go/analysis/passes/atomicalign: add atomicalign ckecker

The atomicalign Analyzer checks the alignment of 64-bits variables
accessed atomically via sync/atomic functions on 32-bits
architectures. Per the sync/atomic BUG note those variables must
be 64-bits aligned, otherwise a runtime panic is issued.

The analyzer only shows and runs on 32-bits architectures.

This CL should not introduce any false positives.

Add some tests in testdata/src/a to verify the analyzer behavior
on affected architectures plus some very basic test to verify that
no warning is generated on non-affected ones.

Fixes golang/go#11891

Change-Id: I02cfc574883564cd2a213a92d33bda3cc9a1ea98
Reviewed-on: https://go-review.googlesource.com/c/158277
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

go/analysis/cmd/vet/vet.go

@@ -20,6 +20,7 @@ import (
 	"golang.org/x/tools/go/analysis/passes/asmdecl"
 	"golang.org/x/tools/go/analysis/passes/assign"
 	"golang.org/x/tools/go/analysis/passes/atomic"
+	"golang.org/x/tools/go/analysis/passes/atomicalign"
 	"golang.org/x/tools/go/analysis/passes/bools"
 	"golang.org/x/tools/go/analysis/passes/buildtag"
 	"golang.org/x/tools/go/analysis/passes/cgocall"
@@ -51,6 +52,7 @@ func main() {
 		asmdecl.Analyzer,
 		assign.Analyzer,
 		atomic.Analyzer,
+		atomicalign.Analyzer,
 		bools.Analyzer,
 		buildtag.Analyzer,
 		cgocall.Analyzer,

go/analysis/passes/atomicalign/atomicalign.go

@@ -0,0 +1,126 @@
+// Copyright 2019 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 atomicalign defines an Analyzer that checks for non-64-bit-aligned
+// arguments to sync/atomic functions. On non-32-bit platforms, those functions
+// panic if their argument variables are not 64-bit aligned. It is therefore
+// the caller's responsibility to arrange for 64-bit alignment of such variables.
+// See https://golang.org/pkg/sync/atomic/#pkg-note-BUG
+package atomicalign
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/passes/inspect"
+	"golang.org/x/tools/go/ast/inspector"
+)
+
+var Analyzer = &analysis.Analyzer{
+	Name:     "atomicalign",
+	Doc:      "check for non-64-bits-aligned arguments to sync/atomic functions",
+	Requires: []*analysis.Analyzer{inspect.Analyzer},
+	Run:      run,
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	if 8*pass.TypesSizes.Sizeof(types.Typ[types.Uintptr]) == 64 {
+		return nil, nil // 64-bit platform
+	}
+	if imports(pass.Pkg, "sync/atomic") == nil {
+		return nil, nil // doesn't directly import sync/atomic
+	}
+
+	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
+	nodeFilter := []ast.Node{
+		(*ast.CallExpr)(nil),
+	}
+
+	inspect.Preorder(nodeFilter, func(node ast.Node) {
+		call := node.(*ast.CallExpr)
+		sel, ok := call.Fun.(*ast.SelectorExpr)
+		if !ok {
+			return
+		}
+		pkgIdent, ok := sel.X.(*ast.Ident)
+		if !ok {
+			return
+		}
+		pkgName, ok := pass.TypesInfo.Uses[pkgIdent].(*types.PkgName)
+		if !ok || pkgName.Imported().Path() != "sync/atomic" {
+			return
+		}
+
+		switch sel.Sel.Name {
+		case "AddInt64", "AddUint64",
+			"LoadInt64", "LoadUint64",
+			"StoreInt64", "StoreUint64",
+			"SwapInt64", "SwapUint64",
+			"CompareAndSwapInt64", "CompareAndSwapUint64":
+
+			// For all the listed functions, the expression to check is always the first function argument.
+			check64BitAlignment(pass, sel.Sel.Name, call.Args[0])
+		}
+	})
+
+	return nil, nil
+}
+
+func check64BitAlignment(pass *analysis.Pass, funcName string, arg ast.Expr) {
+	// Checks the argument is made of the address operator (&) applied to
+	// to a struct field (as opposed to a variable as the first word of
+	// uint64 and int64 variables can be relied upon to be 64-bit aligned.
+	unary, ok := arg.(*ast.UnaryExpr)
+	if !ok || unary.Op != token.AND {
+		return
+	}
+
+	// Retrieve the types.Struct in order to get the offset of the
+	// atomically accessed field.
+	sel, ok := unary.X.(*ast.SelectorExpr)
+	if !ok {
+		return
+	}
+	tvar, ok := pass.TypesInfo.Selections[sel].Obj().(*types.Var)
+	if !ok || !tvar.IsField() {
+		return
+	}
+
+	stype, ok := pass.TypesInfo.Types[sel.X].Type.Underlying().(*types.Struct)
+	if !ok {
+		return
+	}
+
+	var offset int64
+	var fields []*types.Var
+	for i := 0; i < stype.NumFields(); i++ {
+		f := stype.Field(i)
+		fields = append(fields, f)
+		if f == tvar {
+			// We're done, this is the field we were looking for,
+			// no need to fill the fields slice further.
+			offset = pass.TypesSizes.Offsetsof(fields)[i]
+			break
+		}
+	}
+	if offset&7 == 0 {
+		return // 64-bit aligned
+	}
+
+	pass.Reportf(arg.Pos(), "address of non 64-bit aligned field .%s passed to atomic.%s", tvar.Name(), funcName)
+}
+
+// imports reports whether pkg has path among its direct imports.
+// It returns the imported package if so, or nil if not.
+// copied from passes/cgocall.
+func imports(pkg *types.Package, path string) *types.Package {
+	for _, imp := range pkg.Imports() {
+		if imp.Path() == path {
+			return imp
+		}
+	}
+	return nil
+}

