tool/gocross: a tool for building Tailscale binaries

Signed-off-by: David Anderson <danderson@tailscale.com>
2023-02-21 16:07:33 -08:00
parent 0b8f89c79c
commit 860734aed9
12 changed files with 1324 additions and 78 deletions
@@ -0,0 +1,132 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// gocross is a wrapper around the `go` tool that invokes `go` from Tailscale's
+// custom toolchain, with the right build parameters injected based on the
+// native+target GOOS/GOARCH.
+//
+// In short, when aliased to `go`, using `go build`, `go test` behave like the
+// upstream Go tools, but produce correctly configured, correctly linked
+// binaries stamped with version information.
+
+package main
+
+import (
+	_ "embed"
+	"fmt"
+	"os"
+	"path/filepath"
+	runtimeDebug "runtime/debug"
+)
+
+func main() {
+	if len(os.Args) > 1 {
+		// These additional subcommands are various support commands to handle
+		// integration with Tailscale's existing build system. Unless otherwise
+		// specified, these are not stable APIs, and may change or go away at
+		// any time.
+		switch os.Args[1] {
+		case "gocross-version":
+			hash, err := embeddedCommit()
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "getting commit hash: %v", err)
+				os.Exit(1)
+			}
+			fmt.Println(hash)
+			os.Exit(0)
+		case "is-gocross":
+			// This subcommand exits with an error code when called on a
+			// regular go binary, so it can be used to detect when `go` is
+			// actually gocross.
+			os.Exit(0)
+		case "make-goroot":
+			_, gorootDir, err := getToolchain()
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "getting toolchain: %v\n", err)
+				os.Exit(1)
+			}
+
+			fmt.Println(gorootDir)
+			os.Exit(0)
+		case "gocross-get-toolchain-go":
+			toolchain, _, err := getToolchain()
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "getting toolchain: %v\n", err)
+				os.Exit(1)
+			}
+			fmt.Println(filepath.Join(toolchain, "bin/go"))
+			os.Exit(0)
+		}
+	}
+
+	toolchain, goroot, err := getToolchain()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "getting toolchain: %v\n", err)
+		os.Exit(1)
+	}
+
+	args := os.Args
+	if os.Getenv("GOCROSS_BYPASS") == "" {
+		newArgv, env, err := Autoflags(os.Args, goroot)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "computing flags: %v\n", err)
+			os.Exit(1)
+		}
+
+		// Make sure the right version of cmd/go is the first thing in the PATH
+		// for tests that execute `go build` or `go test`.
+		// TODO: if we really need to do this, do it inside Autoflags, not here.
+		path := filepath.Join(toolchain, "bin") + string(os.PathListSeparator) + os.Getenv("PATH")
+		env.Set("PATH", path)
+
+		debug("Input: %s\n", formatArgv(os.Args))
+		debug("Command: %s\n", formatArgv(newArgv))
+		debug("Set the following flags/envvars:\n%s\n", env.Diff())
+
+		args = newArgv
+		if err := env.Apply(); err != nil {
+			fmt.Fprintf(os.Stderr, "modifying environment: %v\n", err)
+			os.Exit(1)
+		}
+
+	}
+
+	doExec(filepath.Join(toolchain, "bin/go"), args, os.Environ())
+}
+
+func debug(format string, args ...interface{}) {
+	debug := os.Getenv("GOCROSS_DEBUG")
+	var (
+		out *os.File
+		err error
+	)
+	switch debug {
+	case "0", "":
+		return
+	case "1":
+		out = os.Stderr
+	default:
+		out, err = os.OpenFile(debug, os.O_APPEND|os.O_CREATE|os.O_RDWR, 0640)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "opening debug file %q: %v", debug, err)
+			out = os.Stderr
+		} else {
+			defer out.Close() // May lose some write errors, but we don't care.
+		}
+	}
+
+	fmt.Fprintf(out, format, args...)
+}
+
+func embeddedCommit() (string, error) {
+	bi, ok := runtimeDebug.ReadBuildInfo()
+	if !ok {
+		return "", fmt.Errorf("no build info")
+	}
+	for _, s := range bi.Settings {
+		if s.Key == "vcs.revision" {
+			return s.Value, nil
+		}
+	}
+	return "", fmt.Errorf("no git commit found")
+}