diff --git a/misc/cgo/test/callback.go b/misc/cgo/test/callback.go
index 814888e3ac5..08dd9b39d81 100644
--- a/misc/cgo/test/callback.go
+++ b/misc/cgo/test/callback.go
@@ -182,7 +182,7 @@ func testCallbackCallers(t *testing.T) {
 		"runtime.cgocallbackg1",
 		"runtime.cgocallbackg",
 		"runtime.cgocallback",
-		"runtime.asmcgocall",
+		"runtime.systemstack_switch",
 		"runtime.cgocall",
 		"test._Cfunc_callback",
 		"test.nestedCall.func1",
diff --git a/src/runtime/asm_386.s b/src/runtime/asm_386.s
index 3030101f03d..a59054226c1 100644
--- a/src/runtime/asm_386.s
+++ b/src/runtime/asm_386.s
@@ -352,18 +352,12 @@ TEXT runtime·systemstack(SB), NOSPLIT, $0-4
 	// switch stacks
 	// save our state in g->sched. Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOVL	$runtime·systemstack_switch(SB), (g_sched+gobuf_pc)(AX)
-	MOVL	SP, (g_sched+gobuf_sp)(AX)
-	MOVL	AX, (g_sched+gobuf_g)(AX)
+	CALL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	get_tls(CX)
 	MOVL	DX, g(CX)
 	MOVL	(g_sched+gobuf_sp)(DX), BX
-	// make it look like mstart called systemstack on g0, to stop traceback
-	SUBL	$4, BX
-	MOVL	$runtime·mstart(SB), DX
-	MOVL	DX, 0(BX)
 	MOVL	BX, SP
 
 	// call target function
@@ -601,15 +595,18 @@ TEXT runtime·jmpdefer(SB), NOSPLIT, $0-8
 	MOVL	0(DX), BX
 	JMP	BX	// but first run the deferred function
 
-// Save state of caller into g->sched.
-TEXT gosave<>(SB),NOSPLIT,$0
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT,$0
 	PUSHL	AX
 	PUSHL	BX
 	get_tls(BX)
 	MOVL	g(BX), BX
 	LEAL	arg+0(FP), AX
 	MOVL	AX, (g_sched+gobuf_sp)(BX)
-	MOVL	-4(AX), AX
+	MOVL	$runtime·systemstack_switch(SB), AX
 	MOVL	AX, (g_sched+gobuf_pc)(BX)
 	MOVL	$0, (g_sched+gobuf_ret)(BX)
 	// Assert ctxt is zero. See func save.
@@ -661,7 +658,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-12
 	JEQ	noswitch
 	CMPL	DI, m_gsignal(BP)
 	JEQ	noswitch
-	CALL	gosave<>(SB)
+	CALL	gosave_systemstack_switch<>(SB)
 	get_tls(CX)
 	MOVL	SI, g(CX)
 	MOVL	(g_sched+gobuf_sp)(SI), SP
diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 9362ce12137..cd5ce3effbd 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -338,20 +338,12 @@ TEXT runtime·systemstack(SB), NOSPLIT, $0-8
 	// switch stacks
 	// save our state in g->sched. Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOVQ	$runtime·systemstack_switch(SB), SI
-	MOVQ	SI, (g_sched+gobuf_pc)(AX)
-	MOVQ	SP, (g_sched+gobuf_sp)(AX)
-	MOVQ	AX, (g_sched+gobuf_g)(AX)
-	MOVQ	BP, (g_sched+gobuf_bp)(AX)
+	CALL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOVQ	DX, g(CX)
 	MOVQ	DX, R14 // set the g register
 	MOVQ	(g_sched+gobuf_sp)(DX), BX
-	// make it look like mstart called systemstack on g0, to stop traceback
-	SUBQ	$8, BX
-	MOVQ	$runtime·mstart(SB), DX
-	MOVQ	DX, 0(BX)
 	MOVQ	BX, SP
 
 	// call target function
@@ -660,13 +652,17 @@ TEXT runtime·jmpdefer(SB), NOSPLIT, $0-16
 	MOVQ	0(DX), BX
 	JMP	BX	// but first run the deferred function
 
