[dev.regabi] reflect: support for register ABI on amd64 for reflect.(Value).Call

This change adds support for the new register ABI on amd64 to
reflect.(Value).Call. If internal/abi's register counts are non-zero,
reflect will try to set up arguments in registers on the Call path.

Note that because the register ABI becomes ABI0 with zero registers
available, this should keep working as it did before.

This change does not add any tests for the register ABI case because
there's no way to do so at the moment.

For #40724.

Change-Id: I8aa089a5aa5a31b72e56b3d9388dd3f82203985b
Reviewed-on: https://go-review.googlesource.com/c/go/+/272568
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

15 files changed, 274 insertions, 131 deletions

diff --git a/src/runtime/asm_386.s b/src/runtime/asm_386.s
index 429f3fef82..471451df28 100644
--- a/src/runtime/asm_386.s
+++ b/src/runtime/asm_386.s
@@ -458,7 +458,7 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0
 	JMP runtime·morestack(SB)
 
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 // Caution: ugly multiline assembly macros in your future!
@@ -470,8 +470,8 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0
 	JMP	AX
 // Note: can't just "JMP NAME(SB)" - bad inlining results.
 
-TEXT ·reflectcall(SB), NOSPLIT, $0-20
-	MOVL	argsize+12(FP), CX
+TEXT ·reflectcall(SB), NOSPLIT, $0-28
+	MOVL	frameSize+20(FP), CX
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
 	DISPATCH(runtime·call64, 64)
@@ -503,11 +503,11 @@ TEXT ·reflectcall(SB), NOSPLIT, $0-20
 	JMP	AX
 
 #define CALLFN(NAME,MAXSIZE)			\
-TEXT NAME(SB), WRAPPER, $MAXSIZE-20;		\
+TEXT NAME(SB), WRAPPER, $MAXSIZE-28;		\
 	NO_LOCAL_POINTERS;			\
 	/* copy arguments to stack */		\
-	MOVL	argptr+8(FP), SI;		\
-	MOVL	argsize+12(FP), CX;		\
+	MOVL	stackArgs+8(FP), SI;		\
+	MOVL	stackArgsSize+12(FP), CX;		\
 	MOVL	SP, DI;				\
 	REP;MOVSB;				\
 	/* call function */			\
@@ -516,10 +516,10 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-20;		\
 	PCDATA  $PCDATA_StackMapIndex, $0;	\
 	CALL	AX;				\
 	/* copy return values back */		\
-	MOVL	argtype+0(FP), DX;		\
-	MOVL	argptr+8(FP), DI;		\
-	MOVL	argsize+12(FP), CX;		\
-	MOVL	retoffset+16(FP), BX;		\
+	MOVL	stackArgsType+0(FP), DX;		\
+	MOVL	stackArgs+8(FP), DI;		\
+	MOVL	stackArgsSize+12(FP), CX;		\
+	MOVL	stackRetOffset+16(FP), BX;		\
 	MOVL	SP, SI;				\
 	ADDL	BX, DI;				\
 	ADDL	BX, SI;				\
@@ -531,11 +531,12 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-20;		\
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $16-0
+TEXT callRet<>(SB), NOSPLIT, $20-0
 	MOVL	DX, 0(SP)
 	MOVL	DI, 4(SP)
 	MOVL	SI, 8(SP)
 	MOVL	CX, 12(SP)
+	MOVL	$0, 16(SP)
 	CALL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 93280eee4a..5e1ed9b2ad 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -445,8 +445,74 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0
 	MOVL	$0, DX
 	JMP	runtime·morestack(SB)
 
