On Mon, Oct 19, 2015 at 12:16:12PM +0200, Borislav Petkov wrote: > On Mon, Oct 19, 2015 at 10:58:55AM +0100, Chris Wilson wrote: > > Adding a barrier() into clflushopt() is enough for GCC to dtrt, but > > solving why GCC is not seeing the constraints from the alternative_io() > > would be smarter... > > Hmm, would something like adding the memory clobber to the > alternative_io() definition work? > > --- > diff --git a/arch/x86/include/asm/alternative.h > b/arch/x86/include/asm/alternative.h > index 7bfc85bbb8ff..d923e5dacdb1 100644 > --- a/arch/x86/include/asm/alternative.h > +++ b/arch/x86/include/asm/alternative.h > @@ -207,7 +207,7 @@ static inline int alternatives_text_reserved(void *start, > void *end) > /* Like alternative_input, but with a single output argument */ > #define alternative_io(oldinstr, newinstr, feature, output, input...) > \ > asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \ > - : output : "i" (0), ## input) > + : output : "i" (0), ## input : "memory") > > /* Like alternative_io, but for replacing a direct call with another one. */ > #define alternative_call(oldfunc, newfunc, feature, output, input...) > \
In order to add the clobbers, I had to adjust the macro slightly: +#define alternative_output(oldinstr, newinstr, feature, output) \ + asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \ + : output : "i" (0) : "memory") and that also works. The concern I have here is that the asm does use "+m" as its output already, and the clflush() asm doesn't require the manual clobber. -Chris -- Chris Wilson, Intel Open Source Technology Centre
