Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932585AbbLHC1J (ORCPT ); Mon, 7 Dec 2015 21:27:09 -0500 Received: from szxga01-in.huawei.com ([58.251.152.64]:42629 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932241AbbLHC0V (ORCPT ); Mon, 7 Dec 2015 21:26:21 -0500 From: Wang Nan To: , CC: , , , , Wang Nan , "Arnaldo Carvalho de Melo" Subject: [PATCH v4 02/16] tools lib bpf: Fetch map names from correct strtab Date: Tue, 8 Dec 2015 02:25:30 +0000 Message-ID: <1449541544-67621-3-git-send-email-wangnan0@huawei.com> X-Mailer: git-send-email 1.8.3.4 In-Reply-To: <1449541544-67621-1-git-send-email-wangnan0@huawei.com> References: <1449541544-67621-1-git-send-email-wangnan0@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.107.193.248] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090204.56663FBE.002A,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 2ce4fe290f883d89b2d412a6aece32e5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4103 Lines: 130 Namhyung Kim pointed out a potential problem in original code that it fetches names of maps from section header string table, which is used to store section names. Original code doesn't cause error because of a LLVM behavior that, it combines shstrtab into strtab. For example: $ echo 'int func() {return 0;}' | x86_64-oe-linux-clang -x c -o temp.o -c - $ readelf -h ./temp.o ELF Header: Magic: 7f 45 4c 46 02 01 01 03 00 00 00 00 00 00 00 00 ... Section header string table index: 1 $ readelf -S ./temp.o There are 10 section headers, starting at offset 0x288: Section Headers: [Nr] Name Type Address Offset Size EntSize Flags Link Info Align [ 0] NULL 0000000000000000 00000000 0000000000000000 0000000000000000 0 0 0 [ 1] .strtab STRTAB 0000000000000000 00000230 0000000000000051 0000000000000000 0 0 1 ... $ readelf -p .strtab ./temp.o String dump of section '.strtab': [ 1] .text [ 7] .comment [ 10] .bss [ 15] .note.GNU-stack [ 25] .rela.eh_frame [ 34] func [ 39] .strtab [ 41] .symtab [ 49] .data [ 4f] - $ readelf -p .shstrtab ./temp.o readelf: Warning: Section '.shstrtab' was not dumped because it does not exist! Where, 'section header string table index' points to '.strtab', and symbol names are also stored there. However, in case of gcc: $ echo 'int func() {return 0;}' | gcc -x c -o temp.o -c - $ readelf -p .shstrtab ./temp.o String dump of section '.shstrtab': [ 1] .symtab [ 9] .strtab [ 11] .shstrtab [ 1b] .text [ 21] .data [ 27] .bss [ 2c] .comment [ 35] .note.GNU-stack [ 45] .rela.eh_frame $ readelf -p .strtab ./temp.o String dump of section '.strtab': [ 1] func They are separated sections. Although original code doesn't cause error, we'd better use canonical method for fetching symbol names to avoid potential behavior changing. This patch learns from readelf's code, fetches string from sh_link of .symbol section. Signed-off-by: Wang Nan Acked-by: Namhyung Kim Cc: Arnaldo Carvalho de Melo --- tools/lib/bpf/libbpf.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 16485ab..8334a5a 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -195,6 +195,7 @@ struct bpf_object { Elf *elf; GElf_Ehdr ehdr; Elf_Data *symbols; + size_t strtabidx; struct { GElf_Shdr shdr; Elf_Data *data; @@ -547,7 +548,7 @@ bpf_object__init_maps_name(struct bpf_object *obj, int maps_shndx) continue; map_name = elf_strptr(obj->efile.elf, - obj->efile.ehdr.e_shstrndx, + obj->efile.strtabidx, sym.st_name); map_idx = sym.st_value / sizeof(struct bpf_map_def); if (map_idx >= obj->nr_maps) { @@ -630,8 +631,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj) pr_warning("bpf: multiple SYMTAB in %s\n", obj->path); err = -LIBBPF_ERRNO__FORMAT; - } else + } else { obj->efile.symbols = data; + obj->efile.strtabidx = sh.sh_link; + } } else if ((sh.sh_type == SHT_PROGBITS) && (sh.sh_flags & SHF_EXECINSTR) && (data->d_size > 0)) { @@ -667,6 +670,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj) goto out; } + if (!obj->efile.strtabidx || obj->efile.strtabidx >= idx) { + pr_warning("Corrupted ELF file: index of strtab invalid\n"); + return LIBBPF_ERRNO__FORMAT; + } if (maps_shndx >= 0) err = bpf_object__init_maps_name(obj, maps_shndx); out: -- 1.8.3.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/