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. I can still see several differences to ftrace functions in /sys/kernel/debug/tracing/available_filter_functions file: - available_filter_functions includes modules (7086 functions) - 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 (1164 functions) - 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 (16 functions) With this change I'm getting 38334 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@xxxxxxxxxx> --- btf_encoder.c | 222 +++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 220 insertions(+), 2 deletions(-) diff --git a/btf_encoder.c b/btf_encoder.c index 1866bb16a8ba..0a378aa92142 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -26,6 +26,151 @@ */ #define KSYM_NAME_LEN 128 +struct mcount_symbols { + unsigned long start; + unsigned long stop; + unsigned long init_begin; + unsigned long init_end; + unsigned long start_section; +}; + +struct elf_function { + const char *name; + unsigned long addr; + bool generated; + bool valid; +}; + +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) +{ + 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); + functions = realloc(functions, functions_alloc * sizeof(*functions)); + if (!functions) + return -1; + } + + functions[functions_cnt].name = elf_sym__name(sym, btfe->symtab); + functions[functions_cnt].addr = elf_sym__value(sym); + functions[functions_cnt].generated = false; + functions[functions_cnt].valid = 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; + + return *a - *b; +} + +static int filter_functions(struct btf_elf *btfe, struct mcount_symbols *ms) +{ + bool init_filter = ms->init_begin && ms->init_end; + 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 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. */ + if (init_filter && + func->addr >= ms->init_begin && + func->addr < ms->init_end) + continue; + + /* Make sure function is within mcount addresses. */ + if (bsearch(&func->addr, addrs, count, sizeof(addrs[0]), addrs_cmp)) { + functions_valid++; + func->valid = true; + } + } + + 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_cnt, + sizeof(functions[0]), functions_cmp); + if (!p || !p->valid || p->generated) + return false; + + p->generated = true; + return true; +} + static bool btf_name_char_ok(char c, bool first) { if (c == '_' || c == '.') @@ -207,6 +352,7 @@ 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 +454,27 @@ static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym) return 0; } +#define SET_SYMBOL(__sym, __var) \ + if (!ms->__var && !strcmp(__sym, elf_sym__name(sym, btfe->symtab))) \ + ms->__var = sym->st_value; \ + +static void collect_mcount_symbol(GElf_Sym *sym, struct mcount_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; + } + SET_SYMBOL("__stop_mcount_loc", stop) + SET_SYMBOL("__init_begin", init_begin) + SET_SYMBOL("__init_end", init_end) +} + +#undef SET_SYMBOL + static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars) { + struct mcount_symbols ms = { }; uint32_t core_id; GElf_Sym sym; @@ -320,6 +485,9 @@ 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_mcount_symbol(&sym, &ms); } if (collect_percpu_vars) { @@ -329,9 +497,34 @@ 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) { + qsort(functions, functions_cnt, sizeof(functions[0]), functions_cmp); + if (ms.start && ms.stop && + 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); + } + 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 +600,32 @@ 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 mcount location filter + * for functions. If it's not available keep the current + * dwarf declaration check. + */ + if (functions_valid) { + /* + * We need to generate just single BTF instance for the + * function, while DWARF data contains multiple instances + * of DW_TAG_subprogram tag. + * + * 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 +709,7 @@ 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
