diff --git a/src/cmd/internal/obj/x86/obj6.go b/src/cmd/internal/obj/x86/obj6.go
index b8c7ad7d1bb..06736d43bd1 100644
--- a/src/cmd/internal/obj/x86/obj6.go
+++ b/src/cmd/internal/obj/x86/obj6.go
@@ -912,7 +912,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		}
 
 		if autoffset != deltasp {
-			ctxt.Diag("unbalanced PUSH/POP")
+			ctxt.Diag("%s: unbalanced PUSH/POP", cursym)
 		}
 
 		if autoffset != 0 {
diff --git a/src/runtime/cgo/abi_amd64.h b/src/runtime/cgo/abi_amd64.h
new file mode 100644
index 00000000000..44cc0969dac
--- /dev/null
+++ b/src/runtime/cgo/abi_amd64.h
@@ -0,0 +1,69 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Macros for transitioning from the host ABI to Go ABI0.
+//
+// TODO(austin): Define these for ELF platforms as well.
+
+#ifdef GOOS_windows
+
+// REGS_HOST_TO_ABI0_STACK is the stack bytes used by
+// PUSH_REGS_HOST_TO_ABI0.
+#define REGS_HOST_TO_ABI0_STACK (28*8 + 8)
+
+// PUSH_REGS_HOST_TO_ABI0 prepares for transitioning from
+// the host ABI to Go ABI0 code. It saves all registers that are
+// callee-save in the host ABI and caller-save in Go ABI0 and prepares
+// for entry to Go.
+//
+// Save DI SI BP BX R12 R13 R14 R15 X6-X15 registers and the DF flag.
+// Clear the DF flag for the Go ABI.
+// MXCSR matches the Go ABI, so we don't have to set that,
+// and Go doesn't modify it, so we don't have to save it.
+#define PUSH_REGS_HOST_TO_ABI0()	\
+	PUSHFQ			\
+	CLD			\
+	ADJSP	$(REGS_HOST_TO_ABI0_STACK - 8)	\
+	MOVQ	DI, (0*0)(SP)	\
+	MOVQ	SI, (1*8)(SP)	\
+	MOVQ	BP, (2*8)(SP)	\
+	MOVQ	BX, (3*8)(SP)	\
+	MOVQ	R12, (4*8)(SP)	\
+	MOVQ	R13, (5*8)(SP)	\
+	MOVQ	R14, (6*8)(SP)	\
+	MOVQ	R15, (7*8)(SP)	\
+	MOVUPS	X6, (8*8)(SP)	\
+	MOVUPS	X7, (10*8)(SP)	\
+	MOVUPS	X8, (12*8)(SP)	\
+	MOVUPS	X9, (14*8)(SP)	\
+	MOVUPS	X10, (16*8)(SP)	\
+	MOVUPS	X11, (18*8)(SP)	\
+	MOVUPS	X12, (20*8)(SP)	\
+	MOVUPS	X13, (22*8)(SP)	\
+	MOVUPS	X14, (24*8)(SP)	\
+	MOVUPS	X15, (26*8)(SP)
+
+#define POP_REGS_HOST_TO_ABI0()	\
+	MOVQ	(0*0)(SP), DI	\
+	MOVQ	(1*8)(SP), SI	\
+	MOVQ	(2*8)(SP), BP	\
+	MOVQ	(3*8)(SP), BX	\
+	MOVQ	(4*8)(SP), R12	\
+	MOVQ	(5*8)(SP), R13	\
+	MOVQ	(6*8)(SP), R14	\
+	MOVQ	(7*8)(SP), R15	\
+	MOVUPS	(8*8)(SP), X6	\
+	MOVUPS	(10*8)(SP), X7	\
+	MOVUPS	(12*8)(SP), X8	\
+	MOVUPS	(14*8)(SP), X9	\
+	MOVUPS	(16*8)(SP), X10	\
+	MOVUPS	(18*8)(SP), X11	\
+	MOVUPS	(20*8)(SP), X12	\
+	MOVUPS	(22*8)(SP), X13	\
+	MOVUPS	(24*8)(SP), X14	\
+	MOVUPS	(26*8)(SP), X15	\
+	ADJSP	$-(REGS_HOST_TO_ABI0_STACK - 8)	\
+	POPFQ
+
+#endif
diff --git a/src/runtime/cgo/asm_amd64.s b/src/runtime/cgo/asm_amd64.s
index 5dc8e2d235c..447ddb118df 100644
--- a/src/runtime/cgo/asm_amd64.s
+++ b/src/runtime/cgo/asm_amd64.s
@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 #include "textflag.h"
+#include "abi_amd64.h"
 
