Valgrind reports errors for a very simple C program

Question

I'm learning C language from Learn C The Hard Way. I'm on exercise 6 and while I can make it work, valgrind repots a lot of errors.

Here's the stripped down minimal program from a file ex6.c:

#include <stdio.h>

int main(int argc, char *argv[])
{
    char initial = 'A';
    float power = 2.345f;

    printf("Character is %c.
", initial);
    printf("You have %f levels of power.
", power);

    return 0;
}

Content of Makefile is just CFLAGS=-Wall -g.

I compile the program with $ make ex6 (there are no compiler warnings or errors). Executing with $ ./ex6 produces the expected output.

When I run the program with $ valgrind ./ex6 I get errors which I can't solve. Here's the full output:

==69691== Memcheck, a memory error detector
==69691== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==69691== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==69691== Command: ./ex6
==69691==
--69691-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option
--69691-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 2 times)
--69691-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 4 times)
==69691== Conditional jump or move depends on uninitialised value(s)
==69691==    at 0x1003FBC3F: _platform_memchr$VARIANT$Haswell (in /usr/lib/system/libsystem_platform.dylib)
==69691==    by 0x1001EFBB6: __sfvwrite (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001FA005: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x10021F9CE: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x10021FCA0: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001F5B91: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001F39F7: printf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x100000F1B: main (ex6.c:8)
==69691==
Character is A.
==69691== Invalid read of size 32
==69691==    at 0x1003FBC1D: _platform_memchr$VARIANT$Haswell (in /usr/lib/system/libsystem_platform.dylib)
==69691==    by 0x1001EFBB6: __sfvwrite (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001FA005: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x10021F9CE: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x10021FCA0: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001F5B91: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001F39F7: printf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x100000F31: main (ex6.c:9)
==69691==  Address 0x100809680 is 32 bytes before a block of size 32 in arena "client"
==69691==
You have 2.345000 levels of power.
==69691==
==69691== HEAP SUMMARY:
==69691==     in use at exit: 39,365 bytes in 429 blocks
==69691==   total heap usage: 510 allocs, 81 frees, 45,509 bytes allocated
==69691==
==69691== LEAK SUMMARY:
==69691==    definitely lost: 16 bytes in 1 blocks
==69691==    indirectly lost: 0 bytes in 0 blocks
==69691==      possibly lost: 13,090 bytes in 117 blocks
==69691==    still reachable: 26,259 bytes in 311 blocks
==69691==         suppressed: 0 bytes in 0 blocks
==69691== Rerun with --leak-check=full to see details of leaked memory
==69691==
==69691== For counts of detected and suppressed errors, rerun with: -v
==69691== Use --track-origins=yes to see where uninitialised values come from
==69691== ERROR SUMMARY: 5 errors from 2 contexts (suppressed: 0 from 0)

I'm on OS X yosemite. Valgrind is installed via brew with this command $ brew install valgrind --HEAD.

So, does anyone know what's the issue here? How do I fix the valgrind errors?

Answer 1

If the programme you are running through Valgrind is exactly the one you posted in your question, it clearly doesn't have any memory leaks. In fact, you don't even use malloc/free yourself!

It looks to me like these are spurious errors / false positives that Valgrind detects on OS X (only!), similar to what happened to myself some time ago.

If you have access to a different operating system, e.g. a Linux machine, try to analyze the programme using Valgrind on that system.

EDIT: I haven't tried this myself, since I don't have access to a Mac right now, but you should try what M Oehm suggested: try to use a supressions file as mentioned in this other SO question.