• Adrian Hunter's avatar
    perf symbols: Correct plt entry sizes for x86 · 66fe2d53
    Adrian Hunter authored
    In 32-bit executables the .plt entry size can be set to 4 when it is really
    16. In fact the only sizes used for x86 (32 or 64 bit) are 8 or 16, so
    check for those and, if not, use the alignment to choose which it is.
    
    Example on Ubuntu 22.04 gcc 11.3:
    
      Before:
    
        $ cat tstpltlib.c
        void fn1(void) {}
        void fn2(void) {}
        void fn3(void) {}
        void fn4(void) {}
        $ cat tstplt.c
        void fn1(void);
        void fn2(void);
        void fn3(void);
        void fn4(void);
    
        int main()
        {
                fn4();
                fn1();
                fn2();
                fn3();
                return 0;
        }
        $ gcc --version
        gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0
        Copyright (C) 2021 Free Software Foundation, Inc.
        This is free software; see the source for copying conditions.  There is NO
        warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
        $ gcc -m32 -Wall -Wextra -shared -o libtstpltlib32.so tstpltlib.c
        $ gcc -m32 -Wall -Wextra -o tstplt32 tstplt.c -L . -ltstpltlib32 -Wl,-rpath=$(pwd)
        $ perf record -e intel_pt//u --filter 'filter main @ ./tstplt32' ./tstplt32
        [ perf record: Woken up 1 times to write data ]
        [ perf record: Captured and wrote 0.011 MB perf.data ]
        $ readelf -SW tstplt32 | grep 'plt\|Name'
          [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
          [10] .rel.plt          REL             0000041c 00041c 000028 08  AI  5  22  4
          [12] .plt              PROGBITS        00001030 001030 000060 04  AX  0   0 16   <- ES is 0x04, should be 0x10
          [13] .plt.got          PROGBITS        00001090 001090 000008 08  AX  0   0  8
        $ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
        17894.383903029:   tr strt                               0 [unknown] =>         565b81cd main+0x0
        17894.383903029:   tr end  call                   565b81d4 main+0x7 =>         565b80d0 __x86.get_pc_thunk.bx+0x0
        17894.383903031:   tr strt                               0 [unknown] =>         565b81d9 main+0xc
        17894.383903031:   tr end  call                   565b81df main+0x12 =>         565b8070 [unknown]
        17894.383903032:   tr strt                               0 [unknown] =>         565b81e4 main+0x17
        17894.383903032:   tr end  call                   565b81e4 main+0x17 =>         565b8050 [unknown]
        17894.383903033:   tr strt                               0 [unknown] =>         565b81e9 main+0x1c
        17894.383903033:   tr end  call                   565b81e9 main+0x1c =>         565b8080 [unknown]
        17894.383903033:   tr strt                               0 [unknown] =>         565b81ee main+0x21
        17894.383903033:   tr end  call                   565b81ee main+0x21 =>         565b8060 [unknown]
        17894.383903237:   tr strt                               0 [unknown] =>         565b81f3 main+0x26
        17894.383903237:   tr end  return                 565b81fc main+0x2f =>         f7c21519 [unknown]
    
      After:
    
        $ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
        17894.383903029:   tr strt                               0 [unknown] =>         565b81cd main+0x0
        17894.383903029:   tr end  call                   565b81d4 main+0x7 =>         565b80d0 __x86.get_pc_thunk.bx+0x0
        17894.383903031:   tr strt                               0 [unknown] =>         565b81d9 main+0xc
        17894.383903031:   tr end  call                   565b81df main+0x12 =>         565b8070 fn4@plt+0x0
        17894.383903032:   tr strt                               0 [unknown] =>         565b81e4 main+0x17
        17894.383903032:   tr end  call                   565b81e4 main+0x17 =>         565b8050 fn1@plt+0x0
        17894.383903033:   tr strt                               0 [unknown] =>         565b81e9 main+0x1c
        17894.383903033:   tr end  call                   565b81e9 main+0x1c =>         565b8080 fn2@plt+0x0
        17894.383903033:   tr strt                               0 [unknown] =>         565b81ee main+0x21
        17894.383903033:   tr end  call                   565b81ee main+0x21 =>         565b8060 fn3@plt+0x0
        17894.383903237:   tr strt                               0 [unknown] =>         565b81f3 main+0x26
        17894.383903237:   tr end  return                 565b81fc main+0x2f =>         f7c21519 [unknown]
    Reviewed-by: default avatarNamhyung Kim <namhyung@kernel.org>
    Signed-off-by: default avatarAdrian Hunter <adrian.hunter@intel.com>
    Cc: Ian Rogers <irogers@google.com>
    Cc: Jiri Olsa <jolsa@kernel.org>
    Link: https://lore.kernel.org/r/20230131131625.6964-2-adrian.hunter@intel.comSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    66fe2d53
symbol-elf.c 57.9 KB