On Sat, Oct 31, 2020 at 3:32 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > 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(-) [...] > +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; memory leak right here. You need to use a temporary variable and check if for NULL, before overwriting functions. > + } > + > + 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; this is cute, but is it always correct? instead of thinking how this works with overflows, maybe let's keep it simple with if (*a == *b) return 0; return *a < *b ? -1 : 1; ? > +} > + > +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", typo: failed to get? > + 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; > + } > + [...] > > +#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) please don't use macro here, it doesn't save much code but complicates reading it quite significantly > +} > + > +#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)) { nit: single line should fit well, no? > + fprintf(stderr, "Failed to filter dwarf functions\n"); > + return -1; > + } > + if (btf_elf__verbose) > + printf("Found %d functions!\n", functions_valid); > + } > + > return 0; > } > [...]
