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From: Michael Tuexen <tuexen@freebsd.org>
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Subject: gcc versus clang issue for 32-bit binaries
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Date: Wed, 10 Jun 2020 18:41:50 +0200
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Dear all,

consider the following program test.c:

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

int=20
main(void)
{
	void *p;
=09
	p =3D mmap((void *)0x20000000, 0x1000000, PROT_READ | PROT_WRITE =
| PROT_EXEC, MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
	printf("p=3D %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