Adding "distilled_base" to --btf_features when generating split BTF will create split and .BTF.base BTF - the latter allows us to map references from split BTF to base BTF, even if that base BTF has changed. It does this by providing just enough information about the base types in the .BTF.base section. Patch is applicable on the "next" branch of dwarves, and requires the libbpf from the series in [1] Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx> [1] https://lore.kernel.org/bpf/20240517102246.4070184-1-alan.maguire@xxxxxxxxxx/ --- btf_encoder.c | 40 ++++++++++++++++++++++++++++------------ dwarves.h | 1 + man-pages/pahole.1 | 4 ++++ pahole.c | 1 + 4 files changed, 34 insertions(+), 12 deletions(-) diff --git a/btf_encoder.c b/btf_encoder.c index c2df2bc..0d7c657 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -93,7 +93,8 @@ struct btf_encoder { gen_floats, skip_encoding_decl_tag, tag_kfuncs, - is_rel; + is_rel, + gen_distilled_base; uint32_t array_index_id; struct { struct var_info *vars; @@ -1284,9 +1285,9 @@ static int btf_encoder__write_raw_file(struct btf_encoder *encoder) return err; } -static int btf_encoder__write_elf(struct btf_encoder *encoder) +static int btf_encoder__write_elf(struct btf_encoder *encoder, const struct btf *btf, + const char *btf_secname) { - struct btf *btf = encoder->btf; const char *filename = encoder->filename; GElf_Shdr shdr_mem, *shdr; Elf_Data *btf_data = NULL; @@ -1326,7 +1327,7 @@ static int btf_encoder__write_elf(struct btf_encoder *encoder) if (shdr == NULL) continue; char *secname = elf_strptr(elf, strndx, shdr->sh_name); - if (strcmp(secname, ".BTF") == 0) { + if (strcmp(secname, btf_secname) == 0) { btf_data = elf_getdata(scn, btf_data); break; } @@ -1370,11 +1371,11 @@ static int btf_encoder__write_elf(struct btf_encoder *encoder) goto unlink; } - snprintf(cmd, sizeof(cmd), "%s --add-section .BTF=%s %s", - llvm_objcopy, tmp_fn, filename); + snprintf(cmd, sizeof(cmd), "%s --add-section %s=%s %s", + llvm_objcopy, btf_secname, tmp_fn, filename); if (system(cmd)) { - fprintf(stderr, "%s: failed to add .BTF section to '%s': %d!\n", - __func__, filename, errno); + fprintf(stderr, "%s: failed to add %s section to '%s': %d!\n", + __func__, btf_secname, filename, errno); goto unlink; } @@ -1755,12 +1756,26 @@ int btf_encoder__encode(struct btf_encoder *encoder) fprintf(stderr, "%s: btf__dedup failed!\n", __func__); return -1; } - - if (encoder->raw_output) + if (encoder->raw_output) { err = btf_encoder__write_raw_file(encoder); - else - err = btf_encoder__write_elf(encoder); + } else { + struct btf *btf = encoder->btf, *distilled_base; + if (encoder->gen_distilled_base) { + if (btf__distill_base(encoder->btf, &distilled_base, &btf) < 0) { + fprintf(stderr, "could not generate distilled base BTF: %s\n", + strerror(errno)); + return -1; + } + } + err = btf_encoder__write_elf(encoder, btf, BTF_ELF_SEC); + if (!err && encoder->gen_distilled_base) + err = btf_encoder__write_elf(encoder, distilled_base, BTF_BASE_ELF_SEC); + if (btf != encoder->btf) { + btf__free((struct btf *)btf__base_btf(btf)); + btf__free(btf); + } + } return err; } @@ -2037,6 +2052,7 @@ struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filenam 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->gen_distilled_base = conf_load->btf_gen_distilled_base; encoder->verbose = verbose; encoder->has_index_type = false; encoder->need_index_type = false; diff --git a/dwarves.h b/dwarves.h index 7d566b6..b9e88e3 100644 --- a/dwarves.h +++ b/dwarves.h @@ -95,6 +95,7 @@ struct conf_load { bool btf_encode_force; bool reproducible_build; bool btf_decl_tag_kfuncs; + bool btf_gen_distilled_base; 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 f060593..2f623b4 100644 --- a/man-pages/pahole.1 +++ b/man-pages/pahole.1 @@ -317,6 +317,10 @@ Supported non-standard features (not enabled for 'default') without this parallel BTF encoding can result in inconsistent BTF ids. decl_tag_kfuncs Inject a BTF_KIND_DECL_TAG for each discovered kfunc. + distilled_base For split BTF, generate a distilled version of + the associated base BTF to support later relocation + of split BTF with a possibly changed base, storing + it in a .BTF.base ELF section. .fi So for example, specifying \-\-btf_encode=var,enum64 will result in a BTF encoding that (as well as encoding basic BTF information) will contain variables and enum64 values. diff --git a/pahole.c b/pahole.c index 954498d..fdb65d4 100644 --- a/pahole.c +++ b/pahole.c @@ -1291,6 +1291,7 @@ struct btf_feature { 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), + BTF_NON_DEFAULT_FEATURE(distilled_base, btf_gen_distilled_base, false), }; #define BTF_MAX_FEATURE_STR 1024 -- 2.31.1
