| 1 | // Copyright 2019 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 atomicalign defines an Analyzer that checks for non-64-bit-aligned |
| 6 | // arguments to sync/atomic functions. On non-32-bit platforms, those functions |
| 7 | // panic if their argument variables are not 64-bit aligned. It is therefore |
| 8 | // the caller's responsibility to arrange for 64-bit alignment of such variables. |
| 9 | // See https://golang.org/pkg/sync/atomic/#pkg-note-BUG |
| 10 | package atomicalign |
| 11 | |
| 12 | import ( |
| 13 | "go/ast" |
| 14 | "go/token" |
| 15 | "go/types" |
| 16 | |
| 17 | "golang.org/x/tools/go/analysis" |
| 18 | "golang.org/x/tools/go/analysis/passes/inspect" |
| 19 | "golang.org/x/tools/go/analysis/passes/internal/analysisutil" |
| 20 | "golang.org/x/tools/go/ast/inspector" |
| 21 | ) |
| 22 | |
| 23 | const Doc = "check for non-64-bits-aligned arguments to sync/atomic functions" |
| 24 | |
| 25 | var Analyzer = &analysis.Analyzer{ |
| 26 | Name: "atomicalign", |
| 27 | Doc: Doc, |
| 28 | Requires: []*analysis.Analyzer{inspect.Analyzer}, |
| 29 | Run: run, |
| 30 | } |
| 31 | |
| 32 | func run(pass *analysis.Pass) (interface{}, error) { |
| 33 | if 8*pass.TypesSizes.Sizeof(types.Typ[types.Uintptr]) == 64 { |
| 34 | return nil, nil // 64-bit platform |
| 35 | } |
| 36 | if !analysisutil.Imports(pass.Pkg, "sync/atomic") { |
| 37 | return nil, nil // doesn't directly import sync/atomic |
| 38 | } |
| 39 | |
| 40 | inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector) |
| 41 | nodeFilter := []ast.Node{ |
| 42 | (*ast.CallExpr)(nil), |
| 43 | } |
| 44 | |
| 45 | inspect.Preorder(nodeFilter, func(node ast.Node) { |
| 46 | call := node.(*ast.CallExpr) |
| 47 | sel, ok := call.Fun.(*ast.SelectorExpr) |
| 48 | if !ok { |
| 49 | return |
| 50 | } |
| 51 | pkgIdent, ok := sel.X.(*ast.Ident) |
| 52 | if !ok { |
| 53 | return |
| 54 | } |
| 55 | pkgName, ok := pass.TypesInfo.Uses[pkgIdent].(*types.PkgName) |
| 56 | if !ok || pkgName.Imported().Path() != "sync/atomic" { |
| 57 | return |
| 58 | } |
| 59 | |
| 60 | switch sel.Sel.Name { |
| 61 | case "AddInt64", "AddUint64", |
| 62 | "LoadInt64", "LoadUint64", |
| 63 | "StoreInt64", "StoreUint64", |
| 64 | "SwapInt64", "SwapUint64", |
| 65 | "CompareAndSwapInt64", "CompareAndSwapUint64": |
| 66 | |
| 67 | // For all the listed functions, the expression to check is always the first function argument. |
| 68 | check64BitAlignment(pass, sel.Sel.Name, call.Args[0]) |
| 69 | } |
| 70 | }) |
| 71 | |
| 72 | return nil, nil |
| 73 | } |
| 74 | |
| 75 | func check64BitAlignment(pass *analysis.Pass, funcName string, arg ast.Expr) { |
| 76 | // Checks the argument is made of the address operator (&) applied to |
| 77 | // to a struct field (as opposed to a variable as the first word of |
| 78 | // uint64 and int64 variables can be relied upon to be 64-bit aligned. |
| 79 | unary, ok := arg.(*ast.UnaryExpr) |
| 80 | if !ok || unary.Op != token.AND { |
| 81 | return |
| 82 | } |
| 83 | |
| 84 | // Retrieve the types.Struct in order to get the offset of the |
| 85 | // atomically accessed field. |
| 86 | sel, ok := unary.X.(*ast.SelectorExpr) |
| 87 | if !ok { |
| 88 | return |
| 89 | } |
| 90 | tvar, ok := pass.TypesInfo.Selections[sel].Obj().(*types.Var) |
| 91 | if !ok || !tvar.IsField() { |
| 92 | return |
| 93 | } |
| 94 | |
| 95 | stype, ok := pass.TypesInfo.Types[sel.X].Type.Underlying().(*types.Struct) |
| 96 | if !ok { |
| 97 | return |
| 98 | } |
| 99 | |
| 100 | var offset int64 |
| 101 | var fields []*types.Var |
| 102 | for i := 0; i < stype.NumFields(); i++ { |
| 103 | f := stype.Field(i) |
| 104 | fields = append(fields, f) |
| 105 | if f == tvar { |
| 106 | // We're done, this is the field we were looking for, |
| 107 | // no need to fill the fields slice further. |
| 108 | offset = pass.TypesSizes.Offsetsof(fields)[i] |
| 109 | break |
| 110 | } |
| 111 | } |
| 112 | if offset&7 == 0 { |
| 113 | return // 64-bit aligned |
| 114 | } |
| 115 | |
| 116 | pass.ReportRangef(arg, "address of non 64-bit aligned field .%s passed to atomic.%s", tvar.Name(), funcName) |
| 117 | } |
| 118 |
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