| Message ID | 0f25134ec999e368478c4ca993b3b729c2a03383.1706491733.git.dxu@dxuuu.xyz (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [dwarves,v3] pahole: Inject kfunc decl tags into BTF | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On 29/01/2024 01:30, 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. > > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> > This should probably be a BTF feature supported by --btf_features; that way we'd have a mechanism to switch it off if needed. Can you look at adding a "tag_kfunc" or whatever name suits into the btf_features[] array in pahole.c? Something like: BTF_FEATURE(tag_kfunc, btf_tag_kfunc, false), You'll also then need to add a btf_tag_kfunc boolean field to struct conf_load, and generation of kfunc tags should then be guarded by if (conf_load->btf_tag_kfunc) ...so that the tags are added conditionally depending on whether the user wants them. Then if a user specifies --btf_features=all or some subset of BTF features including "tag_kfunc" they will get kfunc tags. We probably should also move to using --btf_features instead of the current combination of "--" parameters when pahole is bumped to v1.26. > --- > Changes from v2: > * More reliably detect kfunc membership in set8 by tracking set addr ranges > * Rename some variables/functions to be more clear about kfunc vs func > > Changes from v1: > * Fix resource leaks > * Fix callee -> caller typo > * Rename btf_decl_tag from kfunc -> bpf_kfunc > * Only grab btf_id_set funcs tagged kfunc > * Presort btf func list > > btf_encoder.c | 347 ++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 347 insertions(+)rre > > diff --git a/btf_encoder.c b/btf_encoder.c > index fd04008..4f742b1 100644 > --- a/btf_encoder.c > +++ b/btf_encoder.c > @@ -34,6 +34,11 @@ > #include <pthread.h> > > #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" > > /* state used to do later encoding of saved functions */ > struct btf_encoder_state { > @@ -79,6 +84,7 @@ struct btf_encoder { > gen_floats, > is_rel; > uint32_t array_index_id; > + struct gobuffer btf_funcs; > struct { > struct var_info vars[MAX_PERCPU_VAR_CNT]; > int var_cnt; > @@ -94,6 +100,17 @@ 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; > > @@ -1352,6 +1369,327 @@ 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) > +{ > + int *ptr = idlist->d_buf; > + int idx, flags; > + bool is_set8; > + > + /* 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; > + > + idx = sym->st_value - idlist_addr; > + if (idx >= 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 */ > + idx = idx / sizeof(int); > + flags = ptr[idx + 1]; > + return 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); > + > + /* 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 = &encoder->btf_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, 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(&encoder->btf_funcs); > + cnt = gobuffer__nr_entries(&encoder->btf_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 = {}; > + Elf_Scn *symscn = NULL; > + int symbols_shndx = -1; > + int fd = -1, err = -1; > + int idlist_shndx = -1; > + Elf_Scn *scn = NULL; > + size_t idlist_addr; > + Elf_Data *symbols; > + Elf_Data *idlist; > + size_t strtabidx; > + 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; > + } > + > + /* Location symbol table and .BTF_ids sections */ > + elf_getshdrstrndx(elf, &strndx); > + 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); > + 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) > + continue; > + > + err = btf_encoder__tag_kfunc(encoder, 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_kfunc_ranges); > + if (elf) > + elf_end(elf); > + if (fd != -1) > + close(fd); > + return err; > +} > + > int btf_encoder__encode(struct btf_encoder *encoder) > { > int err; > @@ -1366,6 +1704,14 @@ 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(). > + */ > + if (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; > @@ -1712,6 +2058,7 @@ void btf_encoder__delete(struct btf_encoder *encoder) > > btf_encoders__delete(encoder); > __gobuffer__delete(&encoder->percpu_secinfo); > + __gobuffer__delete(&encoder->btf_funcs); > zfree(&encoder->filename); > btf__free(encoder->btf); > encoder->btf = NULL;
