gcc versus clang issue for 32-bit binaries

[Michael Tuexen]

Dear all,

consider the following program test.c:

#include <sys/mman.h>
#include <stdio.h>

int 
main(void)
{
	void *p;
	
	p = mmap((void *)0x20000000, 0x1000000, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
	printf("p= %p\n", p);
	return (0);
}

On i386 the following happens:
* when compiling it with cc and running it, it crashes.
* when compiling it with gcc it runs fine.

On amd64 the following happens:
* when compiling it with cc -m64 it runs fine.
* when compiling it with cc -m32 is crashes.
* when compiling it with gcc -m64 it runs fine.
* when compiling it with gcc -m32 it runs fine.

So why does the above program crash when compiled for 32-bit when using clang, but runs fine when compiled with gcc.
I'm testing this on 32-bit and 64-bit head systems. gcc is from ports.

The reason I'm looking into it is that I want to get syzkaller working on 32-bit with clang.

Best regards
Michael