Date:   Wed, 30 Oct 2019 14:04:19 -0700
In-Reply-To: <20191030210419.213407-1-morbo@google.com>
Message-Id: <20191030210419.213407-7-morbo@google.com>
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References: <20191015000411.59740-1-morbo@google.com> <20191030210419.213407-1-morbo@google.com>
Subject: [kvm-unit-tests PATCH v3 6/6] x86: use inline asm to retrieve stack pointer
From:   Bill Wendling <morbo@google.com>
To:     kvm@vger.kernel.org, pbonzini@redhat.com, thuth@redhat.com
Cc:     jmattson@google.com, sean.j.christopherson@intel.com,
        Bill Wendling <morbo@google.com>
Content-Type: text/plain; charset="UTF-8"
Sender: kvm-owner@vger.kernel.org
Precedence: bulk

According to GCC's documentation, the only supported use for specifying
registers for local variables is "to specify registers for input and
output operands when calling Extended asm." Using it as a shortcut to
get the value in a register isn't guaranteed to work, and clang
complains that the variable is uninitialized.

Signed-off-by: Bill Wendling <morbo@google.com>
---
 x86/vmx_tests.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
index 4aebc3f..565b69b 100644
--- a/x86/vmx_tests.c
+++ b/x86/vmx_tests.c
@@ -2138,7 +2138,9 @@ static void into_guest_main(void)
 		.offset = (uintptr_t)&&into,
 		.selector = KERNEL_CS32,
 	};
-	register uintptr_t rsp asm("rsp");
+	uintptr_t rsp;
+
+	asm volatile ("mov %%rsp, %0" : "=r"(rsp));
 
 	if (fp.offset != (uintptr_t)&&into) {
 		printf("Code address too high.\n");
@@ -3221,7 +3223,9 @@ static void try_compat_invvpid(void *unused)
 		.offset = (uintptr_t)&&invvpid,
 		.selector = KERNEL_CS32,
 	};
-	register uintptr_t rsp asm("rsp");
+	uintptr_t rsp;
+
+	asm volatile ("mov %%rsp, %0" : "=r"(rsp));
 
 	TEST_ASSERT_MSG(fp.offset == (uintptr_t)&&invvpid,
 			"Code address too high.");
-- 
2.24.0.rc1.363.gb1bccd3e3d-goog