-// Save state of caller into g->sched. Smashes R9.
-TEXT gosave<>(SB),NOSPLIT,$0
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+// Smashes R9.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT,$0
 #ifndef GOEXPERIMENT_REGABI
 	get_tls(R14)
 	MOVQ	g(R14), R14
 #endif
-	MOVQ	0(SP), R9
+	MOVQ	$runtime·systemstack_switch(SB), R9
 	MOVQ	R9, (g_sched+gobuf_pc)(R14)
 	LEAQ	8(SP), R9
 	MOVQ	R9, (g_sched+gobuf_sp)(R14)
@@ -724,7 +720,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 
 	// Switch to system stack.
 	MOVQ	m_g0(R8), SI
-	CALL	gosave<>(SB)
+	CALL	gosave_systemstack_switch<>(SB)
 	MOVQ	SI, g(CX)
 	MOVQ	(g_sched+gobuf_sp)(SI), SP
 
diff --git a/src/runtime/asm_arm.s b/src/runtime/asm_arm.s
index 109030aada4..c8c53e70dba 100644
--- a/src/runtime/asm_arm.s
+++ b/src/runtime/asm_arm.s
@@ -305,24 +305,14 @@ TEXT runtime·systemstack(SB),NOSPLIT,$0-4
 switch:
 	// save our state in g->sched. Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOVW	$runtime·systemstack_switch(SB), R3
-	ADD	$4, R3, R3 // get past push {lr}
-	MOVW	R3, (g_sched+gobuf_pc)(g)
-	MOVW	R13, (g_sched+gobuf_sp)(g)
-	MOVW	LR, (g_sched+gobuf_lr)(g)
-	MOVW	g, (g_sched+gobuf_g)(g)
+	BL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOVW	R0, R5
 	MOVW	R2, R0
 	BL	setg<>(SB)
 	MOVW	R5, R0
-	MOVW	(g_sched+gobuf_sp)(R2), R3
-	// make it look like mstart called systemstack on g0, to stop traceback
-	SUB	$4, R3, R3
-	MOVW	$runtime·mstart(SB), R4
-	MOVW	R4, 0(R3)
-	MOVW	R3, R13
+	MOVW	(g_sched+gobuf_sp)(R2), R13
 
 	// call target function
 	MOVW	R0, R7
@@ -537,19 +527,25 @@ TEXT runtime·jmpdefer(SB),NOSPLIT,$0-8
 	MOVW	0(R7), R1
 	B	(R1)
 
-// Save state of caller into g->sched. Smashes R11.
-TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
-	MOVW	LR, (g_sched+gobuf_pc)(g)
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+// Smashes R11.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
+	MOVW	$runtime·systemstack_switch(SB), R11
+	ADD	$4, R11 // get past push {lr}
+	MOVW	R11, (g_sched+gobuf_pc)(g)
 	MOVW	R13, (g_sched+gobuf_sp)(g)
+	MOVW	g, (g_sched+gobuf_g)(g)
 	MOVW	$0, R11
 	MOVW	R11, (g_sched+gobuf_lr)(g)
 	MOVW	R11, (g_sched+gobuf_ret)(g)
-	MOVW	R11, (g_sched+gobuf_ctxt)(g)
 	// Assert ctxt is zero. See func save.
 	MOVW	(g_sched+gobuf_ctxt)(g), R11
-	CMP	$0, R11
+	TST	R11, R11
 	B.EQ	2(PC)
-	CALL	runtime·badctxt(SB)
+	BL	runtime·badctxt(SB)
 	RET
 
