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  	"golang.org/x/tools/go/types/typeutil"
    22  )
    23  
    24  const Doc = "check for non-64-bits-aligned arguments to sync/atomic functions"
    25  
    26  var Analyzer = &analysis.Analyzer{
    27  	Name:     "atomicalign",
    28  	Doc:      Doc,
    29  	URL:      "https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/atomicalign",
    30  	Requires: []*analysis.Analyzer{inspect.Analyzer},
    31  	Run:      run,
    32  }
    33  
    34  func run(pass *analysis.Pass) (interface{}, error) {
    35  	if 8*pass.TypesSizes.Sizeof(types.Typ[types.Uintptr]) == 64 {
    36  		return nil, nil // 64-bit platform
    37  	}
    38  	if !analysisutil.Imports(pass.Pkg, "sync/atomic") {
    39  		return nil, nil // doesn't directly import sync/atomic
    40  	}
    41  
    42  	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
    43  	nodeFilter := []ast.Node{
    44  		(*ast.CallExpr)(nil),
    45  	}
    46  	funcNames := []string{
    47  		"AddInt64", "AddUint64",
    48  		"LoadInt64", "LoadUint64",
    49  		"StoreInt64", "StoreUint64",
    50  		"SwapInt64", "SwapUint64",
    51  		"CompareAndSwapInt64", "CompareAndSwapUint64",
    52  	}
    53  
    54  	inspect.Preorder(nodeFilter, func(node ast.Node) {
    55  		call := node.(*ast.CallExpr)
    56  		fn := typeutil.StaticCallee(pass.TypesInfo, call)
    57  		if analysisutil.IsFunctionNamed(fn, "sync/atomic", funcNames...) {
    58  			// For all the listed functions, the expression to check is always the first function argument.
    59  			check64BitAlignment(pass, fn.Name(), call.Args[0])
    60  		}
    61  	})
    62  
    63  	return nil, nil
    64  }
    65  
    66  func check64BitAlignment(pass *analysis.Pass, funcName string, arg ast.Expr) {
    67  	// Checks the argument is made of the address operator (&) applied to
    68  	// a struct field (as opposed to a variable as the first word of
    69  	// uint64 and int64 variables can be relied upon to be 64-bit aligned).
    70  	unary, ok := arg.(*ast.UnaryExpr)
    71  	if !ok || unary.Op != token.AND {
    72  		return
    73  	}
    74  
    75  	// Retrieve the types.Struct in order to get the offset of the
    76  	// atomically accessed field.
    77  	sel, ok := unary.X.(*ast.SelectorExpr)
    78  	if !ok {
    79  		return
    80  	}
    81  	tvar, ok := pass.TypesInfo.Selections[sel].Obj().(*types.Var)
    82  	if !ok || !tvar.IsField() {
    83  		return
    84  	}
    85  
    86  	stype, ok := pass.TypesInfo.Types[sel.X].Type.Underlying().(*types.Struct)
    87  	if !ok {
    88  		return
    89  	}
    90  
    91  	var offset int64
    92  	var fields []*types.Var
    93  	for i := 0; i < stype.NumFields(); i++ {
    94  		f := stype.Field(i)
    95  		fields = append(fields, f)
    96  		if f == tvar {
    97  			// We're done, this is the field we were looking for,
    98  			// no need to fill the fields slice further.
    99  			offset = pass.TypesSizes.Offsetsof(fields)[i]
   100  			break
   101  		}
   102  	}
   103  	if offset&7 == 0 {
   104  		return // 64-bit aligned
   105  	}
   106  
   107  	pass.ReportRangef(arg, "address of non 64-bit aligned field .%s passed to atomic.%s", tvar.Name(), funcName)
   108  }
   109
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