On Tue, Feb 02, 2016 at 08:56:06AM +0000, Wang Nan wrote:
> 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.
>
> 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);
s/fix/fib/ ?
> 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/[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 | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 5227186..d4e59dd 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 ||
It seems there's no need to check the e_type anymore..
Thanks,
Namhyung
> dso__is_vdso(dso) ||
> elf_section_by_name(elf, &ehdr, &shdr,
> ".gnu.prelink_undo",
> --
> 1.8.3.4
>
