build: improve cross compilation setup (#22804)

This PR cleans up the CI build system and fixes a couple of issues.

- The go tool launcher code has been moved to internal/build. With the new
  toolchain functions, the environment of the host Go (i.e. the one that built
  ci.go) and the target Go (i.e. the toolchain downloaded by -dlgo) are isolated
  more strictly. This is important to make cross compilation and -dlgo work
  correctly in more cases.
- The -dlgo option now skips the download and uses the host Go if the running Go
  version matches dlgoVersion exactly.
- The 'test' command now supports -dlgo, -cc and -arch. Running unit tests with
  foreign GOARCH is occasionally useful. For example, it can be used to run
  32-bit tests on Windows. It can also be used to run darwin/amd64 tests on
  darwin/arm64 using Rosetta 2.
- The 'aar', 'xcode' and 'xgo' commands now use a slightly different method to
  install external tools. They previously used `go get`, but this comes with the
  annoying side effect of modifying go.mod. They now use `go install` instead,
  which is the recommended way of installing tools without modifying the local
  module.
- The old build warning about outdated Go version has been removed because we're
  much better at keeping backwards compatibility now.

Makefile

@@ -26,7 +26,7 @@ android:
 	@echo "Import \"$(GOBIN)/geth.aar\" to use the library."
 	@echo "Import \"$(GOBIN)/geth-sources.jar\" to add javadocs"
 	@echo "For more info see https://stackoverflow.com/questions/20994336/android-studio-how-to-attach-javadoc"
-	
+
 ios:
 	$(GORUN) build/ci.go xcode --local
 	@echo "Done building."
@@ -46,12 +46,11 @@ clean:
 # You need to put $GOBIN (or $GOPATH/bin) in your PATH to use 'go generate'.
 
 devtools:
-	env GOBIN= go get -u golang.org/x/tools/cmd/stringer
-	env GOBIN= go get -u github.com/kevinburke/go-bindata/go-bindata
-	env GOBIN= go get -u github.com/fjl/gencodec
-	env GOBIN= go get -u github.com/golang/protobuf/protoc-gen-go
+	env GOBIN= go install golang.org/x/tools/cmd/stringer@latest
+	env GOBIN= go install github.com/kevinburke/go-bindata/go-bindata@latest
+	env GOBIN= go install github.com/fjl/gencodec@latest
+	env GOBIN= go install github.com/golang/protobuf/protoc-gen-go@latest
 	env GOBIN= go install ./cmd/abigen
-	@type "npm" 2> /dev/null || echo 'Please install node.js and npm'
 	@type "solc" 2> /dev/null || echo 'Please install solc'
 	@type "protoc" 2> /dev/null || echo 'Please install protoc'
 

build/ci.go

@@ -208,58 +208,25 @@ func doInstall(cmdline []string) {
 		cc   = flag.String("cc", "", "C compiler to cross build with")
 	)
 	flag.CommandLine.Parse(cmdline)
-	env := build.Env()
 
-	// Check local Go version. People regularly open issues about compilation
-	// failure with outdated Go. This should save them the trouble.
-	if !strings.Contains(runtime.Version(), "devel") {
-		// Figure out the minor version number since we can't textually compare (1.10 < 1.9)
-		var minor int
-		fmt.Sscanf(strings.TrimPrefix(runtime.Version(), "go1."), "%d", &minor)
-		if minor < 13 {
-			log.Println("You have Go version", runtime.Version())
-			log.Println("go-ethereum requires at least Go version 1.13 and cannot")
-			log.Println("be compiled with an earlier version. Please upgrade your Go installation.")
-			os.Exit(1)
-		}
-	}
-
-	// Choose which go command we're going to use.
-	var gobuild *exec.Cmd
-	if !*dlgo {
-		// Default behavior: use the go version which runs ci.go right now.
-		gobuild = goTool("build")
-	} else {
-		// Download of Go requested. This is for build environments where the
-		// installed version is too old and cannot be upgraded easily.
-		cachedir := filepath.Join("build", "cache")
-		goroot := downloadGo(runtime.GOARCH, runtime.GOOS, cachedir)
-		gobuild = localGoTool(goroot, "build")
+	// Configure the toolchain.
+	tc := build.GoToolchain{GOARCH: *arch, CC: *cc}
+	if *dlgo {
+		csdb := build.MustLoadChecksums("build/checksums.txt")
+		tc.Root = build.DownloadGo(csdb, dlgoVersion)
 	}
 
