runtime/cgo: save callee-saved xmm registers on windows/amd64

For #14876.

Change-Id: I33947f74e8058437a784862f1f064974afc99250
Reviewed-on: https://go-review.googlesource.com/21084Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/cgo/asm_amd64.s

@@ -9,7 +9,11 @@
  * Save registers and call fn with two arguments.
  */
 TEXT crosscall2(SB),NOSPLIT,$0
+#ifndef GOOS_windows
 	SUBQ	$0x58, SP	/* keeps stack pointer 32-byte aligned */
+#else
+	SUBQ	$0xf8, SP	/* also need to save xmm6 - xmm15 */
+#endif
 	MOVQ	BX, 0x10(SP)
 	MOVQ	BP, 0x18(SP)
 	MOVQ	R12, 0x20(SP)
@@ -18,9 +22,19 @@ TEXT crosscall2(SB),NOSPLIT,$0
 	MOVQ	R15, 0x38(SP)
 
 #ifdef GOOS_windows
-	// Win64 save RBX, RBP, RDI, RSI, RSP, R12, R13, R14, and R15
+	// Win64 save RBX, RBP, RDI, RSI, RSP, R12, R13, R14, R15 and XMM6 -- XMM15.
 	MOVQ	DI, 0x40(SP)
 	MOVQ	SI, 0x48(SP)
+	MOVUPS	X6, 0x50(SP)
+	MOVUPS	X7, 0x60(SP)
+	MOVUPS	X8, 0x70(SP)
+	MOVUPS	X9, 0x80(SP)
+	MOVUPS	X10, 0x90(SP)
+	MOVUPS	X11, 0xa0(SP)
+	MOVUPS	X12, 0xb0(SP)
+	MOVUPS	X13, 0xc0(SP)
+	MOVUPS	X14, 0xd0(SP)
+	MOVUPS	X15, 0xe0(SP)
 
 	MOVQ	DX, 0(SP)	/* arg */
 	MOVQ	R8, 8(SP)	/* argsize (includes padding) */
@@ -29,6 +43,16 @@ TEXT crosscall2(SB),NOSPLIT,$0
 	
 	MOVQ	0x40(SP), DI
 	MOVQ	0x48(SP), SI
+	MOVUPS	0x50(SP), X6
+	MOVUPS	0x60(SP), X7
+	MOVUPS	0x70(SP), X8
+	MOVUPS	0x80(SP), X9
+	MOVUPS	0x90(SP), X10
+	MOVUPS	0xa0(SP), X11
+	MOVUPS	0xb0(SP), X12
+	MOVUPS	0xc0(SP), X13
+	MOVUPS	0xd0(SP), X14
+	MOVUPS	0xe0(SP), X15
 #else
 	MOVQ	SI, 0(SP)	/* arg */
 	MOVQ	DX, 8(SP)	/* argsize (includes padding) */
@@ -43,5 +67,9 @@ TEXT crosscall2(SB),NOSPLIT,$0
 	MOVQ	0x30(SP), R14
 	MOVQ	0x38(SP), R15
 	
+#ifndef GOOS_windows
 	ADDQ	$0x58, SP
+#else
+	ADDQ	$0xf8, SP
+#endif
 	RET