diff --git a/src/cmd/go/bug.go b/src/cmd/go/bug.go
index be64fe80dd..239c27e426 100644
--- a/src/cmd/go/bug.go
+++ b/src/cmd/go/bug.go
@@ -6,8 +6,6 @@ package main
 
 import (
 	"bytes"
-	"cmd/go/internal/base"
-	"cmd/go/internal/cfg"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -17,6 +15,9 @@ import (
 	"regexp"
 	"runtime"
 	"strings"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
 )
 
 var cmdBug = &base.Command{
diff --git a/src/cmd/go/generate.go b/src/cmd/go/generate.go
index 60d4f01e90..bc08e99900 100644
--- a/src/cmd/go/generate.go
+++ b/src/cmd/go/generate.go
@@ -397,7 +397,7 @@ func (g *Generator) exec(words []string) {
 	cmd.Stderr = os.Stderr
 	// Run the command in the package directory.
 	cmd.Dir = g.dir
-	cmd.Env = mergeEnvLists(g.env, cfg.OrigEnv)
+	cmd.Env = base.MergeEnvLists(g.env, cfg.OrigEnv)
 	err := cmd.Run()
 	if err != nil {
 		g.errorf("running %q: %s", words[0], err)
diff --git a/src/cmd/go/internal/base/env.go b/src/cmd/go/internal/base/env.go
index fb5956dfe3..fcade9d84e 100644
--- a/src/cmd/go/internal/base/env.go
+++ b/src/cmd/go/internal/base/env.go
@@ -6,7 +6,7 @@ package base
 
 import "strings"
 
-// envForDir returns a copy of the environment
+// EnvForDir returns a copy of the environment
 // suitable for running in the given directory.
 // The environment is the current process's environment
 // but with an updated $PWD, so that an os.Getwd in the
diff --git a/src/cmd/go/test.go b/src/cmd/go/internal/test/test.go
similarity index 98%
rename from src/cmd/go/test.go
rename to src/cmd/go/internal/test/test.go
index c17507041e..366b19a700 100644
--- a/src/cmd/go/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -2,15 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package main
+package test
 
 import (
 	"bytes"
-	"cmd/go/internal/base"
-	"cmd/go/internal/cfg"
-	"cmd/go/internal/load"
-	"cmd/go/internal/str"
-	"cmd/go/internal/work"
 	"errors"
 	"fmt"
 	"go/ast"
@@ -30,16 +25,22 @@ import (
 	"time"
 	"unicode"
 	"unicode/utf8"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/load"
+	"cmd/go/internal/str"
+	"cmd/go/internal/work"
 )
 
 // Break init loop.
 func init() {
-	cmdTest.Run = runTest
+	CmdTest.Run = runTest
 }
 
 const testUsage = "test [build/test flags] [packages] [build/test flags & test binary flags]"
 
-var cmdTest = &base.Command{
+var CmdTest = &base.Command{
 	CustomFlags: true,
 	UsageLine:   testUsage,
 	Short:       "test packages",
@@ -112,7 +113,15 @@ The test binary also accepts flags that control execution of the test; these
 flags are also accessible by 'go test'.
 `
 
-var helpTestflag = &base.Command{
+// Usage prints the usage message for 'go test -h' and exits.
+func Usage() {
+	os.Stderr.WriteString(testUsage + "\n\n" +
+		strings.TrimSpace(testFlag1) + "\n\n\t" +
+		strings.TrimSpace(testFlag2) + "\n")
+	os.Exit(2)
+}
+
+var HelpTestflag = &base.Command{
 	UsageLine: "testflag",
 	Short:     "description of testing flags",
 	Long: `
@@ -317,7 +326,7 @@ In the second example, the argument math is passed through to the test
 binary, instead of being interpreted as the package list.
 `
 
-var helpTestfunc = &base.Command{
+var HelpTestfunc = &base.Command{
 	UsageLine: "testfunc",
 	Short:     "description of testing functions",
 	Long: `
@@ -408,7 +417,7 @@ func runTest(cmd *base.Command, args []string) {
 	var pkgArgs []string
 	pkgArgs, testArgs = testFlags(args)
 
-	findExecCmd() // initialize cached result
+	work.FindExecCmd() // initialize cached result
 
 	work.InstrumentInit()
 	work.BuildModeInit()
@@ -1107,7 +1116,7 @@ var noTestsToRun = []byte("\ntesting: warning: no tests to run\n")
 
