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Wed, 24 Apr 2024 13:34:47 -0400 (EDT) From: Daniel Xu To: acme@kernel.org, jolsa@kernel.org, quentin@isovalent.com, alan.maguire@oracle.com, eddyz87@gmail.com Cc: andrii.nakryiko@gmail.com, ast@kernel.org, daniel@iogearbox.net, bpf@vger.kernel.org Subject: [PATCH dwarves v7 1/2] pahole: Add --btf_feature=decl_tag_kfuncs feature Date: Wed, 24 Apr 2024 11:33:51 -0600 Message-ID: <2a1e69c33d77b1887f72f9226f40bf484b13cf55.1713980005.git.dxu@dxuuu.xyz> X-Mailer: git-send-email 2.44.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Add a feature flag to guard tagging of kfuncs. The next commit will implement the actual tagging. Reviewed-by: Alan Maguire Signed-off-by: Daniel Xu --- btf_encoder.c | 2 ++ dwarves.h | 1 + man-pages/pahole.1 | 1 + pahole.c | 1 + 4 files changed, 5 insertions(+) diff --git a/btf_encoder.c b/btf_encoder.c index e1e3529..850e36f 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -75,6 +75,7 @@ struct btf_encoder { verbose, force, gen_floats, + tag_kfuncs, is_rel; uint32_t array_index_id; struct { @@ -1659,6 +1660,7 @@ struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filenam encoder->force = conf_load->btf_encode_force; encoder->gen_floats = conf_load->btf_gen_floats; encoder->skip_encoding_vars = conf_load->skip_encoding_btf_vars; + encoder->tag_kfuncs = conf_load->btf_decl_tag_kfuncs; encoder->verbose = verbose; encoder->has_index_type = false; encoder->need_index_type = false; diff --git a/dwarves.h b/dwarves.h index dd35a4e..7d566b6 100644 --- a/dwarves.h +++ b/dwarves.h @@ -94,6 +94,7 @@ struct conf_load { bool btf_gen_floats; bool btf_encode_force; bool reproducible_build; + bool btf_decl_tag_kfuncs; uint8_t hashtable_bits; uint8_t max_hashtable_bits; uint16_t kabi_prefix_len; diff --git a/man-pages/pahole.1 b/man-pages/pahole.1 index e3c58e0..4769b58 100644 --- a/man-pages/pahole.1 +++ b/man-pages/pahole.1 @@ -308,6 +308,7 @@ Encode BTF using the specified feature list, or specify 'default' for all standa in some CUs and not others, or when the same function name has inconsistent BTF descriptions in different CUs. + decl_tag_kfuncs Inject a BTF_KIND_DECL_TAG for each discovered kfunc. .fi Supported non-standard features (not enabled for 'default') diff --git a/pahole.c b/pahole.c index 750b847..954498d 100644 --- a/pahole.c +++ b/pahole.c @@ -1289,6 +1289,7 @@ struct btf_feature { BTF_DEFAULT_FEATURE(enum64, skip_encoding_btf_enum64, true), BTF_DEFAULT_FEATURE(optimized_func, btf_gen_optimized, false), BTF_DEFAULT_FEATURE(consistent_func, skip_encoding_btf_inconsistent_proto, false), + BTF_DEFAULT_FEATURE(decl_tag_kfuncs, btf_decl_tag_kfuncs, false), BTF_NON_DEFAULT_FEATURE(reproducible_build, reproducible_build, false), }; 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Wed, 24 Apr 2024 13:34:48 -0400 (EDT) From: Daniel Xu To: acme@kernel.org, jolsa@kernel.org, quentin@isovalent.com, alan.maguire@oracle.com, eddyz87@gmail.com Cc: andrii.nakryiko@gmail.com, ast@kernel.org, daniel@iogearbox.net, bpf@vger.kernel.org Subject: [PATCH dwarves v7 2/2] pahole: Inject kfunc decl tags into BTF Date: Wed, 24 Apr 2024 11:33:52 -0600 Message-ID: X-Mailer: git-send-email 2.44.