[dev.cmdgo] cmd: support space and quotes in CC and CXX

The CC and CXX environment variables now support spaces and quotes
(both double and single). This fixes two issues: first, if CC is a
single path that contains spaces (like 'c:\Program
Files\gcc\bin\gcc.exe'), that should now work if the space is quoted
or escaped (#41400). Second, if CC or CXX has multiple arguments (like
'gcc -O2'), they are now split correctly, and the arguments are passed
before other arguments when invoking the C compiler. Previously,
strings.Fields was used to split arguments, and the arguments were
placed later in the command line. (#43078).

Fixes golang/go#41400
Fixes golang/go#43078

Change-Id: I2d5d89ddb19c94adef65982a8137b01f037d5c11
Reviewed-on: https://go-review.googlesource.com/c/go/+/334732
Trust: Jay Conrod <jayconrod@google.com>
Trust: Michael Matloob <matloob@golang.org>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>

src/cmd/cgo/gcc.go

@@ -23,10 +23,13 @@ import (
 	"internal/xcoff"
 	"math"
 	"os"
+	"os/exec"
 	"strconv"
 	"strings"
 	"unicode"
 	"unicode/utf8"
+
+	"cmd/internal/str"
 )
 
 var debugDefine = flag.Bool("debug-define", false, "print relevant #defines")
@@ -382,7 +385,7 @@ func (p *Package) guessKinds(f *File) []*Name {
 		stderr = p.gccErrors(b.Bytes())
 	}
 	if stderr == "" {
-		fatalf("%s produced no output\non input:\n%s", p.gccBaseCmd()[0], b.Bytes())
+		fatalf("%s produced no output\non input:\n%s", gccBaseCmd[0], b.Bytes())
 	}
 
 	completed := false
@@ -457,7 +460,7 @@ func (p *Package) guessKinds(f *File) []*Name {
 	}
 
 	if !completed {
-		fatalf("%s did not produce error at completed:1\non input:\n%s\nfull error output:\n%s", p.gccBaseCmd()[0], b.Bytes(), stderr)
+		fatalf("%s did not produce error at completed:1\non input:\n%s\nfull error output:\n%s", gccBaseCmd[0], b.Bytes(), stderr)
 	}
 
 	for i, n := range names {
@@ -488,7 +491,7 @@ func (p *Package) guessKinds(f *File) []*Name {
 		// to users debugging preamble mistakes. See issue 8442.
 		preambleErrors := p.gccErrors([]byte(f.Preamble))
 		if len(preambleErrors) > 0 {
-			error_(token.NoPos, "\n%s errors for preamble:\n%s", p.gccBaseCmd()[0], preambleErrors)
+			error_(token.NoPos, "\n%s errors for preamble:\n%s", gccBaseCmd[0], preambleErrors)
 		}
 
 		fatalf("unresolved names")
@@ -1545,20 +1548,37 @@ func gofmtPos(n ast.Expr, pos token.Pos) string {
 	return fmt.Sprintf("/*line :%d:%d*/%s", p.Line, p.Column, s)
 }
 
-// gccBaseCmd returns the start of the compiler command line.
+// checkGCCBaseCmd returns the start of the compiler command line.
 // It uses $CC if set, or else $GCC, or else the compiler recorded
 // during the initial build as defaultCC.
 // defaultCC is defined in zdefaultcc.go, written by cmd/dist.
-func (p *Package) gccBaseCmd() []string {
+//
+// The compiler command line is split into arguments on whitespace. Quotes
+// are understood, so arguments may contain whitespace.
+//
+// checkGCCBaseCmd confirms that the compiler exists in PATH, returning
+// an error if it does not.
+func checkGCCBaseCmd() ([]string, error) {
 	// Use $CC if set, since that's what the build uses.
-	if ret := strings.Fields(os.Getenv("CC")); len(ret) > 0 {
+	value := os.Getenv("CC")
-		return ret
+	if value == "" {
+		// Try $GCC if set, since that's what we used to use.
+		value = os.Getenv("GCC")
 	}
-	// Try $GCC if set, since that's what we used to use.
+	if value == "" {
-	if ret := strings.Fields(os.Getenv("GCC")); len(ret) > 0 {
+		value = defaultCC(goos, goarch)
-		return ret
 	}
-	return strings.Fields(defaultCC(goos, goarch))
+	args, err := str.SplitQuotedFields(value)
+	if err != nil {
+		return nil, err
+	}
+	if len(args) == 0 {
+		return nil, errors.New("CC not set and no default found")
+	}
+	if _, err := exec.LookPath(args[0]); err != nil {
+		return nil, fmt.Errorf("C compiler %q not found: %v", args[0], err)
+	}
+	return args[:len(args):len(args)], nil
 }
 