-	// Configure environment for cross build.
-	if *arch != "" || *arch != runtime.GOARCH {
-		gobuild.Env = append(gobuild.Env, "CGO_ENABLED=1")
-		gobuild.Env = append(gobuild.Env, "GOARCH="+*arch)
-	}
-
-	// Configure C compiler.
-	if *cc != "" {
-		gobuild.Env = append(gobuild.Env, "CC="+*cc)
-	} else if os.Getenv("CC") != "" {
-		gobuild.Env = append(gobuild.Env, "CC="+os.Getenv("CC"))
-	}
+	// Configure the build.
+	env := build.Env()
+	gobuild := tc.Go("build", buildFlags(env)...)
 
 	// arm64 CI builders are memory-constrained and can't handle concurrent builds,
 	// better disable it. This check isn't the best, it should probably
 	// check for something in env instead.
-	if runtime.GOARCH == "arm64" {
+	if env.CI && runtime.GOARCH == "arm64" {
 		gobuild.Args = append(gobuild.Args, "-p", "1")
 	}
 
-	// Put the default settings in.
-	gobuild.Args = append(gobuild.Args, buildFlags(env)...)
-
 	// We use -trimpath to avoid leaking local paths into the built executables.
 	gobuild.Args = append(gobuild.Args, "-trimpath")
 
@@ -301,53 +268,30 @@ func buildFlags(env build.Environment) (flags []string) {
 	return flags
 }
 
-// goTool returns the go tool. This uses the Go version which runs ci.go.
-func goTool(subcmd string, args ...string) *exec.Cmd {
-	cmd := build.GoTool(subcmd, args...)
-	goToolSetEnv(cmd)
-	return cmd
-}
-
-// localGoTool returns the go tool from the given GOROOT.
-func localGoTool(goroot string, subcmd string, args ...string) *exec.Cmd {
-	gotool := filepath.Join(goroot, "bin", "go")
-	cmd := exec.Command(gotool, subcmd)
-	goToolSetEnv(cmd)
-	cmd.Env = append(cmd.Env, "GOROOT="+goroot)
-	cmd.Args = append(cmd.Args, args...)
-	return cmd
-}
-
-// goToolSetEnv forwards the build environment to the go tool.
-func goToolSetEnv(cmd *exec.Cmd) {
-	cmd.Env = append(cmd.Env, "GOBIN="+GOBIN)
-	for _, e := range os.Environ() {
-		if strings.HasPrefix(e, "GOBIN=") || strings.HasPrefix(e, "CC=") {
-			continue
-		}
-		cmd.Env = append(cmd.Env, e)
-	}
-}
-
 // Running The Tests
 //
 // "tests" also includes static analysis tools such as vet.
 
 func doTest(cmdline []string) {
-	coverage := flag.Bool("coverage", false, "Whether to record code coverage")
-	verbose := flag.Bool("v", false, "Whether to log verbosely")
+	var (
+		dlgo     = flag.Bool("dlgo", false, "Download Go and build with it")
+		arch     = flag.String("arch", "", "Run tests for given architecture")
+		cc       = flag.String("cc", "", "Sets C compiler binary")
+		coverage = flag.Bool("coverage", false, "Whether to record code coverage")
+		verbose  = flag.Bool("v", false, "Whether to log verbosely")
+	)
 	flag.CommandLine.Parse(cmdline)
-	env := build.Env()
 
-	packages := []string{"./..."}
-	if len(flag.CommandLine.Args()) > 0 {
-		packages = flag.CommandLine.Args()
+	// Configure the toolchain.
+	tc := build.GoToolchain{GOARCH: *arch, CC: *cc}
+	if *dlgo {
+		csdb := build.MustLoadChecksums("build/checksums.txt")
+		tc.Root = build.DownloadGo(csdb, dlgoVersion)
 	}
+	gotest := tc.Go("test")
 