+#ifdef GOEXPERIMENT_REGABI
+// spillArgs stores return values from registers to a *internal/abi.RegArgs in R12.
+TEXT spillArgs<>(SB),NOSPLIT,$0-0
+	MOVQ AX, 0(R12)
+	MOVQ BX, 8(R12)
+	MOVQ CX, 16(R12)
+	MOVQ DI, 24(R12)
+	MOVQ SI, 32(R12)
+	MOVQ R8, 40(R12)
+	MOVQ R9, 48(R12)
+	MOVQ R10, 56(R12)
+	MOVQ R11, 64(R12)
+	MOVQ X0, 72(R12)
+	MOVQ X1, 80(R12)
+	MOVQ X2, 88(R12)
+	MOVQ X3, 96(R12)
+	MOVQ X4, 104(R12)
+	MOVQ X5, 112(R12)
+	MOVQ X6, 120(R12)
+	MOVQ X7, 128(R12)
+	MOVQ X8, 136(R12)
+	MOVQ X9, 144(R12)
+	MOVQ X10, 152(R12)
+	MOVQ X11, 160(R12)
+	MOVQ X12, 168(R12)
+	MOVQ X13, 176(R12)
+	MOVQ X14, 184(R12)
+	RET
+
+// unspillArgs loads args into registers from a *internal/abi.RegArgs in R12.
+TEXT unspillArgs<>(SB),NOSPLIT,$0-0
+	MOVQ 0(R12), AX
+	MOVQ 8(R12), BX
+	MOVQ 16(R12), CX
+	MOVQ 24(R12), DI
+	MOVQ 32(R12), SI
+	MOVQ 40(R12), R8
+	MOVQ 48(R12), R9
+	MOVQ 56(R12), R10
+	MOVQ 64(R12), R11
+	MOVQ 72(R12), X0
+	MOVQ 80(R12), X1
+	MOVQ 88(R12), X2
+	MOVQ 96(R12), X3
+	MOVQ 104(R12), X4
+	MOVQ 112(R12), X5
+	MOVQ 120(R12), X6
+	MOVQ 128(R12), X7
+	MOVQ 136(R12), X8
+	MOVQ 144(R12), X9
+	MOVQ 152(R12), X10
+	MOVQ 160(R12), X11
+	MOVQ 168(R12), X12
+	MOVQ 176(R12), X13
+	MOVQ 184(R12), X14
+	RET
+#else
+// spillArgs stores return values from registers to a pointer in R12.
+TEXT spillArgs<>(SB),NOSPLIT,$0-0
+	RET
+
+// unspillArgs loads args into registers from a pointer in R12.
+TEXT unspillArgs<>(SB),NOSPLIT,$0-0
+	RET
+#endif
+
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 // Caution: ugly multiline assembly macros in your future!
@@ -458,8 +524,8 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0
 	JMP	AX
 // Note: can't just "JMP NAME(SB)" - bad inlining results.
 
-TEXT ·reflectcall<ABIInternal>(SB), NOSPLIT, $0-32
-	MOVLQZX argsize+24(FP), CX
+TEXT ·reflectcall<ABIInternal>(SB), NOSPLIT, $0-48
+	MOVLQZX frameSize+32(FP), CX
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
 	DISPATCH(runtime·call64, 64)
@@ -491,23 +557,28 @@ TEXT ·reflectcall<ABIInternal>(SB), NOSPLIT, $0-32
 	JMP	AX
 
 #define CALLFN(NAME,MAXSIZE)			\
-TEXT NAME(SB), WRAPPER, $MAXSIZE-32;		\
+TEXT NAME(SB), WRAPPER, $MAXSIZE-48;		\
 	NO_LOCAL_POINTERS;			\
 	/* copy arguments to stack */		\
-	MOVQ	argptr+16(FP), SI;		\
-	MOVLQZX argsize+24(FP), CX;		\
+	MOVQ	stackArgs+16(FP), SI;		\
+	MOVLQZX stackArgsSize+24(FP), CX;		\
 	MOVQ	SP, DI;				\
 	REP;MOVSB;				\
+	/* set up argument registers */		\
+	MOVQ    regArgs+40(FP), R12;		\
+	CALL    unspillArgs<>(SB);		\
 	/* call function */			\
 	MOVQ	f+8(FP), DX;			\
 	PCDATA  $PCDATA_StackMapIndex, $0;	\
-	MOVQ	(DX), AX;			\
-	CALL	AX;				\
-	/* copy return values back */		\
-	MOVQ	argtype+0(FP), DX;		\
-	MOVQ	argptr+16(FP), DI;		\
-	MOVLQZX	argsize+24(FP), CX;		\
-	MOVLQZX	retoffset+28(FP), BX;		\
+	MOVQ	(DX), R12;			\
+	CALL	R12;				\
+	/* copy register return values back */		\
+	MOVQ    regArgs+40(FP), R12;		\
+	CALL    spillArgs<>(SB);		\
+	MOVLQZX	stackArgsSize+24(FP), CX;		\
+	MOVLQZX	stackRetOffset+28(FP), BX;		\
+	MOVQ	stackArgs+16(FP), DI;		\
+	MOVQ	stackArgsType+0(FP), DX;		\
 	MOVQ	SP, SI;				\
 	ADDQ	BX, DI;				\
 	ADDQ	BX, SI;				\
@@ -519,12 +590,13 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-32;		\
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $32-0
+TEXT callRet<>(SB), NOSPLIT, $40-0
 	NO_LOCAL_POINTERS
 	MOVQ	DX, 0(SP)
 	MOVQ	DI, 8(SP)
 	MOVQ	SI, 16(SP)
 	MOVQ	CX, 24(SP)
+	MOVQ	R12, 32(SP)
 	CALL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_arm.s b/src/runtime/asm_arm.s
index 8eec84d3f2..23619b1408 100644
--- a/src/runtime/asm_arm.s
+++ b/src/runtime/asm_arm.s
@@ -404,7 +404,7 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	B runtime·morestack(SB)
 
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 // Caution: ugly multiline assembly macros in your future!
@@ -415,8 +415,8 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	MOVW	$NAME(SB), R1;		\
 	B	(R1)
 
-TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-20
-	MOVW	argsize+12(FP), R0
+TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-28
+	MOVW	frameSize+20(FP), R0
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
 	DISPATCH(runtime·call64, 64)
@@ -448,11 +448,11 @@ TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-20
 	B	(R1)
 
