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X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: O4Uo5HPBkTvf4rruBA72HkjdzFSWzvvKuIWyEs0droUbG1sV+YMBFxoOL6KHNi1nOA6HRp2EJSNo2wlIBu+BsQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR10MB5006 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-03-20_08,2024-03-18_03,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 suspectscore=0 malwarescore=0 spamscore=0 mlxscore=0 phishscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2403140000 definitions=main-2403200102 X-Proofpoint-ORIG-GUID: gkMppOTv18rk-d8MSscIOrrKOIkyWPi- X-Proofpoint-GUID: gkMppOTv18rk-d8MSscIOrrKOIkyWPi- --------------93E2bcJ688PL4aBr3ZQnkk0S Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 15/03/2024 19:48, Daniel Xu wrote: > 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. > > Signed-off-by: Daniel Xu This is great work; a lot of steps needed to collect this info, but it's really valuable! Reviewed-by: Alan Maguire Tested-by: Alan Maguire BTW we need something like the attached patch to switch to using --btf_features for pahole 1.26 and later; will I send it officially or do you have something that does the same that you want to roll into your bpf-next series? Let me know what works from your side. Thanks! > --- > btf_encoder.c | 368 ++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 368 insertions(+) > > diff --git a/btf_encoder.c b/btf_encoder.c > index 850e36f..31848e2 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 { > + size_t start; > + size_t end; > +}; > + > static LIST_HEAD(encoders); > static pthread_mutex_t encoders__lock = PTHREAD_MUTEX_INITIALIZER; > > @@ -1363,8 +1390,339 @@ 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; > + bool is_set8; > + int off; > + > + /* kfuncs are only found in BTF_SET8's */ > + is_set8 = !strncmp(name, BTF_ID_SET8_PFX, sizeof(BTF_ID_SET8_PFX) - 1); > + if (!is_set8) > + 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; > + > + if (strncmp(sym, BTF_ID_FUNC_PFX, sizeof(BTF_ID_FUNC_PFX) - 1)) > + return NULL; > + > + /* Strip prefix */ > + 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 */ > + qsort((void *)gobuffer__entries(funcs), gobuffer__nr_entries(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 +1735,15 @@ 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 +2027,7 @@ 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; --------------93E2bcJ688PL4aBr3ZQnkk0S Content-Type: text/x-patch; charset=UTF-8; name="0001-switch.patch" Content-Disposition: attachment; filename="0001-switch.patch" Content-Transfer-Encoding: base64 RnJvbSAyY2EzN2NmYTFlOWJlNGY0ZDk3MTdmYzNkYzM0NmNkZDdjNjE3ZTMyIE1vbiBTZXAgMTcg MDA6MDA6MDAgMjAwMQpGcm9tOiBBbGFuIE1hZ3VpcmUgPGFsYW4ubWFndWlyZUBvcmFjbGUuY29t PgpEYXRlOiBNb24sIDExIE1hciAyMDI0IDEwOjE3OjQ3ICswMDAwClN1YmplY3Q6IFtQQVRDSCBi cGYtbmV4dF0ga2J1aWxkLGJwZjogc3dpdGNoIHRvIHVzaW5nIC0tYnRmX2ZlYXR1cmVzIGZvcgog cGFob2xlIHYxLjI2IGFuZCBsYXRlcgoKVGhlIGJ0Zl9mZWF0dXJlcyBsaXN0IGNhbiBiZSB1c2Vk IGZvciBwYWhvbGUgdjEuMjYgYW5kIGxhdGVyIC0KaXQgaXMgdXNlZnVsIGJlY2F1c2UgaWYgYSBm ZWF0dXJlIGlzIG5vdCB5ZXQgaW1wbGVtZW50ZWQgaXQgd2lsbApub3QgZXhpdCB3aXRoIGEgZmFp bHVyZSBtZXNzYWdlLiAgVGhpcyB3aWxsIGFsbG93IHVzIHRvIGFkZCBmZWF0dXJlCnJlcXVlc3Rz IHRvIHRoZSBwYWhvbGUgb3B0aW9ucyB3aXRob3V0IGhhdmluZyB0byBjaGVjayBwYWhvbGUgdmVy c2lvbnMKaW4gZnV0dXJlOyBpZiB0aGUgdmVyc2lvbiBvZiBwYWhvbGUgc3VwcG9ydHMgdGhlIGZl YXR1cmUgaXQgd2lsbCBiZQphZGRlZC4KClNpZ25lZC1vZmYtYnk6IEFsYW4gTWFndWlyZSA8YWxh bi5tYWd1aXJlQG9yYWNsZS5jb20+Ci0tLQogc2NyaXB0cy9NYWtlZmlsZS5idGYgfCA3ICsrKysr LS0KIDEgZmlsZSBjaGFuZ2VkLCA1IGluc2VydGlvbnMoKyksIDIgZGVsZXRpb25zKC0pCgpkaWZm IC0tZ2l0IGEvc2NyaXB0cy9NYWtlZmlsZS5idGYgYi9zY3JpcHRzL01ha2VmaWxlLmJ0ZgppbmRl eCA4MjM3N2U0NzBhZWQuLjk2OTRjYTNjNTI1MiAxMDA2NDQKLS0tIGEvc2NyaXB0cy9NYWtlZmls ZS5idGYKKysrIGIvc2NyaXB0cy9NYWtlZmlsZS5idGYKQEAgLTEyLDggKzEyLDExIEBAIHBhaG9s ZS1mbGFncy0kKGNhbGwgdGVzdC1nZSwgJChwYWhvbGUtdmVyKSwgMTIxKQkrPSAtLWJ0Zl9nZW5f ZmxvYXRzCiAKIHBhaG9sZS1mbGFncy0kKGNhbGwgdGVzdC1nZSwgJChwYWhvbGUtdmVyKSwgMTIy KQkrPSAtagogCi1wYWhvbGUtZmxhZ3MtJChDT05GSUdfUEFIT0xFX0hBU19MQU5HX0VYQ0xVREUp CQkrPSAtLWxhbmdfZXhjbHVkZT1ydXN0Ci0KIHBhaG9sZS1mbGFncy0kKGNhbGwgdGVzdC1nZSwg JChwYWhvbGUtdmVyKSwgMTI1KQkrPSAtLXNraXBfZW5jb2RpbmdfYnRmX2luY29uc2lzdGVudF9w cm90byAtLWJ0Zl9nZW5fb3B0aW1pemVkCiAKKyMgU3dpdGNoIHRvIHVzaW5nIC0tYnRmX2ZlYXR1 cmVzIGZvciB2MS4yNiBhbmQgbGF0ZXIuCitwYWhvbGUtZmxhZ3MtJChjYWxsIHRlc3QtZ2UsICQo cGFob2xlLXZlciksIDEyNikJPSAtaiAtLWJ0Zl9mZWF0dXJlcz1lbmNvZGVfZm9yY2UsdmFyLGZs b2F0LGVtdW02NCxkZWNsX3RhZyx0eXBlX3RhZyxvcHRpbWl6ZWRfZnVuYyxjb25zaXN0ZW50X2Z1 bmMKKworcGFob2xlLWZsYWdzLSQoQ09ORklHX1BBSE9MRV9IQVNfTEFOR19FWENMVURFKQkJKz0g LS1sYW5nX2V4Y2x1ZGU9cnVzdAorCiBleHBvcnQgUEFIT0xFX0ZMQUdTIDo9ICQocGFob2xlLWZs YWdzLXkpCi0tIAoyLjM5LjMKCg== --------------93E2bcJ688PL4aBr3ZQnkk0S--