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

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Message-Id: <20240813104515.19152-4-ilpo.jarvinen@linux.intel.com>
Date: Tue, 13 Aug 2024 13:45:15 +0300
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>,
	Shuah Khan <shuah@...nel.org>,
	Reinette Chatre <reinette.chatre@...el.com>,
	linux-kselftest@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Shaopeng Tan <tan.shaopeng@...fujitsu.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [RFC PATCH 3/3] kselftest: Provide __cpuid_count() stub on non-x86 archs

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>
---
 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)
-- 
2.39.2