Valgrind 'noise', what does it mean?

Question

When I used valgrind to help debug an app I was working on I notice a huge about of noise which seems to be complaining about standard libraries. As a test I did this;

echo 'int main() {return 0;}' | gcc -x c -o test -

Then I did this;

valgrind ./test

==1096== Use of uninitialised value of size 8
==1096==    at 0x400A202: _dl_new_object (in /lib64/ld-2.10.1.so)
==1096==    by 0x400607F: _dl_map_object_from_fd (in /lib64/ld-2.10.1.so)
==1096==    by 0x4007A2C: _dl_map_object (in /lib64/ld-2.10.1.so)
==1096==    by 0x400199A: map_doit (in /lib64/ld-2.10.1.so)
==1096==    by 0x400D495: _dl_catch_error (in /lib64/ld-2.10.1.so)
==1096==    by 0x400189E: do_preload (in /lib64/ld-2.10.1.so)
==1096==    by 0x4003CCD: dl_main (in /lib64/ld-2.10.1.so)
==1096==    by 0x401404B: _dl_sysdep_start (in /lib64/ld-2.10.1.so)
==1096==    by 0x4001471: _dl_start (in /lib64/ld-2.10.1.so)
==1096==    by 0x4000BA7: (within /lib64/ld-2.10.1.so)
* large block of similar snipped *
==1096== Use of uninitialised value of size 8
==1096==    at 0x4F35FDD: (within /lib64/libc-2.10.1.so)
==1096==    by 0x4F35B11: (within /lib64/libc-2.10.1.so)
==1096==    by 0x4A1E61C: _vgnU_freeres (vg_preloaded.c:60)
==1096==    by 0x4E5F2E4: __run_exit_handlers (in /lib64/libc-2.10.1.so)
==1096==    by 0x4E5F354: exit (in /lib64/libc-2.10.1.so)
==1096==    by 0x4E48A2C: (below main) (in /lib64/libc-2.10.1.so)
==1096==
==1096== ERROR SUMMARY: 3819 errors from 298 contexts (suppressed: 876 from 4)
==1096== malloc/free: in use at exit: 0 bytes in 0 blocks.
==1096== malloc/free: 0 allocs, 0 frees, 0 bytes allocated.
==1096== For counts of detected errors, rerun with: -v
==1096== Use --track-origins=yes to see where uninitialised values come from
==1096== All heap blocks were freed -- no leaks are possible.

You can see the full result here: http://pastebin.com/gcTN8xGp

I have two questions; firstly is there a way to suppress all the noise?

--show-below-main is set to no by default, but there doesn't appear to be a --show-after-main equivalent.

Answer 1

You can suppress the output by appending

{
   ld error suppression
   Memcheck:Cond
   fun:dl_main
   fun:_dl_sysdep_start
   fun:_dl_start
   obj:/lib64/ld-2.10.1.so
}

to /usr/lib/valgrind/default.supp (or defining your own suppression file).

It appears to be a known linker/loader bug, at least to Debian & Arch Linux developers; I'm unsure about the rest, as well as their planned course of action.

Answer 2

Upgrade to Valgrind 3.5.0 or better. Amongst other things the default .supp files have been updated.

Answer 3

I have these symptoms from time to time, and the solution is always to upgrade my valgrind and libc packages to be in sync . The nice little elves at Debian take care of the rest.