 // func asmcgocall_no_g(fn, arg unsafe.Pointer)
@@ -590,7 +586,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-12
 	MOVW	m_g0(R8), R3
 	CMP	R3, g
 	BEQ	nosave
-	BL	gosave<>(SB)
+	BL	gosave_systemstack_switch<>(SB)
 	MOVW	R0, R5
 	MOVW	R3, R0
 	BL	setg<>(SB)
diff --git a/src/runtime/asm_arm64.s b/src/runtime/asm_arm64.s
index 79efd4cb17a..31a6fe57b9b 100644
--- a/src/runtime/asm_arm64.s
+++ b/src/runtime/asm_arm64.s
@@ -205,24 +205,12 @@ TEXT runtime·systemstack(SB), NOSPLIT, $0-8
 switch:
 	// save our state in g->sched. Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOVD	$runtime·systemstack_switch(SB), R6
-	ADD	$8, R6	// get past prologue
-	MOVD	R6, (g_sched+gobuf_pc)(g)
-	MOVD	RSP, R0
-	MOVD	R0, (g_sched+gobuf_sp)(g)
-	MOVD	R29, (g_sched+gobuf_bp)(g)
-	MOVD	$0, (g_sched+gobuf_lr)(g)
-	MOVD	g, (g_sched+gobuf_g)(g)
+	BL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOVD	R5, g
 	BL	runtime·save_g(SB)
 	MOVD	(g_sched+gobuf_sp)(g), R3
-	// make it look like mstart called systemstack on g0, to stop traceback
-	SUB	$16, R3
-	AND	$~15, R3
-	MOVD	$runtime·mstart(SB), R4
-	MOVD	R4, 0(R3)
 	MOVD	R3, RSP
 	MOVD	(g_sched+gobuf_bp)(g), R29
 
@@ -859,14 +847,21 @@ TEXT runtime·jmpdefer(SB), NOSPLIT|NOFRAME, $0-16
 	MOVD	0(R26), R3
 	B	(R3)
 
-// Save state of caller into g->sched. Smashes R0.
-TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
-	MOVD	LR, (g_sched+gobuf_pc)(g)
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+// Smashes R0.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
+	MOVD	$runtime·systemstack_switch(SB), R0
+	ADD	$8, R0	// get past prologue
+	MOVD	R0, (g_sched+gobuf_pc)(g)
 	MOVD	RSP, R0
 	MOVD	R0, (g_sched+gobuf_sp)(g)
 	MOVD	R29, (g_sched+gobuf_bp)(g)
 	MOVD	$0, (g_sched+gobuf_lr)(g)
 	MOVD	$0, (g_sched+gobuf_ret)(g)
+	MOVD	g, (g_sched+gobuf_g)(g)
 	// Assert ctxt is zero. See func save.
 	MOVD	(g_sched+gobuf_ctxt)(g), R0
 	CBZ	R0, 2(PC)
@@ -908,8 +903,8 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 	BEQ	nosave
 
 	// Switch to system stack.
-	MOVD	R0, R9	// gosave<> and save_g might clobber R0
-	BL	gosave<>(SB)
+	MOVD	R0, R9	// gosave_systemstack_switch<> and save_g might clobber R0
+	BL	gosave_systemstack_switch<>(SB)
 	MOVD	R3, g
 	BL	runtime·save_g(SB)
 	MOVD	(g_sched+gobuf_sp)(g), R0
diff --git a/src/runtime/asm_mips64x.s b/src/runtime/asm_mips64x.s
index 6e1d25cd90c..75bb2230664 100644
--- a/src/runtime/asm_mips64x.s
+++ b/src/runtime/asm_mips64x.s
@@ -169,21 +169,12 @@ TEXT runtime·systemstack(SB), NOSPLIT, $0-8
 switch:
 	// save our state in g->sched. Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOVV	$runtime·systemstack_switch(SB), R4
-	ADDV	$8, R4	// get past prologue
-	MOVV	R4, (g_sched+gobuf_pc)(g)
-	MOVV	R29, (g_sched+gobuf_sp)(g)
-	MOVV	R0, (g_sched+gobuf_lr)(g)
-	MOVV	g, (g_sched+gobuf_g)(g)
+	JAL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOVV	R3, g
 	JAL	runtime·save_g(SB)
 	MOVV	(g_sched+gobuf_sp)(g), R1
-	// make it look like mstart called systemstack on g0, to stop traceback
-	ADDV	$-8, R1
-	MOVV	$runtime·mstart(SB), R2
-	MOVV	R2, 0(R1)
 	MOVV	R1, R29
 
