fix callback calling convention (#26)

runtime.cgocallback takes a function pointer to the ABIInternal entry. The only way to get the ABIInternal entry is using the ABI selector <ABIInternal>. However, this is only available when compiling the runtime.  This commit circumvents this limitation by using build constraints to determine if the Go version uses stack or register calling convention. Then in callbackWrapPicker the proper argument is sent to the real callbackWrap function.

Closes #25

commit: 6ed67cd5f570b9c0d5710dfced2b1e77ad92ca1b
author: TotallyGamerJet · 4y ago · 2022-08-29 17:19 UTC
committer: GitHub · 4y ago · 2022-08-29 17:19 UTC
parent: 58aa9be
signature: GPG Unverified4AEE18F83AFDEB23 The key is unknown

5 files · +50 -8

A registercc_darwin.go +12 -0

@@ -0,0 +1,12 @@
	1	+	// SPDX-License-Identifier: Apache-2.0
	2	+	// SPDX-FileCopyrightText: 2022 The Ebitengine Authors
	3	+
	4	+	//go:build (arm64 && go1.18) \|\| (amd64 && go1.17)
	5	+	// +build arm64,go1.18 amd64,go1.17
	6	+
	7	+	package purego
	8	+
	9	+	// stackCallingConvention represents whether the stacks or the
	10	+	// registers are used to pass parameters to functions. This is used to circumvent
	11	+	// the need for ABIInternal tag which is only allowed in the runtime.
	12	+	const stackCallingConvention = false

@@ -0,0 +1,12 @@
	1	+	// SPDX-License-Identifier: Apache-2.0
	2	+	// SPDX-FileCopyrightText: 2022 The Ebitengine Authors
	3	+
	4	+	//go:build (arm64 && go1.18) \|\| (amd64 && go1.17)
	5	+	// +build arm64,go1.18 amd64,go1.17
	6	+
	7	+	package purego
	8	+
	9	+	// stackCallingConvention represents whether the stacks or the
	10	+	// registers are used to pass parameters to functions. This is used to circumvent
	11	+	// the need for ABIInternal tag which is only allowed in the runtime.
	12	+	const stackCallingConvention = false

A stackcc_darwin.go +12 -0

@@ -0,0 +1,12 @@
	1	+	// SPDX-License-Identifier: Apache-2.0
	2	+	// SPDX-FileCopyrightText: 2022 The Ebitengine Authors
	3	+
	4	+	//go:build (arm64 && !go1.18) \|\| (amd64 && !go1.17)
	5	+	// +build arm64,!go1.18 amd64,!go1.17
	6	+
	7	+	package purego
	8	+
	9	+	// stackCallingConvention represents whether the stacks or the
	10	+	// registers are used to pass parameters to functions. This is used to circumvent
	11	+	// the need for ABIInternal tag which is only allowed in the runtime.
	12	+	const stackCallingConvention = true

@@ -0,0 +1,12 @@
	1	+	// SPDX-License-Identifier: Apache-2.0
	2	+	// SPDX-FileCopyrightText: 2022 The Ebitengine Authors
	3	+
	4	+	//go:build (arm64 && !go1.18) \|\| (amd64 && !go1.17)
	5	+	// +build arm64,!go1.18 amd64,!go1.17
	6	+
	7	+	package purego
	8	+
	9	+	// stackCallingConvention represents whether the stacks or the
	10	+	// registers are used to pass parameters to functions. This is used to circumvent
	11	+	// the need for ABIInternal tag which is only allowed in the runtime.
	12	+	const stackCallingConvention = true

M sys_darwin_amd64.s +6 -4


@@ -74,11 +74,13 @@ TEXT syscall9X(SB), NOSPLIT, $0
74	74
75	75		// runtime·cgocallback expects a call to the ABIInternal function
76	76		// However, the tag <ABIInternal> is only available in the runtime :(
77		-	// This is a small wrapper function that moves the parameter from AX to the stack
78		-	// where the Go function can find it. It then jumps to callbackWrap
	77	+	// This is a small wrapper function that copies both whatever is in the register
	78	+	// and is on the stack and places both on the stack. It then calls callbackWrapPicker
	79	+	// which will choose which parameter should be used depending on the version of Go.
	80	+	// It then calls the real version of callbackWrap
79	81		TEXT callbackWrapInternal<>(SB), NOSPLIT, $0-0
80		-	MOVQ AX, arg+8(SP)
81		-	JMP ·callbackWrap(SB)
	82	+	MOVQ AX, arg+16(SP)
	83	+	JMP ·callbackWrapPicker(SB)
82	84		RET
83	85
84	86		TEXT callbackasm1(SB), NOSPLIT, $0

