Re: [Xen-devel] [PATCH 08/12] xen/arm: cpufeature: Match register size with value size in cpus_have_const_cap

[Julien Grall <julien.grall@xxxxxxx>]

On 4/17/19 9:29 PM, Stefano Stabellini wrote:
> On Wed, 27 Mar 2019, Julien Grall wrote:
> > Clang is pickier than GCC for the register size in asm statement. It
> > expects the register size to match the value size.
> >
> > The asm statement expects a 32-bit (resp. 64-bit) value on Arm32
> > (resp. Arm64) whereas the value is a boolean (Clang consider to be
> > 32-bit).
> >
> > It would be possible to impose 32-bit register for both architecture
> > but this require the code to use __OP32. However, it does no really
> > improve the assembly generated. Instead, replace switch the variable to
> > use register_t.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> > ---
> >   xen/include/asm-arm/cpufeature.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
> > index c2c8f3417c..d06f09ecfa 100644
> > --- a/xen/include/asm-arm/cpufeature.h
> > +++ b/xen/include/asm-arm/cpufeature.h
> > @@ -67,7 +67,7 @@ static inline bool cpus_have_cap(unsigned int num)
> >   
> >   /* System capability check for constant cap */
> >   #define cpus_have_const_cap(num) ({                 \
> > -        bool __ret;                                 \
> > +        register_t __ret;                           \
> >                                                       \
> >           asm volatile (ALTERNATIVE("mov %0, #0",     \
> >                                     "mov %0, #1",     \
> As per the previous one, this is fine, but could you also change the
> last statement below to unlikely(!!__ret);
As per the previous one, the current code is valid. Please justify why 
!! is necessary.
Cheers,

--
Julien Grall

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