1 // Copyright 2013 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.
5 // Package cgo handles cgo preprocessing of files containing `import "C"`.
9 // The approach taken is to run the cgo processor on the package's
10 // CgoFiles and parse the output, faking the filenames of the
11 // resulting ASTs so that the synthetic file containing the C types is
12 // called "C" (e.g. "~/go/src/net/C") and the preprocessed files
13 // have their original names (e.g. "~/go/src/net/cgo_unix.go"),
14 // not the names of the actual temporary files.
16 // The advantage of this approach is its fidelity to 'go build'. The
17 // downside is that the token.Position.Offset for each AST node is
18 // incorrect, being an offset within the temporary file. Line numbers
19 // should still be correct because of the //line comments.
21 // The logic of this file is mostly plundered from the 'go build'
22 // tool, which also invokes the cgo preprocessor.
25 // REJECTED ALTERNATIVE
27 // An alternative approach that we explored is to extend go/types'
28 // Importer mechanism to provide the identity of the importing package
29 // so that each time `import "C"` appears it resolves to a different
30 // synthetic package containing just the objects needed in that case.
31 // The loader would invoke cgo but parse only the cgo_types.go file
32 // defining the package-level objects, discarding the other files
33 // resulting from preprocessing.
35 // The benefit of this approach would have been that source-level
36 // syntax information would correspond exactly to the original cgo
37 // file, with no preprocessing involved, making source tools like
38 // godoc, guru, and eg happy. However, the approach was rejected
39 // due to the additional complexity it would impose on go/types. (It
40 // made for a beautiful demo, though.)
42 // cgo files, despite their *.go extension, are not legal Go source
43 // files per the specification since they may refer to unexported
44 // members of package "C" such as C.int. Also, a function such as
45 // C.getpwent has in effect two types, one matching its C type and one
46 // which additionally returns (errno C.int). The cgo preprocessor
47 // uses name mangling to distinguish these two functions in the
48 // processed code, but go/types would need to duplicate this logic in
49 // its handling of function calls, analogous to the treatment of map
50 // lookups in which y=m[k] and y,ok=m[k] are both legal.
69 // ProcessFiles invokes the cgo preprocessor on bp.CgoFiles, parses
70 // the output and returns the resulting ASTs.
72 func ProcessFiles(bp *build.Package, fset *token.FileSet, DisplayPath func(path string) string, mode parser.Mode) ([]*ast.File, error) {
73 tmpdir, err := ioutil.TempDir("", strings.Replace(bp.ImportPath, "/", "_", -1)+"_C")
77 defer os.RemoveAll(tmpdir)
80 if DisplayPath != nil {
81 pkgdir = DisplayPath(pkgdir)
84 cgoFiles, cgoDisplayFiles, err := Run(bp, pkgdir, tmpdir, false)
89 for i := range cgoFiles {
90 rd, err := os.Open(cgoFiles[i])
94 display := filepath.Join(bp.Dir, cgoDisplayFiles[i])
95 f, err := parser.ParseFile(fset, display, rd, mode)
100 files = append(files, f)
105 var cgoRe = regexp.MustCompile(`[/\\:]`)
107 // Run invokes the cgo preprocessor on bp.CgoFiles and returns two
108 // lists of files: the resulting processed files (in temporary
109 // directory tmpdir) and the corresponding names of the unprocessed files.
111 // Run is adapted from (*builder).cgo in
112 // $GOROOT/src/cmd/go/build.go, but these features are unsupported:
113 // Objective C, CGOPKGPATH, CGO_FLAGS.
115 // If useabs is set to true, absolute paths of the bp.CgoFiles will be passed in
116 // to the cgo preprocessor. This in turn will set the // line comments
117 // referring to those files to use absolute paths. This is needed for
118 // go/packages using the legacy go list support so it is able to find
119 // the original files.
120 func Run(bp *build.Package, pkgdir, tmpdir string, useabs bool) (files, displayFiles []string, err error) {
121 cgoCPPFLAGS, _, _, _ := cflags(bp, true)
122 _, cgoexeCFLAGS, _, _ := cflags(bp, false)
124 if len(bp.CgoPkgConfig) > 0 {
125 pcCFLAGS, err := pkgConfigFlags(bp)
129 cgoCPPFLAGS = append(cgoCPPFLAGS, pcCFLAGS...)
132 // Allows including _cgo_export.h from .[ch] files in the package.
133 cgoCPPFLAGS = append(cgoCPPFLAGS, "-I", tmpdir)
135 // _cgo_gotypes.go (displayed "C") contains the type definitions.
136 files = append(files, filepath.Join(tmpdir, "_cgo_gotypes.go"))
137 displayFiles = append(displayFiles, "C")
138 for _, fn := range bp.CgoFiles {
139 // "foo.cgo1.go" (displayed "foo.go") is the processed Go source.
140 f := cgoRe.ReplaceAllString(fn[:len(fn)-len("go")], "_")
141 files = append(files, filepath.Join(tmpdir, f+"cgo1.go"))
142 displayFiles = append(displayFiles, fn)
145 var cgoflags []string
146 if bp.Goroot && bp.ImportPath == "runtime/cgo" {
147 cgoflags = append(cgoflags, "-import_runtime_cgo=false")
149 if bp.Goroot && bp.ImportPath == "runtime/race" || bp.ImportPath == "runtime/cgo" {
150 cgoflags = append(cgoflags, "-import_syscall=false")
153 var cgoFiles []string = bp.CgoFiles
155 cgoFiles = make([]string, len(bp.CgoFiles))
156 for i := range cgoFiles {
157 cgoFiles[i] = filepath.Join(pkgdir, bp.CgoFiles[i])
162 "go", "tool", "cgo", "-objdir", tmpdir, cgoflags, "--",
163 cgoCPPFLAGS, cgoexeCFLAGS, cgoFiles,
166 log.Printf("Running cgo for package %q: %s (dir=%s)", bp.ImportPath, args, pkgdir)
168 cmd := exec.Command(args[0], args[1:]...)
170 cmd.Stdout = os.Stderr
171 cmd.Stderr = os.Stderr
172 if err := cmd.Run(); err != nil {
173 return nil, nil, fmt.Errorf("cgo failed: %s: %s", args, err)
176 return files, displayFiles, nil
179 // -- unmodified from 'go build' ---------------------------------------
181 // Return the flags to use when invoking the C or C++ compilers, or cgo.
182 func cflags(p *build.Package, def bool) (cppflags, cflags, cxxflags, ldflags []string) {
188 cppflags = stringList(envList("CGO_CPPFLAGS", ""), p.CgoCPPFLAGS)
189 cflags = stringList(envList("CGO_CFLAGS", defaults), p.CgoCFLAGS)
190 cxxflags = stringList(envList("CGO_CXXFLAGS", defaults), p.CgoCXXFLAGS)
191 ldflags = stringList(envList("CGO_LDFLAGS", defaults), p.CgoLDFLAGS)
195 // envList returns the value of the given environment variable broken
196 // into fields, using the default value when the variable is empty.
197 func envList(key, def string) []string {
202 return strings.Fields(v)
205 // stringList's arguments should be a sequence of string or []string values.
206 // stringList flattens them into a single []string.
207 func stringList(args ...interface{}) []string {
209 for _, arg := range args {
210 switch arg := arg.(type) {
212 x = append(x, arg...)
216 panic("stringList: invalid argument")