Em Mon, Jan 29, 2024 at 01:05:05PM +0000, Alan Maguire escreveu: > This should probably be a BTF feature supported by --btf_features; that > way we'd have a mechanism to switch it off if needed. Can you look at > adding a "tag_kfunc" or whatever name suits into the btf_features[] > array in pahole.c? Something like: > BTF_FEATURE(tag_kfunc, btf_tag_kfunc, false), > You'll also then need to add a btf_tag_kfunc boolean field to > struct conf_load, and generation of kfunc tags should then be guarded by > if (conf_load->btf_tag_kfunc) > ...so that the tags are added conditionally depending on whether > the user wants them. > Then if a user specifies --btf_features=all or some subset of BTF > features including "tag_kfunc" they will get kfunc tags. Agreed. > We probably should also move to using --btf_features instead of the > current combination of "--" parameters when pahole is bumped to v1.26. Alan, talking about that, I guess we better tag v1.26 before merging this new kfunc work, wdyt? - Arnaldo
Hi Alan, Arnaldo, On Mon, Jan 29, 2024 at 11:24:13AM -0300, Arnaldo Carvalho de Melo wrote: > Em Mon, Jan 29, 2024 at 01:05:05PM +0000, Alan Maguire escreveu: > > This should probably be a BTF feature supported by --btf_features; that > > way we'd have a mechanism to switch it off if needed. Can you look at > > adding a "tag_kfunc" or whatever name suits into the btf_features[] > > array in pahole.c? Something like: > > > BTF_FEATURE(tag_kfunc, btf_tag_kfunc, false), > > > You'll also then need to add a btf_tag_kfunc boolean field to > > struct conf_load, and generation of kfunc tags should then be guarded by > > > if (conf_load->btf_tag_kfunc) > > > ...so that the tags are added conditionally depending on whether > > the user wants them. > > > Then if a user specifies --btf_features=all or some subset of BTF > > features including "tag_kfunc" they will get kfunc tags. > > Agreed. Ack. Will add for next rev. > > > We probably should also move to using --btf_features instead of the > > current combination of "--" parameters when pahole is bumped to v1.26. > > Alan, talking about that, I guess we better tag v1.26 before merging > this new kfunc work, wdyt? > > - Arnaldo
On 29/01/2024 14:24, Arnaldo Carvalho de Melo wrote: > Em Mon, Jan 29, 2024 at 01:05:05PM +0000, Alan Maguire escreveu: >> This should probably be a BTF feature supported by --btf_features; that >> way we'd have a mechanism to switch it off if needed. Can you look at >> adding a "tag_kfunc" or whatever name suits into the btf_features[] >> array in pahole.c? Something like: > >> BTF_FEATURE(tag_kfunc, btf_tag_kfunc, false), > >> You'll also then need to add a btf_tag_kfunc boolean field to >> struct conf_load, and generation of kfunc tags should then be guarded by > >> if (conf_load->btf_tag_kfunc) > >> ...so that the tags are added conditionally depending on whether >> the user wants them. > >> Then if a user specifies --btf_features=all or some subset of BTF >> features including "tag_kfunc" they will get kfunc tags. > > Agreed. > >> We probably should also move to using --btf_features instead of the >> current combination of "--" parameters when pahole is bumped to v1.26. > > Alan, talking about that, I guess we better tag v1.26 before merging > this new kfunc work, wdyt? > Good idea - I think it'd definitely help if "pahole --version" started emitting v1.26 alright, as it would allow us to start supporting --btf_features for cases like this. Thanks! Alan > - Arnaldo
On Sun, Jan 28, 2024 at 06:30:19PM -0700, 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. > > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> > > --- > Changes from v2: > * More reliably detect kfunc membership in set8 by tracking set addr ranges > * Rename some variables/functions to be more clear about kfunc vs func > > Changes from v1: > * Fix resource leaks > * Fix callee -> caller typo > * Rename btf_decl_tag from kfunc -> bpf_kfunc > * Only grab btf_id_set funcs tagged kfunc > * Presort btf func list > > btf_encoder.c | 347 ++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 347 insertions(+) > > diff --git a/btf_encoder.c b/btf_encoder.c > index fd04008..4f742b1 100644 > --- a/btf_encoder.c > +++ b/btf_encoder.c > @@ -34,6 +34,11 @@ > #include <pthread.h> > > #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" > > /* state used to do later encoding of saved functions */ > struct btf_encoder_state { > @@ -79,6 +84,7 @@ struct btf_encoder { > gen_floats, > is_rel; > uint32_t array_index_id; > + struct gobuffer btf_funcs; why does this need to be stored in encoder? > struct { > struct var_info vars[MAX_PERCPU_VAR_CNT]; > int var_cnt; > @@ -94,6 +100,17 @@ struct btf_encoder { > } functions; > }; > SNIP > +/* 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) > +{ > + int *ptr = idlist->d_buf; > + int idx, flags; > + bool is_set8; > + > + /* 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; > + > + idx = sym->st_value - idlist_addr; > + if (idx >= 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 */ > + idx = idx / sizeof(int); > + flags = ptr[idx + 1]; > + return flags & BTF_SET8_KFUNCS; I wonder it'd be easier to read/follow if we