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 This commit teaches pahole to parse symbols in .BTF_ids section in vmlinux and discover exported kfuncs. Pahole then takes the list of kfuncs and injects a BTF_KIND_DECL_TAG for each kfunc. Example of encoding: $ bpftool btf dump file .tmp_vmlinux.btf | rg "DECL_TAG 'bpf_kfunc'" | wc -l 121 $ bpftool btf dump file .tmp_vmlinux.btf | rg 56337 [56337] FUNC 'bpf_ct_change_timeout' type_id=56336 linkage=static [127861] DECL_TAG 'bpf_kfunc' type_id=56337 component_idx=-1 This enables downstream users and tools to dynamically discover which kfuncs are available on a system by parsing vmlinux or module BTF, both available in /sys/kernel/btf. This feature is enabled with --btf_features=decl_tag,decl_tag_kfuncs. Acked-by: Jiri Olsa Tested-by: Jiri Olsa Reviewed-by: Alan Maguire Tested-by: Alan Maguire Signed-off-by: Daniel Xu --- btf_encoder.c | 372 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 372 insertions(+) diff --git a/btf_encoder.c b/btf_encoder.c index 850e36f..d326404 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -34,6 +34,21 @@ #include #define BTF_ENCODER_MAX_PROTO 512 +#define BTF_IDS_SECTION ".BTF_ids" +#define BTF_ID_FUNC_PFX "__BTF_ID__func__" +#define BTF_ID_SET8_PFX "__BTF_ID__set8__" +#define BTF_SET8_KFUNCS (1 << 0) +#define BTF_KFUNC_TYPE_TAG "bpf_kfunc" + +/* Adapted from include/linux/btf_ids.h */ +struct btf_id_set8 { + uint32_t cnt; + uint32_t flags; + struct { + uint32_t id; + uint32_t flags; + } pairs[]; +}; /* state used to do later encoding of saved functions */ struct btf_encoder_state { @@ -75,6 +90,7 @@ struct btf_encoder { verbose, force, gen_floats, + skip_encoding_decl_tag, tag_kfuncs, is_rel; uint32_t array_index_id; @@ -94,6 +110,17 @@ struct btf_encoder { } functions; }; +struct btf_func { + const char *name; + int type_id; +}; + +/* Half open interval representing range of addresses containing kfuncs */ +struct btf_kfunc_set_range { + uint64_t start; + uint64_t end; +}; + static LIST_HEAD(encoders); static pthread_mutex_t encoders__lock = PTHREAD_MUTEX_INITIALIZER; @@ -1363,8 +1390,343 @@ out: return err; } +/* Returns if `sym` points to a kfunc set */ +static int is_sym_kfunc_set(GElf_Sym *sym, const char *name, Elf_Data *idlist, size_t idlist_addr) +{ + void *ptr = idlist->d_buf; + struct btf_id_set8 *set; + int off; + + /* kfuncs are only found in BTF_SET8's */ + if (!strstarts(name, BTF_ID_SET8_PFX)) + return false; + + off = sym->st_value - idlist_addr; + if (off >= idlist->d_size) { + fprintf(stderr, "%s: symbol '%s' out of bounds\n", __func__, name); + return false; + } + + /* Check the set8 flags to see if it was marked as kfunc */ + set = ptr + off; + return set->flags & BTF_SET8_KFUNCS; +} + +/* + * Parse BTF_ID symbol and return the func name. + * + * Returns: + * Caller-owned string containing func name if successful. + * NULL if !func or on error. + */ +static char *get_func_name(const char *sym) +{ + char *func, *end; + + /* Example input: __BTF_ID__func__vfs_close__1 + * + * The goal is to strip the prefix and suffix such that we only + * return vfs_close. + */ + + if (!strstarts(sym, BTF_ID_FUNC_PFX)) + return NULL; + + /* Strip prefix and handle malformed input such as __BTF_ID__func___ */ + func = strdup(sym + sizeof(BTF_ID_FUNC_PFX) - 1); + if (strlen(func) < 2) { + free(func); + return NULL; + } + + /* Strip suffix */ + end = strrchr(func, '_'); + if (!end || *(end - 1) != '_') { + free(func); + return NULL; + } + *(end - 1) = '\0'; + + return func; +} + +static int btf_func_cmp(const void *_a, const void *_b) +{ + const struct btf_func *a = _a; + const struct btf_func *b = _b; + + return strcmp(a->name, b->name); +} + +/* + * Collects all functions described in BTF. + * Returns non-zero on error. + */ +static int btf_encoder__collect_btf_funcs(struct btf_encoder *encoder, struct gobuffer *funcs) +{ + struct btf *btf = encoder->btf; + int nr_types, type_id; + int err = -1; + + /* First