cmd/cgo: fix unaligned arguments typedmemmove crash on iOS

Irregularly typedmemmove and bulkBarrierPreWrite crashes on unaligned
arguments. By aligning the arguments this is fixed.

Fixes #46893

Change-Id: I7beb9fdc31053fcb71bee6c6cb906dea31718c56
GitHub-Last-Rev: 46ae8b9688
GitHub-Pull-Request: golang/go#74868
Reviewed-on: https://go-review.googlesource.com/c/go/+/692935
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/cgo/internal/testout/out_test.go

@@ -0,0 +1,144 @@
+// Copyright 2025 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.
+
+package out_test
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"internal/testenv"
+	"internal/goarch"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+type methodAlign struct {
+	Method string
+	Align  int
+}
+
+var wantAligns = map[string]int{
+	"ReturnEmpty":         1,
+	"ReturnOnlyUint8":     1,
+	"ReturnOnlyUint16":    2,
+	"ReturnOnlyUint32":    4,
+	"ReturnOnlyUint64":    goarch.PtrSize,
+	"ReturnOnlyInt":       goarch.PtrSize,
+	"ReturnOnlyPtr":       goarch.PtrSize,
+	"ReturnByteSlice":     goarch.PtrSize,
+	"ReturnString":        goarch.PtrSize,
+	"InputAndReturnUint8": 1,
+	"MixedTypes":          goarch.PtrSize,
+}
+
+// TestAligned tests that the generated _cgo_export.c file has the wanted
+// align attributes for struct types used as arguments or results of
+// //exported functions.
+func TestAligned(t *testing.T) {
+	testenv.MustHaveGoRun(t)
+	testenv.MustHaveCGO(t)
+
+	testdata, err := filepath.Abs("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	objDir := t.TempDir()
+
+	cmd := testenv.Command(t, testenv.GoToolPath(t), "tool", "cgo",
+		"-objdir", objDir,
+		filepath.Join(testdata, "aligned.go"))
+	cmd.Stderr = new(bytes.Buffer)
+
+	err = cmd.Run()
+	if err != nil {
+		t.Fatalf("%#q: %v\n%s", cmd, err, cmd.Stderr)
+	}
+
+	haveAligns, err := parseAlign(filepath.Join(objDir, "_cgo_export.c"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Check that we have all the wanted methods
+	if len(haveAligns) != len(wantAligns) {
+		t.Fatalf("have %d methods with aligned, want %d", len(haveAligns), len(wantAligns))
+	}
+
+	for i := range haveAligns {
+		method := haveAligns[i].Method
+		haveAlign := haveAligns[i].Align
+
+		wantAlign, ok := wantAligns[method]
+		if !ok {
+			t.Errorf("method %s: have aligned %d, want missing entry", method, haveAlign)
+		} else if haveAlign != wantAlign {
+			t.Errorf("method %s: have aligned %d, want %d", method, haveAlign, wantAlign)
+		}
+	}
+}
+
+func parseAlign(filename string) ([]methodAlign, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open file: %w", err)
+	}
+	defer file.Close()
+
+	var results []methodAlign
+	scanner := bufio.NewScanner(file)
+
+	// Regex to match function declarations like "struct MethodName_return MethodName("
+	funcRegex := regexp.MustCompile(`^struct\s+(\w+)_return\s+(\w+)\(`)
+	// Regex to match simple function declarations like "GoSlice MethodName("
+	simpleFuncRegex := regexp.MustCompile(`^Go\w+\s+(\w+)\(`)
+	// Regex to match void-returning exported functions like "void ReturnEmpty("
+	voidFuncRegex := regexp.MustCompile(`^void\s+(\w+)\(`)
+	// Regex to match align attributes like "__attribute__((aligned(8)))"
+	alignRegex := regexp.MustCompile(`__attribute__\(\(aligned\((\d+)\)\)\)`)
+
+	var currentMethod string
+
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+
+		// Check if this line declares a function with struct return type
+		if matches := funcRegex.FindStringSubmatch(line); matches != nil {
+			currentMethod = matches[2] // Extract the method name
+		} else if matches := simpleFuncRegex.FindStringSubmatch(line); matches != nil {
+			// Check if this line declares a function with simple return type (like GoSlice)
+			currentMethod = matches[1] // Extract the method name
+		} else if matches := voidFuncRegex.FindStringSubmatch(line); matches != nil {
+			// Check if this line declares a void-returning function
+			currentMethod = matches[1] // Extract the method name
+		}
+
+		// Check if this line contains align information
+		if alignMatches := alignRegex.FindStringSubmatch(line); alignMatches != nil && currentMethod != "" {
+			alignStr := alignMatches[1]
+			align, err := strconv.Atoi(alignStr)
+			if err != nil {
+				// Skip this entry if we can't parse the align as integer
+				currentMethod = ""
+				continue
+			}
+			results = append(results, methodAlign{
+				Method: currentMethod,
+				Align:  align,
+			})
+			currentMethod = "" // Reset for next method
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, fmt.Errorf("error reading file: %w", err)
+	}
+
+	return results, nil
+}

