linux-kernel - Re: [RFC PATCH 3/3] kselftest: Provide __cpuid

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Message-ID: <b6372b9e-f93d-4243-9acd-64b60a6dc779@collabora.com>
Date: Thu, 22 Aug 2024 09:49:31 +0500
From: Muhammad Usama Anjum <Usama.Anjum@...labora.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Shuah Khan <shuah@...nel.org>, Reinette Chatre <reinette.chatre@...el.com>,
 linux-kselftest@...r.kernel.org
Cc: Usama.Anjum@...labora.com, linux-kernel@...r.kernel.org,
 Shaopeng Tan <tan.shaopeng@...fujitsu.com>, Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [RFC PATCH 3/3] kselftest: Provide __cpuid_count() stub on
 non-x86 archs

On 8/13/24 3:45 PM, Ilpo Järvinen wrote:
> Building resctrl selftest fails on ARM because it uses __cpuid_count()
> that fails the build with error:
> 
>   CC       resctrl_tests
> In file included from resctrl.h:24,
>                  from cat_test.c:11:
> In function 'arch_supports_noncont_cat',
>     inlined from 'noncont_cat_run_test' at cat_test.c:323:6:
> ../kselftest.h:74:9: error: impossible constraint in 'asm'
>    74 |         __asm__ __volatile__ ("cpuid\n\t"
>        \
>       |         ^~~~~~~
> cat_test.c:301:17: note: in expansion of macro '__cpuid_count'
>   301 |                 __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:303:17: note: in expansion of macro '__cpuid_count'
>   303 |                 __cpuid_count(0x10, 2, eax, ebx, ecx, edx);
>       |                 ^~~~~~~~~~~~~
> 
> The resctrl selftest would run that code only on Intel CPUs but
> as is, the code cannot be build at all.
> 
> Provide an empty stub for __cpuid_count() if it is not supported
> to allow build to succeed.
> 
> Reported-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@...labora.com>

> ---
>  tools/testing/selftests/kselftest.h | 6 ++++++
>  tools/testing/selftests/lib.mk      | 4 ++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/tools/testing/selftests/kselftest.h b/tools/testing/selftests/kselftest.h
> index b8967b6e29d5..71593add1b39 100644
> --- a/tools/testing/selftests/kselftest.h
> +++ b/tools/testing/selftests/kselftest.h
> @@ -70,10 +70,16 @@
>   * have __cpuid_count().
>   */
>  #ifndef __cpuid_count
> +#ifdef HAVE_CPUID
>  #define __cpuid_count(level, count, a, b, c, d)				\
>  	__asm__ __volatile__ ("cpuid\n\t"				\
>  			      : "=a" (a), "=b" (b), "=c" (c), "=d" (d)	\
>  			      : "0" (level), "2" (count))
> +#else
> +#define __cpuid_count(level, count, a, b, c, d)	do {			\
> +	(void)a; (void)b; (void)c; (void)d;				\
> +} while (0)
> +#endif
>  #endif
>  
>  /* define kselftest exit codes */
> diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
> index d6edcfcb5be8..236db9b24037 100644
> --- a/tools/testing/selftests/lib.mk
> +++ b/tools/testing/selftests/lib.mk
> @@ -199,6 +199,10 @@ clean: $(if $(TEST_GEN_MODS_DIR),clean_mods_dir)
>  # Build with _GNU_SOURCE by default
>  CFLAGS += -D_GNU_SOURCE=
>  
> +ifeq ($(ARCH),$(filter $(ARCH),x86 x86_64))
> +CFLAGS += -DHAVE_CPUID=
> +endif
> +
>  # Enables to extend CFLAGS and LDFLAGS from command line, e.g.
>  # make USERCFLAGS=-Werror USERLDFLAGS=-static
>  CFLAGS += $(USERCFLAGS)

-- 
BR,
Muhammad Usama Anjum