101 lines
2.6 KiB
Go
101 lines
2.6 KiB
Go
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package sa9006
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import (
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"fmt"
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"go/ast"
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"go/types"
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"honnef.co/go/tools/analysis/code"
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"honnef.co/go/tools/analysis/lint"
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"honnef.co/go/tools/analysis/report"
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"honnef.co/go/tools/pattern"
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"golang.org/x/tools/go/analysis"
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)
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var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
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Analyzer: &analysis.Analyzer{
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Name: "SA9006",
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Run: run,
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Requires: code.RequiredAnalyzers,
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},
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Doc: &lint.RawDocumentation{
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Title: `Dubious bit shifting of a fixed size integer value`,
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Text: `Bit shifting a value past its size will always clear the value.
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For instance:
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v := int8(42)
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v >>= 8
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will always result in 0.
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This check flags bit shifting operations on fixed size integer values only.
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That is, int, uint and uintptr are never flagged to avoid potential false
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positives in somewhat exotic but valid bit twiddling tricks:
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// Clear any value above 32 bits if integers are more than 32 bits.
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func f(i int) int {
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v := i >> 32
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v = v << 32
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return i-v
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}`,
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Since: "2020.2",
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Severity: lint.SeverityWarning,
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// Technically this should be MergeIfAll, because the type of
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// v might be different for different build tags. Practically,
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// don't write code that depends on that.
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MergeIf: lint.MergeIfAny,
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},
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})
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var Analyzer = SCAnalyzer.Analyzer
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var (
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checkFixedLengthTypeShiftQ = pattern.MustParse(`
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(Or
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(AssignStmt _ (Or ">>=" "<<=") _)
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(BinaryExpr _ (Or ">>" "<<") _))
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`)
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)
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func run(pass *analysis.Pass) (any, error) {
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isDubiousShift := func(x, y ast.Expr) (int64, int64, bool) {
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typ, ok := pass.TypesInfo.TypeOf(x).Underlying().(*types.Basic)
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if !ok {
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return 0, 0, false
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}
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switch typ.Kind() {
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case types.Int8, types.Int16, types.Int32, types.Int64,
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types.Uint8, types.Uint16, types.Uint32, types.Uint64:
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// We're only interested in fixed–size types.
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default:
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return 0, 0, false
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}
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const bitsInByte = 8
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typeBits := pass.TypesSizes.Sizeof(typ) * bitsInByte
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shiftLength, ok := code.ExprToInt(pass, y)
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if !ok {
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return 0, 0, false
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}
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return typeBits, shiftLength, shiftLength >= typeBits
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}
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for node := range code.Matches(pass, checkFixedLengthTypeShiftQ) {
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switch e := node.(type) {
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case *ast.AssignStmt:
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if size, shift, yes := isDubiousShift(e.Lhs[0], e.Rhs[0]); yes {
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report.Report(pass, e, fmt.Sprintf("shifting %d-bit value by %d bits will always clear it", size, shift))
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}
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case *ast.BinaryExpr:
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if size, shift, yes := isDubiousShift(e.X, e.Y); yes {
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report.Report(pass, e, fmt.Sprintf("shifting %d-bit value by %d bits will always clear it", size, shift))
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}
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}
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}
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return nil, nil
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}
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