1// Copyright 2022 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package runtime_test
6
7import (
8	"go/ast"
9	"go/build"
10	"go/importer"
11	"go/parser"
12	"go/printer"
13	"go/token"
14	"go/types"
15	"internal/testenv"
16	"os"
17	"regexp"
18	"runtime"
19	"strings"
20	"testing"
21)
22
23// Check that 64-bit fields on which we apply atomic operations
24// are aligned to 8 bytes. This can be a problem on 32-bit systems.
25func TestAtomicAlignment(t *testing.T) {
26	testenv.MustHaveGoBuild(t) // go command needed to resolve std .a files for importer.Default().
27
28	// Read the code making the tables above, to see which fields and
29	// variables we are currently checking.
30	checked := map[string]bool{}
31	x, err := os.ReadFile("./align_runtime_test.go")
32	if err != nil {
33		t.Fatalf("read failed: %v", err)
34	}
35	fieldDesc := map[int]string{}
36	r := regexp.MustCompile(`unsafe[.]Offsetof[(](\w+){}[.](\w+)[)]`)
37	matches := r.FindAllStringSubmatch(string(x), -1)
38	for i, v := range matches {
39		checked["field runtime."+v[1]+"."+v[2]] = true
40		fieldDesc[i] = v[1] + "." + v[2]
41	}
42	varDesc := map[int]string{}
43	r = regexp.MustCompile(`unsafe[.]Pointer[(]&(\w+)[)]`)
44	matches = r.FindAllStringSubmatch(string(x), -1)
45	for i, v := range matches {
46		checked["var "+v[1]] = true
47		varDesc[i] = v[1]
48	}
49
50	// Check all of our alignments. This is the actual core of the test.
51	for i, d := range runtime.AtomicFields {
52		if d%8 != 0 {
53			t.Errorf("field alignment of %s failed: offset is %d", fieldDesc[i], d)
54		}
55	}
56	for i, p := range runtime.AtomicVariables {
57		if uintptr(p)%8 != 0 {
58			t.Errorf("variable alignment of %s failed: address is %x", varDesc[i], p)
59		}
60	}
61
62	// The code above is the actual test. The code below attempts to check
63	// that the tables used by the code above are exhaustive.
64
65	// Parse the whole runtime package, checking that arguments of
66	// appropriate atomic operations are in the list above.
67	fset := token.NewFileSet()
68	m, err := parser.ParseDir(fset, ".", nil, 0)
69	if err != nil {
70		t.Fatalf("parsing runtime failed: %v", err)
71	}
72	pkg := m["runtime"] // Note: ignore runtime_test and main packages
73
74	// Filter files by those for the current architecture/os being tested.
75	fileMap := map[string]bool{}
76	for _, f := range buildableFiles(t, ".") {
77		fileMap[f] = true
78	}
79	var files []*ast.File
80	for fname, f := range pkg.Files {
81		if fileMap[fname] {
82			files = append(files, f)
83		}
84	}
85
86	// Call go/types to analyze the runtime package.
87	var info types.Info
88	info.Types = map[ast.Expr]types.TypeAndValue{}
89	conf := types.Config{Importer: importer.Default()}
90	_, err = conf.Check("runtime", fset, files, &info)
91	if err != nil {
92		t.Fatalf("typechecking runtime failed: %v", err)
93	}
94
95	// Analyze all atomic.*64 callsites.
96	v := Visitor{t: t, fset: fset, types: info.Types, checked: checked}
97	ast.Walk(&v, pkg)
98}
99
100type Visitor struct {
101	fset    *token.FileSet
102	types   map[ast.Expr]types.TypeAndValue
103	checked map[string]bool
104	t       *testing.T
105}
106
107func (v *Visitor) Visit(n ast.Node) ast.Visitor {
108	c, ok := n.(*ast.CallExpr)
109	if !ok {
110		return v
111	}
112	f, ok := c.Fun.(*ast.SelectorExpr)
113	if !ok {
114		return v
115	}
116	p, ok := f.X.(*ast.Ident)
117	if !ok {
118		return v
119	}
120	if p.Name != "atomic" {
121		return v
122	}
123	if !strings.HasSuffix(f.Sel.Name, "64") {
124		return v
125	}
126
127	a := c.Args[0]
128
129	// This is a call to atomic.XXX64(a, ...). Make sure a is aligned to 8 bytes.
130	// XXX = one of Load, Store, Cas, etc.
131	// The arg we care about the alignment of is always the first one.
132
133	if u, ok := a.(*ast.UnaryExpr); ok && u.Op == token.AND {
134		v.checkAddr(u.X)
135		return v
136	}
137
138	// Other cases there's nothing we can check. Assume we're ok.
139	v.t.Logf("unchecked atomic operation %s %v", v.fset.Position(n.Pos()), v.print(n))
140
141	return v
142}
143
144// checkAddr checks to make sure n is a properly aligned address for a 64-bit atomic operation.
145func (v *Visitor) checkAddr(n ast.Node) {
146	switch n := n.(type) {
147	case *ast.IndexExpr:
148		// Alignment of an array element is the same as the whole array.
149		v.checkAddr(n.X)
150		return
151	case *ast.Ident:
152		key := "var " + v.print(n)
153		if !v.checked[key] {
154			v.t.Errorf("unchecked variable %s %s", v.fset.Position(n.Pos()), key)
155		}
156		return
157	case *ast.SelectorExpr:
158		t := v.types[n.X].Type
159		if t == nil {
160			// Not sure what is happening here, go/types fails to
161			// type the selector arg on some platforms.
162			return
163		}
164		if p, ok := t.(*types.Pointer); ok {
165			// Note: we assume here that the pointer p in p.foo is properly
166			// aligned. We just check that foo is at a properly aligned offset.
167			t = p.Elem()
168		} else {
169			v.checkAddr(n.X)
170		}
171		if t.Underlying() == t {
172			v.t.Errorf("analysis can't handle unnamed type %s %v", v.fset.Position(n.Pos()), t)
173		}
174		key := "field " + t.String() + "." + n.Sel.Name
175		if !v.checked[key] {
176			v.t.Errorf("unchecked field %s %s", v.fset.Position(n.Pos()), key)
177		}
178	default:
179		v.t.Errorf("unchecked atomic address %s %v", v.fset.Position(n.Pos()), v.print(n))
180
181	}
182}
183
184func (v *Visitor) print(n ast.Node) string {
185	var b strings.Builder
186	printer.Fprint(&b, v.fset, n)
187	return b.String()
188}
189
190// buildableFiles returns the list of files in the given directory
191// that are actually used for the build, given GOOS/GOARCH restrictions.
192func buildableFiles(t *testing.T, dir string) []string {
193	ctxt := build.Default
194	ctxt.CgoEnabled = true
195	pkg, err := ctxt.ImportDir(dir, 0)
196	if err != nil {
197		t.Fatalf("can't find buildable files: %v", err)
198	}
199	return pkg.GoFiles
200}
201