svn commit: r348843 - head/sys/vm

[Andriy Gapon]

On 10/06/2019 09:42, Doug Moore wrote:
> -fwrapv concerns signed arithmetic.  This calculation is with unsigned
> arithmetic, and the possibility of wrapping around to 0 is part of the
> language.

Oh, sorry for the noise!

> On 6/10/19 1:35 AM, Andriy Gapon wrote:
>> On 10/06/2019 06:07, Doug Moore wrote:
>>> Author: dougm
>>> Date: Mon Jun 10 03:07:10 2019
>>> New Revision: 348843
>>> URL: https://svnweb.freebsd.org/changeset/base/348843
>>>
>>> Log:
>>>   There are times when a len==0 parameter to mmap is okay. But on a
>>>   32-bit machine, a len parameter just a few bytes short of 4G, rounded
>>>   up to a page boundary and hitting zero then, is not okay. Return
>>>   failure in that case.
>>>   
>>>   Reported by: pho
>>>   Reviewed by: alc, kib (mentor)
>>>   Tested by: pho
>>>   Differential Revision: https://reviews.freebsd.org/D20580
>>>
>>> Modified:
>>>   head/sys/vm/vm_mmap.c
>>>
>>> Modified: head/sys/vm/vm_mmap.c
>>> ==============================================================================
>>> --- head/sys/vm/vm_mmap.c	Sun Jun  9 22:55:21 2019	(r348842)
>>> +++ head/sys/vm/vm_mmap.c	Mon Jun 10 03:07:10 2019	(r348843)
>>> @@ -257,7 +257,10 @@ kern_mmap(struct thread *td, uintptr_t addr0, size_t s
>>>  
>>>  	/* Adjust size for rounding (on both ends). */
>>>  	size += pageoff;			/* low end... */
>>> -	size = (vm_size_t) round_page(size);	/* hi end */
>>> +	/* Check for rounding up to zero. */
>>> +	if (round_page(size) < size)
>> Is this guaranteed to work with all compilers?
>> I think that some smart compilers may think that this condition is impossible.
>> Are we finally using -fwrapv or something like it for kernel builds?
>>
>>> +		return (EINVAL);
>>> +	size = round_page(size);		/* hi end */
>>>  
>>>  	/* Ensure alignment is at least a page and fits in a pointer. */
>>>  	align = flags & MAP_ALIGNMENT_MASK;
>>>
>>


-- 
Andriy Gapon