[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>
Subject: [kvm-unit-tests PATCH v3 6/6] x86: use inline asm to retrieve stack pointer
Date: Wed, 30 Oct 2019 14:04:19 -0700	[thread overview]
Message-ID: <20191030210419.213407-7-morbo@google.com> (raw)
In-Reply-To: <20191030210419.213407-1-morbo@google.com>

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

