Re: [Xen-devel] [PATCH] x86: use gcc6'es flags asm() output support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.07.16 at 17:38, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 01/07/16 16:01, Jan Beulich wrote:
>> TBD: Do we want to abstract the pattern
>>      asm ( "...; set<cc> %<out>" : "=<cons>" (var) ... )
>> matching
>>      asm ( "..." : "=@cc<cc>" (var) ... )
>> via some macro? While this would eliminate many (all?) of the
>> conditionals added here, it would result in the : no longer being
>> visible in the actual source, making the asm()s look somewhat odd.
>> Otherwise, to limit code duplication, it may be preferable to put
>> the #ifdef-s inside the asm()s instead of around them.
> 
> I would recommend not abstracting them.  asm() statements are already
> subtle/hard enough to get right, and hiding the :'s will only make
> matters worse.

Right, that's why I didn't do that right away. Otoh the alternative
asm macros hide colons too.

> As for interleaving inside the asm statement itself, we already have
> precedent for that with the HAVE_GAS_* predicates.  It would make the
> patch rather larger, but might end up looking cleaner.  It is probably
> also worth switching to named parameters to reduce the risk of getting
> positional parameters out of order.

I don't really see that risk, but I'll try to judge on a case by case
basis.

> As for the content of the change itself, Reviewed-by: Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>

Since the adjustments will be significant, I'll have to drop that
anyway, but thanks.

Jan


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