 // gccMachine returns the gcc -m flag to use, either "-m32", "-m64" or "-marm".
@@ -1604,7 +1624,7 @@ func gccTmp() string {
 // gccCmd returns the gcc command line to use for compiling
 // the input.
 func (p *Package) gccCmd() []string {
-	c := append(p.gccBaseCmd(),
+	c := append(gccBaseCmd,
 		"-w",          // no warnings
 		"-Wno-error",  // warnings are not errors
 		"-o"+gccTmp(), // write object to tmp
@@ -2005,7 +2025,7 @@ func (p *Package) gccDebug(stdin []byte, nnames int) (d *dwarf.Data, ints []int6
 // #defines that gcc encountered while processing the input
 // and its included files.
 func (p *Package) gccDefines(stdin []byte) string {
-	base := append(p.gccBaseCmd(), "-E", "-dM", "-xc")
+	base := append(gccBaseCmd, "-E", "-dM", "-xc")
 	base = append(base, p.gccMachine()...)
 	stdout, _ := runGcc(stdin, append(append(base, p.GccOptions...), "-"))
 	return stdout

src/cmd/cgo/main.go

@@ -21,7 +21,6 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"reflect"
 	"runtime"
@@ -248,6 +247,7 @@ var importSyscall = flag.Bool("import_syscall", true, "import syscall in generat
 var trimpath = flag.String("trimpath", "", "applies supplied rewrites or trims prefixes to recorded source file paths")
 
 var goarch, goos, gomips, gomips64 string
+var gccBaseCmd []string
 
 func main() {
 	objabi.AddVersionFlag() // -V
@@ -305,10 +305,10 @@ func main() {
 	p := newPackage(args[:i])
 
 	// We need a C compiler to be available. Check this.
-	gccName := p.gccBaseCmd()[0]
+	var err error
-	_, err := exec.LookPath(gccName)
+	gccBaseCmd, err = checkGCCBaseCmd()
 	if err != nil {
-		fatalf("C compiler %q not found: %v", gccName, err)
+		fatalf("%v", err)
 		os.Exit(2)
 	}
 

src/cmd/compile/internal/ssa/stmtlines_test.go

@@ -2,6 +2,7 @@ package ssa_test
 
 import (
 	cmddwarf "cmd/internal/dwarf"
+	"cmd/internal/str"
 	"debug/dwarf"
 	"debug/elf"
 	"debug/macho"
@@ -57,7 +58,11 @@ func TestStmtLines(t *testing.T) {
 		if extld == "" {
 			extld = "gcc"
 		}
-		enabled, err := cmddwarf.IsDWARFEnabledOnAIXLd(extld)
+		extldArgs, err := str.SplitQuotedFields(extld)
+		if err != nil {
+			t.Fatal(err)
+		}
+		enabled, err := cmddwarf.IsDWARFEnabledOnAIXLd(extldArgs)
 		if err != nil {
 			t.Fatal(err)
 		}

src/cmd/dist/buildtool.go

@@ -47,6 +47,7 @@ var bootstrapDirs = []string{
 	"cmd/internal/objabi",
 	"cmd/internal/pkgpath",
 	"cmd/internal/src",
+	"cmd/internal/str",
 	"cmd/internal/sys",
 	"cmd/link",
 	"cmd/link/internal/...",

src/cmd/go/internal/envcmd/env.go

@@ -26,6 +26,7 @@ import (
 	"cmd/go/internal/load"
 	"cmd/go/internal/modload"
 	"cmd/go/internal/work"
+	"cmd/internal/str"
 )
 
 var CmdEnv = &base.Command{
@@ -104,13 +105,13 @@ func MkEnv() []cfg.EnvVar {
 		env = append(env, cfg.EnvVar{Name: key, Value: val})
 	}
 
