1. 18 Jan, 2009 2 commits
    • Steven Rostedt's avatar
      ftrace: test for running of recordmcount.pl twice on an object · b43f7093
      Steven Rostedt authored
      Impact: fix failure of dynamic function tracer selftest
      
      In a course of development, a developer does several makes on their
      kernel. Sometimes, the make might do something abnormal. In the
      case of running the recordmcount.pl script on an object twice,
      the script will duplicate all the calls to mcount in the __mcount_loc
      section.
      
      On boot up, the dynamic function tracer is careful when it modifies
      code, and performs several consistency checks. One is to not modify
      the call site if it is not what it expects it to be. If a function
      call site is listed twice, the first entry will convert the site
      to a nop, and the second will fail because it expected to see a
      call to mcount, but instead it sees a nop. Thus, the function tracer
      is disabled.
      
      Eric Sesterhenn reported seeing:
      
      [    1.055440] ftrace: converting mcount calls to 0f 1f 44 00 00
      [    1.055568] ftrace: allocating 29418 entries in 116 pages
      [    1.061000] ------------[ cut here ]------------
      [    1.061000] WARNING: at kernel/trace/ftrace.c:441
      
       [...]
      
      [    1.060000] ---[ end trace 4eaa2a86a8e2da23 ]---
      [    1.060000] ftrace failed to modify [<c0118072>] check_corruption+0x3/0x2d
      [    1.060000]  actual: 0f:1f:44:00:00
      
      This warning shows that check_corruption+0x3 already had a nop in
      its place (0x0f1f440000). After compiling another kernel the problem
      went away.
      
      Later Eric Paris notice the same type of issue. Luckily, he saved
      the vmlinux file that caused it. In the file we found a bunch of
      duplicate mcount call site records, which lead us to the script.
      
      Perhaps this problem only happens to people named Eric.
      
      This patch changes the script to test if the __mcount_loc already
      exists in the object file, and if it does, it will print out
      an error message and kill the compile.
      Reported-by: default avatarEric Sesterhenn <snakebyte@gmx.de>
      Reported-by: default avatarEric Paris <eparis@redhat.com>
      Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      b43f7093
    • Ingo Molnar's avatar
  2. 16 Jan, 2009 38 commits