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 the missing of symbol adjustment for normal
shared objects. In most of the cases it works correctly, but when
'.text' section have different '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.
Now nearly all type of ELF file should adjust symbols. Makes
ss->adjust_symbols default to true.
Steps to reproduce the problem:
$ cat ./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
$ cat ./buggy.c
int fib(int x)
{
return (x == 0) ? 1 : (x == 1) ? 1 : fib(x - 1) + fib(x - 2);
}
$ cat ./main.c
#include <stdio.h>
extern int fib(int x);
int main()
{
int i;
for (i = 0; i < 40; i++)
printf("%d\n", fib(i));
return 0;
}
$ 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/[email protected]
Signed-off-by: Wang Nan <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Cody P Schafer <[email protected]>
Cc: He Kuang <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kirill Smelkov <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: [email protected]
---
tools/perf/util/symbol-elf.c | 13 +++----------
1 file changed, 3 insertions(+), 10 deletions(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 5227186..6a9a53a 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -708,17 +708,10 @@ int symsrc__init(struct symsrc *ss, struct dso *dso,
const char *name,
if (ss->opdshdr.sh_type != SHT_PROGBITS)
ss->opdsec = NULL;
- if (dso->kernel == DSO_TYPE_USER) {
- GElf_Shdr shdr;
- ss->adjust_symbols = (ehdr.e_type == ET_EXEC ||
- ehdr.e_type == ET_REL ||
- dso__is_vdso(dso) ||
- elf_section_by_name(elf, &ehdr, &shdr,
- ".gnu.prelink_undo",
- NULL) != NULL);
- } else {
+ if (dso->kernel == DSO_TYPE_USER)
+ ss->adjust_symbols = true;
+ else
ss->adjust_symbols = elf__needs_adjust_symbols(ehdr);
- }
ss->name = strdup(name);
if (!ss->name) {
--
1.8.3.4