-	cc := cfg.DefaultCC(cfg.Goos, cfg.Goarch)
+	cc := cfg.Getenv("CC")
-	if env := strings.Fields(cfg.Getenv("CC")); len(env) > 0 {
+	if cc == "" {
-		cc = env[0]
+		cc = cfg.DefaultCC(cfg.Goos, cfg.Goarch)
 	}
-	cxx := cfg.DefaultCXX(cfg.Goos, cfg.Goarch)
+	cxx := cfg.Getenv("CXX")
-	if env := strings.Fields(cfg.Getenv("CXX")); len(env) > 0 {
+	if cxx == "" {
-		cxx = env[0]
+		cxx = cfg.DefaultCXX(cfg.Goos, cfg.Goarch)
 	}
 	env = append(env, cfg.EnvVar{Name: "AR", Value: envOr("AR", "ar")})
 	env = append(env, cfg.EnvVar{Name: "CC", Value: cc})
@@ -458,10 +459,23 @@ func checkEnvWrite(key, val string) error {
 		if !filepath.IsAbs(val) && val != "" {
 			return fmt.Errorf("GOPATH entry is relative; must be absolute path: %q", val)
 		}
-	// Make sure CC and CXX are absolute paths
+	case "GOMODCACHE":
-	case "CC", "CXX", "GOMODCACHE":
+		if !filepath.IsAbs(val) && val != "" {
-		if !filepath.IsAbs(val) && val != "" && val != filepath.Base(val) {
+			return fmt.Errorf("GOMODCACHE entry is relative; must be absolute path: %q", val)
-			return fmt.Errorf("%s entry is relative; must be absolute path: %q", key, val)
+		}
+	case "CC", "CXX":
+		if val == "" {
+			break
+		}
+		args, err := str.SplitQuotedFields(val)
+		if err != nil {
+			return fmt.Errorf("invalid %s: %v", key, err)
+		}
+		if len(args) == 0 {
+			return fmt.Errorf("%s entry cannot contain only space", key)
+		}
+		if !filepath.IsAbs(args[0]) && args[0] != filepath.Base(args[0]) {
+			return fmt.Errorf("%s entry is relative; must be absolute path: %q", key, args[0])
 		}
 	}
 

src/cmd/go/internal/work/exec.go

@@ -1480,6 +1480,8 @@ func (b *Builder) getPkgConfigFlags(p *load.Package) (cflags, ldflags []string,
 			return nil, nil, errPrintedOutput
 		}
 		if len(out) > 0 {
+			// NOTE: we don't attempt to parse quotes and unescapes here. pkg-config
+			// is typically used within shell backticks, which treats quotes literally.
 			ldflags = strings.Fields(string(out))
 			if err := checkLinkerFlags("LDFLAGS", "pkg-config --libs", ldflags); err != nil {
 				return nil, nil, err
@@ -2422,12 +2424,6 @@ func (b *Builder) gccld(a *Action, p *load.Package, objdir, outfile string, flag
 	return err
 }
 
-// Grab these before main helpfully overwrites them.
-var (
-	origCC  = cfg.Getenv("CC")
-	origCXX = cfg.Getenv("CXX")
-)
-
 // gccCmd returns a gcc command line prefix
 // defaultCC is defined in zdefaultcc.go, written by cmd/dist.
 func (b *Builder) GccCmd(incdir, workdir string) []string {
@@ -2447,40 +2443,23 @@ func (b *Builder) gfortranCmd(incdir, workdir string) []string {
 
 // ccExe returns the CC compiler setting without all the extra flags we add implicitly.
 func (b *Builder) ccExe() []string {
-	return b.compilerExe(origCC, cfg.DefaultCC(cfg.Goos, cfg.Goarch))
+	return envList("CC", cfg.DefaultCC(cfg.Goos, cfg.Goarch))
 }
 
