Re: [Xen-devel] [PATCH 1/2] libs/gnttab: do not use alloca(3)

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 22/08/16 11:10, Wei Liu wrote:
> On Mon, Aug 22, 2016 at 10:46:50AM +0100, David Vrabel wrote:
>> On 17/08/16 15:33, Wei Liu wrote:
>>> The semantics of alloca(3) is not very nice. If the stack overflows,
>>> program behaviour is undefined.
>>>
>>> Remove the use of alloca(3) and always use mmap.
>>
>> This is only using alloca() if the allocation is < PAGE_SIZE.  I think
>> assuming there's this much extra stack is fine.
>>
> 
> A library is not in a position assume how deep the stack is IMHO.

This suggests a library cannot use any stack, which is clearly silly.

But ok, in which case you should consider using malloc() instead of
alloca()/mmap(), then small allocation might come out of some
pre-existing or cached allocations.

David

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