 #define CALLFN(NAME,MAXSIZE)			\
-TEXT NAME(SB), WRAPPER, $MAXSIZE-20;		\
+TEXT NAME(SB), WRAPPER, $MAXSIZE-28;		\
 	NO_LOCAL_POINTERS;			\
 	/* copy arguments to stack */		\
-	MOVW	argptr+8(FP), R0;		\
-	MOVW	argsize+12(FP), R2;		\
+	MOVW	stackArgs+8(FP), R0;		\
+	MOVW	stackArgsSize+12(FP), R2;		\
 	ADD	$4, R13, R1;			\
 	CMP	$0, R2;				\
 	B.EQ	5(PC);				\
@@ -466,10 +466,10 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-20;		\
 	PCDATA  $PCDATA_StackMapIndex, $0;	\
 	BL	(R0);				\
 	/* copy return values back */		\
-	MOVW	argtype+0(FP), R4;		\
-	MOVW	argptr+8(FP), R0;		\
-	MOVW	argsize+12(FP), R2;		\
-	MOVW	retoffset+16(FP), R3;		\
+	MOVW	stackArgsType+0(FP), R4;		\
+	MOVW	stackArgs+8(FP), R0;		\
+	MOVW	stackArgsSize+12(FP), R2;		\
+	MOVW	stackArgsRetOffset+16(FP), R3;		\
 	ADD	$4, R13, R1;			\
 	ADD	R3, R1;				\
 	ADD	R3, R0;				\
@@ -481,11 +481,13 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-20;		\
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $16-0
+TEXT callRet<>(SB), NOSPLIT, $20-0
 	MOVW	R4, 4(R13)
 	MOVW	R0, 8(R13)
 	MOVW	R1, 12(R13)
 	MOVW	R2, 16(R13)
+	MOVW	$0, R7
+	MOVW	R7, 20(R13)
 	BL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_arm64.s b/src/runtime/asm_arm64.s
index 8e4a1f74f9..0ab92be1e4 100644
--- a/src/runtime/asm_arm64.s
+++ b/src/runtime/asm_arm64.s
@@ -312,7 +312,7 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	B runtime·morestack(SB)
 
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 // Caution: ugly multiline assembly macros in your future!
@@ -325,8 +325,8 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	B	(R27)
 // Note: can't just "B NAME(SB)" - bad inlining results.
 
-TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
-	MOVWU argsize+24(FP), R16
+TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-48
+	MOVWU	frameSize+32(FP), R16
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
 	DISPATCH(runtime·call64, 64)
@@ -358,11 +358,11 @@ TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
 	B	(R0)
 
 #define CALLFN(NAME,MAXSIZE)			\
-TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
+TEXT NAME(SB), WRAPPER, $MAXSIZE-48;		\
 	NO_LOCAL_POINTERS;			\
 	/* copy arguments to stack */		\
-	MOVD	arg+16(FP), R3;			\
-	MOVWU	argsize+24(FP), R4;		\
+	MOVD	stackArgs+16(FP), R3;			\
+	MOVWU	stackArgsSize+24(FP), R4;		\
 	ADD	$8, RSP, R5;			\
 	BIC	$0xf, R4, R6;			\
 	CBZ	R6, 6(PC);			\
@@ -388,10 +388,10 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
 	PCDATA  $PCDATA_StackMapIndex, $0;	\
 	BL	(R0);				\
 	/* copy return values back */		\
-	MOVD	argtype+0(FP), R7;		\
-	MOVD	arg+16(FP), R3;			\
-	MOVWU	n+24(FP), R4;			\
-	MOVWU	retoffset+28(FP), R6;		\
+	MOVD	stackArgsType+0(FP), R7;		\
+	MOVD	stackArgs+16(FP), R3;			\
+	MOVWU	stackArgsSize+24(FP), R4;			\
+	MOVWU	stackRetOffset+28(FP), R6;		\
 	ADD	$8, RSP, R5;			\
 	ADD	R6, R5; 			\
 	ADD	R6, R3;				\
@@ -403,11 +403,12 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $40-0
+TEXT callRet<>(SB), NOSPLIT, $48-0
 	MOVD	R7, 8(RSP)
 	MOVD	R3, 16(RSP)
 	MOVD	R5, 24(RSP)
 	MOVD	R4, 32(RSP)
+	MOVD	$0, 40(RSP)
 	BL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_mips64x.s b/src/runtime/asm_mips64x.s
index 054a89dc37..694950663a 100644
--- a/src/runtime/asm_mips64x.s
+++ b/src/runtime/asm_mips64x.s
@@ -264,7 +264,7 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	JMP	runtime·morestack(SB)
 
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 // Caution: ugly multiline assembly macros in your future!
@@ -277,8 +277,8 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	JMP	(R4)
 // Note: can't just "BR NAME(SB)" - bad inlining results.
 
-TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
-	MOVWU argsize+24(FP), R1
+TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-48
+	MOVWU	frameSize+32(FP), R1
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
 	DISPATCH(runtime·call64, 64)
@@ -310,11 +310,11 @@ TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
 	JMP	(R4)
 
 #define CALLFN(NAME,MAXSIZE)			\
-TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
+TEXT NAME(SB), WRAPPER, $MAXSIZE-48;		\
 	NO_LOCAL_POINTERS;			\
 	/* copy arguments to stack */		\
-	MOVV	arg+16(FP), R1;			\
-	MOVWU	argsize+24(FP), R2;			\
+	MOVV	stackArgs+16(FP), R1;			\
+	MOVWU	stackArgsSize+24(FP), R2;			\
 	MOVV	R29, R3;				\
 	ADDV	$8, R3;			\
 	ADDV	R3, R2;				\
@@ -330,10 +330,10 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
 	PCDATA  $PCDATA_StackMapIndex, $0;	\
 	JAL	(R4);				\
 	/* copy return values back */		\
-	MOVV	argtype+0(FP), R5;		\
-	MOVV	arg+16(FP), R1;			\
-	MOVWU	n+24(FP), R2;			\
-	MOVWU	retoffset+28(FP), R4;		\
+	MOVV	stackArgsType+0(FP), R5;		\
+	MOVV	stackArgs+16(FP), R1;			\
+	MOVWU	stackArgsSize+24(FP), R2;			\
+	MOVWU	stackRetOffset+28(FP), R4;		\
 	ADDV	$8, R29, R3;				\
 	ADDV	R4, R3; 			\
 	ADDV	R4, R1;				\
@@ -345,11 +345,12 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $32-0
+TEXT callRet<>(SB), NOSPLIT, $40-0
 	MOVV	R5, 8(R29)
 	MOVV	R1, 16(R29)
 	MOVV	R3, 24(R29)
 	MOVV	R2, 32(R29)
+	MOVV	$0, 40(R29)
 	JAL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_mipsx.s b/src/runtime/asm_mipsx.s
index f57437d590..8e5753d255 100644
--- a/src/runtime/asm_mipsx.s
+++ b/src/runtime/asm_mipsx.s
@@ -265,7 +265,7 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0
 	JMP	runtime·morestack(SB)
 
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 
@@ -276,8 +276,8 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0
 	MOVW	$NAME(SB), R4;	\
 	JMP	(R4)
 
-TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-20
-	MOVW	argsize+12(FP), R1
+TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-28
+	MOVW	frameSize+20(FP), R1
 
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
@@ -310,11 +310,11 @@ TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-20
 	JMP	(R4)
 
 #define CALLFN(NAME,MAXSIZE)	\
-TEXT NAME(SB),WRAPPER,$MAXSIZE-20;	\
+TEXT NAME(SB),WRAPPER,$MAXSIZE-28;	\
 	NO_LOCAL_POINTERS;	\
 	/* copy arguments to stack */		\
-	MOVW	arg+8(FP), R1;	\
-	MOVW	argsize+12(FP), R2;	\
+	MOVW	stackArgs+8(FP), R1;	\
+	MOVW	stackArgsSize+12(FP), R2;	\
 	MOVW	R29, R3;	\
 	ADDU	$4, R3;	\
 	ADDU	R3, R2;	\
@@ -330,10 +330,10 @@ TEXT NAME(SB),WRAPPER,$MAXSIZE-20;	\
 	PCDATA	$PCDATA_StackMapIndex, $0;	\
 	JAL	(R4);	\
 	/* copy return values back */		\
-	MOVW	argtype+0(FP), R5;	\
-	MOVW	arg+8(FP), R1;	\
-	MOVW	n+12(FP), R2;	\
-	MOVW	retoffset+16(FP), R4;	\
+	MOVW	stackArgsType+0(FP), R5;	\
+	MOVW	stackArgs+8(FP), R1;	\
+	MOVW	stackArgsSize+12(FP), R2;	\
+	MOVW	stackRetOffset+16(FP), R4;	\
 	ADDU	$4, R29, R3;	\
 	ADDU	R4, R3;	\
 	ADDU	R4, R1;	\
@@ -345,11 +345,12 @@ TEXT NAME(SB),WRAPPER,$MAXSIZE-20;	\
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $16-0
+TEXT callRet<>(SB), NOSPLIT, $20-0
 	MOVW	R5, 4(R29)
 	MOVW	R1, 8(R29)
 	MOVW	R3, 12(R29)
 	MOVW	R2, 16(R29)
+	MOVW    $0, 20(R29)
 	JAL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_ppc64x.s b/src/runtime/asm_ppc64x.s
index 763a92adf1..834023cce1 100644
--- a/src/runtime/asm_ppc64x.s
+++ b/src/runtime/asm_ppc64x.s
@@ -339,7 +339,7 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	BR	runtime·morestack(SB)
 
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 // Caution: ugly multiline assembly macros in your future!
@@ -353,8 +353,8 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	BR	(CTR)
 // Note: can't just "BR NAME(SB)" - bad inlining results.
 
-TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
-	MOVWZ argsize+24(FP), R3
+TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-48
+	MOVWZ	frameSize+32(FP), R3
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
 	DISPATCH(runtime·call64, 64)
@@ -387,11 +387,11 @@ TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
 	BR	(CTR)
 
 #define CALLFN(NAME,MAXSIZE)			\
-TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
+TEXT NAME(SB), WRAPPER, $MAXSIZE-48;		\
 	NO_LOCAL_POINTERS;			\
 	/* copy arguments to stack */		\
-	MOVD	arg+16(FP), R3;			\
-	MOVWZ	argsize+24(FP), R4;			\
+	MOVD	stackArgs+16(FP), R3;			\
+	MOVWZ	stackArgsSize+24(FP), R4;			\
 	MOVD    R1, R5;				\
 	CMP	R4, $8;				\
 	BLT	tailsetup;			\
@@ -439,10 +439,10 @@ callfn: \
 	MOVD	24(R1), R2;			\
 #endif						\
 	/* copy return values back */		\
-	MOVD	argtype+0(FP), R7;		\
-	MOVD	arg+16(FP), R3;			\
-	MOVWZ	n+24(FP), R4;			\
-	MOVWZ	retoffset+28(FP), R6;		\
+	MOVD	stackArgsType+0(FP), R7;		\
+	MOVD	stackArgs+16(FP), R3;			\
+	MOVWZ	stackArgsSize+24(FP), R4;			\
+	MOVWZ	stackRetOffset+28(FP), R6;		\
 	ADD	$FIXED_FRAME, R1, R5;		\
 	ADD	R6, R5; 			\
 	ADD	R6, R3;				\
@@ -454,11 +454,12 @@ callfn: \
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $32-0
+TEXT callRet<>(SB), NOSPLIT, $40-0
 	MOVD	R7, FIXED_FRAME+0(R1)
 	MOVD	R3, FIXED_FRAME+8(R1)
 	MOVD	R5, FIXED_FRAME+16(R1)
 	MOVD	R4, FIXED_FRAME+24(R1)
+	MOVD	$0, FIXED_FRAME+32(R1)
 	BL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_riscv64.s b/src/runtime/asm_riscv64.s
index cf460d1586..31e324d677 100644
--- a/src/runtime/asm_riscv64.s
+++ b/src/runtime/asm_riscv64.s
@@ -359,7 +359,7 @@ TEXT runtime·asminit(SB),NOSPLIT|NOFRAME,$0-0
 	RET
 
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 // Caution: ugly multiline assembly macros in your future!
@@ -371,13 +371,13 @@ TEXT runtime·asminit(SB),NOSPLIT|NOFRAME,$0-0
 	JALR	ZERO, T2
 // Note: can't just "BR NAME(SB)" - bad inlining results.
 
-// func call(argtype *rtype, fn, arg unsafe.Pointer, n uint32, retoffset uint32)
+// func call(stackArgsType *rtype, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 TEXT reflect·call(SB), NOSPLIT, $0-0
 	JMP	·reflectcall(SB)
 
-// func reflectcall(argtype *_type, fn, arg unsafe.Pointer, argsize uint32, retoffset uint32)
-TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
-	MOVWU argsize+24(FP), T0
+// func call(stackArgsType *_type, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
+TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-48
+	MOVWU	frameSize+32(FP), T0
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
 	DISPATCH(runtime·call64, 64)
@@ -409,11 +409,11 @@ TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
 	JALR	ZERO, T2
 
 #define CALLFN(NAME,MAXSIZE)			\
-TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
+TEXT NAME(SB), WRAPPER, $MAXSIZE-48;		\
 	NO_LOCAL_POINTERS;			\
 	/* copy arguments to stack */		\
-	MOV	arg+16(FP), A1;			\
-	MOVWU	argsize+24(FP), A2;		\
+	MOV	stackArgs+16(FP), A1;			\
+	MOVWU	stackArgsSize+24(FP), A2;		\
 	MOV	X2, A3;				\
 	ADD	$8, A3;				\
 	ADD	A3, A2;				\
@@ -429,10 +429,10 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
 	PCDATA  $PCDATA_StackMapIndex, $0;	\
 	JALR	RA, A4;				\
 	/* copy return values back */		\
-	MOV	argtype+0(FP), A5;		\
-	MOV	arg+16(FP), A1;			\
-	MOVWU	n+24(FP), A2;			\
-	MOVWU	retoffset+28(FP), A4;		\
+	MOV	stackArgsType+0(FP), A5;		\
+	MOV	stackArgs+16(FP), A1;			\
+	MOVWU	stackArgsSize+24(FP), A2;			\
+	MOVWU	stackRetOffset+28(FP), A4;		\
 	ADD	$8, X2, A3;			\
 	ADD	A4, A3; 			\
 	ADD	A4, A1;				\
@@ -444,11 +444,12 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $32-0
+TEXT callRet<>(SB), NOSPLIT, $40-0
 	MOV	A5, 8(X2)
 	MOV	A1, 16(X2)
 	MOV	A3, 24(X2)
 	MOV	A2, 32(X2)
+	MOV	$0, 40(X2)
 	CALL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_s390x.s b/src/runtime/asm_s390x.s
index 1cd5eca06f..fbd185c353 100644
--- a/src/runtime/asm_s390x.s
+++ b/src/runtime/asm_s390x.s
@@ -353,7 +353,7 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	BR	runtime·morestack(SB)
 