 // cxxExe returns the CXX compiler setting without all the extra flags we add implicitly.
 func (b *Builder) cxxExe() []string {
-	return b.compilerExe(origCXX, cfg.DefaultCXX(cfg.Goos, cfg.Goarch))
+	return envList("CXX", cfg.DefaultCXX(cfg.Goos, cfg.Goarch))
 }
 
 // fcExe returns the FC compiler setting without all the extra flags we add implicitly.
 func (b *Builder) fcExe() []string {
-	return b.compilerExe(cfg.Getenv("FC"), "gfortran")
+	return envList("FC", "gfortran")
-}
-
-// compilerExe returns the compiler to use given an
-// environment variable setting (the value not the name)
-// and a default. The resulting slice is usually just the name
-// of the compiler but can have additional arguments if they
-// were present in the environment value.
-// For example if CC="gcc -DGOPHER" then the result is ["gcc", "-DGOPHER"].
-func (b *Builder) compilerExe(envValue string, def string) []string {
-	compiler := strings.Fields(envValue)
-	if len(compiler) == 0 {
-		compiler = strings.Fields(def)
-	}
-	return compiler
 }
 
 // compilerCmd returns a command line prefix for the given environment
 // variable and using the default command when the variable is empty.
 func (b *Builder) compilerCmd(compiler []string, incdir, workdir string) []string {
-	// NOTE: env.go's mkEnv knows that the first three
+	a := append(compiler, "-I", incdir)
-	// strings returned are "gcc", "-I", incdir (and cuts them off).
-	a := []string{compiler[0], "-I", incdir}
-	a = append(a, compiler[1:]...)
 
 	// Definitely want -fPIC but on Windows gcc complains
 	// "-fPIC ignored for target (all code is position independent)"
@@ -2651,12 +2630,20 @@ func (b *Builder) gccArchArgs() []string {
 
 // envList returns the value of the given environment variable broken
 // into fields, using the default value when the variable is empty.
+//
+// The environment variable must be quoted correctly for
+// str.SplitQuotedFields. This should be done before building
+// anything, for example, in BuildInit.
 func envList(key, def string) []string {
 	v := cfg.Getenv(key)
 	if v == "" {
 		v = def
 	}
-	return strings.Fields(v)
+	args, err := str.SplitQuotedFields(v)
+	if err != nil {
+		panic(fmt.Sprintf("could not parse environment variable %s with value %q: %v", key, v, err))
+	}
+	return args
 }
 
 // CFlags returns the flags to use when invoking the C, C++ or Fortran compilers, or cgo.

src/cmd/go/internal/work/gc.go

@@ -536,33 +536,18 @@ func packInternal(afile string, ofiles []string) error {
 }
 
 // setextld sets the appropriate linker flags for the specified compiler.
-func setextld(ldflags []string, compiler []string) []string {
+func setextld(ldflags []string, compiler []string) ([]string, error) {
 	for _, f := range ldflags {
 		if f == "-extld" || strings.HasPrefix(f, "-extld=") {
 			// don't override -extld if supplied
-			return ldflags
+			return ldflags, nil
 		}
 	}
-	ldflags = append(ldflags, "-extld="+compiler[0])
+	joined, err := str.JoinAndQuoteFields(compiler)
-	if len(compiler) > 1 {
+	if err != nil {
-		extldflags := false
+		return nil, err
-		add := strings.Join(compiler[1:], " ")
-		for i, f := range ldflags {
-			if f == "-extldflags" && i+1 < len(ldflags) {
-				ldflags[i+1] = add + " " + ldflags[i+1]
-				extldflags = true
-				break
-			} else if strings.HasPrefix(f, "-extldflags=") {
-				ldflags[i] = "-extldflags=" + add + " " + ldflags[i][len("-extldflags="):]
-				extldflags = true
-				break
-			}
-		}
-		if !extldflags {
-			ldflags = append(ldflags, "-extldflags="+add)
-		}
 	}
-	return ldflags
+	return append(ldflags, "-extld="+joined), nil
 }
 
 // pluginPath computes the package path for a plugin main package.
@@ -649,7 +634,10 @@ func (gcToolchain) ld(b *Builder, root *Action, out, importcfg, mainpkg string)
 	}
 	ldflags = append(ldflags, forcedLdflags...)
 	ldflags = append(ldflags, root.Package.Internal.Ldflags...)
-	ldflags = setextld(ldflags, compiler)
+	ldflags, err := setextld(ldflags, compiler)
+	if err != nil {
+		return err
+	}
 
