Valgrind reports uninitialized values on empty C p

Question

I have this C program compiled with either gcc test.c or clang test.c:

int main (void) {
    return 0;
}

valgrind ./a.out gives me this:

==9232== Memcheck, a memory error detector
==9232== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==9232== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==9232== Command: ./a.out
==9232== 
==9232== Conditional jump or move depends on uninitialised value(s)
==9232==    at 0x4017876: index (in /usr/lib/ld-2.16.so)
==9232==    by 0x4007902: expand_dynamic_string_token (in /usr/lib/ld-2.16.so)
==9232==    by 0x4008204: _dl_map_object (in /usr/lib/ld-2.16.so)
==9232==    by 0x400180D: map_doit (in /usr/lib/ld-2.16.so)
==9232==    by 0x400E785: _dl_catch_error (in /usr/lib/ld-2.16.so)
==9232==    by 0x40010DB: do_preload (in /usr/lib/ld-2.16.so)
==9232==    by 0x4004546: dl_main (in /usr/lib/ld-2.16.so)
==9232==    by 0x4014B5D: _dl_sysdep_start (in /usr/lib/ld-2.16.so)
==9232==    by 0x4004DFD: _dl_start (in /usr/lib/ld-2.16.so)
==9232==    by 0x4001627: ??? (in /usr/lib/ld-2.16.so)
==9232== 
==9232== Conditional jump or move depends on uninitialised value(s)
==9232==    at 0x401787B: index (in /usr/lib/ld-2.16.so)
==9232==    by 0x4007902: expand_dynamic_string_token (in /usr/lib/ld-2.16.so)
==9232==    by 0x4008204: _dl_map_object (in /usr/lib/ld-2.16.so)
==9232==    by 0x400180D: map_doit (in /usr/lib/ld-2.16.so)
==9232==    by 0x400E785: _dl_catch_error (in /usr/lib/ld-2.16.so)
==9232==    by 0x40010DB: do_preload (in /usr/lib/ld-2.16.so)
==9232==    by 0x4004546: dl_main (in /usr/lib/ld-2.16.so)
==9232==    by 0x4014B5D: _dl_sysdep_start (in /usr/lib/ld-2.16.so)
==9232==    by 0x4004DFD: _dl_start (in /usr/lib/ld-2.16.so)
==9232==    by 0x4001627: ??? (in /usr/lib/ld-2.16.so)
==9232== 
==9232== 
==9232== HEAP SUMMARY:
==9232==     in use at exit: 0 bytes in 0 blocks
==9232==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==9232== 
==9232== All heap blocks were freed -- no leaks are possible
==9232== 
==9232== For counts of detected and suppressed errors, rerun with: -v
==9232== Use --track-origins=yes to see where uninitialised values come from
==9232== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

GCC version 4.7.1 and Clang version 3.1. What is up with this? Is there something wrong with my memory? There's some time since I last used valgrind but this I think is not normal behaviour. Yelp?

---

Solution: It is possible from what I learned from @Shawn to suppress these linker errors using a valgrind .supp file. What I did was running valgrind on my program using the --gen-suppressions=all option:

valgrind --gen-suppressions=all ./a.out 

Then I extract the new chunks enclosed in brackets and put them directly into a file my.supp:

{  
   <linker>
   Memcheck:Cond
   fun:index
   fun:expand_dynamic_string_token
   fun:_dl_map_object
   fun:map_doit
   fun:_dl_catch_error
   fun:do_preload
   fun:dl_main
   fun:_dl_sysdep_start
   fun:_dl_start
   obj:/usr/lib/ld-2.16.so
}  

Now I can run valgrind with the --suppressions option to point to my new file and the messages will be suppressed:

valgrind --suppressions=/home/foo/my.supp ./a.out

Answer 1

This is a know issue with valgrind which is typically addressed using valgrind suppressions. Assuming the issue has been reported for your distro, the suppressions list should be updated shortly and will disappear in the next update.

For now, it is safe to ignore the message.

If it bothers you, you can maintain your own suppressions file and use it until your distro updates the default file (usually /var/lib/valgrind/default.supp).

Answer 2

This is a "problem" in the dynamic linker and it is common. It appears before main() is called. You can ignore the message.