 	// call target function
@@ -401,12 +392,19 @@ TEXT runtime·jmpdefer(SB), NOSPLIT|NOFRAME, $0-16
 	MOVV	0(REGCTXT), R4
 	JMP	(R4)
 
-// Save state of caller into g->sched. Smashes R1.
-TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
-	MOVV	R31, (g_sched+gobuf_pc)(g)
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+// Smashes R1.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
+	MOVV	$runtime·systemstack_switch(SB), R1
+	ADDV	$8, R1	// get past prologue
+	MOVV	R1, (g_sched+gobuf_pc)(g)
 	MOVV	R29, (g_sched+gobuf_sp)(g)
 	MOVV	R0, (g_sched+gobuf_lr)(g)
 	MOVV	R0, (g_sched+gobuf_ret)(g)
+	MOVV	g, (g_sched+gobuf_g)(g)
 	// Assert ctxt is zero. See func save.
 	MOVV	(g_sched+gobuf_ctxt)(g), R1
 	BEQ	R1, 2(PC)
@@ -440,7 +438,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 	MOVV	m_g0(R5), R6
 	BEQ	R6, g, g0
 
-	JAL	gosave<>(SB)
+	JAL	gosave_systemstack_switch<>(SB)
 	MOVV	R6, g
 	JAL	runtime·save_g(SB)
 	MOVV	(g_sched+gobuf_sp)(g), R29
diff --git a/src/runtime/asm_mipsx.s b/src/runtime/asm_mipsx.s
index 8e5753d2557..341da8e8d71 100644
--- a/src/runtime/asm_mipsx.s
+++ b/src/runtime/asm_mipsx.s
@@ -170,21 +170,12 @@ TEXT runtime·systemstack(SB),NOSPLIT,$0-4
 switch:
 	// save our state in g->sched.  Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOVW	$runtime·systemstack_switch(SB), R4
-	ADDU	$8, R4	// get past prologue
-	MOVW	R4, (g_sched+gobuf_pc)(g)
-	MOVW	R29, (g_sched+gobuf_sp)(g)
-	MOVW	R0, (g_sched+gobuf_lr)(g)
-	MOVW	g, (g_sched+gobuf_g)(g)
+	JAL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOVW	R3, g
 	JAL	runtime·save_g(SB)
 	MOVW	(g_sched+gobuf_sp)(g), R1
-	// make it look like mstart called systemstack on g0, to stop traceback
-	ADDU	$-4, R1
-	MOVW	$runtime·mstart(SB), R2
-	MOVW	R2, 0(R1)
 	MOVW	R1, R29
 
 	// call target function
@@ -401,12 +392,19 @@ TEXT runtime·jmpdefer(SB),NOSPLIT,$0-8
 	MOVW	0(REGCTXT), R4
 	JMP	(R4)
 
-// Save state of caller into g->sched. Smashes R1.
-TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
-	MOVW	R31, (g_sched+gobuf_pc)(g)
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+// Smashes R1.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
+	MOVW	$runtime·systemstack_switch(SB), R1
+	ADDU	$8, R1	// get past prologue
+	MOVW	R1, (g_sched+gobuf_pc)(g)
 	MOVW	R29, (g_sched+gobuf_sp)(g)
 	MOVW	R0, (g_sched+gobuf_lr)(g)
 	MOVW	R0, (g_sched+gobuf_ret)(g)
+	MOVW	g, (g_sched+gobuf_g)(g)
 	// Assert ctxt is zero. See func save.
 	MOVW	(g_sched+gobuf_ctxt)(g), R1
 	BEQ	R1, 2(PC)
@@ -431,7 +429,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-12
 	MOVW	m_g0(R5), R6
 	BEQ	R6, g, g0
 