-	// Run the actual tests.
 	// Test a single package at a time. CI builders are slow
 	// and some tests run into timeouts under load.
-	gotest := goTool("test", buildFlags(env)...)
 	gotest.Args = append(gotest.Args, "-p", "1")
 	if *coverage {
 		gotest.Args = append(gotest.Args, "-covermode=atomic", "-cover")
@@ -356,6 +300,10 @@ func doTest(cmdline []string) {
 		gotest.Args = append(gotest.Args, "-v")
 	}
 
+	packages := []string{"./..."}
+	if len(flag.CommandLine.Args()) > 0 {
+		packages = flag.CommandLine.Args()
+	}
 	gotest.Args = append(gotest.Args, packages...)
 	build.MustRun(gotest)
 }
@@ -415,8 +363,7 @@ func doArchive(cmdline []string) {
 	}
 
 	var (
-		env = build.Env()
-
+		env      = build.Env()
 		basegeth = archiveBasename(*arch, params.ArchiveVersion(env.Commit))
 		geth     = "geth-" + basegeth + ext
 		alltools = "geth-alltools-" + basegeth + ext
@@ -492,15 +439,15 @@ func archiveUpload(archive string, blobstore string, signer string, signifyVar s
 // skips archiving for some build configurations.
 func maybeSkipArchive(env build.Environment) {
 	if env.IsPullRequest {
-		log.Printf("skipping because this is a PR build")
+		log.Printf("skipping archive creation because this is a PR build")
 		os.Exit(0)
 	}
 	if env.IsCronJob {
-		log.Printf("skipping because this is a cron job")
+		log.Printf("skipping archive creation because this is a cron job")
 		os.Exit(0)
 	}
 	if env.Branch != "master" && !strings.HasPrefix(env.Tag, "v1.") {
-		log.Printf("skipping because branch %q, tag %q is not on the whitelist", env.Branch, env.Tag)
+		log.Printf("skipping archive creation because branch %q, tag %q is not on the whitelist", env.Branch, env.Tag)
 		os.Exit(0)
 	}
 }
@@ -518,6 +465,7 @@ func doDebianSource(cmdline []string) {
 	flag.CommandLine.Parse(cmdline)
 	*workdir = makeWorkdir(*workdir)
 	env := build.Env()
+	tc := new(build.GoToolchain)
 	maybeSkipArchive(env)
 
 	// Import the signing key.
@@ -531,12 +479,12 @@ func doDebianSource(cmdline []string) {
 	gobundle := downloadGoSources(*cachedir)
 
 	// Download all the dependencies needed to build the sources and run the ci script
-	srcdepfetch := goTool("mod", "download")
-	srcdepfetch.Env = append(os.Environ(), "GOPATH="+filepath.Join(*workdir, "modgopath"))
+	srcdepfetch := tc.Go("mod", "download")
+	srcdepfetch.Env = append(srcdepfetch.Env, "GOPATH="+filepath.Join(*workdir, "modgopath"))
 	build.MustRun(srcdepfetch)
 
-	cidepfetch := goTool("run", "./build/ci.go")
-	cidepfetch.Env = append(os.Environ(), "GOPATH="+filepath.Join(*workdir, "modgopath"))
+	cidepfetch := tc.Go("run", "./build/ci.go")
+	cidepfetch.Env = append(cidepfetch.Env, "GOPATH="+filepath.Join(*workdir, "modgopath"))
 	cidepfetch.Run() // Command fails, don't care, we only need the deps to start it
 
 	// Create Debian packages and upload them.
@@ -592,41 +540,6 @@ func downloadGoSources(cachedir string) string {
 	return dst
 }
 
-// downloadGo downloads the Go binary distribution and unpacks it into a temporary
-// directory. It returns the GOROOT of the unpacked toolchain.
-func downloadGo(goarch, goos, cachedir string) string {
-	if goarch == "arm" {
-		goarch = "armv6l"
-	}
-
-	csdb := build.MustLoadChecksums("build/checksums.txt")
-	file := fmt.Sprintf("go%s.%s-%s", dlgoVersion, goos, goarch)
-	if goos == "windows" {
-		file += ".zip"
-	} else {
-		file += ".tar.gz"
-	}
-	url := "https://golang.org/dl/" + file
-	dst := filepath.Join(cachedir, file)
-	if err := csdb.DownloadFile(url, dst); err != nil {
-		log.Fatal(err)
-	}
-
-	ucache, err := os.UserCacheDir()
-	if err != nil {
-		log.Fatal(err)
-	}
-	godir := filepath.Join(ucache, fmt.Sprintf("geth-go-%s-%s-%s", dlgoVersion, goos, goarch))
-	if err := build.ExtractArchive(dst, godir); err != nil {
-		log.Fatal(err)
-	}
-	goroot, err := filepath.Abs(filepath.Join(godir, "go"))
-	if err != nil {
-		log.Fatal(err)
-	}
-	return goroot
-}
-
 func ppaUpload(workdir, ppa, sshUser string, files []string) {
 	p := strings.Split(ppa, "/")
 	if len(p) != 2 {
@@ -901,13 +814,23 @@ func doAndroidArchive(cmdline []string) {
 	)
 	flag.CommandLine.Parse(cmdline)
 	env := build.Env()
+	tc := new(build.GoToolchain)
 
