[Scummvm-devel] Weird crash (Mac OS X only? big endian only?)

[Max Horn]

Just a small update: running with a 6 MB buffer and full checking 
produced no results: it worked just fine (albeit super slow), no crash, 
no buffer modification detected.

I also made a check: the stripped binary (w/o simon and sky support) is 
802412 bytes. The "dummyHeapBuffer" variable (the pointer to my heap 
block) sits at address 791928 (i.e. well inside the code block, as was 
to be expected), roughly 800kb. The heap block itself, however, starts 
at 24272896 ~ 24 MB. So clearly there is already a large block of data 
in between.

This could have various causes. E.g. on Mac OS X, before the scummvm 
main() is called, SDL executes code to allocate the window etc. Maybe 
that's what is taking up all that memory. That complicates the picture 
a bit. It could be that memory corruption occurs inside that block, or 
worse, might even be caused by SDL / OS specific code. But I have my 
doubts, because other SDL apps have no similar problems, AFAIK.


I'll try to learn a bit more about the OS X memory layout. In the 
meantime, I made a tiny test program:

#include <stdio.h>
#include <stdlib.h>

const int kDummyHeapBufferSize = 6 * 1024 * 1024;
void *dummyHeapBuffer;

int main(int argc, char *argv[]) {
	dummyHeapBuffer = malloc(kDummyHeapBufferSize);
	printf("&dummyHeapBuffer = %d, dummyHeapBuffer = %d\n", 
(int)&dummyHeapBuffer, (int)dummyHeapBuffer);
	free(dummyHeapBuffer);
}

File size is 9552 bytes, output is:
&dummyHeapBuffer = 8396, dummyHeapBuffer = 540672

-> so there are already 500 KB between the code and the first heap 
block we allocated. Maybe by the C library (buffers etc.) ?




Cheers,

Max