 // reflectcall: call a function with the given argument list
-// func call(argtype *_type, f *FuncVal, arg *byte, argsize, retoffset uint32).
+// func call(stackArgsType *_type, f *FuncVal, stackArgs *byte, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs).
 // we don't have variable-sized frames, so we use a small number
 // of constant-sized-frame functions to encode a few bits of size in the pc.
 // Caution: ugly multiline assembly macros in your future!
@@ -366,8 +366,8 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	BR	(R5)
 // Note: can't just "BR NAME(SB)" - bad inlining results.
 
-TEXT ·reflectcall(SB), NOSPLIT, $-8-32
-	MOVWZ argsize+24(FP), R3
+TEXT ·reflectcall(SB), NOSPLIT, $-8-48
+	MOVWZ	frameSize+32(FP), R3
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
 	DISPATCH(runtime·call64, 64)
@@ -399,11 +399,11 @@ TEXT ·reflectcall(SB), NOSPLIT, $-8-32
 	BR	(R5)
 
 #define CALLFN(NAME,MAXSIZE)			\
-TEXT NAME(SB), WRAPPER, $MAXSIZE-24;		\
+TEXT NAME(SB), WRAPPER, $MAXSIZE-48;		\
 	NO_LOCAL_POINTERS;			\
 	/* copy arguments to stack */		\
-	MOVD	arg+16(FP), R4;			\
-	MOVWZ	argsize+24(FP), R5;		\
+	MOVD	stackArgs+16(FP), R4;			\
+	MOVWZ	stackArgsSize+24(FP), R5;		\
 	MOVD	$stack-MAXSIZE(SP), R6;		\
 loopArgs: /* copy 256 bytes at a time */	\
 	CMP	R5, $256;			\
@@ -424,11 +424,11 @@ callFunction:					\
 	PCDATA  $PCDATA_StackMapIndex, $0;	\
 	BL	(R8);				\
 	/* copy return values back */		\
-	MOVD	argtype+0(FP), R7;		\
-	MOVD	arg+16(FP), R6;			\
-	MOVWZ	n+24(FP), R5;			\
+	MOVD	stackArgsType+0(FP), R7;		\
+	MOVD	stackArgs+16(FP), R6;			\
+	MOVWZ	stackArgsSize+24(FP), R5;			\
 	MOVD	$stack-MAXSIZE(SP), R4;		\
-	MOVWZ	retoffset+28(FP), R1;		\
+	MOVWZ	stackRetOffset+28(FP), R1;		\
 	ADD	R1, R4;				\
 	ADD	R1, R6;				\
 	SUB	R1, R5;				\
@@ -439,11 +439,12 @@ callFunction:					\
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $32-0
+TEXT callRet<>(SB), NOSPLIT, $40-0
 	MOVD	R7, 8(R15)
 	MOVD	R6, 16(R15)
 	MOVD	R4, 24(R15)
 	MOVD	R5, 32(R15)
+	MOVD	$0, 40(R15)
 	BL	runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/asm_wasm.s b/src/runtime/asm_wasm.s
index fcb780f1dc..cf3d961b74 100644
--- a/src/runtime/asm_wasm.s
+++ b/src/runtime/asm_wasm.s
@@ -296,14 +296,14 @@ TEXT ·asmcgocall(SB), NOSPLIT, $0-0
 		JMP NAME(SB); \
 	End
 
-TEXT ·reflectcall(SB), NOSPLIT, $0-32
+TEXT ·reflectcall(SB), NOSPLIT, $0-48
 	I64Load fn+8(FP)
 	I64Eqz
 	If
 		CALLNORESUME runtime·sigpanic<ABIInternal>(SB)
 	End
 
-	MOVW argsize+24(FP), R0
+	MOVW frameSize+32(FP), R0
 
 	DISPATCH(runtime·call16, 16)
 	DISPATCH(runtime·call32, 32)
@@ -335,18 +335,18 @@ TEXT ·reflectcall(SB), NOSPLIT, $0-32
 	JMP runtime·badreflectcall(SB)
 
