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| 1 | +// Copyright 2020 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 framepointer defines an Analyzer that reports assembly code |
| 6 | +// that clobbers the frame pointer before saving it. |
| 7 | +package framepointer |
| 8 | + |
| 9 | +import ( |
| 10 | + "go/build" |
| 11 | + "regexp" |
| 12 | + "strings" |
| 13 | + |
| 14 | + "golang.org/x/tools/go/analysis" |
| 15 | + "golang.org/x/tools/go/analysis/passes/internal/analysisutil" |
| 16 | +) |
| 17 | + |
| 18 | +const Doc = "report assembly that clobbers the frame pointer before saving it" |
| 19 | + |
| 20 | +var Analyzer = &analysis.Analyzer{ |
| 21 | + Name: "framepointer", |
| 22 | + Doc: Doc, |
| 23 | + Run: run, |
| 24 | +} |
| 25 | + |
| 26 | +var ( |
| 27 | + re = regexp.MustCompile |
| 28 | + asmWriteBP = re(`,\s*BP$`) // TODO: can have false positive, e.g. for TESTQ BP,BP. Seems unlikely. |
| 29 | + asmMentionBP = re(`\bBP\b`) |
| 30 | + asmControlFlow = re(`^(J|RET)`) |
| 31 | +) |
| 32 | + |
| 33 | +func run(pass *analysis.Pass) (interface{}, error) { |
| 34 | + if build.Default.GOARCH != "amd64" { // TODO: arm64 also? |
| 35 | + return nil, nil |
| 36 | + } |
| 37 | + if build.Default.GOOS != "linux" && build.Default.GOOS != "darwin" { |
| 38 | + return nil, nil |
| 39 | + } |
| 40 | + |
| 41 | + // Find assembly files to work on. |
| 42 | + var sfiles []string |
| 43 | + for _, fname := range pass.OtherFiles { |
| 44 | + if strings.HasSuffix(fname, ".s") { |
| 45 | + sfiles = append(sfiles, fname) |
| 46 | + } |
| 47 | + } |
| 48 | + |
| 49 | + for _, fname := range sfiles { |
| 50 | + content, tf, err := analysisutil.ReadFile(pass.Fset, fname) |
| 51 | + if err != nil { |
| 52 | + return nil, err |
| 53 | + } |
| 54 | + |
| 55 | + lines := strings.SplitAfter(string(content), "\n") |
| 56 | + active := false |
| 57 | + for lineno, line := range lines { |
| 58 | + lineno++ |
| 59 | + |
| 60 | + // Ignore comments and commented-out code. |
| 61 | + if i := strings.Index(line, "//"); i >= 0 { |
| 62 | + line = line[:i] |
| 63 | + } |
| 64 | + line = strings.TrimSpace(line) |
| 65 | + |
| 66 | + // We start checking code at a TEXT line for a frameless function. |
| 67 | + if strings.HasPrefix(line, "TEXT") && strings.Contains(line, "(SB)") && strings.Contains(line, "$0") { |
| 68 | + active = true |
| 69 | + continue |
| 70 | + } |
| 71 | + if !active { |
| 72 | + continue |
| 73 | + } |
| 74 | + |
| 75 | + if asmWriteBP.MatchString(line) { // clobber of BP, function is not OK |
| 76 | + pass.Reportf(analysisutil.LineStart(tf, lineno), "frame pointer is clobbered before saving") |
| 77 | + active = false |
| 78 | + continue |
| 79 | + } |
| 80 | + if asmMentionBP.MatchString(line) { // any other use of BP might be a read, so function is OK |
| 81 | + active = false |
| 82 | + continue |
| 83 | + } |
| 84 | + if asmControlFlow.MatchString(line) { // give up after any branch instruction |
| 85 | + active = false |
| 86 | + continue |
| 87 | + } |
| 88 | + } |
| 89 | + } |
| 90 | + return nil, nil |
| 91 | +} |
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