linux-kernel - Re: selftests: resctrl: cat_test.c: In function 'noncont_cat_run_test': ../kselftest.h:74:9: error: impossible constraint in 'asm' 74

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Date: Thu, 18 Apr 2024 10:14:02 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Naresh Kamboju <naresh.kamboju@...aro.org>, open list
	<linux-kernel@...r.kernel.org>, "open list:KERNEL SELFTEST FRAMEWORK"
	<linux-kselftest@...r.kernel.org>, <lkft-triage@...ts.linaro.org>, "Linux
 Regressions" <regressions@...ts.linux.dev>
CC: Fenghua Yu <fenghua.yu@...el.com>, Shuah Khan <shuah@...nel.org>, "Anders
 Roxell" <anders.roxell@...aro.org>, Arnd Bergmann <arnd@...db.de>, "Dan
 Carpenter" <dan.carpenter@...aro.org>
Subject: 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"



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@...aro.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