 // Called by C code generated by cmd/cgo.
 // func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
@@ -11,57 +12,18 @@
 // This signature is known to SWIG, so we can't change it.
 #ifndef GOOS_windows
 TEXT crosscall2(SB),NOSPLIT,$0x50-0 /* keeps stack pointer 32-byte aligned */
-#else
-TEXT crosscall2(SB),NOSPLIT,$0x110-0 /* also need to save xmm6 - xmm15 */
-#endif
 	MOVQ	BX, 0x18(SP)
 	MOVQ	R12, 0x28(SP)
 	MOVQ	R13, 0x30(SP)
 	MOVQ	R14, 0x38(SP)
 	MOVQ	R15, 0x40(SP)
 
-#ifdef GOOS_windows
-	// Win64 save RBX, RBP, RDI, RSI, RSP, R12, R13, R14, R15 and XMM6 -- XMM15.
-	MOVQ	DI, 0x48(SP)
-	MOVQ	SI, 0x50(SP)
-	MOVUPS	X6, 0x60(SP)
-	MOVUPS	X7, 0x70(SP)
-	MOVUPS	X8, 0x80(SP)
-	MOVUPS	X9, 0x90(SP)
-	MOVUPS	X10, 0xa0(SP)
-	MOVUPS	X11, 0xb0(SP)
-	MOVUPS	X12, 0xc0(SP)
-	MOVUPS	X13, 0xd0(SP)
-	MOVUPS	X14, 0xe0(SP)
-	MOVUPS	X15, 0xf0(SP)
-
-	MOVQ	CX, 0x0(SP)	/* fn */
-	MOVQ	DX, 0x8(SP)	/* arg */
-	// Skip n in R8.
-	MOVQ	R9, 0x10(SP)	/* ctxt */
-
-	CALL	runtime·cgocallback(SB)
-
-	MOVQ	0x48(SP), DI
-	MOVQ	0x50(SP), SI
-	MOVUPS	0x60(SP), X6
-	MOVUPS	0x70(SP), X7
-	MOVUPS	0x80(SP), X8
-	MOVUPS	0x90(SP), X9
-	MOVUPS	0xa0(SP), X10
-	MOVUPS	0xb0(SP), X11
-	MOVUPS	0xc0(SP), X12
-	MOVUPS	0xd0(SP), X13
-	MOVUPS	0xe0(SP), X14
-	MOVUPS	0xf0(SP), X15
-#else
 	MOVQ	DI, 0x0(SP)	/* fn */
 	MOVQ	SI, 0x8(SP)	/* arg */
 	// Skip n in DX.
 	MOVQ	CX, 0x10(SP)	/* ctxt */
 
 	CALL	runtime·cgocallback(SB)
-#endif
 
 	MOVQ	0x18(SP), BX
 	MOVQ	0x28(SP), R12
@@ -70,3 +32,21 @@ TEXT crosscall2(SB),NOSPLIT,$0x110-0 /* also need to save xmm6 - xmm15 */
 	MOVQ	0x40(SP), R15
 
 	RET
+
+#else
+TEXT crosscall2(SB),NOSPLIT,$0-0
+	PUSH_REGS_HOST_TO_ABI0()
+
+	// Make room for arguments to cgocallback.
+	ADJSP	$0x18
+	MOVQ	CX, 0x0(SP)	/* fn */
+	MOVQ	DX, 0x8(SP)	/* arg */
+	// Skip n in R8.
+	MOVQ	R9, 0x10(SP)	/* ctxt */
+
+	CALL	runtime·cgocallback(SB)
+
+	ADJSP	$-0x18
+	POP_REGS_HOST_TO_ABI0()
+	RET
+#endif
diff --git a/src/runtime/sys_windows_amd64.s b/src/runtime/sys_windows_amd64.s
index 68963313297..a9a7dfdd494 100644
--- a/src/runtime/sys_windows_amd64.s
+++ b/src/runtime/sys_windows_amd64.s
@@ -5,6 +5,7 @@
 #include "go_asm.h"
 #include "go_tls.h"
 #include "textflag.h"
+#include "cgo/abi_amd64.h"
 
 // maxargs should be divisible by 2, as Windows stack
 // must be kept 16-byte aligned on syscall entry.
@@ -111,18 +112,10 @@ TEXT runtime·getlasterror(SB),NOSPLIT,$0
 TEXT sigtramp<>(SB),NOSPLIT|NOFRAME,$0-0
 	// CX: PEXCEPTION_POINTERS ExceptionInfo
 
-	// DI SI BP BX R12 R13 R14 R15 registers and DF flag are preserved
-	// as required by windows callback convention.
-	PUSHFQ
-	SUBQ	$112, SP
-	MOVQ	DI, 80(SP)
-	MOVQ	SI, 72(SP)
-	MOVQ	BP, 64(SP)
-	MOVQ	BX, 56(SP)
-	MOVQ	R12, 48(SP)
-	MOVQ	R13, 40(SP)
-	MOVQ	R14, 32(SP)
-	MOVQ	R15, 88(SP)
+	// Switch from the host ABI to the Go ABI.
+	PUSH_REGS_HOST_TO_ABI0()
+	// Make stack space for the rest of the function.
+	ADJSP	$48
 
