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Date: Fri, 9 Jul 2004 23:45:22 -0700
From: Andrew Morton <akpm@osdl.org>
To: Daniel McNeil <daniel@osdl.org>
Cc: bryce@osdl.org, wli@holomorphy.com, ltp-list@lists.sourceforge.net,
       linux-kernel@vger.kernel.org, testdev@osdl.org, markh@osdl.org
Subject: Re: [LTP] Re: Recent changes in LTP test results
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Daniel McNeil <daniel@osdl.org> wrote:
>
> The /proc/pid/maps looked like this:
> 
>  without nx-update patch:
>  40017000-40018000 ---p 40017000 00:00 0
>  =====
>  with -mm1:
>  40017000-40018000 --xp 40017000 00:00 0

Here's mine, with current -linus bk:

40000000-40001000 ---p 40000000 00:00 0 

>  So it looks like the page being executable allows read
>  access.
> 
>  Not sure why you do not see this on your machine.  This
>  fails on my 2-proc xeon box (and all the STP machines).
> 


#include <unistd.h>
#include <errno.h>
#include <sys/mman.h>


main()
{
	char *p0 = 0;
	char *p1 = (char *)-1;
	char *p2;
	int err;

	p2 = mmap(0, 4096, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);

	printf("p2=%p\n", p2);
	printf("pid=%d\n", getpid());

	getchar();

	errno = 0;
	err = access(p0, R_OK);
	printf("access 0 ptr %p return code %d errno %d\n", p0, err, errno);
	perror("access result:");
	errno = 0;
	err = access(p1, R_OK);
	printf("access 1 ptr %p return code %d errno %d\n", p1, err, errno);
	perror("access result:");
	errno = 0;
	err = access(p2, R_OK);
	printf("access 2 ptr %p return code %d errno %d\n", p2, err, errno);
	perror("access result:");
}

vmm:/home/akpm> ./x
p2=0x40000000
pid=2038

access 0 ptr (nil) return code -1 errno 14
access result:: Bad address
access 1 ptr 0xffffffff return code -1 errno 14
access result:: Bad address
access 2 ptr 0x40000000 return code -1 errno 14
access result:: Bad address

I get this result on both p4 xeon and p3 xeon.