Re: [Xen-devel] [PATCH for-4.13 4/6] xen/arm: cpufeature: Match register size with value size in cpus_have_const_cap

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 2 Oct 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>


With or without !! given that it's part of unlikely.

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>     Changes in v2:
>         - Use !! per Stefano's request
> ---
>  xen/include/asm-arm/cpufeature.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/include/asm-arm/cpufeature.h 
> b/xen/include/asm-arm/cpufeature.h
> index c2c8f3417c..4c5ff6e8ac 100644
> --- a/xen/include/asm-arm/cpufeature.h
> +++ b/xen/include/asm-arm/cpufeature.h
> @@ -67,14 +67,14 @@ 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",     \
>                                    num)              \
>                        : "=r" (__ret));              \
>                                                      \
> -        unlikely(__ret);                            \
> +        unlikely(!!__ret);                          \
>          })
>  
>  static inline void cpus_set_cap(unsigned int num)
> -- 
> 2.11.0
> 

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