-	JAL	gosave<>(SB)
+	JAL	gosave_systemstack_switch<>(SB)
 	MOVW	R6, g
 	JAL	runtime·save_g(SB)
 	MOVW	(g_sched+gobuf_sp)(g), R29
diff --git a/src/runtime/asm_ppc64x.s b/src/runtime/asm_ppc64x.s
index 834023cce19..a99a61fd88a 100644
--- a/src/runtime/asm_ppc64x.s
+++ b/src/runtime/asm_ppc64x.s
@@ -229,22 +229,12 @@ TEXT runtime·systemstack(SB), NOSPLIT, $0-8
 switch:
 	// save our state in g->sched. Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOVD	$runtime·systemstack_switch(SB), R6
-	ADD     $16, R6 // get past prologue (including r2-setting instructions when they're there)
-	MOVD	R6, (g_sched+gobuf_pc)(g)
-	MOVD	R1, (g_sched+gobuf_sp)(g)
-	MOVD	R0, (g_sched+gobuf_lr)(g)
-	MOVD	g, (g_sched+gobuf_g)(g)
+	BL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOVD	R5, g
 	BL	runtime·save_g(SB)
-	MOVD	(g_sched+gobuf_sp)(g), R3
-	// make it look like mstart called systemstack on g0, to stop traceback
-	SUB	$FIXED_FRAME, R3
-	MOVD	$runtime·mstart(SB), R4
-	MOVD	R4, 0(R3)
-	MOVD	R3, R1
+	MOVD	(g_sched+gobuf_sp)(g), R1
 
 	// call target function
 	MOVD	0(R11), R12	// code pointer
@@ -534,13 +524,19 @@ TEXT runtime·jmpdefer(SB), NOSPLIT|NOFRAME, $0-16
 	MOVD	R12, CTR
 	BR	(CTR)
 
-// Save state of caller into g->sched. Smashes R31.
-TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
-	MOVD	LR, R31
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+// Smashes R31.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
+	MOVD	$runtime·systemstack_switch(SB), R31
+	ADD     $16, R31 // get past prologue (including r2-setting instructions when they're there)
 	MOVD	R31, (g_sched+gobuf_pc)(g)
 	MOVD	R1, (g_sched+gobuf_sp)(g)
 	MOVD	R0, (g_sched+gobuf_lr)(g)
 	MOVD	R0, (g_sched+gobuf_ret)(g)
+	MOVD	g, (g_sched+gobuf_g)(g)
 	// Assert ctxt is zero. See func save.
 	MOVD	(g_sched+gobuf_ctxt)(g), R31
 	CMP	R0, R31
@@ -577,7 +573,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 	MOVD	m_g0(R8), R6
 	CMP	R6, g
 	BEQ	g0
-	BL	gosave<>(SB)
+	BL	gosave_systemstack_switch<>(SB)
 	MOVD	R6, g
 	BL	runtime·save_g(SB)
 	MOVD	(g_sched+gobuf_sp)(g), R1
diff --git a/src/runtime/asm_riscv64.s b/src/runtime/asm_riscv64.s
index 3d0349471a2..fb7c6530dcd 100644
--- a/src/runtime/asm_riscv64.s
+++ b/src/runtime/asm_riscv64.s
@@ -114,21 +114,12 @@ TEXT runtime·systemstack(SB), NOSPLIT, $0-8
 switch:
 	// save our state in g->sched. Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOV	$runtime·systemstack_switch(SB), T2
-	ADD	$8, T2	// get past prologue
-	MOV	T2, (g_sched+gobuf_pc)(g)
-	MOV	X2, (g_sched+gobuf_sp)(g)
-	MOV	ZERO, (g_sched+gobuf_lr)(g)
-	MOV	g, (g_sched+gobuf_g)(g)
+	CALL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOV	T1, g
 	CALL	runtime·save_g(SB)
 	MOV	(g_sched+gobuf_sp)(g), T0
-	// make it look like mstart called systemstack on g0, to stop traceback
-	ADD	$-8, T0
-	MOV	$runtime·mstart(SB), T1
-	MOV	T1, 0(T0)
 	MOV	T0, X2
 
 	// call target function
@@ -297,12 +288,19 @@ TEXT runtime·mcall(SB), NOSPLIT|NOFRAME, $0-8
 	JALR	RA, T1
 	JMP	runtime·badmcall2(SB)
 
