Use __GLIBC__ in the hardware disable test to detect when selftests are
being built/linked against glibc and thus pthread_attr_setaffinity_np() is
(hopefully) available.  As pointed out by Sashiko and Hisam, _GNU_SOURCE is
effectively a "request" macro to enable functionality, whereas __GLIBC__ is
an announcement of support and selftests' idiomatic way of guarding code
that's specific to glibc.

Fixes: 496779b54943 ("KVM: selftests: Pre-set threads affinity in hardware disable test when possible")
Reported-by: Sashiko Bot <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260731201140.5AF0C1F00AC4@smtp.kernel.org
Suggested-by: Hisam Mehboob <hisamshar@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/hardware_disable_test.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/kvm/hardware_disable_test.c b/tools/testing/selftests/kvm/hardware_disable_test.c
index 43a36ef3ead8..1c20892d6782 100644
--- a/tools/testing/selftests/kvm/hardware_disable_test.c
+++ b/tools/testing/selftests/kvm/hardware_disable_test.c
@@ -37,7 +37,7 @@ static void *run_vcpu(void *arg)
 	struct kvm_vcpu *vcpu = arg;
 	struct kvm_run *run = vcpu->run;
 
-#ifndef _GNU_SOURCE
+#ifndef __GLIBC__
 	kvm_sched_setaffinity(0, sizeof(cpu_set_t), &threads_cpu_set);
 #endif
 
@@ -51,7 +51,7 @@ static void *sleeping_thread(void *arg)
 {
 	int fd;
 
-#ifndef _GNU_SOURCE
+#ifndef __GLIBC__
 	kvm_sched_setaffinity(0, sizeof(cpu_set_t), &threads_cpu_set);
 #endif
 
@@ -71,7 +71,7 @@ static void run_test(u32 run)
 	u32 i, j;
 
 	TEST_ASSERT_EQ(pthread_attr_init(&attr), 0);
-#ifdef _GNU_SOURCE
+#ifdef __GLIBC__
 	TEST_ASSERT_EQ(pthread_attr_setaffinity_np(&attr, sizeof(cpu_set_t), &threads_cpu_set), 0);
 #endif
 

base-commit: 76671054f9a1ff6abb976583cd8da37650acdc97
-- 
2.55.0.860.g4b6b3295ed-goog

On Wed, 26 Aug 2026 09:14:30 -0700, Sean Christopherson wrote:
> Use __GLIBC__ in the hardware disable test to detect when selftests are
> being built/linked against glibc and thus pthread_attr_setaffinity_np() is
> (hopefully) available.  As pointed out by Sashiko and Hisam, _GNU_SOURCE is
> effectively a "request" macro to enable functionality, whereas __GLIBC__ is
> an announcement of support and selftests' idiomatic way of guarding code
> that's specific to glibc.
> 
> [...]

Applied to kvm-x86 fixes, thanks!

[1/1] KVM: selftests: Use __GLIBC__, not _GNU_SOURCE, to detect actual glibc
      https://github.com/kvm-x86/linux/commit/f13368e0acff

--
https://github.com/kvm-x86/linux/tree/next