Re: [PATCH v3 3/3] kselftest: Provide __cpuid_count() stub on non-x86 archs

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Thu, 29 Aug 2024, 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.
> 
> Define HAVE_CPUID in lib.mk based on ARCH (x86 or x86_64). If ARCH is
> not set, acquire it using uname -m.
> 
> Provide a stub for __cpuid_count() if HAVE_CPUID is not present to
> allow build to succeed. The stub casts its arguments to void to avoid
> causing "unused variable" or "set but not used" warnings.
> 
> Fixes: ae638551ab64 ("selftests/resctrl: Add non-contiguous CBMs CAT test")
> Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> ---
> v3:
> - Remove "empty" wording
> - Also cast input parameters to void
> - Initialize ARCH from uname -m if not set (this might allow cleaning
>   up some other makefiles but that is left as future work)
> v2:
> - Removed RFC & added Fixes and Tested-by
> - Fixed the error message's line splits
> - Noted down the reason for void casts in the stub
> ---
>  tools/testing/selftests/kselftest.h | 6 ++++++
>  tools/testing/selftests/lib.mk      | 6 ++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/tools/testing/selftests/kselftest.h b/tools/testing/selftests/kselftest.h
> index b8967b6e29d5..9c4bfbf107f1 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)level; (void)count; (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..8e3069926153 100644
> --- a/tools/testing/selftests/lib.mk
> +++ b/tools/testing/selftests/lib.mk
> @@ -23,6 +23,8 @@ CLANG_TARGET_FLAGS_x86_64       := x86_64-linux-gnu
>  
>  # Default to host architecture if ARCH is not explicitly given.
>  ifeq ($(ARCH),)
> +ARCH := $(shell uname -m 2>/dev/null || echo not)
> +ARCH := $(shell echo $(ARCH) | sed -e s/i.86/x86/)
>  CLANG_TARGET_FLAGS := $(shell $(CLANG) -print-target-triple)
>  else
>  CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(ARCH))
> @@ -199,6 +201,10 @@ 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

Hpmf, scratch this. CFLAGS are overwritten by x86 selftest makefile so I 
need to reorder things there before making this change.

-- 
 i.