 	// Sanity check that the SDK and NDK are installed and set
 	if os.Getenv("ANDROID_HOME") == "" {
 		log.Fatal("Please ensure ANDROID_HOME points to your Android SDK")
 	}
+
+	// Build gomobile.
+	install := tc.Install(GOBIN, "golang.org/x/mobile/cmd/gomobile@latest", "golang.org/x/mobile/cmd/gobind@latest")
+	install.Env = append(install.Env)
+	build.MustRun(install)
+
+	// Ensure all dependencies are available. This is required to make
+	// gomobile bind work because it expects go.sum to contain all checksums.
+	build.MustRun(tc.Go("mod", "download"))
+
 	// Build the Android archive and Maven resources
-	build.MustRun(goTool("get", "golang.org/x/mobile/cmd/gomobile", "golang.org/x/mobile/cmd/gobind"))
 	build.MustRun(gomobileTool("bind", "-ldflags", "-s -w", "--target", "android", "--javapkg", "org.ethereum", "-v", "github.com/ethereum/go-ethereum/mobile"))
 
 	if *local {
@@ -1027,10 +950,16 @@ func doXCodeFramework(cmdline []string) {
 	)
 	flag.CommandLine.Parse(cmdline)
 	env := build.Env()
+	tc := new(build.GoToolchain)
+
+	// Build gomobile.
+	build.MustRun(tc.Install(GOBIN, "golang.org/x/mobile/cmd/gomobile@latest", "golang.org/x/mobile/cmd/gobind@latest"))
+
+	// Ensure all dependencies are available. This is required to make
+	// gomobile bind work because it expects go.sum to contain all checksums.
+	build.MustRun(tc.Go("mod", "download"))
 
 	// Build the iOS XCode framework
-	build.MustRun(goTool("get", "golang.org/x/mobile/cmd/gomobile", "golang.org/x/mobile/cmd/gobind"))
-	build.MustRun(gomobileTool("init"))
 	bind := gomobileTool("bind", "-ldflags", "-s -w", "--target", "ios", "-v", "github.com/ethereum/go-ethereum/mobile")
 
 	if *local {
@@ -1039,17 +968,14 @@ func doXCodeFramework(cmdline []string) {
 		build.MustRun(bind)
 		return
 	}
+
+	// Create the archive.
+	maybeSkipArchive(env)
 	archive := "geth-" + archiveBasename("ios", params.ArchiveVersion(env.Commit))
-	if err := os.Mkdir(archive, os.ModePerm); err != nil {
-		log.Fatal(err)
-	}
 	bind.Dir, _ = filepath.Abs(archive)
 	build.MustRun(bind)
 	build.MustRunCommand("tar", "-zcvf", archive+".tar.gz", archive)
 
-	// Skip CocoaPods deploy and Azure upload for PR builds
-	maybeSkipArchive(env)
-
 	// Sign and upload the framework to Azure
 	if err := archiveUpload(archive+".tar.gz", *upload, *signer, *signify); err != nil {
 		log.Fatal(err)
@@ -1115,10 +1041,10 @@ func doXgo(cmdline []string) {
 	)
 	flag.CommandLine.Parse(cmdline)
 	env := build.Env()
+	var tc build.GoToolchain
 
 	// Make sure xgo is available for cross compilation
-	gogetxgo := goTool("get", "github.com/karalabe/xgo")
-	build.MustRun(gogetxgo)
+	build.MustRun(tc.Install(GOBIN, "github.com/karalabe/xgo@latest"))
 
