[Valgrind-users] Strange behaviour with both 1.9.x and 1.0.x

[Sebastian <sc...@nb...>]

Hello,


  I use valgrind a lot and its a really decent program. Today I stumbled
across a quite weird thing which might be a bug in my program, in valgrind
or in both.

This is how both valgrind 1.0.4 (debian unstable) and 1.9.4 (selfcompiled)
complains about code in my program. The first complaint is:

==1682== Use of uninitialised value of size 8
==1682==    at 0x804AB95: be_random_prob (utility.c:111)
==1682==    by 0x804F7CB: codegen_getreg (codegen.c:165)


Where the interesting part of this function is this:

0x804ab7e <be_random_prob+69>:  push   $0xffffffff
0x804ab80 <be_random_prob+71>:  call   0x804aa89 <be_random>
0x804ab85 <be_random_prob+76>:  add    $0x10,%esp
0x804ab88 <be_random_prob+79>:  mov    %eax,0xffffffec(%ebp)
0x804ab8b <be_random_prob+82>:  mov    0xffffffec(%ebp),%eax
0x804ab8e <be_random_prob+85>:  mov    $0x0,%edx
0x804ab93 <be_random_prob+90>:  push   %edx
0x804ab94 <be_random_prob+91>:  push   %eax
0x804ab95 <be_random_prob+92>:  fildll (%esp,1)
0x804ab98 <be_random_prob+95>:  lea    0x8(%esp,1),%esp
0x804ab9c <be_random_prob+99>:  fstpl  0xfffffff0(%ebp)


It extracted all functions taking part in this code to extra files and ran
some tests, without successes. The situation is quite simple: be_random
returns one random unsigned int (in %eax), %edx is zeroed out, a 64 bit
integer is temporarily created on the stack and the resulting number is
loaded into a double register (fildll). The code was generated by gcc 3.2.3
without any optimizations active.

I attached a test program to this mail, which does _not_ reproduce the bug,
but contains exactly the same code (which I believe to be correct).

So, could the valgrind complaint be a side effect of an uncatched bug
in my program earlier or is it possibly a bug in valgrind? (I can provide
the original program triggering the bug as binary to the authors if they
wish so, but not to the list).


ciao,
Sebastian

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