-// Save state of caller into g->sched. Smashes X31.
-TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
-	MOV	X1, (g_sched+gobuf_pc)(g)
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+// Smashes X31.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
+	MOV	$runtime·systemstack_switch(SB), X31
+	ADD	$8, X31	// get past prologue
+	MOV	X31, (g_sched+gobuf_pc)(g)
 	MOV	X2, (g_sched+gobuf_sp)(g)
 	MOV	ZERO, (g_sched+gobuf_lr)(g)
 	MOV	ZERO, (g_sched+gobuf_ret)(g)
+	MOV	g, (g_sched+gobuf_g)(g)
 	// Assert ctxt is zero. See func save.
 	MOV	(g_sched+gobuf_ctxt)(g), X31
 	BEQ	ZERO, X31, 2(PC)
@@ -327,7 +325,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 	MOV	m_g0(X6), X7
 	BEQ	X7, g, g0
 
-	CALL	gosave<>(SB)
+	CALL	gosave_systemstack_switch<>(SB)
 	MOV	X7, g
 	CALL	runtime·save_g(SB)
 	MOV	(g_sched+gobuf_sp)(g), X2
diff --git a/src/runtime/asm_s390x.s b/src/runtime/asm_s390x.s
index fbd185c3533..43244d961fb 100644
--- a/src/runtime/asm_s390x.s
+++ b/src/runtime/asm_s390x.s
@@ -256,22 +256,12 @@ TEXT runtime·systemstack(SB), NOSPLIT, $0-8
 switch:
 	// save our state in g->sched.  Pretend to
 	// be systemstack_switch if the G stack is scanned.
-	MOVD	$runtime·systemstack_switch(SB), R6
-	ADD	$16, R6	// get past prologue
-	MOVD	R6, (g_sched+gobuf_pc)(g)
-	MOVD	R15, (g_sched+gobuf_sp)(g)
-	MOVD	$0, (g_sched+gobuf_lr)(g)
-	MOVD	g, (g_sched+gobuf_g)(g)
+	BL	gosave_systemstack_switch<>(SB)
 
 	// switch to g0
 	MOVD	R5, g
 	BL	runtime·save_g(SB)
-	MOVD	(g_sched+gobuf_sp)(g), R3
-	// make it look like mstart called systemstack on g0, to stop traceback
-	SUB	$8, R3
-	MOVD	$runtime·mstart(SB), R4
-	MOVD	R4, 0(R3)
-	MOVD	R3, R15
+	MOVD	(g_sched+gobuf_sp)(g), R15
 
 	// call target function
 	MOVD	0(R12), R3	// code pointer
@@ -498,12 +488,19 @@ TEXT runtime·jmpdefer(SB),NOSPLIT|NOFRAME,$0-16
 	MOVD	0(R12), R3
 	BR	(R3)
 
-// Save state of caller into g->sched. Smashes R1.
-TEXT gosave<>(SB),NOSPLIT|NOFRAME,$0
-	MOVD	LR, (g_sched+gobuf_pc)(g)
+// Save state of caller into g->sched,
+// but using fake PC from systemstack_switch.
+// Must only be called from functions with no locals ($0)
+// or else unwinding from systemstack_switch is incorrect.
+// Smashes R1.
+TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
+	MOVD	$runtime·systemstack_switch(SB), R1
+	ADD	$16, R1	// get past prologue
+	MOVD	R1, (g_sched+gobuf_pc)(g)
 	MOVD	R15, (g_sched+gobuf_sp)(g)
 	MOVD	$0, (g_sched+gobuf_lr)(g)
 	MOVD	$0, (g_sched+gobuf_ret)(g)
+	MOVD	g, (g_sched+gobuf_g)(g)
 	// Assert ctxt is zero. See func save.
 	MOVD	(g_sched+gobuf_ctxt)(g), R1
 	CMPBEQ	R1, $0, 2(PC)
@@ -529,7 +526,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 	MOVD	g_m(g), R6
 	MOVD	m_g0(R6), R6
 	CMPBEQ	R6, g, g0
-	BL	gosave<>(SB)
+	BL	gosave_systemstack_switch<>(SB)
 	MOVD	R6, g
 	BL	runtime·save_g(SB)
 	MOVD	(g_sched+gobuf_sp)(g), R15
diff --git a/src/runtime/sys_windows_386.s b/src/runtime/sys_windows_386.s
index c556e3a3c25..576dd287719 100644
--- a/src/runtime/sys_windows_386.s
+++ b/src/runtime/sys_windows_386.s
@@ -94,7 +94,7 @@ TEXT sigtramp<>(SB),NOSPLIT,$0-0
 	JNE	2(PC)
 	CALL	runtime·badsignal2(SB)
 
