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[94.113.247.30]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3825fb27386sm5275231f8f.51.2024.11.23.05.24.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 Nov 2024 05:24:58 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Sat, 23 Nov 2024 14:24:56 +0100 To: Eduard Zingerman Cc: dwarves@vger.kernel.org, arnaldo.melo@gmail.com, bpf@vger.kernel.org, kernel-team@fb.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, yonghong.song@linux.dev, Alan Maguire , Daniel Xu , Jiri Olsa , Kumar Kartikeya Dwivedi , Vadim Fedorenko , Vadim Fedorenko Subject: Re: [PATCH dwarves v2 1/1] btf_encoder: handle .BTF_ids section endianness Message-ID: References: <20241122214431.292196-1-eddyz87@gmail.com> <20241122214431.292196-2-eddyz87@gmail.com> Precedence: bulk X-Mailing-List: dwarves@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241122214431.292196-2-eddyz87@gmail.com> On Fri, Nov 22, 2024 at 01:44:31PM -0800, Eduard Zingerman wrote: > btf_encoder__tag_kfuncs() reads .BTF_ids section to identify a set of > kfuncs present in the ELF file being processed. > This section consists of: > - arrays of uint32_t elements; > - arrays of records with the following structure: > struct btf_id_and_flag { > uint32_t id; > uint32_t flags; > }; > > When endianness of a binary operated by pahole differs from the host > system's endianness, these fields require byte-swapping before use. > Currently, this byte-swapping does not occur, resulting in kfuncs not > being marked with declaration tags. > > This commit resolves the issue by introducing an endianness conversion > step for the .BTF_ids section data before the main processing stage. > Since the ELF file is opened in O_RDONLY mode, gelf_xlatetom() > cannot be used for endianness conversion. > Instead, a new type is introduced: > > struct local_elf_data { > void *d_buf; > size_t d_size; > int64_t d_off; > bool owns_buf; > }; > > This structure is populated from the Elf_Data object representing > the .BTF_ids section. When byte-swapping is required, a local copy > of d_buf is created. > > Cc: Alan Maguire > Cc: Daniel Xu > Cc: Jiri Olsa > Cc: Kumar Kartikeya Dwivedi > Cc: Vadim Fedorenko > Fixes: 72e88f29c6f7 ("pahole: Inject kfunc decl tags into BTF") > Reviewed-by: Vadim Fedorenko > Signed-off-by: Eduard Zingerman Acked-by: Jiri Olsa thanks, jirka > --- > btf_encoder.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 59 insertions(+), 6 deletions(-) > > diff --git a/btf_encoder.c b/btf_encoder.c > index e1adddf..06d4a61 100644 > --- a/btf_encoder.c > +++ b/btf_encoder.c > @@ -33,6 +33,7 @@ > #include > #include /* for tsearch(), tfind() and tdestroy() */ > #include > +#include > > #define BTF_IDS_SECTION ".BTF_ids" > #define BTF_ID_FUNC_PFX "__BTF_ID__func__" > @@ -145,6 +146,14 @@ struct btf_kfunc_set_range { > uint64_t end; > }; > > +/* Like Elf_Data, but when there is a need to change the data read from ELF */ > +struct local_elf_data { > + void *d_buf; > + size_t d_size; > + int64_t d_off; > + bool owns_buf; > +}; > + > static LIST_HEAD(encoders); > static pthread_mutex_t encoders__lock = PTHREAD_MUTEX_INITIALIZER; > > @@ -1681,7 +1690,8 @@ out: > } > > /* 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) > +static int is_sym_kfunc_set(GElf_Sym *sym, const char *name, struct local_elf_data *idlist, > + size_t idlist_addr) > { > void *ptr = idlist->d_buf; > struct btf_id_set8 *set; > @@ -1847,13 +1857,52 @@ static int btf_encoder__tag_kfunc(struct btf_encoder *encoder, struct gobuffer * > return 0; > } > > +/* If byte order of 'elf' differs from current byte order, convert the data->d_buf. > + * ELF file is opened in a readonly mode, so data->d_buf cannot be modified in place. > + * Instead, allocate a new buffer if modification is necessary. > + */ > +static int convert_idlist_endianness(Elf *elf, Elf_Data *src, struct local_elf_data *dst) > +{ > + int byteorder, i; > + char *elf_ident; > + uint32_t *tmp; > + > + dst->d_size = src->d_size; > + dst->d_off = src->d_off; > + elf_ident = elf_getident(elf, NULL); > + if (elf_ident == NULL) { > + fprintf(stderr, "Cannot get ELF identification from header\n"); > + return -EINVAL; > + } > + byteorder = elf_ident[EI_DATA]; > + if ((BYTE_ORDER == LITTLE_ENDIAN && byteorder == ELFDATA2LSB) > + || (BYTE_ORDER == BIG_ENDIAN && byteorder == ELFDATA2MSB)) { > + dst->d_buf = src->d_buf; > + dst->owns_buf = false; > + return 0; > + } > + tmp = malloc(src->d_size); > + if (tmp == NULL) { > + fprintf(stderr, "Cannot allocate %lu bytes of memory\n", src->d_size); > + return -ENOMEM; > + } > + memcpy(tmp, src->d_buf, src->d_size); > + dst->d_buf = tmp; > + dst->owns_buf = true; > + > + /* .BTF_ids sections consist of u32 objects */ > + for (i = 0; i < dst->d_size / sizeof(uint32_t); i++) > + tmp[i] = bswap_32(tmp[i]); > + return 0; > +} > + > static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder) > { > const char *filename = encoder->source_filename; > struct gobuffer btf_kfunc_ranges = {}; > + struct local_elf_data idlist = {}; > 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; > @@ -1918,7 +1967,9 @@ static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder) > } else if (!strcmp(secname, BTF_IDS_SECTION)) { > idlist_shndx = i; > idlist_addr = shdr.sh_addr; > - idlist = data; > + err = convert_idlist_endianness(elf, data, &idlist); > + if (err < 0) > + goto out; > } > } > > @@ -1960,7 +2011,7 @@ static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder) > continue; > > name = elf_strptr(elf, strtabidx, sym.st_name); > - if (!is_sym_kfunc_set(&sym, name, idlist, idlist_addr)) > + if (!is_sym_kfunc_set(&sym, name, &idlist, idlist_addr)) > continue; > > range.start = sym.st_value; > @@ -2003,13 +2054,13 @@ static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder) > if (ranges[j].start <= addr && addr < ranges[j].end) { > found = true; > off = addr - idlist_addr; > - if (off < 0 || off + sizeof(*pair) > idlist->d_size) { > + if (off < 0 || off + sizeof(*pair) > idlist.d_size) { > fprintf(stderr, "%s: kfunc '%s' offset outside section '%s'\n", > __func__, func, BTF_IDS_SECTION); > free(func); > goto out; > } > - pair = idlist->d_buf + off; > + pair = idlist.d_buf + off; > break; > } > } > @@ -2031,6 +2082,8 @@ static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder) > out: > __gobuffer__delete(&btf_funcs); > __gobuffer__delete(&btf_kfunc_ranges); > + if (idlist.owns_buf) > + free(idlist.d_buf); > if (elf) > elf_end(elf); > if (fd != -1) > -- > 2.47.0 >