 // builderRunTest is the action for running a test binary.
 func builderRunTest(b *work.Builder, a *work.Action) error {
-	args := str.StringList(findExecCmd(), a.Deps[0].Target, testArgs)
+	args := str.StringList(work.FindExecCmd(), a.Deps[0].Target, testArgs)
 	a.TestOutput = new(bytes.Buffer)
 
 	if cfg.BuildN || cfg.BuildX {
@@ -1127,7 +1136,7 @@ func builderRunTest(b *work.Builder, a *work.Action) error {
 
 	cmd := exec.Command(args[0], args[1:]...)
 	cmd.Dir = a.Package.Dir
-	cmd.Env = envForDir(cmd.Dir, cfg.OrigEnv)
+	cmd.Env = base.EnvForDir(cmd.Dir, cfg.OrigEnv)
 	var buf bytes.Buffer
 	if testStreamOutput {
 		cmd.Stdout = os.Stdout
diff --git a/src/cmd/go/testflag.go b/src/cmd/go/internal/test/testflag.go
similarity index 98%
rename from src/cmd/go/testflag.go
rename to src/cmd/go/internal/test/testflag.go
index 4f519a4af6..1c44af5a00 100644
--- a/src/cmd/go/testflag.go
+++ b/src/cmd/go/internal/test/testflag.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package main
+package test
 
 import (
 	"flag"
@@ -138,7 +138,6 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 		} else {
 			// Test-only flags.
 			// Arguably should be handled by f.flagValue, but aren't.
-			var err error
 			switch f.name {
 			// bool flags.
 			case "c", "i", "v", "cover":
@@ -147,10 +146,11 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 				testO = value
 				testNeedBinary = true
 			case "exec":
-				execCmd, err = str.SplitQuotedFields(value)
+				xcmd, err := str.SplitQuotedFields(value)
 				if err != nil {
 					base.Fatalf("invalid flag argument for -%s: %v", f.name, err)
 				}
+				work.ExecCmd = xcmd
 			case "bench":
 				// record that we saw the flag; don't care about the value
 				testBench = true
diff --git a/src/cmd/go/internal/work/build.go b/src/cmd/go/internal/work/build.go
index 830015e947..63731e1dfa 100644
--- a/src/cmd/go/internal/work/build.go
+++ b/src/cmd/go/internal/work/build.go
@@ -3622,3 +3622,28 @@ func InstrumentInit() {
 		cfg.BuildContext.BuildTags = append(cfg.BuildContext.BuildTags, "msan")
 	}
 }
+
+// ExecCmd is the command to use to run user binaries.
+// Normally it is empty, meaning run the binaries directly.
+// If cross-compiling and running on a remote system or
+// simulator, it is typically go_GOOS_GOARCH_exec, with
+// the target GOOS and GOARCH substituted.
+// The -exec flag overrides these defaults.
+var ExecCmd []string
+
+// FindExecCmd derives the value of ExecCmd to use.
+// It returns that value and leaves ExecCmd set for direct use.
+func FindExecCmd() []string {
+	if ExecCmd != nil {
+		return ExecCmd
+	}
+	ExecCmd = []string{} // avoid work the second time
+	if cfg.Goos == runtime.GOOS && cfg.Goarch == runtime.GOARCH {
+		return ExecCmd
+	}
+	path, err := exec.LookPath(fmt.Sprintf("go_%s_%s_exec", cfg.Goos, cfg.Goarch))
+	if err == nil {
+		ExecCmd = []string{path}
+	}
+	return ExecCmd
+}
diff --git a/src/cmd/go/main.go b/src/cmd/go/main.go
index 64cde307c9..502e571682 100644
--- a/src/cmd/go/main.go
+++ b/src/cmd/go/main.go
@@ -16,6 +16,7 @@ import (
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/help"
+	"cmd/go/internal/test"
 	"cmd/go/internal/work"
 )
 
@@ -33,7 +34,7 @@ func init() {
 		work.CmdInstall,
 		cmdList,
 		cmdRun,
-		cmdTest,
+		test.CmdTest,
 		cmdTool,
 		cmdVersion,
 		cmdVet,
@@ -45,8 +46,8 @@ func init() {
 		help.HelpEnvironment,
 		help.HelpImportPath,
 		help.HelpPackages,
-		helpTestflag,
-		helpTestfunc,
+		test.HelpTestflag,
+		test.HelpTestfunc,
 	}
 }
 
