cmd/cgo: split gofrontend mangling checks into cmd/internal/pkgpath

This is a step toward porting https://golang.org/cl/219817 from the
gofrontend repo to the main repo.

Note that this also corrects the implementation of the v2 mangling
scheme to use ..u and ..U where appropriate.

For #37272

Change-Id: I64a1e7ca1c84348efcbf1cf62049eeb05c830ed8
Reviewed-on: https://go-review.googlesource.com/c/go/+/259298
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

1 files changed, 114 insertions, 0 deletions

diff --git a/src/cmd/internal/pkgpath/pkgpath.go b/src/cmd/internal/pkgpath/pkgpath.go
new file mode 100644
index 0000000000..0b24468be6
--- /dev/null
+++ b/src/cmd/internal/pkgpath/pkgpath.go
@@ -0,0 +1,114 @@
+// 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 pkgpath determines the package path used by gccgo/GoLLVM symbols.
+// This package is not used for the gc compiler.
+package pkgpath
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+// ToSymbolFunc returns a function that may be used to convert a
+// package path into a string suitable for use as a symbol.
+// cmd is the gccgo/GoLLVM compiler in use, and tmpdir is a temporary
+// directory to pass to ioutil.TempFile.
+// For example, this returns a function that converts "net/http"
+// into a string like "net..z2fhttp". The actual string varies for
+// different gccgo/GoLLVM versions, which is why this returns a function
+// that does the conversion appropriate for the compiler in use.
+func ToSymbolFunc(cmd, tmpdir string) (func(string) string, error) {
+	// To determine the scheme used by cmd, we compile a small
+	// file and examine the assembly code. Older versions of gccgo
+	// use a simple mangling scheme where there can be collisions
+	// between packages whose paths are different but mangle to
+	// the same string. More recent versions use a new mangler
+	// that avoids these collisions.
+	const filepat = "*_gccgo_manglechck.go"
+	f, err := ioutil.TempFile(tmpdir, filepat)
+	if err != nil {
+		return nil, err
+	}
+	gofilename := f.Name()
+	f.Close()
+	defer os.Remove(gofilename)
+
+	if err := ioutil.WriteFile(gofilename, []byte(mangleCheckCode), 0644); err != nil {
+		return nil, err
+	}
+
+	command := exec.Command(cmd, "-S", "-o", "-", gofilename)
+	buf, err := command.Output()
+	if err != nil {
+		return nil, err
+	}
+
+	// New mangling: expect go.l..u00e4ufer.Run
+	// Old mangling: expect go.l__ufer.Run
+	if bytes.Contains(buf, []byte("go.l..u00e4ufer.Run")) {
+		return toSymbolV2, nil
+	} else if bytes.Contains(buf, []byte("go.l__ufer.Run")) {
+		return toSymbolV1, nil
+	} else {
+		return nil, errors.New(cmd + ": unrecognized mangling scheme")
+	}
+}
+
+// mangleCheckCode is the package we compile to determine the mangling scheme.
+const mangleCheckCode = `
+package läufer
+func Run(x int) int {
+  return 1
+}
+`
+
+// toSymbolV1 converts a package path using the original mangling scheme.
+func toSymbolV1(ppath string) string {
+	clean := func(r rune) rune {
+		switch {
+		case 'A' <= r && r <= 'Z', 'a' <= r && r <= 'z',
+			'0' <= r && r <= '9':
+			return r
+		}
+		return '_'
+	}
+	return strings.Map(clean, ppath)
+}
+
+// toSymbolV2 converts a package path using the newer mangling scheme.
+func toSymbolV2(ppath string) string {
+	// This has to build at boostrap time, so it has to build
+	// with Go 1.4, so we don't use strings.Builder.
+	bsl := make([]byte, 0, len(ppath))
+	changed := false
+	for _, c := range ppath {
+		if ('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z') || ('0' <= c && c <= '9') || c == '_' {
+			bsl = append(bsl, byte(c))
+			continue
+		}
+		var enc string
+		switch {
+		case c == '.':
+			enc = ".x2e"
+		case c < 0x80:
+			enc = fmt.Sprintf("..z%02x", c)
+		case c < 0x10000:
+			enc = fmt.Sprintf("..u%04x", c)
+		default:
+			enc = fmt.Sprintf("..U%08x", c)
+		}
+		bsl = append(bsl, enc...)
+		changed = true
+	}
+	if !changed {
+		return ppath
+	}
+	return string(bsl)
+}