SDL_LoadFile() Linux segmentation fault reading datasize

[logos-maker]

When reading the length pointed to to get the datasize, I get a segmentation fault. This only seams to occur if I have a path for the file, but not if the file is in the working directory. But I can still read the data from the file but not get the length as I will get a segmentation fault. So I can read the pointer but not the length that it points to.

It looks like my system is using version 2.0.10

[1bsyl]

@logos-maker
do you have a test case ?

[sezero]

I tried with the following, can't get a segfault. Must see the particular test case from @logos-maker

#include "SDL.h"
#include <stdio.h>

int main (int argc, char **argv) {
  SDL_RWops *rw;
  void *loaded;
  size_t sz;

  if (argc != 2) {
    return 1;
  }
  rw = SDL_RWFromFile(argv[1], "rb");
  if (!rw) {
    fprintf(stderr, "Failed opening %s\n", argv[1]);
    return 1;
  }
  loaded = SDL_LoadFile_RW(rw, &sz, 1);
  if (!loaded) {
    fprintf(stderr, "Failed loading from %s\n", argv[1]);
    return 1;
  }
  SDL_free(loaded);
  fprintf(stderr, "DATASIZE: %lu\n", (unsigned long)sz);
  return 0;
}

[logos-maker]

The code by sezero gives the size even if it isn't a file in the same directory as the program. So it works fine.
But the problem is with SDL_LoadFile() not SDL_LoadFile_RW so I changed that code to reflect that by the following...

#include "SDL2/SDL.h"
#include <stdio.h>

int main (int argc, char **argv) {
  void *loaded;
  size_t *sz;

  if (argc != 2) {
    return 1;
  }
  loaded = SDL_LoadFile(argv[1], sz);
  if (!loaded) {
    fprintf(stderr, "Failed loading from %s\n", argv[1]);
    return 1;
  }
  SDL_free(loaded);
  fprintf(stderr, "DATASIZE: %lu\n", (unsigned long)*sz);
  return 0;
}

...but that didn't give the segmentation fault. But the same code still gives a segmentation fault if I have a window open and drops a file on the window. I'm not sure whats happening. I'll have some code that I will post that recreates the problem. Or is the code above faulty, but gives the right result by some fluke?

[logos-maker]

The code bellow recreates the problem. And then it also gives a segmentation fault if you give a file name in the terminal. So that's strange.

#include "SDL2/SDL.h"
#include <stdio.h>

int main (int argc, char **argv) {
  void *loaded;
  size_t *sz;

  if (argc == 2) {
	  loaded = SDL_LoadFile(argv[1], sz);
	  if (!loaded) {
	    fprintf(stderr, "Failed loading from %s\n", argv[1]);
	    return 1;
	  }
	  SDL_free(loaded);
	  fprintf(stderr, "DATASIZE: %lu\n", (unsigned long)*sz);
	  return 0;
  }
	SDL_Window *window;
	SDL_Renderer *renderer;
	SDL_Event event;

	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
		SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't initialize SDL: %s", SDL_GetError());
		return 3;
	}

	if (SDL_CreateWindowAndRenderer(256,256, SDL_WINDOW_RESIZABLE, &window, &renderer)) {
		SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't create window and renderer: %s",SDL_GetError());
		return 3;
	}
	while (1) {
		while( SDL_PollEvent( &event ) ){	// drain all events in que for SDL2
			switch( event.type ){
				case  SDL_QUIT:
					goto end_program;
				break;
				
				case SDL_DROPFILE:
					if(!(loaded = SDL_LoadFile(event.drop.file,sz))){
						SDL_Log("could not load file\n");
					};
					SDL_Log("%s",event.drop.file);
					SDL_Log("DATASIZE: %lu\n",(unsigned long)*sz);
					SDL_SetWindowTitle(window, strcat("test", event.drop.file));

					SDL_free(event.drop.file);
				break;
			}
		}

		SDL_SetRenderDrawColor(renderer, 0x00, 0x00, 0x00, 0x00);
		SDL_RenderClear(renderer);

		SDL_RenderPresent(renderer);
		SDL_Delay(16);
	}
	end_program:
	SDL_DestroyRenderer(renderer);
	SDL_DestroyWindow(window);
}

[sezero]

Your test code is definitely wrong:

1.c: In function 'main':
1.c:11:12: warning: 'sz' may be used uninitialized in this function [-Wmaybe-uninitialized]
     loaded = SDL_LoadFile(argv[1], sz);
            ^

$ ./a.out /home/sezero/.gitconfig
Segmentation fault (core dumped)

What you want is this:

#include "SDL.h"
#include <stdio.h>

int main (int argc, char **argv) {
    void *loaded;
    size_t sz;

    if (argc != 2) {
        return 1;
    }
    loaded = SDL_LoadFile(argv[1], &sz);
    if (!loaded) {
        fprintf(stderr, "Failed loading from %s\n", argv[1]);
        return 1;
    }
    SDL_free(loaded);
    fprintf(stderr, "DATASIZE: %lu\n", (unsigned long)sz);
    return 0;
}

... which works just fine:

$ ./a.out /home/ozzie/.gitconfig
DATASIZE: 110

Closing as invalid.

[logos-maker]

What sezero says is the way to do it doesn't even compile.

test.c: In function ‘main’:
test.c:11:34: warning: passing argument 2 of ‘SDL_LoadFile’ makes pointer from integer without a cast [-Wint-conversion]
   11 |   loaded = SDL_LoadFile(argv[1], sz);
      |                                  ^~
      |                                  |
      |                                  size_t {aka long unsigned int}
In file included from /usr/include/SDL2/SDL_audio.h:36,
                 from /usr/include/SDL2/SDL.h:36,
                 from test.c:1:
/usr/include/SDL2/SDL_rwops.h:251:31: note: expected ‘size_t *’ {aka ‘long unsigned int *’} but argument is of type ‘size_t’ {aka ‘long unsigned int’}
  251 | extern DECLSPEC void *SDLCALL SDL_LoadFile(const char *file, size_t *datasize);
      |                               ^~~~~~~~~~~~

[sezero]

Look carefully at how I define sz and pass it to SDL_LoadFile.

[logos-maker]

Thanks!!!
Maybe the corrected code given by sezero could be used as an example in the wiki at wiki.libsdl.org