[LLVMdev] Fwd: Profile (-pg) segfault

Renato Golin renato.golin at linaro.org
Fri Sep 13 08:28:02 PDT 2013


I'm trying to profile a code compiled with Clang and I'm getting a segfault
on mcount independently of the program I run:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b1245b in mcount () from /lib/x86_64-linux-gnu/libc.so.6
(gdb) bt
#0  0x00007ffff7b1245b in mcount () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007ffff7dd6588 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x0000000000000000 in ?? ()
(gdb) disas
Dump of assembler code for function mcount:
   0x00007ffff7b12430 <+0>: sub    $0x38,%rsp
   0x00007ffff7b12434 <+4>: mov    %rax,(%rsp)
   0x00007ffff7b12438 <+8>: mov    %rcx,0x8(%rsp)
   0x00007ffff7b1243d <+13>: mov    %rdx,0x10(%rsp)
   0x00007ffff7b12442 <+18>: mov    %rsi,0x18(%rsp)
   0x00007ffff7b12447 <+23>: mov    %rdi,0x20(%rsp)
   0x00007ffff7b1244c <+28>: mov    %r8,0x28(%rsp)
   0x00007ffff7b12451 <+33>: mov    %r9,0x30(%rsp)
   0x00007ffff7b12456 <+38>: mov    0x38(%rsp),%rsi
=> 0x00007ffff7b1245b <+43>: mov    0x8(%rbp),%rdi
   0x00007ffff7b1245f <+47>: callq  0x7ffff7b116a0
   0x00007ffff7b12464 <+52>: mov    0x30(%rsp),%r9
   0x00007ffff7b12469 <+57>: mov    0x28(%rsp),%r8
   0x00007ffff7b1246e <+62>: mov    0x20(%rsp),%rdi
   0x00007ffff7b12473 <+67>: mov    0x18(%rsp),%rsi
   0x00007ffff7b12478 <+72>: mov    0x10(%rsp),%rdx
   0x00007ffff7b1247d <+77>: mov    0x8(%rsp),%rcx
   0x00007ffff7b12482 <+82>: mov    (%rsp),%rax
   0x00007ffff7b12486 <+86>: add    $0x38,%rsp
   0x00007ffff7b1248a <+90>: retq
End of assembler dump.
(gdb) p $rdi
$1 = 1
(gdb) p $rsp
$2 = (void *) 0x7fffffffded0
(gdb) p $rbp
$3 = (void *) 0x0

This is Ubuntu 12.10, libc6 2.15, gcc 4.7.2, and of course, it works with

I'm not sure how to begin debugging it, since mcount was probably compiled
with gcc, but it looks like LLVM is generating the wrong call standard.

It only appears in -O1 upwards, but there's not stack trace, and I suspect
this is due to how the profiling instrumentation work... Any pointers?

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