 	MOVQ	AX, R15	// save handler address
 
@@ -138,8 +131,8 @@ TEXT sigtramp<>(SB),NOSPLIT|NOFRAME,$0-0
 	CALL	runtime·badsignal2(SB)
 
 	// save g and SP in case of stack switch
-	MOVQ	DX, 96(SP) // g
-	MOVQ	SP, 104(SP)
+	MOVQ	DX, 32(SP) // g
+	MOVQ	SP, 40(SP)
 
 	// do we need to switch to the g0 stack?
 	MOVQ	g_m(DX), BX
@@ -153,9 +146,11 @@ TEXT sigtramp<>(SB),NOSPLIT|NOFRAME,$0-0
 	MOVQ	(g_sched+gobuf_sp)(BX), DI
 	// make room for sighandler arguments
 	// and re-save old SP for restoring later.
-	// (note that the 104(DI) here must match the 104(SP) above.)
-	SUBQ	$120, DI
-	MOVQ	SP, 104(DI)
+	// Adjust g0 stack by the space we're using and
+	// save SP at the same place on the g0 stack.
+	// The 32(DI) here must match the 32(SP) above.
+	SUBQ	$(REGS_HOST_TO_ABI0_STACK + 48), DI
+	MOVQ	SP, 40(DI)
 	MOVQ	DI, SP
 
 g0:
@@ -170,23 +165,14 @@ g0:
 
 	// switch back to original stack and g
 	// no-op if we never left.
-	MOVQ	104(SP), SP
-	MOVQ	96(SP), DX
+	MOVQ	40(SP), SP
+	MOVQ	32(SP), DX
 	get_tls(BP)
 	MOVQ	DX, g(BP)
 
 done:
-	// restore registers as required for windows callback
-	MOVQ	88(SP), R15
-	MOVQ	32(SP), R14
-	MOVQ	40(SP), R13
-	MOVQ	48(SP), R12
-	MOVQ	56(SP), BX
-	MOVQ	64(SP), BP
-	MOVQ	72(SP), SI
-	MOVQ	80(SP), DI
-	ADDQ	$112, SP
-	POPFQ
+	ADJSP	$-48
+	POP_REGS_HOST_TO_ABI0()
 
 	RET
 
@@ -230,21 +216,8 @@ TEXT runtime·callbackasm1(SB),NOSPLIT,$0
 	DIVL	CX
 	SUBQ	$1, AX	// subtract 1 because return PC is to the next slot
 
-	// DI SI BP BX R12 R13 R14 R15 registers and DF flag are preserved
-	// as required by windows callback convention.
-	PUSHFQ
-	SUBQ	$64, SP
-	MOVQ	DI, 56(SP)
-	MOVQ	SI, 48(SP)
-	MOVQ	BP, 40(SP)
-	MOVQ	BX, 32(SP)
-	MOVQ	R12, 24(SP)
-	MOVQ	R13, 16(SP)
-	MOVQ	R14, 8(SP)
-	MOVQ	R15, 0(SP)
-
-	// Go ABI requires DF flag to be cleared.
-	CLD
+	// Switch from the host ABI to the Go ABI.
+	PUSH_REGS_HOST_TO_ABI0()
 
 	// Create a struct callbackArgs on our stack to be passed as
 	// the "frame" to cgocallback and on to callbackWrap.
@@ -263,23 +236,16 @@ TEXT runtime·callbackasm1(SB),NOSPLIT,$0
 	MOVQ	(24+callbackArgs_result)(SP), AX
 	ADDQ	$(24+callbackArgs__size), SP
 
-	// restore registers as required for windows callback
-	MOVQ	0(SP), R15
-	MOVQ	8(SP), R14
-	MOVQ	16(SP), R13
-	MOVQ	24(SP), R12
-	MOVQ	32(SP), BX
-	MOVQ	40(SP), BP
-	MOVQ	48(SP), SI
-	MOVQ	56(SP), DI
-	ADDQ	$64, SP
-	POPFQ
+	POP_REGS_HOST_TO_ABI0()
 
 	// The return value was placed in AX above.
 	RET
 
 // uint32 tstart_stdcall(M *newm);
 TEXT runtime·tstart_stdcall<ABIInternal>(SB),NOSPLIT,$0
+	// Switch from the host ABI to the Go ABI.
+	PUSH_REGS_HOST_TO_ABI0()
+
 	// CX contains first arg newm
 	MOVQ	m_g0(CX), DX		// g
 
@@ -298,12 +264,11 @@ TEXT runtime·tstart_stdcall<ABIInternal>(SB),NOSPLIT,$0
 	MOVQ	CX, g_m(DX)
 	MOVQ	DX, g(SI)
 
-	// Someday the convention will be D is always cleared.
-	CLD
-
 	CALL	runtime·stackcheck(SB)	// clobbers AX,CX
 	CALL	runtime·mstart(SB)
 
+	POP_REGS_HOST_TO_ABI0()
+
 	XORL	AX, AX			// return 0 == success
 	RET