linux-kernel - [PATCH] KVM: selftests: Fix hyperv_features test failure when built on Clang

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Date:   Wed, 21 Sep 2022 16:11:51 -0700
From:   Vipin Sharma <vipinsh@...gle.com>
To:     seanjc@...gle.com, pbonzini@...hat.com
Cc:     jmattson@...gle.com, vkuznets@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Vipin Sharma <vipinsh@...gle.com>
Subject: [PATCH] KVM: selftests: Fix hyperv_features test failure when built
 on Clang

hyperv_features test fails when built on Clang. It throws error:

	 Failed guest assert: !hcall->ud_expected || res == hcall->expect at
	 x86_64/hyperv_features.c:90

On GCC, EAX is set to 0 before the hypercall whereas in Clang it is not,
this causes EAX to have garbage value when hypercall is returned in Clang
binary.

Fix by executing the guest assertion only when ud_expected is false.

Fixes: cc5851c6be86 ("KVM: selftests: Use exception fixup for #UD/#GP Hyper-V MSR/hcall tests")
Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
Suggested-by: Sean Christopherson <seanjc@...gle.com>

---
 tools/testing/selftests/kvm/x86_64/hyperv_features.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86_64/hyperv_features.c b/tools/testing/selftests/kvm/x86_64/hyperv_features.c
index 79ab0152d281..ad01868548f9 100644
--- a/tools/testing/selftests/kvm/x86_64/hyperv_features.c
+++ b/tools/testing/selftests/kvm/x86_64/hyperv_features.c
@@ -81,13 +81,13 @@ static void guest_hcall(vm_vaddr_t pgs_gpa, struct hcall_data *hcall)
 	}
 
 	vector = hypercall(hcall->control, input, output, &res);
-	if (hcall->ud_expected)
+	if (hcall->ud_expected) {
 		GUEST_ASSERT_2(vector == UD_VECTOR, hcall->control, vector);
-	else
+	} else {
 		GUEST_ASSERT_2(!vector, hcall->control, vector);
+		GUEST_ASSERT_2(res == hcall->expect, hcall->expect, res);
+	}
 
-	GUEST_ASSERT_2(!hcall->ud_expected || res == hcall->expect,
-			hcall->expect, res);
 	GUEST_DONE();
 }
 
-- 
2.37.3.968.ga6b4b080e4-goog