collect all the func entries into an array */ + nr_types = btf__type_cnt(btf); + for (type_id = 1; type_id < nr_types; type_id++) { + const struct btf_type *type; + struct btf_func func = {}; + const char *name; + + type = btf__type_by_id(btf, type_id); + if (!type) { + fprintf(stderr, "%s: malformed BTF, can't resolve type for ID %d\n", + __func__, type_id); + err = -EINVAL; + goto out; + } + + if (!btf_is_func(type)) + continue; + + name = btf__name_by_offset(btf, type->name_off); + if (!name) { + fprintf(stderr, "%s: malformed BTF, can't resolve name for ID %d\n", + __func__, type_id); + err = -EINVAL; + goto out; + } + + func.name = name; + func.type_id = type_id; + err = gobuffer__add(funcs, &func, sizeof(func)); + if (err < 0) + goto out; + } + + /* Now that we've collected funcs, sort them by name */ + gobuffer__sort(funcs, sizeof(struct btf_func), btf_func_cmp); + + err = 0; +out: + return err; +} + +static int btf_encoder__tag_kfunc(struct btf_encoder *encoder, struct gobuffer *funcs, const char *kfunc) +{ + struct btf_func key = { .name = kfunc }; + struct btf *btf = encoder->btf; + struct btf_func *target; + const void *base; + unsigned int cnt; + int err = -1; + + base = gobuffer__entries(funcs); + cnt = gobuffer__nr_entries(funcs); + target = bsearch(&key, base, cnt, sizeof(key), btf_func_cmp); + if (!target) { + fprintf(stderr, "%s: failed to find kfunc '%s' in BTF\n", __func__, kfunc); + goto out; + } + + /* Note we are unconditionally adding the btf_decl_tag even + * though vmlinux may already contain btf_decl_tags for kfuncs. + * We are ok to do this b/c we will later btf__dedup() to remove + * any duplicates. + */ + err = btf__add_decl_tag(btf, BTF_KFUNC_TYPE_TAG, target->type_id, -1); + if (err < 0) { + fprintf(stderr, "%s: failed to insert kfunc decl tag for '%s': %d\n", + __func__, kfunc, err); + goto out; + } + + err = 0; +out: + return err; +} + +static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder) +{ + const char *filename = encoder->filename; + struct gobuffer btf_kfunc_ranges = {}; + struct gobuffer btf_funcs = {}; + Elf_Data *symbols = NULL; + Elf_Data *idlist = NULL; + Elf_Scn *symscn = NULL; + int symbols_shndx = -1; + size_t idlist_addr = 0; + int fd = -1, err = -1; + int idlist_shndx = -1; + size_t strtabidx = 0; + Elf_Scn *scn = NULL; + Elf *elf = NULL; + GElf_Shdr shdr; + size_t strndx; + char *secname; + int nr_syms; + int i = 0; + + fd = open(filename, O_RDONLY); + if (fd < 0) { + fprintf(stderr, "Cannot open %s\n", filename); + goto out; + } + + if (elf_version(EV_CURRENT) == EV_NONE) { + elf_error("Cannot set libelf version"); + goto out; + } + + elf = elf_begin(fd, ELF_C_READ, NULL); + if (elf == NULL) { + elf_error("Cannot update ELF file"); + goto out; + } + + /* Locate symbol table and .BTF_ids sections */ + if (elf_getshdrstrndx(elf, &strndx) < 0) + goto out; + + while ((scn = elf_nextscn(elf, scn)) != NULL) { + Elf_Data *data; + + i++; + if (!gelf_getshdr(scn, &shdr)) { + elf_error("Failed to get ELF section(%d) hdr", i); + goto out; + } + + secname = elf_strptr(elf, strndx, shdr.sh_name); + if (!secname) { + elf_error("Failed to get ELF section(%d) hdr name", i); + goto out; + } + + data = elf_getdata(scn, 0); + if (!data) { + elf_error("Failed to get ELF section(%d) data", i); + goto out; + } + + if (shdr.sh_type == SHT_SYMTAB) { + symbols_shndx = i; + symscn = scn; + symbols = data; + strtabidx = shdr.sh_link; + } else if (!strcmp(secname, BTF_IDS_SECTION)) { + idlist_shndx = i; + idlist_addr = shdr.sh_addr; + idlist = data; + } + } + + /* Cannot resolve symbol or .BTF_ids sections. Nothing to do. */ + if (symbols_shndx == -1 || idlist_shndx == -1) { + err = 0; + goto out; + } + + if (!gelf_getshdr(symscn, &shdr)) { + elf_error("Failed to get ELF symbol table header"); + goto out; + } + nr_syms = shdr.sh_size / shdr.sh_entsize; + + err = btf_encoder__collect_btf_funcs(encoder, &btf_funcs); + if (err) { + fprintf(stderr, "%s: failed to collect BTF funcs\n", __func__); + goto out; + } + + /* First collect all kfunc set ranges. + * + * Note we choose not to sort these ranges and accept a linear + * search when doing lookups. Reasoning is that the number of + * sets is ~O(100) and not worth the additional code to optimize. + */ + for (i = 0; i < nr_syms; i++) { + struct btf_kfunc_set_range range = {}; + const char *name; + GElf_Sym sym; + + if (!gelf_getsym(symbols, i, &sym)) { + elf_error("Failed to get ELF symbol(%d)", i); + goto out; + } + + if (sym.st_shndx != idlist_shndx) + continue; + + name = elf_strptr(elf, strtabidx, sym.st_name); + if (!is_sym_kfunc_set(&sym, name, idlist, idlist_addr)) + continue; + + range.start = sym.st_value; + range.end = sym.st_value + sym.st_size; + gobuffer__add(&btf_kfunc_ranges, &range, sizeof(range)); + } + + /* Now inject BTF with kfunc decl tag for detected kfuncs */ + for (i = 0; i < nr_syms; i++) { + const struct btf_kfunc_set_range *ranges; + unsigned int ranges_cnt; + char *func, *name; + GElf_Sym sym; + bool found; + int err; + int j; + + if (!gelf_getsym(symbols, i, &sym)) { + elf_error("Failed to get ELF symbol(%d)", i); + goto out; + } + + if (sym.st_shndx != idlist_shndx) + continue; + + name = elf_strptr(elf, strtabidx, sym.st_name); + func = get_func_name(name); + if (!func) + continue; + + /* Check if function belongs to a kfunc set */ + ranges = gobuffer__entries(&btf_kfunc_ranges); + ranges_cnt = gobuffer__nr_entries(&btf_kfunc_ranges); + found = false; + for (j = 0; j < ranges_cnt; j++) { + size_t addr = sym.st_value; + + if (ranges[j].start <= addr && addr < ranges[j].end) { + found = true; + break; + } + } + if (!found) { + free(func); + continue; + } + + err = btf_encoder__tag_kfunc(encoder, &btf_funcs, func); + if (err) { + fprintf(stderr, "%s: failed to tag kfunc '%s'\n", __func__, func); + free(func); + goto out; + } + free(func); + } + + err = 0; +out: + __gobuffer__delete(&btf_funcs); + __gobuffer__delete(&btf_kfunc_ranges); + if (elf) + elf_end(elf); + if (fd != -1) + close(fd); + return err; +} + int btf_encoder__encode(struct btf_encoder *encoder) { + bool should_tag_kfuncs; int err; /* for single-threaded case, saved funcs are added here */ @@ -1377,6 +1739,15 @@ int btf_encoder__encode(struct btf_encoder *encoder) if (btf__type_cnt(encoder->btf) == 1) return 0; + /* Note vmlinux may already contain btf_decl_tag's for kfuncs. So + * take care to call this before btf_dedup(). + */ + should_tag_kfuncs = encoder->tag_kfuncs && !encoder->skip_encoding_decl_tag; + if (should_tag_kfuncs && btf_encoder__tag_kfuncs(encoder)) { + fprintf(stderr, "%s: failed to tag kfuncs!\n", __func__); + return -1; + } + if (btf__dedup(encoder->btf, NULL)) { fprintf(stderr, "%s: btf__dedup failed!\n", __func__); return -1; @@ -1660,6 +2031,7 @@ struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filenam encoder->force = conf_load->btf_encode_force; encoder->gen_floats = conf_load->btf_gen_floats; encoder->skip_encoding_vars = conf_load->skip_encoding_btf_vars; + encoder->skip_encoding_decl_tag = conf_load->skip_encoding_btf_decl_tag; encoder->tag_kfuncs = conf_load->btf_decl_tag_kfuncs; encoder->verbose = verbose; encoder->has_index_type = false;