Re: [Xen-devel] [PATCH 3/5] x86/hvm: Adjust hvmemul_rep_stos() to compile with -Wvla

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.09.18 at 12:31, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 24/09/18 15:16, Jan Beulich wrote:
>>>>> On 24.09.18 at 15:00, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> For at least "gcc (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609", the
>>> typecast of buf triggers a Variable Length Array warning.
>>>
>>> Alter the asm expression to avoid the typecast, which necessitates the
>>> introduction of a memory clobber as the compiler can no longer identify
>>> the total quantity of written memory.
>> I dislike this, but what do you do. Would be quite helpful though to
>> have a comment there, or else I might be tempted to undo the
>> memory clobber in a couple of months/years time.
> 
> On further investigation, its all versions of GCC and Clang when using
> -Wvla.  I'll tweak the commit message so it doesn't read as if it might
> be a quirk in that specific compiler.

Well, it's a quirk in all compilers then. That type cast certainly is not
an _instantiation_ of a VLA, yet only those are what we want to
prevent (and what I understand the warning is to point out).

Jan



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