-	// save g and SP in case of stack switch
+	// save g in case of stack switch
 	MOVL	DX, 32(SP)	// g
 	MOVL	SP, 36(SP)
 
@@ -108,13 +108,9 @@ TEXT sigtramp<>(SB),NOSPLIT,$0-0
 	get_tls(BP)
 	MOVL	BX, g(BP)
 	MOVL	(g_sched+gobuf_sp)(BX), DI
-	// make it look like mstart called us on g0, to stop traceback
-	SUBL	$4, DI
-	MOVL	$runtime·mstart(SB), 0(DI)
-	// traceback will think that we've done SUBL
-	// on this stack, so subtract them here to match.
-	// (we need room for sighandler arguments anyway).
+	// make room for sighandler arguments
 	// and re-save old SP for restoring later.
+	// (note that the 36(DI) here must match the 36(SP) above.)
 	SUBL	$40, DI
 	MOVL	SP, 36(DI)
 	MOVL	DI, SP
@@ -132,7 +128,7 @@ g0:
 	// switch back to original stack and g
 	// no-op if we never left.
 	MOVL	36(SP), SP
-	MOVL	32(SP), DX
+	MOVL	32(SP), DX	// note: different SP
 	get_tls(BP)
 	MOVL	DX, g(BP)
 
diff --git a/src/runtime/sys_windows_amd64.s b/src/runtime/sys_windows_amd64.s
index 9cd14016b01..6f2abb5444b 100644
--- a/src/runtime/sys_windows_amd64.s
+++ b/src/runtime/sys_windows_amd64.s
@@ -151,16 +151,10 @@ TEXT sigtramp<>(SB),NOSPLIT|NOFRAME,$0-0
 	get_tls(BP)
 	MOVQ	BX, g(BP)
 	MOVQ	(g_sched+gobuf_sp)(BX), DI
-	// make it look like mstart called us on g0, to stop traceback
-	SUBQ	$8, DI
-	MOVQ	$runtime·mstart(SB), SI
-	MOVQ	SI, 0(DI)
-	// traceback will think that we've done PUSHFQ and SUBQ
-	// on this stack, so subtract them here to match.
-	// (we need room for sighandler arguments anyway).
+	// make room for sighandler arguments
 	// and re-save old SP for restoring later.
-	SUBQ	$(112+8), DI
-	// save g, save old stack pointer.
+	// (note that the 104(DI) here must match the 104(SP) above.)
+	SUBQ	$120, DI
 	MOVQ	SP, 104(DI)
 	MOVQ	DI, SP
 
diff --git a/src/runtime/sys_windows_arm.s b/src/runtime/sys_windows_arm.s
index d2bdc50e3b6..7d134dd3f41 100644
--- a/src/runtime/sys_windows_arm.s
+++ b/src/runtime/sys_windows_arm.s
@@ -6,6 +6,8 @@
 #include "go_tls.h"
 #include "textflag.h"
 
+// Note: For system ABI, R0-R3 are args, R4-R11 are callee-save.
+
 // void runtime·asmstdcall(void *c);
 TEXT runtime·asmstdcall(SB),NOSPLIT|NOFRAME,$0
 	MOVM.DB.W [R4, R5, R14], (R13)	// push {r4, r5, lr}
@@ -139,11 +141,10 @@ TEXT sigtramp<>(SB),NOSPLIT|NOFRAME,$0
 	MOVW	(g_sched+gobuf_sp)(g), R3	// R3 = g->gobuf.sp
 	BL      runtime·save_g(SB)
 