 #define CALLFN(NAME, MAXSIZE) \
-TEXT NAME(SB), WRAPPER, $MAXSIZE-32; \
+TEXT NAME(SB), WRAPPER, $MAXSIZE-48; \
 	NO_LOCAL_POINTERS; \
-	MOVW argsize+24(FP), R0; \
+	MOVW stackArgsSize+24(FP), R0; \
 	\
 	Get R0; \
 	I64Eqz; \
 	Not; \
 	If; \
 		Get SP; \
-		I64Load argptr+16(FP); \
+		I64Load stackArgs+16(FP); \
 		I32WrapI64; \
-		I64Load argsize+24(FP); \
+		I64Load stackArgsSize+24(FP); \
 		I64Const $3; \
 		I64ShrU; \
 		I32WrapI64; \
@@ -359,12 +359,12 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-32; \
 	I64Load $0; \
 	CALL; \
 	\
-	I64Load32U retoffset+28(FP); \
+	I64Load32U stackRetOffset+28(FP); \
 	Set R0; \
 	\
-	MOVD argtype+0(FP), RET0; \
+	MOVD stackArgsType+0(FP), RET0; \
 	\
-	I64Load argptr+16(FP); \
+	I64Load stackArgs+16(FP); \
 	Get R0; \
 	I64Add; \
 	Set RET1; \
@@ -375,7 +375,7 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-32; \
 	I64Add; \
 	Set RET2; \
 	\
-	I64Load32U argsize+24(FP); \
+	I64Load32U stackArgsSize+24(FP); \
 	Get R0; \
 	I64Sub; \
 	Set RET3; \
@@ -387,12 +387,13 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-32; \
 // separate function so it can allocate stack space for the arguments
 // to reflectcallmove. It does not follow the Go ABI; it expects its
 // arguments in registers.
-TEXT callRet<>(SB), NOSPLIT, $32-0
+TEXT callRet<>(SB), NOSPLIT, $40-0
 	NO_LOCAL_POINTERS
 	MOVD RET0, 0(SP)
 	MOVD RET1, 8(SP)
 	MOVD RET2, 16(SP)
 	MOVD RET3, 24(SP)
+	MOVD $0,   32(SP)
 	CALL runtime·reflectcallmove(SB)
 	RET
 
diff --git a/src/runtime/mbarrier.go b/src/runtime/mbarrier.go
index 2b5affce52..4994347bde 100644
--- a/src/runtime/mbarrier.go
+++ b/src/runtime/mbarrier.go
@@ -14,6 +14,7 @@
 package runtime
 
 import (
+	"internal/abi"
 	"runtime/internal/sys"
 	"unsafe"
 )
@@ -223,11 +224,18 @@ func reflect_typedmemmovepartial(typ *_type, dst, src unsafe.Pointer, off, size
 // stack map of reflectcall is wrong.
 //
 //go:nosplit
-func reflectcallmove(typ *_type, dst, src unsafe.Pointer, size uintptr) {
+func reflectcallmove(typ *_type, dst, src unsafe.Pointer, size uintptr, regs *abi.RegArgs) {
 	if writeBarrier.needed && typ != nil && typ.ptrdata != 0 && size >= sys.PtrSize {
 		bulkBarrierPreWrite(uintptr(dst), uintptr(src), size)
 	}
 	memmove(dst, src, size)
+
+	// Move pointers returned in registers to a place where the GC can see them.
+	for i := range regs.Ints {
+		if regs.ReturnIsPtr.Get(i) {
+			regs.Ptrs[i] = unsafe.Pointer(regs.Ints[i])
+		}
+	}
 }
 
 //go:nosplit
diff --git a/src/runtime/mfinal.go b/src/runtime/mfinal.go
index f4dbd77252..7d0313be12 100644
--- a/src/runtime/mfinal.go
+++ b/src/runtime/mfinal.go
@@ -7,6 +7,7 @@
 package runtime
 
 import (
+	"internal/abi"
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
@@ -219,7 +220,11 @@ func runfinq() {
 					throw("bad kind in runfinq")
 				}
 				fingRunning = true
-				reflectcall(nil, unsafe.Pointer(f.fn), frame, uint32(framesz), uint32(framesz))
+				// Pass a dummy RegArgs for now.
+				//
+				// TODO(mknyszek): Pass arguments in registers.
+				var regs abi.RegArgs
+				reflectcall(nil, unsafe.Pointer(f.fn), frame, uint32(framesz), uint32(framesz), uint32(framesz), &regs)
 				fingRunning = false
 
 				// Drop finalizer queue heap references
diff --git a/src/runtime/panic.go b/src/runtime/panic.go
index 5b2ccdd874..e320eaa596 100644
--- a/src/runtime/panic.go
+++ b/src/runtime/panic.go
@@ -5,6 +5,7 @@
 package runtime
 
 import (
+	"internal/abi"
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
@@ -874,7 +875,13 @@ func reflectcallSave(p *_panic, fn, arg unsafe.Pointer, argsize uint32) {
 		p.pc = getcallerpc()
 		p.sp = unsafe.Pointer(getcallersp())
 	}
-	reflectcall(nil, fn, arg, argsize, argsize)
+	// Pass a dummy RegArgs for now since no function actually implements
+	// the register-based ABI.
+	//
+	// TODO(mknyszek): Implement this properly, setting up arguments in
+	// registers as necessary in the caller.
+	var regs abi.RegArgs
+	reflectcall(nil, fn, arg, argsize, argsize, argsize, &regs)
 	if p != nil {
 		p.pc = 0
 		p.sp = unsafe.Pointer(nil)
@@ -968,7 +975,9 @@ func gopanic(e interface{}) {
 			}
 		} else {
 			p.argp = unsafe.Pointer(getargp(0))
-			reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
+
+			var regs abi.RegArgs
+			reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz), uint32(d.siz), &regs)
 		}
 		p.argp = nil
 
diff --git a/src/runtime/stubs.go b/src/runtime/stubs.go
index 3d1e0c0bb4..c0cc95ec65 100644
--- a/src/runtime/stubs.go
+++ b/src/runtime/stubs.go
@@ -4,7 +4,10 @@
 
 package runtime
 
-import "unsafe"
+import (
+	"internal/abi"
+	"unsafe"
+)
 
