align_test.go

     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  
     5  package runtime_test
     6  
     7  import (
     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.
    25  func 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  
   100  type Visitor struct {
   101  	fset    *token.FileSet
   102  	types   map[ast.Expr]types.TypeAndValue
   103  	checked map[string]bool
   104  	t       *testing.T
   105  }
   106  
   107  func (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.
   145  func (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  
   184  func (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.
   192  func 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
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