| 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") && pass.Pkg.Path() != "runtime" { |
| 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 | } |
| 92 |
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