rune/libenclave/skeleton: Simplify get_sgx_xfrm_by_cpuid()

Signed-off-by: NShirong Hao <shirong@linux.alibaba.com>

rune/libenclave/internal/runtime/pal/skeleton/sgxutils.c

@@ -49,44 +49,30 @@ static inline uint64_t get_xcr0()
 	return xgetbv(0);
 }
 
-static bool try_get_xcr0(uint64_t *value)
+static uint64_t try_get_xcr0()
 {
 	int cpu_info[4] = {0, 0, 0, 0};
 
-	*value = SGX_XFRM_LEGACY;
-
-	// check if xgetbv instruction is supported
+	// Check if xgetbv instruction is supported.
 	__cpuid(cpu_info, 1);
-	// ecx[27:26] indicate whether support xsave/xrstor, and whether enable xgetbv, xsetbv
-	if (!(cpu_info[2] & (1<<XSAVE_SHIFT)) || !(cpu_info[2] & (1<<OSXSAVE_SHIFT)))
-		return false;
-
-	*value = get_xcr0();
+	// ecx[27:26] indicate whether support xsave/xrstor, and whether enable xgetbv, xsetbv.
+	if (!(cpu_info[2] & (1 << OSXSAVE_SHIFT)))
+		return SGX_XFRM_LEGACY;
 
-	// check if xsavec is supported
-	// Assume that XSAVEC is always supported if XSAVE is supported
-	cpu_info[0] = cpu_info[1] = cpu_info[2] = cpu_info[3] = 0;
+	// If XSAVE is supported, while XSAVEC is not supported,
+	// set xfrm to legacy, because skeleton requires XSAVEC feature available on the path of enclave-exit.
 	__cpuidex(cpu_info, 0xD, 1);
-	if (!(cpu_info[0] & (1<<XSAVEC_SHIFT)))
-		return false;
+	if (!(cpu_info[0] & (1 << XSAVEC_SHIFT)))
+		return SGX_XFRM_LEGACY;
 
-	return true;
+	// If x-feature is supported and enabled by OS, we need make sure it is also supported in enclave.
+	__cpuidex(cpu_info, SGX_LEAF, 1);
+	return (get_xcr0() & (((uint64_t)cpu_info[3] << 32) | cpu_info[2]));
 }
 
 void get_sgx_xfrm_by_cpuid(uint64_t *xfrm)
 {
-	int cpu_info[4] = {0, 0, 0, 0};
-
-	__cpuidex(cpu_info, SGX_LEAF, 1);
-
-	if (try_get_xcr0(xfrm) == false) {
-	// if XSAVE is supported, while XSAVEC is not supported,
-	// set xfrm to legacy, because XSAVEC cannot be executed within enclave.
-		*xfrm = SGX_XFRM_LEGACY;
-	} else {
-	// If x-feature is supported and enabled by OS, we need make sure it is also supported in enclave.
-		*xfrm &= (((uint64_t)cpu_info[3] << 32) | cpu_info[2]);
-	}
+	*xfrm = try_get_xcr0();
 }
 
 bool is_launch_control_supported(void)