 // runtime·cgocallback expects a call to the ABIInternal function
 // However, the tag <ABIInternal> is only available in the runtime :(
-// This is a small wrapper function that moves the parameter from AX to the stack
+// This is a small wrapper function that copies both whatever is in the register
-// where the Go function can find it. It then jumps to callbackWrap
+// and is on the stack and places both on the stack. It then calls callbackWrapPicker
+// which will choose which parameter should be used depending on the version of Go.
+// It then calls the real version of callbackWrap
 TEXT callbackWrapInternal<>(SB), NOSPLIT, $0-0
-	MOVQ AX, arg+8(SP)
+	MOVQ AX, arg+16(SP)
-	JMP  ·callbackWrap(SB)
+	JMP  ·callbackWrapPicker(SB)
 	RET
 TEXT callbackasm1(SB), NOSPLIT, $0

M sys_darwin_arm64.s +6 -4


@@ -65,11 +65,13 @@ TEXT syscall9X(SB), NOSPLIT, $0
65	65
66	66		// runtime·cgocallback expects a call to the ABIInternal function
67	67		// However, the tag <ABIInternal> is only available in the runtime :(
68		-	// This is a small wrapper function that moves the parameter from R0 to the stack
69		-	// where the Go function can find it. It then branches without link.
	68	+	// This is a small wrapper function that copies both whatever is in the register
	69	+	// and is on the stack and places both on the stack. It then calls callbackWrapPicker
	70	+	// which will choose which parameter should be used depending on the version of Go.
	71	+	// It then calls the real version of callbackWrap
70	72		TEXT callbackWrapInternal<>(SB), NOSPLIT, $0-0
71		-	MOVD R0, 8(RSP)
72		-	B ·callbackWrap(SB)
	73	+	MOVD R0, 16(RSP)
	74	+	B ·callbackWrapPicker(SB)
73	75		RET
74	76
75	77		TEXT callbackasm1(SB), NOSPLIT, $208-0

 // runtime·cgocallback expects a call to the ABIInternal function
 // However, the tag <ABIInternal> is only available in the runtime :(
-// This is a small wrapper function that moves the parameter from R0 to the stack
+// This is a small wrapper function that copies both whatever is in the register
-// where the Go function can find it. It then branches without link.
+// and is on the stack and places both on the stack. It then calls callbackWrapPicker
+// which will choose which parameter should be used depending on the version of Go.
+// It then calls the real version of callbackWrap
 TEXT callbackWrapInternal<>(SB), NOSPLIT, $0-0
-	MOVD R0, 8(RSP)
+	MOVD R0, 16(RSP)
-	B    ·callbackWrap(SB)
+	B    ·callbackWrapPicker(SB)
 	RET
 TEXT callbackasm1(SB), NOSPLIT, $208-0

M syscall_darwin.go +14 -0


@@ -95,6 +95,20 @@ const callbackMaxFrame = 64 * ptrSize
95	95		// callbackasmABI0 is implemented in zcallback_GOOS_GOARCH.s
96	96		var callbackasmABI0 uintptr
97	97
	98	+	// callbackWrapPicker gets whatever is on the stack and in the first register.
	99	+	// Depending on which version of Go that uses stack or register-based
	100	+	// calling it passes the respective argument to the real calbackWrap function.
	101	+	// The other argument is therefore invalid and points to undefined memory so don't use it.
	102	+	// This function is necessary since we can't use the ABIInternal selector which is only
	103	+	// valid in the runtime.
	104	+	func callbackWrapPicker(stack, register *callbackArgs) {
	105	+	if stackCallingConvention {
	106	+	callbackWrap(stack)
	107	+	} else {
	108	+	callbackWrap(register)
	109	+	}
	110	+	}
	111	+
98	112		// callbackWrap is called by assembly code which determines which Go function to call.
99	113		// This function takes the arguments and passes them to the Go function and returns the result.
100	114		func callbackWrap(a *callbackArgs) {


@@ -95,6 +95,20 @@ const callbackMaxFrame = 64 * ptrSize
95	// callbackasmABI0 is implemented in zcallback_GOOS_GOARCH.s	95		// callbackasmABI0 is implemented in zcallback_GOOS_GOARCH.s
96	var callbackasmABI0 uintptr	96		var callbackasmABI0 uintptr
97		97
		98	+	// callbackWrapPicker gets whatever is on the stack and in the first register.
		99	+	// Depending on which version of Go that uses stack or register-based
		100	+	// calling it passes the respective argument to the real calbackWrap function.
		101	+	// The other argument is therefore invalid and points to undefined memory so don't use it.
		102	+	// This function is necessary since we can't use the ABIInternal selector which is only
		103	+	// valid in the runtime.
		104	+	func callbackWrapPicker(stack, register *callbackArgs) {
		105	+	if stackCallingConvention {
		106	+	callbackWrap(stack)
		107	+	} else {
		108	+	callbackWrap(register)
		109	+	}
		110	+	}
		111	+
98	// callbackWrap is called by assembly code which determines which Go function to call.	112		// callbackWrap is called by assembly code which determines which Go function to call.
99	// This function takes the arguments and passes them to the Go function and returns the result.	113		// This function takes the arguments and passes them to the Go function and returns the result.
100	func callbackWrap(a *callbackArgs) {	114		func callbackWrap(a *callbackArgs) {