 	// If all tools building is requested, build everything the builder wants
 	args := append(buildFlags(env), flag.Args()...)
@@ -1129,27 +1055,23 @@ func doXgo(cmdline []string) {
 			if strings.HasPrefix(res, GOBIN) {
 				// Binary tool found, cross build it explicitly
 				args = append(args, "./"+filepath.Join("cmd", filepath.Base(res)))
-				xgo := xgoTool(args)
-				build.MustRun(xgo)
+				build.MustRun(xgoTool(args))
 				args = args[:len(args)-1]
 			}
 		}
 		return
 	}
-	// Otherwise xxecute the explicit cross compilation
+
+	// Otherwise execute the explicit cross compilation
 	path := args[len(args)-1]
 	args = append(args[:len(args)-1], []string{"--dest", GOBIN, path}...)
-
-	xgo := xgoTool(args)
-	build.MustRun(xgo)
+	build.MustRun(xgoTool(args))
 }
 
 func xgoTool(args []string) *exec.Cmd {
 	cmd := exec.Command(filepath.Join(GOBIN, "xgo"), args...)
 	cmd.Env = os.Environ()
-	cmd.Env = append(cmd.Env, []string{
-		"GOBIN=" + GOBIN,
-	}...)
+	cmd.Env = append(cmd.Env, []string{"GOBIN=" + GOBIN}...)
 	return cmd
 }
 

internal/build/env.go

@@ -38,6 +38,7 @@ var (
 
 // Environment contains metadata provided by the build environment.
 type Environment struct {
+	CI                        bool
 	Name                      string // name of the environment
 	Repo                      string // name of GitHub repo
 	Commit, Date, Branch, Tag string // Git info
@@ -61,6 +62,7 @@ func Env() Environment {
 			commit = os.Getenv("TRAVIS_COMMIT")
 		}
 		return Environment{
+			CI:            true,
 			Name:          "travis",
 			Repo:          os.Getenv("TRAVIS_REPO_SLUG"),
 			Commit:        commit,
@@ -77,6 +79,7 @@ func Env() Environment {
 			commit = os.Getenv("APPVEYOR_REPO_COMMIT")
 		}
 		return Environment{
+			CI:            true,
 			Name:          "appveyor",
 			Repo:          os.Getenv("APPVEYOR_REPO_NAME"),
 			Commit:        commit,