-	// traceback will think that we've done PUSH and SUB
-	// on this stack, so subtract them here to match.
-	// (we need room for sighandler arguments anyway).
+	// make room for sighandler arguments
 	// and re-save old SP for restoring later.
-	SUB	$(40+8+20), R3
+	// (note that the 24(R3) here must match the 24(R13) above.)
+	SUB	$40, R3
 	MOVW	R13, 24(R3)		// save old stack pointer
 	MOVW	R3, R13			// switch stack
 
@@ -151,22 +152,14 @@ g0:
 	MOVW	0(R6), R2	// R2 = ExceptionPointers->ExceptionRecord
 	MOVW	4(R6), R3	// R3 = ExceptionPointers->ContextRecord
 
-	// make it look like mstart called us on g0, to stop traceback
-	MOVW    $runtime·mstart(SB), R4
-
-	MOVW	R4, 0(R13)	// Save link register for traceback
+	MOVW	$0, R4
+	MOVW	R4, 0(R13)	// No saved link register.
 	MOVW	R2, 4(R13)	// Move arg0 (ExceptionRecord) into position
 	MOVW	R3, 8(R13)	// Move arg1 (ContextRecord) into position
 	MOVW	R5, 12(R13)	// Move arg2 (original g) into position
 	BL	(R7)		// Call the go routine
 	MOVW	16(R13), R4	// Fetch return value from stack
 
-	// Compute the value of the g0 stack pointer after deallocating
-	// this frame, then allocating 8 bytes. We may need to store
-	// the resume SP and PC on the g0 stack to work around
-	// control flow guard when we resume from the exception.
-	ADD	$(40+20), R13, R12
-
 	// switch back to original stack and g
 	MOVW	24(R13), R13
 	MOVW	20(R13), g
@@ -192,33 +185,36 @@ done:
 	// If returntramp has already been set up by a previous exception
 	// handler, don't clobber the stored SP and PC on the stack.
 	MOVW	4(R3), R3			// PEXCEPTION_POINTERS->Context
-	MOVW	0x40(R3), R2			// load PC from context record
+	MOVW	context_pc(R3), R2		// load PC from context record
 	MOVW	$returntramp<>(SB), R1
 	CMP	R1, R2
 	B.EQ	return				// do not clobber saved SP/PC
 
-	// Save resume SP and PC on g0 stack
-	MOVW	0x38(R3), R2			// load SP from context record
-	MOVW	R2, 0(R12)			// Store resume SP on g0 stack
-	MOVW	0x40(R3), R2			// load PC from context record
-	MOVW	R2, 4(R12)			// Store resume PC on g0 stack
+	// Save resume SP and PC into R0, R1.
+	MOVW	context_spr(R3), R2
+	MOVW	R2, context_r0(R3)
+	MOVW	context_pc(R3), R2
+	MOVW	R2, context_r1(R3)
 
 	// Set up context record to return to returntramp on g0 stack
-	MOVW	R12, 0x38(R3)			// save g0 stack pointer
-						// in context record
-	MOVW	$returntramp<>(SB), R2	// save resume address
-	MOVW	R2, 0x40(R3)			// in context record
+	MOVW	R12, context_spr(R3)
+	MOVW	$returntramp<>(SB), R2
+	MOVW	R2, context_pc(R3)
 
 return:
 	B	(R14)				// return
 
-//
 // Trampoline to resume execution from exception handler.
 // This is part of the control flow guard workaround.
 // It switches stacks and jumps to the continuation address.
-//
+// R0 and R1 are set above at the end of sigtramp<>
+// in the context that starts executing at returntramp<>.
 TEXT returntramp<>(SB),NOSPLIT|NOFRAME,$0
-	MOVM.IA	(R13), [R13, R15]		// ldm sp, [sp, pc]
+	// Important: do not smash LR,
+	// which is set to a live value when handling
+	// a signal by pushing a call to sigpanic onto the stack.
+	MOVW	R0, R13
+	B	(R1)
 
 TEXT runtime·exceptiontramp(SB),NOSPLIT|NOFRAME,$0
 	MOVW	$runtime·exceptionhandler(SB), R1