purego: fix arm64 argument corruption on alignment flush (#360)

Fix a critical bug in ARM64 struct argument packing where the register
value (val) and class were not being reset after flushing due to
alignment requirements.

When packing struct fields into registers, if a field's alignment
causes shift >= 64, the current register is flushed. However, the
code was not resetting 'val' and 'class' after the flush, causing
subsequent fields to be ORed with stale data from previous fields.

Example bug with FourInt32s{1, 2, 3, 4}:
- Fields 0,1 packed: val = 0x0000000200000001
- Flush at field 2 due to shift >= 64
- BUG: val still contains 0x0000000200000001
- Field 2 packs: val |= 3 becomes 0x0000000200000003 (should be 0x03)
- Field 3 packs: val |= (4<<32) becomes 0x0000000400000003
- Result: field 3 = 6 instead of 4 (bit 1 from field 1 leaked)

This fix ensures val and class are properly reset after each flush,
preventing data corruption between register boundaries.

Closes #359

commit: b9d062cb1754bcd2f306c75ff1bf229023c7cd30
author: Travis Cline · 11mo ago · 2025-10-31 18:09 UTC
committer: Hajime Hoshi · 11mo ago · 2025-10-31 18:10 UTC
parent: cdb7cab
signature: unsigned
refs: tag: v0.9.1

3 files · +31 -3

M struct_arm64.go +2 -0


@@ -117,6 +117,8 @@ func placeRegisters(v reflect.Value, addFloat func(uintptr), addInt func(uintptr
117	117		} else {
118	118		addInt(uintptr(val))
119	119		}
	120	+	val = 0
	121	+	class = _NO_CLASS
120	122		}
121	123		switch f.Type().Kind() {
122	124		case reflect.Struct:


@@ -117,6 +117,8 @@ func placeRegisters(v reflect.Value, addFloat func(uintptr), addInt func(uintptr
117	} else {	117		} else {
118	addInt(uintptr(val))	118		addInt(uintptr(val))
119	}	119		}
		120	+	val = 0
		121	+	class = _NO_CLASS
120	}	122		}
121	switch f.Type().Kind() {	123		switch f.Type().Kind() {
122	case reflect.Struct:	124		case reflect.Struct:

M struct_test.go +15 -2


@@ -373,8 +373,9 @@ func TestRegisterFunc_structArgs(t *testing.T) {
373	373		}
374	374		var Array4CharsFn func(chars Array4Chars) int32
375	375		purego.RegisterLibFunc(&Array4CharsFn, lib, "Array4Chars")
376		-	if ret := Array4CharsFn(Array4Chars{a: [...]int8{100, -127, 4, -100}}); ret != expectedSigned {
377		-	t.Fatalf("Array4CharsFn returned %#x wanted %#x", ret, expectedSigned)
	376	+	const expectedSum = 1 + 2 + 4 + 8
	377	+	if ret := Array4CharsFn(Array4Chars{a: [...]int8{1, 2, 4, 8}}); ret != expectedSum {
	378	+	t.Fatalf("Array4CharsFn returned %d wanted %d", ret, expectedSum)
378	379		}
379	380		}
380	381		{

@@ -486,6 +487,18 @@ func TestRegisterFunc_structArgs(t *testing.T) {
486	487		t.Fatalf("FloatAndBool(y: false) = %d, want 0", ret)
487	488		}
488	489		}
	490	+	{
	491	+	type FourInt32s struct {
	492	+	f0, f1, f2, f3 int32
	493	+	}
	494	+	var FourInt32sFn func(FourInt32s) int32
	495	+	purego.RegisterLibFunc(&FourInt32sFn, lib, "FourInt32s")
	496	+	result := FourInt32sFn(FourInt32s{100, -127, 4, -100})
	497	+	const want = 100 - 127 + 4 - 100
	498	+	if result != want {
	499	+	t.Fatalf("FourInt32s returned %d wanted %d", result, want)
	500	+	}
	501	+	}
489	502		}
490	503
491	504		func TestRegisterFunc_structReturns(t *testing.T) {

