[ovs-discuss] [PATCH net-next] fast_hash: clobber registers correctly for inline function use

Hannes Frederic Sowa hannes at stressinduktion.org
Fri Nov 14 20:10:36 UTC 2014


On Fr, 2014-11-14 at 21:04 +0100, Hannes Frederic Sowa wrote:
> On Fr, 2014-11-14 at 13:38 -0500, David Miller wrote:
> > From: Hannes Frederic Sowa <hannes at stressinduktion.org>
> > Date: Fri, 14 Nov 2014 16:46:18 +0100
> > 
> > > I would still like to see the current proposed fix getting applied and
> > > we can do this on-top. The inline call after this patch reassembles a
> > > direct function call, so besides the long list of clobbers, it should
> > > still be pretty fast.
> > 
> > I would rather revert the change entirely until it is implemented
> > properly.
> > 
> > Also, I am strongly of the opinion that this is a mis-use of the
> > alternative call interface.  It was never intended to be used for
> > things that can make real function calls.
> 
> I tend to disagree. Grepping e.g. shows
> 
>         alternative_call_2(copy_user_generic_unrolled,
>                          copy_user_generic_string,
>                          X86_FEATURE_REP_GOOD,
>                          copy_user_enhanced_fast_string,
>                          X86_FEATURE_ERMS,
>                          ASM_OUTPUT2("=a" (ret), "=D" (to), "=S" (from),
>                                      "=d" (len)),
>                          "1" (to), "2" (from), "3" (len)
>                          : "memory", "rcx", "r8", "r9", "r10", "r11");

Oh, I need to take this back, These are actually assembler functions.





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