• Masami Hiramatsu's avatar
    perf probe: Fix to fall back to find probe point in symbols · 906451b9
    Masami Hiramatsu authored
    Fix to fall back to find a probe point in symbols if perf fails to find
    it in debuginfo.
    
    This can happen when the target function is an alias of another
    function. Such alias doesn't have an entry in debuginfo but in symbols.
    
    David Ahern reported this problem in https://lkml.org/lkml/2014/12/29/355
    
    I ensured the problem and deeper investigation discovers it.
     -----
     eu-readelf --debug-dump=info /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.19.so | grep \"malloc\" -A6
                 name                 (strp) "malloc"
                 decl_file            (data1) 25
                 decl_line            (data2) 466
                 prototyped           (flag_present)
                 type                 (ref4) [  81b5]
                 declaration          (flag_present)
     [  8f58]      formal_parameter
     --
                 name                 (strp) "malloc"
                 decl_file            (data1) 23
                 decl_line            (data2) 466
                 prototyped           (flag_present)
                 type                 (ref4) [  9f4a]
                 declaration          (flag_present)
                 sibling              (ref4) [  bb29]
     ...
     -----
    All these entires have no instances (all of them are declarations)
    This is why the perf probe failed to find it in debuginfo.
    
    However, there are some malloc instances in symbols.
     -----
     eu-readelf --symbols /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.19.so | grep malloc$
      1181: 0000000000080700   5332 FUNC    LOCAL  DEFAULT       12 _int_malloc
      4537: 00000000000831d0    339 FUNC    LOCAL  DEFAULT       12 __GI___libc_malloc
      5545: 00000000000831d0    339 FUNC    LOCAL  DEFAULT       12 __malloc
      6063: 00000000000831d0    339 FUNC    GLOBAL DEFAULT       12 malloc
      7302: 00000000000831d0    339 FUNC    GLOBAL DEFAULT       12 __libc_malloc
     -----
    As you an see, malloc and __libc_malloc have same address, and actually
    __libc_malloc has an entry in debuginfo. So you can set up a probe on
    __libc_malloc.
    
    To fix this problem shortly, perf probe simply falls back to find probe
    point(malloc) in symbols if it is not found in debuginfo.
    Reported-by: default avatarDavid Ahern <dsahern@gmail.com>
    Signed-off-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Acked-by: default avatarNamhyung Kim <namhyung@kernel.org>
    Cc: David Ahern <dsahern@gmail.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: yrl.pp-manager.tt@hitachi.com
    Link: http://lkml.kernel.org/r/20141231062747.2087.80961.stgit@localhost.localdomainSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    906451b9
probe-event.c 57.7 KB