internal/build/gotool.go

@@ -0,0 +1,149 @@
+// Copyright 2021 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package build
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+type GoToolchain struct {
+	Root string // GOROOT
+
+	// Cross-compilation variables. These are set when running the go tool.
+	GOARCH string
+	GOOS   string
+	CC     string
+}
+
+// Go creates an invocation of the go command.
+func (g *GoToolchain) Go(command string, args ...string) *exec.Cmd {
+	tool := g.goTool(command, args...)
+
+	// Configure environment for cross build.
+	if g.GOARCH != "" && g.GOARCH != runtime.GOARCH {
+		tool.Env = append(tool.Env, "CGO_ENABLED=1")
+		tool.Env = append(tool.Env, "GOARCH="+g.GOARCH)
+	}
+	if g.GOOS != "" && g.GOOS != runtime.GOOS {
+		tool.Env = append(tool.Env, "GOOS="+g.GOOS)
+	}
+	// Configure C compiler.
+	if g.CC != "" {
+		tool.Env = append(tool.Env, "CC="+g.CC)
+	} else if os.Getenv("CC") != "" {
+		tool.Env = append(tool.Env, "CC="+os.Getenv("CC"))
+	}
+	return tool
+}
+
+// Install creates an invocation of 'go install'. The command is configured to output
+// executables to the given 'gobin' directory.
+//
+// This can be used to install auxiliary build tools without modifying the local go.mod and
+// go.sum files. To install tools which are not required by go.mod, ensure that all module
+// paths in 'args' contain a module version suffix (e.g. "...@latest").
+func (g *GoToolchain) Install(gobin string, args ...string) *exec.Cmd {
+	if !filepath.IsAbs(gobin) {
+		panic("GOBIN must be an absolute path")
+	}
+	tool := g.goTool("install")
+	tool.Env = append(tool.Env, "GOBIN="+gobin)
+	tool.Args = append(tool.Args, "-mod=readonly")
+	tool.Args = append(tool.Args, args...)
+
+	// Ensure GOPATH is set because go install seems to absolutely require it. This uses
+	// 'go env' because it resolves the default value when GOPATH is not set in the
+	// environment. Ignore errors running go env and leave any complaining about GOPATH to
+	// the install command.
+	pathTool := g.goTool("env", "GOPATH")
+	output, _ := pathTool.Output()
+	tool.Env = append(tool.Env, "GOPATH="+string(output))
+	return tool
+}
+
+func (g *GoToolchain) goTool(command string, args ...string) *exec.Cmd {
+	if g.Root == "" {
+		g.Root = runtime.GOROOT()
+	}
+	tool := exec.Command(filepath.Join(g.Root, "bin", "go"), command)
+	tool.Args = append(tool.Args, args...)
+	tool.Env = append(tool.Env, "GOROOT="+g.Root)
+
+	// Forward environment variables to the tool, but skip compiler target settings.
+	// TODO: what about GOARM?
+	skip := map[string]struct{}{"GOROOT": {}, "GOARCH": {}, "GOOS": {}, "GOBIN": {}, "CC": {}}
+	for _, e := range os.Environ() {
+		if i := strings.IndexByte(e, '='); i >= 0 {
+			if _, ok := skip[e[:i]]; ok {
+				continue
+			}
+		}
+		tool.Env = append(tool.Env, e)
+	}
+	return tool
+}
+
+// DownloadGo downloads the Go binary distribution and unpacks it into a temporary
+// directory. It returns the GOROOT of the unpacked toolchain.
+func DownloadGo(csdb *ChecksumDB, version string) string {
+	// Shortcut: if the Go version that runs this script matches the
+	// requested version exactly, there is no need to download anything.
+	activeGo := strings.TrimPrefix(runtime.Version(), "go")
+	if activeGo == version {
+		log.Printf("-dlgo version matches active Go version %s, skipping download.", activeGo)
+		return runtime.GOROOT()
+	}
+
+	ucache, err := os.UserCacheDir()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// For Arm architecture, GOARCH includes ISA version.
+	os := runtime.GOOS
+	arch := runtime.GOARCH
+	if arch == "arm" {
+		arch = "armv6l"
+	}
+	file := fmt.Sprintf("go%s.%s-%s", version, os, arch)
+	if os == "windows" {
+		file += ".zip"
+	} else {
+		file += ".tar.gz"
+	}
+	url := "https://golang.org/dl/" + file
+	dst := filepath.Join(ucache, file)
+	if err := csdb.DownloadFile(url, dst); err != nil {
+		log.Fatal(err)
+	}
+
+	godir := filepath.Join(ucache, fmt.Sprintf("geth-go-%s-%s-%s", version, os, arch))
+	if err := ExtractArchive(dst, godir); err != nil {
+		log.Fatal(err)
+	}
+	goroot, err := filepath.Abs(filepath.Join(godir, "go"))
+	if err != nil {
+		log.Fatal(err)
+	}
+	return goroot
+}

internal/build/util.go

@@ -29,7 +29,6 @@ import (
 	"os/exec"
 	"path"
 	"path/filepath"
-	"runtime"
 	"strings"
 	"text/template"
 )
@@ -111,19 +110,6 @@ func render(tpl *template.Template, outputFile string, outputPerm os.FileMode, x
 	}
 }
 
-// GoTool returns the command that runs a go tool. This uses go from GOROOT instead of PATH
-// so that go commands executed by build use the same version of Go as the 'host' that runs
-// build code. e.g.
-//
-//     /usr/lib/go-1.12.1/bin/go run build/ci.go ...
-//
-// runs using go 1.12.1 and invokes go 1.12.1 tools from the same GOROOT. This is also important
-// because runtime.Version checks on the host should match the tools that are run.
-func GoTool(tool string, args ...string) *exec.Cmd {
-	args = append([]string{tool}, args...)
-	return exec.Command(filepath.Join(runtime.GOROOT(), "bin", "go"), args...)
-}
-
 // UploadSFTP uploads files to a remote host using the sftp command line tool.
 // The destination host may be specified either as [user@]host[: or as a URI in
 // the form sftp://[user@]host[:port].