@@ -134,41 +135,8 @@ func init() {
 func mainUsage() {
 	// special case "go test -h"
 	if len(os.Args) > 1 && os.Args[1] == "test" {
-		os.Stderr.WriteString(testUsage + "\n\n" +
-			strings.TrimSpace(testFlag1) + "\n\n\t" +
-			strings.TrimSpace(testFlag2) + "\n")
-		os.Exit(2)
+		test.Usage()
 	}
 	help.PrintUsage(os.Stderr)
 	os.Exit(2)
 }
-
-// envForDir returns a copy of the environment
-// suitable for running in the given directory.
-// The environment is the current process's environment
-// but with an updated $PWD, so that an os.Getwd in the
-// child will be faster.
-func envForDir(dir string, base []string) []string {
-	// Internally we only use rooted paths, so dir is rooted.
-	// Even if dir is not rooted, no harm done.
-	return mergeEnvLists([]string{"PWD=" + dir}, base)
-}
-
-// mergeEnvLists merges the two environment lists such that
-// variables with the same name in "in" replace those in "out".
-// This always returns a newly allocated slice.
-func mergeEnvLists(in, out []string) []string {
-	out = append([]string(nil), out...)
-NextVar:
-	for _, inkv := range in {
-		k := strings.SplitAfterN(inkv, "=", 2)[0]
-		for i, outkv := range out {
-			if strings.HasPrefix(outkv, k) {
-				out[i] = inkv
-				continue NextVar
-			}
-		}
-		out = append(out, inkv)
-	}
-	return out
-}
diff --git a/src/cmd/go/run.go b/src/cmd/go/run.go
index 398a298fdc..37209b3660 100644
--- a/src/cmd/go/run.go
+++ b/src/cmd/go/run.go
@@ -7,8 +7,6 @@ package main
 import (
 	"fmt"
 	"os"
-	"os/exec"
-	"runtime"
 	"strings"
 
 	"cmd/go/internal/base"
@@ -18,23 +16,6 @@ import (
 	"cmd/go/internal/work"
 )
 
-var execCmd []string // -exec flag, for run and test
-
-func findExecCmd() []string {
-	if execCmd != nil {
-		return execCmd
-	}
-	execCmd = []string{} // avoid work the second time
-	if cfg.Goos == runtime.GOOS && cfg.Goarch == runtime.GOARCH {
-		return execCmd
-	}
-	path, err := exec.LookPath(fmt.Sprintf("go_%s_%s_exec", cfg.Goos, cfg.Goarch))
-	if err == nil {
-		execCmd = []string{path}
-	}
-	return execCmd
-}
-
 var cmdRun = &base.Command{
 	UsageLine: "run [build flags] [-exec xprog] gofiles... [arguments...]",
 	Short:     "compile and run Go program",
@@ -62,7 +43,7 @@ func init() {
 	cmdRun.Run = runRun // break init loop
 
 	work.AddBuildFlags(cmdRun)
-	cmdRun.Flag.Var((*base.StringsFlag)(&execCmd), "exec", "")
+	cmdRun.Flag.Var((*base.StringsFlag)(&work.ExecCmd), "exec", "")
 }
 
 func printStderr(args ...interface{}) (int, error) {
@@ -136,7 +117,7 @@ func runRun(cmd *base.Command, args []string) {
 // buildRunProgram is the action for running a binary that has already
 // been compiled. We ignore exit status.
 func buildRunProgram(b *work.Builder, a *work.Action) error {
-	cmdline := str.StringList(findExecCmd(), a.Deps[0].Target, a.Args)
+	cmdline := str.StringList(work.FindExecCmd(), a.Deps[0].Target, a.Args)
 	if cfg.BuildN || cfg.BuildX {
 		b.Showcmd("", "%s", strings.Join(cmdline, " "))
 		if cfg.BuildN {
diff --git a/src/cmd/go/tool.go b/src/cmd/go/tool.go
index e6b3fd1e1b..2f08c419f3 100644
--- a/src/cmd/go/tool.go
+++ b/src/cmd/go/tool.go
@@ -72,7 +72,7 @@ func runTool(cmd *base.Command, args []string) {
 		Stdout: os.Stdout,
 		Stderr: os.Stderr,
 		// Set $GOROOT, mainly for go tool dist.
-		Env: mergeEnvLists([]string{"GOROOT=" + cfg.GOROOT}, os.Environ()),
+		Env: base.MergeEnvLists([]string{"GOROOT=" + cfg.GOROOT}, os.Environ()),
 	}
 	err := toolCmd.Run()
 	if err != nil {
diff --git a/src/cmd/go/vcs.go b/src/cmd/go/vcs.go
index bcb602c69b..bb82deb379 100644
--- a/src/cmd/go/vcs.go
+++ b/src/cmd/go/vcs.go
@@ -6,7 +6,6 @@ package main
 
 import (
 	"bytes"
-	"cmd/go/internal/cfg"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -19,6 +18,9 @@ import (
 	"regexp"
 	"strings"
 	"sync"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
 )
 
 // A vcsCmd describes how to use a version control system
@@ -373,7 +375,7 @@ func (v *vcsCmd) run1(dir string, cmdline string, keyval []string, verbose bool)
 
 	cmd := exec.Command(v.cmd, args...)
 	cmd.Dir = dir
-	cmd.Env = envForDir(cmd.Dir, os.Environ())
+	cmd.Env = base.EnvForDir(cmd.Dir, os.Environ())
 	if cfg.BuildX {
 		fmt.Printf("cd %s\n", dir)
 		fmt.Printf("%s %s\n", v.cmd, strings.Join(args, " "))