src/cmd/cgo/internal/testout/testdata/aligned.go

@@ -0,0 +1,63 @@
+// Copyright 2025 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.
+
+package main
+
+import "C"
+
+//export ReturnEmpty
+func ReturnEmpty() {
+	return
+}
+
+//export ReturnOnlyUint8
+func ReturnOnlyUint8() (uint8, uint8, uint8) {
+	return 1, 2, 3
+}
+
+//export ReturnOnlyUint16
+func ReturnOnlyUint16() (uint16, uint16, uint16) {
+	return 1, 2, 3
+}
+
+//export ReturnOnlyUint32
+func ReturnOnlyUint32() (uint32, uint32, uint32) {
+	return 1, 2, 3
+}
+
+//export ReturnOnlyUint64
+func ReturnOnlyUint64() (uint64, uint64, uint64) {
+	return 1, 2, 3
+}
+
+//export ReturnOnlyInt
+func ReturnOnlyInt() (int, int, int) {
+	return 1, 2, 3
+}
+
+//export ReturnOnlyPtr
+func ReturnOnlyPtr() (*int, *int, *int) {
+	a, b, c := 1, 2, 3
+	return &a, &b, &c
+}
+
+//export ReturnString
+func ReturnString() string {
+	return "hello"
+}
+
+//export ReturnByteSlice
+func ReturnByteSlice() []byte {
+	return []byte{1, 2, 3}
+}
+
+//export InputAndReturnUint8
+func InputAndReturnUint8(a, b, c uint8) (uint8, uint8, uint8) {
+	return a, b, c
+}
+
+//export MixedTypes
+func MixedTypes(a uint8, b uint16, c uint32, d uint64, e int, f *int) (uint8, uint16, uint32, uint64, int, *int) {
+	return a, b, c, d, e, f
+}

src/cmd/cgo/out.go

@@ -949,6 +949,8 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		fmt.Fprintf(gotype, "struct {\n")
 		off := int64(0)
 		npad := 0
+		// the align is at least 1 (for char)
+		maxAlign := int64(1)
 		argField := func(typ ast.Expr, namePat string, args ...interface{}) {
 			name := fmt.Sprintf(namePat, args...)
 			t := p.cgoType(typ)
@@ -963,6 +965,11 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			noSourceConf.Fprint(gotype, fset, typ)
 			fmt.Fprintf(gotype, "\n")
 			off += t.Size
+			// keep track of the maximum alignment among all fields
+			// so that we can align the struct correctly
+			if t.Align > maxAlign {
+				maxAlign = t.Align
+			}
 		}
 		if fn.Recv != nil {
 			argField(fn.Recv.List[0].Type, "recv")
@@ -1047,7 +1054,11 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		// string.h for memset, and is also robust to C++
 		// types with constructors. Both GCC and LLVM optimize
 		// this into just zeroing _cgo_a.
-		fmt.Fprintf(fgcc, "\ttypedef %s %v _cgo_argtype;\n", ctype.String(), p.packedAttribute())
+		//
+		// The struct should be aligned to the maximum alignment
+		// of any of its fields. This to avoid alignment
+		// issues.
+		fmt.Fprintf(fgcc, "\ttypedef %s %v __attribute__((aligned(%d))) _cgo_argtype;\n", ctype.String(), p.packedAttribute(), maxAlign)
 		fmt.Fprintf(fgcc, "\tstatic _cgo_argtype _cgo_zero;\n")
 		fmt.Fprintf(fgcc, "\t_cgo_argtype _cgo_a = _cgo_zero;\n")
 		if gccResult != "void" && (len(fntype.Results.List) > 1 || len(fntype.Results.List[0].Names) > 1) {