• Paul Clarke's avatar
    perf symbols: Allow user probes on versioned symbols · d8040645
    Paul Clarke authored
    Symbol versioning, as in glibc, results in symbols being defined as:
    
      <real symbol>@[@]<version>
    
    (Note that "@@" identifies a default symbol, if the symbol name is
    repeated.)
    
    perf is currently unable to deal with this, and is unable to create user
    probes at such symbols:
    
      --
      $ nm /lib/powerpc64le-linux-gnu/libpthread.so.0 | grep pthread_create
      0000000000008d30 t __pthread_create_2_1
      0000000000008d30 T pthread_create@@GLIBC_2.17
      $ /usr/bin/sudo perf probe -v -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create
      probe-definition(0): pthread_create
      symbol:pthread_create file:(null) line:0 offset:0 return:0 lazy:(null)
      0 arguments
      Open Debuginfo file: /usr/lib/debug/lib/powerpc64le-linux-gnu/libpthread-2.19.so
      Try to find probe point from debuginfo.
      Probe point 'pthread_create' not found.
         Error: Failed to add events. Reason: No such file or directory (Code: -2)
      --
    
    One is not able to specify the fully versioned symbol, either, due to
    syntactic conflicts with other uses of "@" by perf:
    
      --
      $ /usr/bin/sudo perf probe -v -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create@@GLIBC_2.17
      probe-definition(0): pthread_create@@GLIBC_2.17
      Semantic error :SRC@SRC is not allowed.
      0 arguments
         Error: Command Parse Error. Reason: Invalid argument (Code: -22)
      --
    
    This patch ignores versioning for default symbols, thus allowing probes to be
    created for these symbols:
    
      --
      $ /usr/bin/sudo ./perf probe -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create
      Added new event:
         probe_libpthread:pthread_create (on pthread_create in /lib/powerpc64le-linux-gnu/libpthread-2.19.so)
    
      You can now use it in all perf tools, such as:
    
               perf record -e probe_libpthread:pthread_create -aR sleep 1
    
      $ /usr/bin/sudo ./perf record -e probe_libpthread:pthread_create -aR ./test 2
      [ perf record: Woken up 1 times to write data ]
      [ perf record: Captured and wrote 0.052 MB perf.data (2 samples) ]
      $ /usr/bin/sudo ./perf script
                   test  2915 [000] 19124.260729: probe_libpthread:pthread_create: (3fff99248d38)
                   test  2916 [000] 19124.260962: probe_libpthread:pthread_create: (3fff99248d38)
      $ /usr/bin/sudo ./perf probe --del=probe_libpthread:pthread_create
      Removed event: probe_libpthread:pthread_create
      --
    
    Committer note:
    
    Change the variable storing the result of strlen() to 'int', to fix the build
    on debian:experimental-x-mipsel, fedora:24-x-ARC-uClibc, ubuntu:16.04-x-arm,
    etc:
    
      util/symbol.c: In function 'symbol__match_symbol_name':
      util/symbol.c:422:11: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
         if (len < versioning - name)
                 ^
    Signed-off-by: default avatarPaul A. Clarke <pc@us.ibm.com>
    Tested-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
    Cc: David Ahern <dsahern@gmail.com>
    Link: http://lkml.kernel.org/r/c2b18d9c-17f8-9285-4868-f58b6359ccac@us.ibm.comSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    d8040645
symbol.c 48 KB