[kvm-unit-tests PATCH v2] x86: Do not assign values to unaligned pointer to 128 bits

From: Jacob Xu <jacobhxu@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	Jim Mattson <jmattson@google.com>,
	Sean Christopherson <seanjc@google.com>
Cc: kvm@vger.kernel.org, Jacob Xu <jacobhxu@google.com>
Subject: [kvm-unit-tests PATCH v2] x86: Do not assign values to unaligned pointer to 128 bits
Date: Thu,  6 May 2021 11:49:25 -0700	[thread overview]
Message-ID: <20210506184925.290359-1-jacobhxu@google.com> (raw)

When compiled with clang, the following statement gets converted into a
movaps instructions.
mem->u[0] = 5; mem->u[1] = 6; mem->u[2] = 7; mem->u[3] = 8;

Since mem is an unaligned pointer to a union of an sse, we get a GP when
running.

All we want is to make the values between mem and v different for this
testcase, so let's just memset the pointer at mem, and convert to
uint32_t pointer. Then the compiler will not assume the pointer is
aligned to 128 bits.

Fixes: e5e76263b5 ("x86: add additional test cases for sse exceptions to
emulator.c")

Signed-off-by: Jacob Xu <jacobhxu@google.com>
---
 x86/emulator.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/x86/emulator.c b/x86/emulator.c
index 9705073..a2c7e5b 100644
--- a/x86/emulator.c
+++ b/x86/emulator.c
@@ -716,12 +716,12 @@ static __attribute__((target("sse2"))) void test_sse_exceptions(void *cross_mem)
 
 	// test unaligned access for movups, movupd and movaps
 	v.u[0] = 1; v.u[1] = 2; v.u[2] = 3; v.u[3] = 4;
-	mem->u[0] = 5; mem->u[1] = 6; mem->u[2] = 7; mem->u[3] = 8;
+	memset((uint32_t *)mem, 0xdecafbad, sizeof(mem));
 	asm("movups %1, %0" : "=m"(*mem) : "x"(v.sse));
 	report(sseeq(&v, mem), "movups unaligned");
 
 	v.u[0] = 1; v.u[1] = 2; v.u[2] = 3; v.u[3] = 4;
-	mem->u[0] = 5; mem->u[1] = 6; mem->u[2] = 7; mem->u[3] = 8;
+	memset((uint32_t *)mem, 0xdecafbad, sizeof(mem));
 	asm("movupd %1, %0" : "=m"(*mem) : "x"(v.sse));
 	report(sseeq(&v, mem), "movupd unaligned");
 	exceptions = 0;
@@ -734,7 +734,7 @@ static __attribute__((target("sse2"))) void test_sse_exceptions(void *cross_mem)
 	// setup memory for cross page access
 	mem = (sse_union *)(&bytes[4096-8]);
 	v.u[0] = 1; v.u[1] = 2; v.u[2] = 3; v.u[3] = 4;
-	mem->u[0] = 5; mem->u[1] = 6; mem->u[2] = 7; mem->u[3] = 8;
+	memset((uint32_t *)mem, 0xdecafbad, sizeof(mem));
 
 	asm("movups %1, %0" : "=m"(*mem) : "x"(v.sse));
 	report(sseeq(&v, mem), "movups unaligned crosspage");
-- 
2.31.1.607.g51e8a6a459-goog

