1 files changed, 200 insertions, 0 deletions
diff --git a/src/runtime/align_test.go b/src/runtime/align_test.go
new file mode 100644
index 0000000..2bad5b1
--- /dev/null
+++ b/src/runtime/align_test.go
@@ -0,0 +1,200 @@
+// Copyright 2022 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 runtime_test
+
+import (
+	"go/ast"
+	"go/build"
+	"go/importer"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"go/types"
+	"internal/testenv"
+	"os"
+	"regexp"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+// Check that 64-bit fields on which we apply atomic operations
+// are aligned to 8 bytes. This can be a problem on 32-bit systems.
+func TestAtomicAlignment(t *testing.T) {
+	testenv.MustHaveGoBuild(t) // go command needed to resolve std .a files for importer.Default().
+
+	// Read the code making the tables above, to see which fields and
+	// variables we are currently checking.
+	checked := map[string]bool{}
+	x, err := os.ReadFile("./align_runtime_test.go")
+	if err != nil {
+		t.Fatalf("read failed: %v", err)
+	}
+	fieldDesc := map[int]string{}
+	r := regexp.MustCompile(`unsafe[.]Offsetof[(](\w+){}[.](\w+)[)]`)
+	matches := r.FindAllStringSubmatch(string(x), -1)
+	for i, v := range matches {
+		checked["field runtime."+v[1]+"."+v[2]] = true
+		fieldDesc[i] = v[1] + "." + v[2]
+	}
+	varDesc := map[int]string{}
+	r = regexp.MustCompile(`unsafe[.]Pointer[(]&(\w+)[)]`)
+	matches = r.FindAllStringSubmatch(string(x), -1)
+	for i, v := range matches {
+		checked["var "+v[1]] = true
+		varDesc[i] = v[1]
+	}
+
+	// Check all of our alignments. This is the actual core of the test.
+	for i, d := range runtime.AtomicFields {
+		if d%8 != 0 {
+			t.Errorf("field alignment of %s failed: offset is %d", fieldDesc[i], d)
+		}
+	}
+	for i, p := range runtime.AtomicVariables {
+		if uintptr(p)%8 != 0 {
+			t.Errorf("variable alignment of %s failed: address is %x", varDesc[i], p)
+		}
+	}
+
+	// The code above is the actual test. The code below attempts to check
+	// that the tables used by the code above are exhaustive.
+
+	// Parse the whole runtime package, checking that arguments of
+	// appropriate atomic operations are in the list above.
+	fset := token.NewFileSet()
+	m, err := parser.ParseDir(fset, ".", nil, 0)
+	if err != nil {
+		t.Fatalf("parsing runtime failed: %v", err)
+	}
+	pkg := m["runtime"] // Note: ignore runtime_test and main packages
+
+	// Filter files by those for the current architecture/os being tested.
+	fileMap := map[string]bool{}
+	for _, f := range buildableFiles(t, ".") {
+		fileMap[f] = true
+	}
+	var files []*ast.File
+	for fname, f := range pkg.Files {
+		if fileMap[fname] {
+			files = append(files, f)
+		}
+	}
+
+	// Call go/types to analyze the runtime package.
+	var info types.Info
+	info.Types = map[ast.Expr]types.TypeAndValue{}
+	conf := types.Config{Importer: importer.Default()}
+	_, err = conf.Check("runtime", fset, files, &info)
+	if err != nil {
+		t.Fatalf("typechecking runtime failed: %v", err)
+	}
+
+	// Analyze all atomic.*64 callsites.
+	v := Visitor{t: t, fset: fset, types: info.Types, checked: checked}
+	ast.Walk(&v, pkg)
+}
+
+type Visitor struct {
+	fset    *token.FileSet
+	types   map[ast.Expr]types.TypeAndValue
+	checked map[string]bool
+	t       *testing.T
+}
+
+func (v *Visitor) Visit(n ast.Node) ast.Visitor {
+	c, ok := n.(*ast.CallExpr)
+	if !ok {
+		return v
+	}
+	f, ok := c.Fun.(*ast.SelectorExpr)
+	if !ok {
+		return v
+	}
+	p, ok := f.X.(*ast.Ident)
+	if !ok {
+		return v
+	}
+	if p.Name != "atomic" {
+		return v
+	}
+	if !strings.HasSuffix(f.Sel.Name, "64") {
+		return v
+	}
+
+	a := c.Args[0]
+
+	// This is a call to atomic.XXX64(a, ...). Make sure a is aligned to 8 bytes.
+	// XXX = one of Load, Store, Cas, etc.
+	// The arg we care about the alignment of is always the first one.
+
+	if u, ok := a.(*ast.UnaryExpr); ok && u.Op == token.AND {
+		v.checkAddr(u.X)
+		return v
+	}
+
+	// Other cases there's nothing we can check. Assume we're ok.
+	v.t.Logf("unchecked atomic operation %s %v", v.fset.Position(n.Pos()), v.print(n))
+
+	return v
+}
+
+// checkAddr checks to make sure n is a properly aligned address for a 64-bit atomic operation.
+func (v *Visitor) checkAddr(n ast.Node) {
+	switch n := n.(type) {
+	case *ast.IndexExpr:
+		// Alignment of an array element is the same as the whole array.
+		v.checkAddr(n.X)
+		return
+	case *ast.Ident:
+		key := "var " + v.print(n)
+		if !v.checked[key] {
+			v.t.Errorf("unchecked variable %s %s", v.fset.Position(n.Pos()), key)
+		}
+		return
+	case *ast.SelectorExpr:
+		t := v.types[n.X].Type
+		if t == nil {
+			// Not sure what is happening here, go/types fails to
+			// type the selector arg on some platforms.
+			return
+		}
+		if p, ok := t.(*types.Pointer); ok {
+			// Note: we assume here that the pointer p in p.foo is properly
+			// aligned. We just check that foo is at a properly aligned offset.
+			t = p.Elem()
+		} else {
+			v.checkAddr(n.X)
+		}
+		if t.Underlying() == t {
+			v.t.Errorf("analysis can't handle unnamed type %s %v", v.fset.Position(n.Pos()), t)
+		}
+		key := "field " + t.String() + "." + n.Sel.Name
+		if !v.checked[key] {
+			v.t.Errorf("unchecked field %s %s", v.fset.Position(n.Pos()), key)
+		}
+	default:
+		v.t.Errorf("unchecked atomic address %s %v", v.fset.Position(n.Pos()), v.print(n))
+
+	}
+}
+
+func (v *Visitor) print(n ast.Node) string {
+	var b strings.Builder
+	printer.Fprint(&b, v.fset, n)
+	return b.String()
+}
+
+// buildableFiles returns the list of files in the given directory
+// that are actually used for the build, given GOOS/GOARCH restrictions.
+func buildableFiles(t *testing.T, dir string) []string {
+	ctxt := build.Default
+	ctxt.CgoEnabled = true
+	pkg, err := ctxt.ImportDir(dir, 0)
+	if err != nil {
+		t.Fatalf("can't find buildable files: %v", err)
+	}
+	return pkg.GoFiles
+}