From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0CB64C43334 for ; Mon, 25 Jul 2022 18:29:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229544AbiGYS3w (ORCPT ); Mon, 25 Jul 2022 14:29:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43328 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235327AbiGYS3w (ORCPT ); Mon, 25 Jul 2022 14:29:52 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 38D581F2E1; Mon, 25 Jul 2022 11:29:49 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B5012613F7; Mon, 25 Jul 2022 18:29:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BC1DBC341C6; Mon, 25 Jul 2022 18:29:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1658773788; bh=bkX5XWZwuPnMLgUAndfCdzgha0AbwCCiEfVFScvVnz4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ZvyVaXhH+Qec7u/tbgmzG1N9uwT1MWtibX97kCenk8sb39YQOZ9wB+eZACTomYlDU nakGyLWIumeLUgqGA1gvtddChQHx7GpmVq84T0qEVrPTOKrach6/KHIGsI+NdXojb8 Nl/SlfXLlkYt0/9yH5roHotSiHlVv9HWGYiloVMczX6jyt+Bb4r9G6cYcygwk9VfJ4 RB3RlevowQk+07Eoi9HwP9eLfakwUVXVmv3f6QE5J161bb0ZgVo/3Mzv35dnv2tn08 pfOVf1Z1Yppi3CmRx7pk7Dglipm4sC7XRL5o4LFiHFmZDZraAdQ1D53Kbp/TCB1end 4ixewRm0Z+cLA== Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id 45F4C40374; Mon, 25 Jul 2022 15:29:45 -0300 (-03) Date: Mon, 25 Jul 2022 15:29:45 -0300 From: Arnaldo Carvalho de Melo To: Leo Yan Cc: Peter Zijlstra , Ingo Molnar , Mark Rutland , Jiri Olsa , Namhyung Kim , Alexander Shishkin , Ian Rogers , Fangrui Song , Chang Rui , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/2] perf symbol: Correct address for bss symbols Message-ID: References: <20220724060013.171050-1-leo.yan@linaro.org> <20220724060013.171050-2-leo.yan@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220724060013.171050-2-leo.yan@linaro.org> X-Url: http://acmel.wordpress.com Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Em Sun, Jul 24, 2022 at 02:00:12PM +0800, Leo Yan escreveu: > When using 'perf mem' and 'perf c2c', an issue is observed that tool > reports the wrong offset for global data symbols. This is a common > issue on both x86 and Arm64 platforms. > > Let's see an example, for a test program, below is the disassembly for > its .bss section which is dumped with objdump: > > ... > > Disassembly of section .bss: > > 0000000000004040 : > ... > > 0000000000004080 : > ... > > 00000000000040c0 : > ... > > 0000000000004100 : > ... > > First we used 'perf mem record' to run the test program and then used > 'perf --debug verbose=4 mem report' to observe what's the symbol info > for 'buf1' and 'buf2' structures. > > # ./perf mem record -e ldlat-loads,ldlat-stores -- false_sharing.exe 8 Can you share the source code for your false sharing proggie? We need to have something in 'perf test' exercising these routines :-) > # ./perf --debug verbose=4 mem report > ... > dso__load_sym_internal: adjusting symbol: st_value: 0x40c0 sh_addr: 0x4040 sh_offset: 0x3028 > symbol__new: buf2 0x30a8-0x30e8 > ... > dso__load_sym_internal: adjusting symbol: st_value: 0x4080 sh_addr: 0x4040 sh_offset: 0x3028 > symbol__new: buf1 0x3068-0x30a8 > ... > > Perf tool relies on libelf to parse symbols, in executable and shared > object files, 'st_value' holds a virtual address; 'sh_addr' is the > address at which section's first byte should reside in memory, and > 'sh_offset' is the byte offset from the beginning of the file to the > first byte in the section. Perf tool uses below formula to convert > symbol's memory address to file address: > > file_address = st_value - sh_addr + sh_offset > ^ > ` Memory address > > We can see the final adjusted address ranges for buf1 and buf2 are > [0x30a8-0x30e8) and [0x3068-0x30a8) respectively, apparently this is > incorrect, in the code, the structure for 'buf1' and 'buf2' specifies > compiler attribute with 64-byte alignment. > > The problem happens for 'sh_offset', libelf returns it as 0x3028 which > is not 64-byte aligned, combining with disassembly, it's likely libelf > doesn't respect the alignment for .bss section, therefore, it doesn't > return the aligned value for 'sh_offset'. > > Suggested by Fangrui Song, elf file contains program header which > contains PT_LOAD segments, the fields p_vaddr and p_offset in PT_LOAD > segments contain the execution info. A better choice for converting > memory address to file address is using the formula: > > file_address = st_value - p_vaddr + p_offset > > This patch introduces function elf_read_program_header() which returns > out the program header based on the passed 'st_value', then it uses > above formula to calculate the symbol file address; and the debugging > log is updated respectively. > > After applying the change: > > # ./perf --debug verbose=4 mem report > ... > dso__load_sym_internal: adjusting symbol: st_value: 0x40c0 p_vaddr: 0x3d28 p_offset: 0x2d28 > symbol__new: buf2 0x30c0-0x3100 > ... > dso__load_sym_internal: adjusting symbol: st_value: 0x4080 p_vaddr: 0x3d28 p_offset: 0x2d28 > symbol__new: buf1 0x3080-0x30c0 > ... > > Fixes: f17e04afaff8 ("perf report: Fix ELF symbol parsing") > Reported-by: Chang Rui > Suggested-by: Fangrui Song > Signed-off-by: Leo Yan > --- > tools/perf/util/symbol-elf.c | 45 ++++++++++++++++++++++++++++++++---- > 1 file changed, 41 insertions(+), 4 deletions(-) > > diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c > index ecd377938eea..ef6ced5c5746 100644 > --- a/tools/perf/util/symbol-elf.c > +++ b/tools/perf/util/symbol-elf.c > @@ -233,6 +233,33 @@ Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep, > return NULL; > } > > +static int elf_read_program_header(Elf *elf, u64 vaddr, GElf_Phdr *phdr) > +{ > + size_t i, phdrnum; > + u64 sz; > + > + if (elf_getphdrnum(elf, &phdrnum)) > + return -1; > + > + for (i = 0; i < phdrnum; i++) { > + if (gelf_getphdr(elf, i, phdr) == NULL) > + return -1; > + > + if (phdr->p_type != PT_LOAD) > + continue; > + > + sz = max(phdr->p_memsz, phdr->p_filesz); > + if (!sz) > + continue; > + > + if (vaddr >= phdr->p_vaddr && (vaddr < phdr->p_vaddr + sz)) > + return 0; > + } > + > + /* Not found any valid program header */ > + return -1; > +} > + > static bool want_demangle(bool is_kernel_sym) > { > return is_kernel_sym ? symbol_conf.demangle_kernel : symbol_conf.demangle; > @@ -1209,6 +1236,7 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss, > sym.st_value); > used_opd = true; > } > + > /* > * When loading symbols in a data mapping, ABS symbols (which > * has a value of SHN_ABS in its st_shndx) failed at > @@ -1262,11 +1290,20 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss, > goto out_elf_end; > } else if ((used_opd && runtime_ss->adjust_symbols) || > (!used_opd && syms_ss->adjust_symbols)) { > + GElf_Phdr phdr; > + > + if (elf_read_program_header(syms_ss->elf, > + (u64)sym.st_value, &phdr)) { > + pr_warning("%s: failed to find program header for " > + "symbol: %s st_value: %#" PRIx64 "\n", > + __func__, elf_name, (u64)sym.st_value); > + continue; > + } > pr_debug4("%s: adjusting symbol: st_value: %#" PRIx64 " " > - "sh_addr: %#" PRIx64 " sh_offset: %#" PRIx64 "\n", __func__, > - (u64)sym.st_value, (u64)shdr.sh_addr, > - (u64)shdr.sh_offset); > - sym.st_value -= shdr.sh_addr - shdr.sh_offset; > + "p_vaddr: %#" PRIx64 " p_offset: %#" PRIx64 "\n", > + __func__, (u64)sym.st_value, (u64)phdr.p_vaddr, > + (u64)phdr.p_offset); > + sym.st_value -= phdr.p_vaddr - phdr.p_offset; > } > > demangled = demangle_sym(dso, kmodule, elf_name); > -- > 2.25.1 -- - Arnaldo