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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package framepointer defines an Analyzer that reports assembly code
// that clobbers the frame pointer before saving it.
package framepointer
import (
"go/build"
"regexp"
"strings"
"golang.org/x/tools/go/analysis"
"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
)
const Doc = "report assembly that clobbers the frame pointer before saving it"
var Analyzer = &analysis.Analyzer{
Name: "framepointer",
Doc: Doc,
URL: "https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/framepointer",
Run: run,
}
var (
re = regexp.MustCompile
asmWriteBP = re(`,\s*BP$`) // TODO: can have false positive, e.g. for TESTQ BP,BP. Seems unlikely.
asmMentionBP = re(`\bBP\b`)
asmControlFlow = re(`^(J|RET)`)
)
func run(pass *analysis.Pass) (interface{}, error) {
if build.Default.GOARCH != "amd64" { // TODO: arm64 also?
return nil, nil
}
if build.Default.GOOS != "linux" && build.Default.GOOS != "darwin" {
return nil, nil
}
// Find assembly files to work on.
var sfiles []string
for _, fname := range pass.OtherFiles {
if strings.HasSuffix(fname, ".s") && pass.Pkg.Path() != "runtime" {
sfiles = append(sfiles, fname)
}
}
for _, fname := range sfiles {
content, tf, err := analysisutil.ReadFile(pass, fname)
if err != nil {
return nil, err
}
lines := strings.SplitAfter(string(content), "\n")
active := false
for lineno, line := range lines {
lineno++
// Ignore comments and commented-out code.
if i := strings.Index(line, "//"); i >= 0 {
line = line[:i]
}
line = strings.TrimSpace(line)
// We start checking code at a TEXT line for a frameless function.
if strings.HasPrefix(line, "TEXT") && strings.Contains(line, "(SB)") && strings.Contains(line, "$0") {
active = true
continue
}
if !active {
continue
}
if asmWriteBP.MatchString(line) { // clobber of BP, function is not OK
pass.Reportf(analysisutil.LineStart(tf, lineno), "frame pointer is clobbered before saving")
active = false
continue
}
if asmMentionBP.MatchString(line) { // any other use of BP might be a read, so function is OK
active = false
continue
}
if asmControlFlow.MatchString(line) { // give up after any branch instruction
active = false
continue
}
}
}
return nil, nil
}
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