go/analysis/passes/atomicalign/atomicalign_test.go

@@ -0,0 +1,17 @@
+// Copyright 2018 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 atomicalign_test
+
+import (
+	"testing"
+
+	"golang.org/x/tools/go/analysis/analysistest"
+	"golang.org/x/tools/go/analysis/passes/atomicalign"
+)
+
+func Test(t *testing.T) {
+	testdata := analysistest.TestData()
+	analysistest.Run(t, testdata, atomicalign.Analyzer, "a", "b")
+}

go/analysis/passes/atomicalign/testdata/src/a/a.go

@@ -0,0 +1,230 @@
+// Copyright 2019 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.
+
+// This file contains tests for the atomic alignment checker.
+
+// +build arm 386
+
+package testdata
+
+import (
+	"io"
+	"sync/atomic"
+)
+
+func intsAlignment() {
+	var s struct {
+		a bool
+		b uint8
+		c int8
+		d byte
+		f int16
+		g int16
+		h int64
+		i byte
+		j uint64
+	}
+	atomic.AddInt64(&s.h, 9)
+	atomic.AddUint64(&s.j, 0) // want "address of non 64-bit aligned field .j passed to atomic.AddUint64"
+}
+
+func floatAlignment() {
+	var s struct {
+		a float32
+		b int64
+		c float32
+		d float64
+		e uint64
+	}
+	atomic.LoadInt64(&s.b) // want "address of non 64-bit aligned field .b passed to atomic.LoadInt64"
+	atomic.LoadUint64(&s.e)
+}
+
+func uintptrAlignment() {
+	var s struct {
+		a uintptr
+		b int64
+		c int
+		d uint
+		e int32
+		f uint64
+	}
+	atomic.StoreInt64(&s.b, 0) // want "address of non 64-bit aligned field .b passed to atomic.StoreInt64"
+	atomic.StoreUint64(&s.f, 0)
+}
+
+func runeAlignment() {
+	var s struct {
+		a rune
+		b int64
+		_ rune
+		c uint64
+	}
+	atomic.SwapInt64(&s.b, 0) // want "address of non 64-bit aligned field .b passed to atomic.SwapInt64"
+	atomic.SwapUint64(&s.c, 0)
+}
+
+func complexAlignment() {
+	var s struct {
+		a complex64
+		b int64
+		c complex128
+		d uint64
+	}
+	atomic.CompareAndSwapInt64(&s.b, 0, 1)
+	atomic.CompareAndSwapUint64(&s.d, 0, 1)
+}
+
+// continuer ici avec les tests
+
+func channelAlignment() {
+	var a struct {
+		a chan struct{}
+		b int64
+		c <-chan struct{}
+		d uint64
+	}
+
+	atomic.AddInt64(&a.b, 0) // want "address of non 64-bit aligned field .b passed to atomic.AddInt64"
+	atomic.AddUint64(&a.d, 0)
+}
+
+func arrayAlignment() {
+	var a struct {
+		a [1]uint16
+		b int64
+		_ [2]uint16
+		c int64
+		d [1]uint16
+		e uint64
+	}
+
+	atomic.LoadInt64(&a.b) // want "address of non 64-bit aligned field .b passed to atomic.LoadInt64"
+	atomic.LoadInt64(&a.c)
+	atomic.LoadUint64(&a.e) // want "address of non 64-bit aligned field .e passed to atomic.LoadUint64"
+}
+
+func anonymousFieldAlignment() {
+	var f struct {
+		a, b int32
+		c, d int64
+		_    bool
+		e, f uint64
+	}
+
+	atomic.StoreInt64(&f.c, 12)
+	atomic.StoreInt64(&f.d, 27)
+	atomic.StoreUint64(&f.e, 6)  // want "address of non 64-bit aligned field .e passed to atomic.StoreUint64"
+	atomic.StoreUint64(&f.f, 79) // want "address of non 64-bit aligned field .f passed to atomic.StoreUint64"
+}
+
+type ts struct {
+	e  int64
+	e2 []int
+	f  uint64
+}
+
+func typedStructAlignment() {
+	var b ts
+	atomic.SwapInt64(&b.e, 9)
