On Wed, Nov 03, 2010 at 01:18:51PM +0200, Alexey Suslikov wrote:

quoted text
> Hello tech@.
> 
> On OpenBSD/amd64, doing something like
>     char *buf = mmap(NULL, len + 1, PROT_READ | PROT_WRITE,
> MAP_PRIVATE, some.fd, 0);
>     buf[len] = '__PLACEHOLDER__0_';
> causes segfault on buf[len] = '__PLACEHOLDER__0_' assignment if len = 16384.
> 
> However doing
>     char *buf = mmap(NULL, len + 1, PROT_READ | PROT_WRITE,
> MAP_PRIVATE, some.fd, 0);
>     char *nbuf = malloc(len + 1);
>     memcpy(nbuf, buf, len);
>     nbuf[len] = '__PLACEHOLDER__0_';
> does not lead to a crash.
> 
> Is it expected behavior of mmap (alignment?) or usage of mmap is wrong?
> 
> Thanks.
> 
> Alexey

This (complete!) program does not show the behahaviour. Please post a
complete testcase. Did you include sys/mman.h?

	-Otto

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

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


int
main()
{
	int fd;
	char *buf;
	size_t len;

	fd = open("file", O_RDWR, 0);
	if (fd == -1)
		err(1, NULL);

	len = 16384;
    	buf = mmap(NULL, len + 1, PROT_READ | PROT_WRITE, MAP_PRIVATE,
	    fd, (off_t)0);
	if (buf == MAP_FAILED)
		err(1, NULL);
	buf[len] = '\0';
}