 		}
 		var Array4CharsFn func(chars Array4Chars) int32
 		purego.RegisterLibFunc(&Array4CharsFn, lib, "Array4Chars")
-		if ret := Array4CharsFn(Array4Chars{a: [...]int8{100, -127, 4, -100}}); ret != expectedSigned {
+		const expectedSum = 1 + 2 + 4 + 8
-			t.Fatalf("Array4CharsFn returned %#x wanted %#x", ret, expectedSigned)
+		if ret := Array4CharsFn(Array4Chars{a: [...]int8{1, 2, 4, 8}}); ret != expectedSum {
+			t.Fatalf("Array4CharsFn returned %d wanted %d", ret, expectedSum)
 		}
 	}
 	{
 			t.Fatalf("FloatAndBool(y: false) = %d, want 0", ret)
 		}
 	}
+	{
+		type FourInt32s struct {
+			f0, f1, f2, f3 int32
+		}
+		var FourInt32sFn func(FourInt32s) int32
+		purego.RegisterLibFunc(&FourInt32sFn, lib, "FourInt32s")
+		result := FourInt32sFn(FourInt32s{100, -127, 4, -100})
+		const want = 100 - 127 + 4 - 100
+		if result != want {
+			t.Fatalf("FourInt32s returned %d wanted %d", result, want)
+		}
+	}
 }
 func TestRegisterFunc_structReturns(t *testing.T) {

M testdata/structtest/struct_test.c +14 -1

@@ -1,7 +1,9 @@
1	1		// SPDX-License-Identifier: Apache-2.0
2	2		// SPDX-FileCopyrightText: 2024 The Ebitengine Authors
3	3
4		-	#include "stdint.h"
	4	+	#include <stdint.h>
	5	+	#include <stdio.h>
	6	+	#include <stdlib.h>
5	7
6	8		#if defined(__x86_64__) \|\| defined(__aarch64__)
7	9		typedef int64_t GoInt;

@@ -361,3 +363,14 @@ struct FloatAndBool {
361	363		int FloatAndBool(struct FloatAndBool f) {
362	364		return f.has_value;
363	365		}
	366	+
	367	+	struct FourInt32s {
	368	+	int32_t f0;
	369	+	int32_t f1;
	370	+	int32_t f2;
	371	+	int32_t f3;
	372	+	};
	373	+
	374	+	int32_t FourInt32s(struct FourInt32s s) {
	375	+	return s.f0 + s.f1 + s.f2 + s.f3;
	376	+	}

@@ -1,7 +1,9 @@
1		// SPDX-License-Identifier: Apache-2.0	1		// SPDX-License-Identifier: Apache-2.0
2		// SPDX-FileCopyrightText: 2024 The Ebitengine Authors	2		// SPDX-FileCopyrightText: 2024 The Ebitengine Authors
3			3
4	-	#include "stdint.h"	4	+	#include <stdint.h>
			5	+	#include <stdio.h>
			6	+	#include <stdlib.h>
5			7
6		#if defined(__x86_64__) \|\| defined(__aarch64__)	8		#if defined(__x86_64__) \|\| defined(__aarch64__)
7		typedef int64_t GoInt;	9		typedef int64_t GoInt;

@@ -361,3 +363,14 @@ struct FloatAndBool {
361		int FloatAndBool(struct FloatAndBool f) {	363		int FloatAndBool(struct FloatAndBool f) {
362		return f.has_value;	364		return f.has_value;
363		}	365		}
			366	+
			367	+	struct FourInt32s {
			368	+	int32_t f0;
			369	+	int32_t f1;
			370	+	int32_t f2;
			371	+	int32_t f3;
			372	+	};
			373	+
			374	+	int32_t FourInt32s(struct FourInt32s s) {
			375	+	return s.f0 + s.f1 + s.f2 + s.f3;
			376	+	}