Date: Mon, 17 Oct 2005 20:09:03 -0400 From: Mark Schreiber <mark7@alumni.cmu.edu> To: ryan@clutteredmind.org Subject: [PATCH]SDL mprotect() crash fix (I'm going to throw this patch your way at the suggestion of #SDL -- for some reason, I had some difficulty sending it to the main list last time, and I go bonkers subscribing to send each email or patch...) Currently, when I run SDL applications as non-root using SDL_VIDEODRIVER=dga, the fbdev fallback mprotect()s read/write the proper size of mmapped /dev/fb0 (7.5MB), but on framebuffer release mprotect()s read-only the range by the entire size of my video memory (128MB), which causes a segfault: #0 0x002a9a27 in ?? () from /lib/libc.so.6 #1 0x04a63eb6 in SDL_XDGAUnmapFramebuffer (screen=3D0) at XF86DGA2.c:978 #2 0x04a63efc in SDL_XDGACloseFramebuffer (dpy=3D0x9d3f008, screen=3D0) at XF86DGA2.c:268 #3 0x04a68b57 in DGA_Available () at SDL_dgavideo.c:98 #4 0x04a53677 in SDL_VideoInit (driver_name=3D0xbfb0bfc7 "dga", flags=3D0) at SDL_video.c:180 #5 0x04a2613f in SDL_InitSubSystem (flags=3D32) at SDL.c:74 #6 0x04a2617c in SDL_Init (flags=3D32) at SDL.c:166 #7 0x08049722 in main (argc=3D1, argv=3D0x0) at testwin.c:32 This is SDL 1.2.8 on Fedora Core 4, radeon driver for a Radeon 9250, xorg-x11-6.8.2-37. I've attached a one-line patch against SDL CVS that updates the size of the framebuffer at framebuffer map time so that the mprotect() on unmap will be the same size. I'm not sure if this is the best approach (i.e. one might want to retain the original value), but it does make my SDL applications work without segfaulting. -- Best of luck, Mark Schreiber

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "SDL_main.h"
#include "SDL_types.h"

/*
 * Watcom C flags these as Warning 201: "Unreachable code" if you just
 *  compare them directly, so we push it through a function to keep the
 *  compiler quiet.  --ryan.
 */
static int badsize(size_t sizeoftype, size_t hardcodetype)
{
    return sizeoftype != hardcodetype;
}

int main(int argc, char *argv[])
{
	int error = 0;
	int verbose = 1;

	if ( argv[1] && (strcmp(argv[1], "-q") == 0) )
		verbose = 0;

	if ( badsize(sizeof(Uint8), 1) ) {
		if ( verbose )
			printf("sizeof(Uint8) != 1, instead = %d\n",
								sizeof(Uint8));
		++error;
	}
	if ( badsize(sizeof(Uint16), 2) ) {
		if ( verbose )
			printf("sizeof(Uint16) != 2, instead = %d\n",
								sizeof(Uint16));
		++error;
	}
	if ( badsize(sizeof(Uint32), 4) ) {
		if ( verbose )
			printf("sizeof(Uint32) != 4, instead = %d\n",
								sizeof(Uint32));
		++error;
	}
#ifdef SDL_HAS_64BIT_TYPE
	if ( badsize(sizeof(Uint64), 8) ) {
		if ( verbose )
			printf("sizeof(Uint64) != 8, instead = %d\n",
								sizeof(Uint64));
		++error;
	}
#else
	if ( verbose ) {
		printf("WARNING: No 64-bit datatype on this platform\n");
	}
#endif
	if ( verbose && ! error )
		printf("All data types are the expected size.\n");

	return( error ? 1 : 0 );
}