linux-kernel - [PATCH 1/2] perf tools: Adjust symbol for shared objects

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Date:	Thu, 28 Jan 2016 13:05:23 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<acme@...hat.com>, <jolsa@...nel.org>
CC:	<linux-kernel@...r.kernel.org>, Wang Nan <wangnan0@...wei.com>,
	He Kuang <hekuang@...wei.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Li Zefan <lizefan@...wei.com>, <pi3orama@....com>
Subject: [PATCH 1/2] perf tools: Adjust symbol for shared objects

He Kuang reported a problem that perf fails to get correct symbol on
Android platform in [1]. The problem can be reproduced on normal x86_64
platform. I will describe the reproducing steps in detail at the end of
commit message.

The reason of this problem is missing of symbol adjustment for normal
shared objects. In most of the cases it works correctly, but when
'.text' section having differeng 'address' and 'offset' the result is
wrong. I checked all shared objects in my working platform, only wine
dll objects and debug objects (in .debug) have this problem. However,
it is common on Android. For example:

 $ readelf -S ./libsurfaceflinger.so | grep \.text
   [10] .text             PROGBITS         0000000000029030  00012030

This patch enables symbol adjustment for dynamic objects so the symbol
address got from elfutils would be adjusted correctly.

Steps to reproduce the problem:

 $ cat << EOF > ./Makefile
PWD := $(shell pwd)
LDFLAGS += "-Wl,-rpath=$(PWD)"
CFLAGS += -g
main: main.c libbuggy.so
libbuggy.so: buggy.c
	gcc -g -shared -fPIC -Wl,-Ttext-segment=0x200000 $< -o $@
clean:
	rm -rf main libbuggy.so *.o
EOF

 $ cat << EOF > ./buggy.c
int fib(int x)
{
	return (x == 0) ? 1 : (x == 1) ? 1 : fib(x - 1) + fib(x - 2);
}
EOF

 $ cat << EOF > ./main.c
#include <stdio.h>

extern int fix(int x);
int main()
{
	int i;

	for (i = 0; i < 40; i++)
		printf("%d\n", fib(i));
	return 0;
}
EOF

 $ make
 $ perf record ./main
 ...
 $ perf report --stdio
 # Overhead  Command  Shared Object      Symbol
 # ........  .......  .................  ...............................
 #
     14.97%  main     libbuggy.so        [.] 0x000000000000066c
      8.68%  main     libbuggy.so        [.] 0x00000000000006aa
      8.52%  main     libbuggy.so        [.] fib@plt
      7.95%  main     libbuggy.so        [.] 0x0000000000000664
      5.94%  main     libbuggy.so        [.] 0x00000000000006a9
      5.35%  main     libbuggy.so        [.] 0x0000000000000678
 ...

The correct result should be (after this patch):

 # Overhead  Command  Shared Object      Symbol
 # ........  .......  .................  ...............................
 #
     91.47%  main     libbuggy.so        [.] fib
      8.52%  main     libbuggy.so        [.] fib@plt
      0.00%  main     [kernel.kallsyms]  [k] kmem_cache_free

[1] http://lkml.kernel.org/g/1452567507-54013-1-git-send-email-hekuang@huawei.com

Signed-off-by: Wang Nan <wangnan0@...wei.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: He Kuang <hekuang@...wei.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Li Zefan <lizefan@...wei.com>
Cc: pi3orama@....com
---
 tools/perf/util/symbol-elf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 562b8eb..d37e206 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -712,6 +712,7 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
 		GElf_Shdr shdr;
 		ss->adjust_symbols = (ehdr.e_type == ET_EXEC ||
 				ehdr.e_type == ET_REL ||
+				ehdr.e_type == ET_DYN ||
 				dso__is_vdso(dso) ||
 				elf_section_by_name(elf, &ehdr, &shdr,
 						     ".gnu.prelink_undo",
-- 
1.8.3.4