bring struct btf_id_set8 declaration in here and use it to get the flags field > +} > + > +/* > + * Parse BTF_ID symbol and return the func name. > + * > + * Returns: > + * Caller-owned string containing func name if successful. > + * NULL if !func or on error. > + */ > + SNIP > + /* 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); > + 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. > + */ I think we could event add gobuffer interface/support to sort and search quickly the data (we use it in other place), but that can be done as follow up when it will become a problem as you pointed out > + 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; missing newline after declaration > + if (ranges[j].start <= addr && addr < ranges[j].end) { > + found = true; > + break; > + } > + } > + if (!found) leaking func jirka > + continue; > + > + err = btf_encoder__tag_kfunc(encoder, 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_kfunc_ranges); > + if (elf) > + elf_end(elf); > + if (fd != -1) > + close(fd); > + return err; > +} > + > int btf_encoder__encode(struct btf_encoder *encoder) > { > int err; > @@ -1366,6 +1704,14 @@ 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(). > + */ > + if (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; > @@ -1712,6 +2058,7 @@ void btf_encoder__delete(struct btf_encoder *encoder) > > btf_encoders__delete(encoder); > __gobuffer__delete(&encoder->percpu_secinfo); > + __gobuffer__delete(&encoder->btf_funcs); > zfree(&encoder->filename); > btf__free(encoder->btf); > encoder->btf = NULL; > -- > 2.42.1 >
On Wed, Jan 31, 2024 at 11:17:23AM +0100, Jiri Olsa wrote: > On Sun, Jan 28, 2024 at 06:30:19PM -0700, 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. > > > > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> > > > > --- > > Changes from v2: > > * More reliably detect kfunc membership in set8 by tracking set addr ranges > > * Rename some variables/functions to be more clear about kfunc vs func > > > > Changes from v1: > > * Fix resource leaks > > * Fix callee -> caller typo > > * Rename btf_decl_tag from kfunc -> bpf_kfunc > > * Only grab btf_id_set funcs tagged kfunc > > * Presort btf func list > > > > btf_encoder.c | 347 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 347 insertions(+) > > > > diff --git a/btf_encoder.c b/btf_encoder.c > > index fd04008..4f742b1 100644 > > --- a/btf_encoder.c > > +++ b/btf_encoder.c > > @@ -34,6 +34,11 @@ > > #include <pthread.h> > > > > #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" > > > > /* state used to do later encoding of saved functions */ > > struct btf_encoder_state { > > @@ -79,6 +84,7 @@ struct btf_encoder { > > gen_floats, > > is_rel; > > uint32_t array_index_id; > > + struct gobuffer btf_funcs; > > why does this need to be stored in encoder? I suppose it doesn't. It's used in multiple functions so I figured it'd be less verbose than passing it around. Also since it's fairly generic. I can move it to explicit arg passing if you want. > > > struct { > > struct var_info vars[MAX_PERCPU_VAR_CNT]; > > int var_cnt; > > @@ -94,6 +100,17 @@ struct btf_encoder { > > } functions; > > }; > > > > SNIP > > > +/* 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) > > +{ > > + int *ptr = idlist->d_buf; > > + int idx, flags; > > + bool is_set8; > > + > > + /* 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; > > + > > + idx = sym->st_value - idlist_addr; > > + if (idx >= 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 */ > > + idx = idx / sizeof(int); > > + flags = ptr[idx + 1]; > > + return flags & BTF_SET8_KFUNCS; > > I wonder it'd be easier to read/follow if we bring struct btf_id_set8 > declaration in here and use it to get the flags field Yeah, it probably would be. Since it looks like resolve_btfids is going that direction, might as well do it here as well. > > > +} > > + > > +/* > > + * Parse BTF_ID symbol and return the func name. > > + * > > + * Returns: > > + * Caller-owned string containing func name if successful. > > + * NULL if !func or on error. > > + */ > > + > > SNIP > > > + /* 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); > > + 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. > > + */ > > I think we could event add gobuffer interface/support to sort and search > quickly the data (we use it in other place), but that can be done as follow > up when it will become a problem as you pointed out > > > + 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; > > missing newline after declaration > > > + if (ranges[j].start <= addr && addr < ranges[j].end) { > > + found = true; > > + break; > > + } > > + } > > + if (!found) > > leaking func Ack, nice catch. [..] Thanks, Daniel
