Re: Update mmap() flags and errors lists

[DJ Delorie <dj@redhat.com>]

Florian Weimer <fweimer@redhat.com> writes:
>>> The question is if MAP_FIXED_NOREPLACE can be silently treated as
>>> MAP_FIXED.
>>
>> I wouldn't think so.  If the kernel supports it, it automatically
>> includes MAP_FIXED.  If the kernel doesn't support it, it's ignored.
>> You'd have to pass MAP_FIXED | MAP_FIXED_NOREPLACE to get the "silent"
>> treatment.
>
> Ahh, so the application has to if the return address changed and unmap?

I suppose that's one way of auto-detecting it, yes.

>>>> The code I was looking at was talking about having 2^32 *pages* mapped.
>>>
>>> See MMAP2_PAGE_UNIT.  On most architectures, it's fixed at 4096,
>>> regardless of page size.
>>>
>>> And it turns out that we do not check that the offset argument fits into
>>> 32 bits after dividing by MMAP2_PAGE_UNIT (on targets where this
>>> matters).  The documentation implies we should return EOVERFLOW in this
>>> case.
>>
>>
>> 	/* offset overflow? */
>> 	if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
>> 		return -EOVERFLOW;
>
> This is kernel code.  We have a shift in userspace on some
> architectures, too.

That shouldn't affect the kernel's computation of that error code,
though?