 // Should be a built-in for unsafe.Pointer?
 //go:nosplit
@@ -174,19 +177,50 @@ func asminit()
 func setg(gg *g)
 func breakpoint()
 
-// reflectcall calls fn with a copy of the n argument bytes pointed at by arg.
-// After fn returns, reflectcall copies n-retoffset result bytes
-// back into arg+retoffset before returning. If copying result bytes back,
-// the caller should pass the argument frame type as argtype, so that
-// call can execute appropriate write barriers during the copy.
+// reflectcall calls fn with arguments described by stackArgs, stackArgsSize,
+// frameSize, and regArgs.
 //
-// Package reflect always passes a frame type. In package runtime,
-// Windows callbacks are the only use of this that copies results
-// back, and those cannot have pointers in their results, so runtime
-// passes nil for the frame type.
+// Arguments passed on the stack and space for return values passed on the stack
+// must be laid out at the space pointed to by stackArgs (with total length
+// stackArgsSize) according to the ABI.
+//
+// stackRetOffset must be some value <= stackArgsSize that indicates the
+// offset within stackArgs where the return value space begins.
+//
+// frameSize is the total size of the argument frame at stackArgs and must
+// therefore be >= stackArgsSize. It must include additional space for spilling
+// register arguments for stack growth and preemption.
+//
+// TODO(mknyszek): Once we don't need the additional spill space, remove frameSize,
+// since frameSize will be redundant with stackArgsSize.
+//
+// Arguments passed in registers must be laid out in regArgs according to the ABI.
+// regArgs will hold any return values passed in registers after the call.
+//
+// reflectcall copies stack arguments from stackArgs to the goroutine stack, and
+// then copies back stackArgsSize-stackRetOffset bytes back to the return space
+// in stackArgs once fn has completed. It also "unspills" argument registers from
+// regArgs before calling fn, and spills them back into regArgs immediately
+// following the call to fn. If there are results being returned on the stack,
+// the caller should pass the argument frame type as stackArgsType so that
+// reflectcall can execute appropriate write barriers during the copy.
+//
+// reflectcall expects regArgs.ReturnIsPtr to be populated indicating which
+// registers on the return path will contain Go pointers. It will then store
+// these pointers in regArgs.Ptrs such that they are visible to the GC.
+//
+// Package reflect passes a frame type. In package runtime, there is only
+// one call that copies results back, in callbackWrap in syscall_windows.go, and it
+// does NOT pass a frame type, meaning there are no write barriers invoked. See that
+// call site for justification.
 //
 // Package reflect accesses this symbol through a linkname.
-func reflectcall(argtype *_type, fn, arg unsafe.Pointer, argsize uint32, retoffset uint32)
+//
+// Arguments passed through to reflectcall do not escape. The type is used
+// only in a very limited callee of reflectcall, the stackArgs are copied, and
+// regArgs is only used in the reflectcall frame.
+//go:noescape
+func reflectcall(stackArgsType *_type, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
 
 func procyield(cycles uint32)
 
diff --git a/src/runtime/syscall_windows.go b/src/runtime/syscall_windows.go
index 7835b492f7..add40bb0b3 100644
--- a/src/runtime/syscall_windows.go
+++ b/src/runtime/syscall_windows.go
@@ -5,6 +5,7 @@
 package runtime
 
 import (
+	"internal/abi"
 	"runtime/internal/sys"
 	"unsafe"
 )
@@ -242,7 +243,11 @@ func callbackWrap(a *callbackArgs) {
 
 	// Even though this is copying back results, we can pass a nil
 	// type because those results must not require write barriers.
-	reflectcall(nil, unsafe.Pointer(c.fn), noescape(goArgs), uint32(c.retOffset)+sys.PtrSize, uint32(c.retOffset))
+	//
+	// Pass a dummy RegArgs for now.
+	// TODO(mknyszek): Pass arguments in registers.
+	var regs abi.RegArgs
+	reflectcall(nil, unsafe.Pointer(c.fn), noescape(goArgs), uint32(c.retOffset)+sys.PtrSize, uint32(c.retOffset), uint32(c.retOffset)+sys.PtrSize, &regs)
 
 	// Extract the result.
 	a.result = *(*uintptr)(unsafe.Pointer(&frame[c.retOffset]))