On Sun, Feb 04, 2024 at 11:08:45AM -0700, Daniel Xu wrote: > On Wed, Jan 31, 2024 at 11:17:23AM +0100, Jiri Olsa wrote: > > On Sun, Jan 28, 2024 at 06:30:19PM -0700, 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. > > > > > > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> > > > > > > --- > > > Changes from v2: > > > * More reliably detect kfunc membership in set8 by tracking set addr ranges > > > * Rename some variables/functions to be more clear about kfunc vs func > > > > > > Changes from v1: > > > * Fix resource leaks > > > * Fix callee -> caller typo > > > * Rename btf_decl_tag from kfunc -> bpf_kfunc > > > * Only grab btf_id_set funcs tagged kfunc > > > * Presort btf func list > > > > > > btf_encoder.c | 347 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > > 1 file changed, 347 insertions(+) > > > > > > diff --git a/btf_encoder.c b/btf_encoder.c > > > index fd04008..4f742b1 100644 > > > --- a/btf_encoder.c > > > +++ b/btf_encoder.c > > > @@ -34,6 +34,11 @@ > > > #include <pthread.h> > > > > > > #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" > > > > > > /* state used to do later encoding of saved functions */ > > > struct btf_encoder_state { > > > @@ -79,6 +84,7 @@ struct btf_encoder { > > > gen_floats, > > > is_rel; > > > uint32_t array_index_id; > > > + struct gobuffer btf_funcs; > > > > why does this need to be stored in encoder? > > I suppose it doesn't. It's used in multiple functions so I figured it'd > be less verbose than passing it around. Also since it's fairly generic. > > I can move it to explicit arg passing if you want. I spent some time trying to figure out why it'd need to be in the btf_encoder object, so if it's not needed there I'd move it out thanks, jirka
diff --git a/btf_encoder.c b/btf_encoder.c index fd04008..4f742b1 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -34,6 +34,11 @@ #include <pthread.h> #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" /* state used to do later encoding of saved functions */ struct btf_encoder_state { @@ -79,6 +84,7 @@ struct btf_encoder { gen_floats, is_rel; uint32_t array_index_id; + struct gobuffer btf_funcs; struct { struct var_info vars[MAX_PERCPU_VAR_CNT]; int var_cnt; @@ -94,6 +100,17 @@ 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; @@ -1352,6 +1369,327 @@ 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) +{ + int *ptr = idlist->d_buf; + int idx, flags; + bool is_set8; + + /* 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; + + idx = sym->st_value - idlist_addr; + if (idx >= 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 */ + idx = idx / sizeof(int); + flags = ptr[idx + 1]; + return 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); + + /* 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 = &encoder->btf_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, 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(&encoder->btf_funcs); + cnt = gobuffer__nr_entries(&encoder->btf_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 = {}; + Elf_Scn *symscn = NULL; + int symbols_shndx = -1; + int fd = -1, err = -1; + int idlist_shndx = -1; + Elf_Scn *scn = NULL; + size_t idlist_addr; + Elf_Data *symbols; + Elf_Data *idlist; + size_t strtabidx; + 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; + } + + /* Location symbol table and .BTF_ids sections */ + elf_getshdrstrndx(elf, &strndx); + 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); + 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) + continue; + + err = btf_encoder__tag_kfunc(encoder, 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_kfunc_ranges); + if (elf) + elf_end(elf); + if (fd != -1) + close(fd); + return err; +} + int btf_encoder__encode(struct btf_encoder *encoder) { int err; @@ -1366,6 +1704,14 @@ 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(). + */ + if (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; @@ -1712,6 +2058,7 @@ void btf_encoder__delete(struct btf_encoder *encoder) btf_encoders__delete(encoder); __gobuffer__delete(&encoder->percpu_secinfo); + __gobuffer__delete(&encoder->btf_funcs); zfree(&encoder->filename); btf__free(encoder->btf); encoder->btf = NULL;
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. Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> --- Changes from v2: * More reliably detect kfunc membership in set8 by tracking set addr ranges * Rename some variables/functions to be more clear about kfunc vs func Changes from v1: * Fix resource leaks * Fix callee -> caller typo * Rename btf_decl_tag from kfunc -> bpf_kfunc * Only grab btf_id_set funcs tagged kfunc * Presort btf func list btf_encoder.c | 347 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 347 insertions(+)