On Wed, Nov 03, 2010 at 01:12:20PM +0100, Otto Moerbeek wrote:
> On Wed, Nov 03, 2010 at 01:18:51PM +0200, Alexey Suslikov wrote:
>
> > Hello t...@.
> >
> > On OpenBSD/amd64, doing something like
> > char *buf = mmap(NULL, len + 1, PROT_READ | PROT_WRITE,
> > MAP_PRIVATE, some.fd, 0);
> > buf[len] = '\0';
> > causes segfault on buf[len] = '\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] = '\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?
BTW, accesses beyond the file do cause a segfault, and that is correct.
Note that your firts case accesses buf[16384], while your memcpy does
not access that address.
-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';
> }
