mmap(2) with MAP_ANON honouring offset although it shouldn't

[John Baldwin]

On Friday 30 October 2009 10:38:24 pm Alexander Best wrote:
> John Baldwin schrieb am 2009-10-21:
> > On Wednesday 21 October 2009 11:51:04 am Alexander Best wrote:
> > > although the mmap(2) manual states in section MAP_ANON:
> 
> > > "The offset argument is ignored."
> 
> > > this doesn't seem to be true. running
> 
> > > printf("%p\n", mmap((void*)0x1000, 0x1000, PROT_NONE, MAP_ANON, -1,
> > > 0x12345678));
> 
> > > and
> 
> > > printf("%p\n", mmap((void*)0x1000, 0x1000, PROT_NONE, MAP_ANON, -1,
> > > 0));
> 
> > > produces different outputs. i've attached a patch to solve the
> > > problem. the
> > > patch is similar to the one proposed in this PR, but should apply
> > > cleanly to
> > > CURRENT: http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/71258
> 
> > A simpler patch would be to simply set pos = 0 below the MAP_STACK
> > line if
> > MAP_ANON is set.
> 
> how about the following patch. problem seems to be that pos = 0 needs to be
> set before pageoff is being calculated.

I think that that patch is fine, but will defer to alc at .  I think he argued 
that any non-zero offset passed to MAP_ANON should fail with EINVAL.

-- 
John Baldwin