FreeSurface() simple crash on MSVC++17

SDL Development
1

Hey guys, having some trouble with a little interesting bug pertaining to FreeSurface().

	SDL_Texture* t = NULL;
	SDL_Surface* s = IMG_Load("assets/textures/alch.png");
	if (s != NULL)
	{
		t = SDL_CreateTextureFromSurface(r, s);
		SDL_FreeSurface(s);
	}

For some reason this is causing an exception in SDL_malloc.c (SDL_free(), line 5432, specifically on (void)SDL_AtomicDecRef(&s_mem.num_allocations);}).

I’m a decently seasoned C++ developer and I feel like I’m going a little crazy trying to figure this out. I’ve tried using both SDL2 libraries from VCPKG and the SDL2 website. No multi-threading or anything crazy. Just these few lines of code after SDL_Init(SDL_INIT_EVERYTHING).

Anyone have any ideas?

2

Have you checked what SDL_CreateTextureFromSurface is returning? And if it’s NULL called SDL_GetError() ?

https://wiki.libsdl.org/SDL_CreateTextureFromSurface

3

Thanks for the reply! The texture it not NULL and I’m not getting anything out of SDL_Error.

The texture draws properly.

4

This definitely looks broken - no matter if creating the texture failed or not, freeing the surface afterwards shouldn’t crash

5

I’m at work now but I’m leaving soon.

When I get home I’ll dig in to it a bit more. IIRC it seemed like num_allocations wasn’t getting incremented properly. But I don’t know enough about the inner workings of SDL2 to know if that’s actually the issue.

6 
s_mem.free_func(ptr);
(void)SDL_AtomicDecRef(&s_mem.num_allocations);

So it looks like it’s these two functions in SDL_Free. This is the contents of the SDL_PixelFormat* before being sent to the SDL_Free function…

https://imgur.com/a/PvbdctZ

Is it possible that it’s how SDL_Image is loading in the surface?

7

can you tell us more about the exception itself?
what kind of exception is it, what exactly does it say? what’s the backtrace?

8

MSVS isn’t giving me any more information other than

“Exception Thrown
TestBench.exe has triggered a breakpoint”.

I’m doing the free from my main function so the callstack goes straight in to SDL2 library code.

[Album] imgur.com
9

HI Just wondering if you got to the bottom of this? I’m having the exact same issue, my image displays fine if I don’t free the surface, but as soon as I put that line back in it crashes.

Only difference I’m using GDB and Mingw. It’s reporting “Exception has occurred”. It’s in SDL_malloc.c line 5432. Using SDL 2.0.16.

10

Hi, is anyone else getting this issue ?
I just cloned a friend’s project and I’m stuck with this crash despite everything working prefectly fine on his side.
Only Difference is mine occuring using SDL_ttf but it seems oddly similar.

this is enough for it to occur :

SDL_Surface* textSurface = TTF_RenderText_Blended(font->ttf, text, color);
if (textSurface) {
	SDL_FreeSurface(textSurface);
}

image

“Unhandled exception at 0x00007FFEE14E9BD5 (ntdll.dll) in modsynth.exe: 0xC0000374” about heap corruption
I can’t find anything online and have been stuck for days now :frowning: