can easily skip
+ * not valid item and move following valid field into
+ * its place, and still keep the 'new' array sorted.
+ */
+ if (i != functions_valid)
+ functions[functions_valid] = functions[i];
+ functions_valid++;
+ }
+ }
+
+ free(addrs);
+ return 0;
+}
+
+static bool should_generate_function(const struct btf_elf *btfe, const char *name)
+{
+ struct elf_function *p;
+ struct elf_function key = { .name = name };
+
+ p = bsearch(&key, functions, functions_valid,
+ sizeof(functions[0]), functions_cmp);
+ if (!p || p->generated)
+ return false;
+
+ p->generated = true;
+ return true;
+}
+
static bool btf_name_char_ok(char c, bool first)
{
if (c == '_' || c == '.')
@@ -207,6 +375,7 @@ int btf_encoder__encode()
btf_elf__add_datasec_type(btfe, PERCPU_SECTION, &btfe->percpu_secinfo);
err = btf_elf__encode(btfe, 0);
+ delete_functions();
btf_elf__delete(btfe);
btfe = NULL;
@@ -308,8 +477,45 @@ static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym)
return 0;
}
+static void collect_symbol(GElf_Sym *sym, struct symbols *ms)
+{
+ if (!ms->start &&
+ !strcmp("__start_mcount_loc", elf_sym__name(sym, btfe->symtab))) {
+ ms->start = sym->st_value;
+ ms->start_section = sym->st_shndx;
+ }
+
+ if (!ms->stop &&
+ !strcmp("__stop_mcount_loc", elf_sym__name(sym, btfe->symtab)))
+ ms->stop = sym->st_value;
+
+ if (!ms->init_begin &&
+ !strcmp("__init_begin", elf_sym__name(sym, btfe->symtab)))
+ ms->init_begin = sym->st_value;
+
+ if (!ms->init_end &&
+ !strcmp("__init_end", elf_sym__name(sym, btfe->symtab)))
+ ms->init_end = sym->st_value;
+
+ if (!ms->init_bpf_begin &&
+ !strcmp("__init_bpf_preserve_type_begin", elf_sym__name(sym, btfe->symtab)))
+ ms->init_bpf_begin = sym->st_value;
+
+ if (!ms->init_bpf_end &&
+ !strcmp("__init_bpf_preserve_type_end", elf_sym__name(sym, btfe->symtab)))
+ ms->init_bpf_end = sym->st_value;
+}
+
+static int has_all_symbols(struct symbols *ms)
+{
+ return ms->start && ms->stop &&
+ ms->init_begin && ms->init_end &&
+ ms->init_bpf_begin && ms->init_bpf_end;
+}
+
static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
{
+ struct symbols ms = { };
uint32_t core_id;
GElf_Sym sym;
@@ -320,6 +526,9 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) {
if (collect_percpu_vars && collect_percpu_var(btfe, &sym))
return -1;
+ if (collect_function(btfe, &sym))
+ return -1;
+ collect_symbol(&sym, &ms);
}
if (collect_percpu_vars) {
@@ -329,9 +538,36 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
if (btf_elf__verbose)
printf("Found %d per-CPU variables!\n", percpu_var_cnt);
}
+
+ if (functions_cnt && has_all_symbols(&ms)) {
+ qsort(functions, functions_cnt, sizeof(functions[0]), functions_cmp);
+ if (filter_functions(btfe, &ms)) {
+ fprintf(stderr, "Failed to filter dwarf functions\n");
+ return -1;
+ }
+ if (btf_elf__verbose)
+ printf("Found %d functions!\n", functions_valid);
+ } else {
+ if (btf_elf__verbose)
+ printf("vmlinux not detected, falling back to dwarf data\n");
+ }
+
return 0;
}
+static bool has_arg_names(struct cu *cu, struct ftype *ftype)
+{
+ struct parameter *param;
+ const char *name;
+
+ ftype__for_each_parameter(ftype, param) {
+ name = dwarves__active_loader->strings__ptr(cu, param->name);
+ if (name == NULL)
+ return false;
+ }
+ return true;
+}
+
int cu__encode_btf(struct cu *cu, int verbose, bool force,
bool skip_encoding_vars)
{
@@ -407,8 +643,28 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
int btf_fnproto_id, btf_fn_id;
const char *name;
- if (fn->declaration || !fn->external)
- continue;
+ /*
+ * The functions_valid != 0 means we parsed all necessary
+ * kernel symbols and we are using ftrace location filter
+ * for functions. If it's not available keep the current
+ * dwarf declaration check.
+ */
+ if (functions_valid) {
+ /*
+ * We check following conditions:
+ * - argument names are defined
+ * - there's symbol and address defined for the function
+ * - function address belongs to ftrace locations
+ * - function is generated only once
+ */
+ if (!has_arg_names(cu, &fn->proto))
+ continue;
+ if (!should_generate_function(btfe, function__name(fn, cu)))
+ continue;
+ } else {
+ if (fn->declaration || !fn->external)
+ continue;
+ }
btf_fnproto_id = btf_elf__add_func_proto(btfe, cu, &fn->proto, type_id_off);
name = dwarves__active_loader->strings__ptr(cu, fn->name);
@@ -492,6 +748,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
out:
if (err) {
+ delete_functions();
btf_elf__delete(btfe);
btfe = NULL;
}
--
2.26.2
^ permalink raw reply related [flat|nested] 8+ messages in thread