Re: selftests: resctrl: cat_test.c: In function 'noncont_cat_run_test': ../kselftest.h:74:9: error: impossible constraint in 'asm' 74 | __asm__ __volatile__ ("cpuid\n\t"

[Reinette Chatre <reinette.chatre@intel.com>]

On 4/18/2024 2:37 AM, Naresh Kamboju wrote:
> The Linux next building selftests with gcc-13 found these build warnings
> and errors.
> 
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> 
> Build log:
> ---------
> Path:
> selftests/resctrl/resctrl_tests/
> 
> In file included from resctrl.h:24,
>                  from cat_test.c:11:
> cat_test.c: In function 'noncont_cat_run_test':
> ../kselftest.h:74:9: error: impossible constraint in 'asm'
>    74 |         __asm__ __volatile__ ("cpuid\n\t"
>          \
>       |         ^~~~~~~
> cat_test.c:308:17: note: in expansion of macro '__cpuid_count'
>   308 |                 __cpuid_count(0x10, 1, eax, ebx, ecx, edx);
>       |                 ^~~~~~~~~~~~~
> ../kselftest.h:74:9: error: impossible constraint in 'asm'
>    74 |         __asm__ __volatile__ ("cpuid\n\t"
>          \
>       |         ^~~~~~~
> cat_test.c:310:17: note: in expansion of macro '__cpuid_count'
>   310 |                 __cpuid_count(0x10, 2, eax, ebx, ecx, edx);
>       |                 ^~~~~~~~~~~~~
> 

This is unexpected to me. kselftest.h intends to and still does define
__cpuid_count() exactly the same as gcc does (in gcc/config/i386/cpuid.h):


 255 #define __cpuid_count(level, count, a, b, c, d)                         \
 256   __asm__ __volatile__ ("cpuid\n\t"                                     \
 257                         : "=a" (a), "=b" (b), "=c" (c), "=d" (d)        \
 258                         : "0" (level), "2" (count))

Reinette