Why does valgrind say basic SDL program is leaking

Question

Here is the SDL program:

#include <SDL/SDL.h>

int main(int argc, char** argv){


  SDL_Init(SDL_INIT_VIDEO);
  SDL_Surface* screen = SDL_SetVideoMode(640, 480, 16, SDL_HWSURFACE);
  SDL_Quit();
  return 0;

}

Compiled with the command:

g++ -o test test.cpp -lSDL

And here is the output of valgrind:

christian@christian-laptop:~/cpp/tetris$ valgrind --leak-check=full ./test
==3271== Memcheck, a memory error detector
==3271== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==3271== Using Valgrind-3.5.0-Debian and LibVEX; rerun with -h for copyright info
==3271== Command: ./test
==3271== 
==3271== 
==3271== HEAP SUMMARY:
==3271==     in use at exit: 91,097 bytes in 1,258 blocks
==3271==   total heap usage: 14,250 allocs, 12,992 frees, 2,615,177 bytes allocated
==3271== 
==3271== 10 bytes in 2 blocks are definitely lost in loss record 8 of 134
==3271==    at 0x4024C1C: malloc (vg_replace_malloc.c:195)
==3271==    by 0x4946F04: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4945DA1: _XimEncodeLocalICAttr (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4947195: _XimSetICValueData (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x493FDF1: _XimLocalCreateIC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4922478: XCreateIC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x407AA64: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x407BCBB: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x4069C2A: SDL_VideoInit (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x403F9D3: SDL_InitSubSystem (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x403FA36: SDL_Init (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x8048658: main (in /home/christian/cpp/tetris/test)
==3271== 
==3271== 12 bytes in 1 blocks are definitely lost in loss record 12 of 134
==3271==    at 0x4024C1C: malloc (vg_replace_malloc.c:195)
==3271==    by 0x4A3DA8D: ???
==3271==    by 0x4A3D48C: ???
==3271==    by 0x4A3D5A4: ???
==3271==    by 0x4A3DD26: ???
==3271==    by 0x4A38BC5: ???
==3271==    by 0x4A38FCD: ???
==3271==    by 0x40717DD: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x407BDCA: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x4069C2A: SDL_VideoInit (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x403F9D3: SDL_InitSubSystem (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x403FA36: SDL_Init (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271== 
==3271== 112 (8 direct, 104 indirect) bytes in 1 blocks are definitely lost in loss record 102 of 134
==3271==    at 0x4024D12: realloc (vg_replace_malloc.c:476)
==3271==    by 0x492847E: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492976D: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492AA41: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492B1A4: _XlcCreateLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x494B4FA: _XlcDefaultLoader (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4933153: _XOpenLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x49332C2: _XlcCurrentLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4933761: XSetLocaleModifiers (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x407161D: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x407AD8F: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x407BCBB: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271== 
==3271== 112 (8 direct, 104 indirect) bytes in 1 blocks are definitely lost in loss record 103 of 134
==3271==    at 0x4024D12: realloc (vg_replace_malloc.c:476)
==3271==    by 0x492847E: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492976D: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492AA41: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492B1A4: _XlcCreateLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x494B4FA: _XlcDefaultLoader (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4933153: _XOpenLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x493327D: _XrmInitParseInfo (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4918F20: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x491AF37: XrmGetStringDatabase (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x48F8459: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x48F864E: XGetDefault (in /usr/lib/libX11.so.6.2.0)
==3271== 
==3271== LEAK SUMMARY:
==3271==    definitely lost: 38 bytes in 5 blocks
==3271==    indirectly lost: 208 bytes in 8 blocks
==3271==      possibly lost: 0 bytes in 0 blocks
==3271==    still reachable: 90,851 bytes in 1,245 blocks
==3271==         suppressed: 0 bytes in 0 blocks
==3271== Reachable blocks (those to which a pointer was found) are not shown.
==3271== To see them, rerun with: --leak-check=full --show-reachable=yes
==3271== 
==3271== For counts of detected and suppressed errors, rerun with: -v
==3271== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 93 from 14)

Why is this basic SDL program leaking memory?

Answer 1

Singletons are pretty much always a 'leak' with standard implementations. That is usually ok, though, since normally it's not like you want to unload your ability to do things like print to the console.

Answer 2

SDL definitely has a memory leak issue with SDL_TLSCleanup and SDL_TLSData.

In fact, SDL_TLSCleanup is never called for the main thread.

Answer 3

Every SDL_Surface you load should be freed before the call of SDL_Quit().

To do this, just use SDL_FreeSurface(surfaceName) to free up the surface that you allocated on memory.

Answer 4

Even for basic OpenGL "hello world" program without the full SDL, Valgrind gives me similar warnings deep inside the OpenGL libraries. It's peculiar, but I've assumed

• The library implementors know what they're doing (probably preallocating some small static buffers they never bother to free),
• Even if they don't, it's a one-time leak that'll be reclaimed by the OS when the program terminates,

and haven't lost much sleep over it.