atomicalign.go

Documentation: golang.org/x/tools/go/analysis/passes/atomicalign

     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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