+	atomic.SwapUint64(&b.f, 9) // want "address of non 64-bit aligned field .f passed to atomic.SwapUint64"
+}
+
+func aliasAlignment() {
+	type (
+		mybytea uint8
+		mybyteb byte
+		mybytec = uint8
+		mybyted = byte
+	)
+
+	var e struct {
+		a    byte
+		b    mybytea
+		c    mybyteb
+		e    mybytec
+		f    int64
+		g, h uint16
+		i    uint64
+	}
+
+	atomic.CompareAndSwapInt64(&e.f, 0, 1) // want "address of non 64-bit aligned field .f passed to atomic.CompareAndSwapInt64"
+	atomic.CompareAndSwapUint64(&e.i, 1, 2)
+}
+
+func stringAlignment() {
+	var a struct {
+		a uint32
+		b string
+		c int64
+	}
+	atomic.AddInt64(&a.c, 10) // want "address of non 64-bit aligned field .c passed to atomic.AddInt64"
+}
+
+func sliceAlignment() {
+	var s struct {
+		a []int32
+		b int64
+		c uint32
+		d uint64
+	}
+
+	atomic.LoadInt64(&s.b) // want "address of non 64-bit aligned field .b passed to atomic.LoadInt64"
+	atomic.LoadUint64(&s.d)
+}
+
+func interfaceAlignment() {
+	var s struct {
+		a interface{}
+		b int64
+		c io.Writer
+		e int64
+		_ int32
+		f uint64
+	}
+
+	atomic.StoreInt64(&s.b, 9)
+	atomic.StoreInt64(&s.e, 9)
+	atomic.StoreUint64(&s.f, 9) // want "address of non 64-bit aligned field .f passed to atomic.StoreUint64"
+}
+
+func pointerAlignment() {
+	var s struct {
+		a, b *int
+		c    int64
+		d    *interface{}
+		e    uint64
+	}
+
+	atomic.SwapInt64(&s.c, 9)
+	atomic.SwapUint64(&s.e, 9) // want "address of non 64-bit aligned field .e passed to atomic.SwapUint64"
+}
+
+// non-struct fields are already 64-bits correctly aligned per Go spec
+func nonStructFields() {
+	var (
+		a *int64
+		b [2]uint64
+		c int64
+	)
+
+	atomic.CompareAndSwapInt64(a, 10, 11)
+	atomic.CompareAndSwapUint64(&b[0], 5, 23)
+	atomic.CompareAndSwapInt64(&c, -1, -15)
+}
+
+func embeddedStructFields() {
+	var s1 struct {
+		_ struct{ _ int32 }
+		a int64
+		_ struct{}
+		b uint64
+		_ struct{ _ [2]uint16 }
+		c int64
+	}
+
+	atomic.AddInt64(&s1.a, 9)  // want "address of non 64-bit aligned field .a passed to atomic.AddInt64"
+	atomic.AddUint64(&s1.b, 9) // want "address of non 64-bit aligned field .b passed to atomic.AddUint64"
+	atomic.AddInt64(&s1.c, 9)
+}

go/analysis/passes/atomicalign/testdata/src/a/stub.go

@@ -0,0 +1,7 @@
+// Copyright 2019 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.
+
+// This file is only here to not trigger "build constraints exclude all Go files" during tests
+
+package testdata

go/analysis/passes/atomicalign/testdata/src/b/b.go

@@ -0,0 +1,19 @@
+// Copyright 2019 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.
+
+// +build !arm,!386
+
+package testdata
+
+import (
+	"sync/atomic"
+)
+
+func nonAffectedArchs() {
+	var s struct {
+		_ bool
+		a uint64
+	}
+	atomic.SwapUint64(&s.a, 9) // ok on 64-bit architectures
+}

go/analysis/passes/atomicalign/testdata/src/b/stub.go

@@ -0,0 +1,7 @@
+// Copyright 2019 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.
+
+// This file is only here to not trigger "build constraints exclude all Go files" during tests
+
+package testdata