 	// On OS X when using external linking to build a shared library,
 	// the argument passed here to -o ends up recorded in the final
@@ -693,7 +681,10 @@ func (gcToolchain) ldShared(b *Builder, root *Action, toplevelactions []*Action,
 	} else {
 		compiler = envList("CC", cfg.DefaultCC(cfg.Goos, cfg.Goarch))
 	}
-	ldflags = setextld(ldflags, compiler)
+	ldflags, err := setextld(ldflags, compiler)
+	if err != nil {
+		return err
+	}
 	for _, d := range toplevelactions {
 		if !strings.HasSuffix(d.Target, ".a") { // omit unsafe etc and actions for other shared libraries
 			continue

src/cmd/go/internal/work/init.go

@@ -11,6 +11,7 @@ import (
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/fsys"
 	"cmd/go/internal/modload"
+	"cmd/internal/str"
 	"cmd/internal/sys"
 	"flag"
 	"fmt"
@@ -39,9 +40,18 @@ func BuildInit() {
 		cfg.BuildPkgdir = p
 	}
 
-	// Make sure CC and CXX are absolute paths
+	// Make sure CC, CXX, and FC are absolute paths.
-	for _, key := range []string{"CC", "CXX"} {
+	for _, key := range []string{"CC", "CXX", "FC"} {
-		if path := cfg.Getenv(key); !filepath.IsAbs(path) && path != "" && path != filepath.Base(path) {
+		value := cfg.Getenv(key)
+		args, err := str.SplitQuotedFields(value)
+		if err != nil {
+			base.Fatalf("go %s: %s environment variable could not be parsed: %v", flag.Args()[0], key, err)
+		}
+		if len(args) == 0 {
+			continue
+		}
+		path := args[0]
+		if !filepath.IsAbs(path) && path != filepath.Base(path) {
 			base.Fatalf("go %s: %s environment variable is relative; must be absolute path: %s\n", flag.Args()[0], key, path)
 		}
 	}

src/cmd/go/script_test.go

@@ -184,6 +184,7 @@ func (ts *testScript) setup() {
 		"devnull=" + os.DevNull,
 		"goversion=" + goVersion(ts),
 		":=" + string(os.PathListSeparator),
+		"/=" + string(os.PathSeparator),
 	}
 	if !testenv.HasExternalNetwork() {
 		ts.env = append(ts.env, "TESTGONETWORK=panic", "TESTGOVCS=panic")

src/cmd/go/testdata/script/cgo_path_space_quote.txt

@@ -0,0 +1,56 @@
+# This test checks that the CC environment variable may contain quotes and
+# spaces. Arguments are normally split on spaces, tabs, newlines. If an
+# argument contains these characters, the entire argument may be quoted
+# with single or double quotes. This is the same as -gcflags and similar
+# options.
+
+[short] skip
+[!exec:clang] [!exec:gcc] skip
+
+env GOENV=$WORK/go.env
+mkdir 'program files'
+go build -o 'program files' './which cc/which cc.go'
+[exec:clang] env CC='"'$PWD${/}program' 'files${/}which' 'cc"' 'clang
+[!exec:clang] env CC='"'$PWD${/}program' 'files${/}which' 'cc"' 'gcc
+go env CC
+stdout 'program files[/\\]which cc" (clang|gcc)$'
+go env -w CC=$CC
+env CC=
+go env CC
+stdout 'program files[/\\]which cc" (clang|gcc)$'
+
+go run .
+
+-- go.mod --
+module test
+
+go 1.17
+-- which cc/which cc.go --
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+)
+
+func main() {
+	args := append([]string{"-DWRAPPER_WAS_USED=1"}, os.Args[2:]...)
+	cmd := exec.Command(os.Args[1], args...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+-- hello.go --
+package main
+
+// int x = WRAPPER_WAS_USED;
+import "C"
+import "fmt"
+
+func main() {
+	fmt.Println(C.x)
+}

src/cmd/internal/dwarf/dwarf.go

@@ -1620,8 +1620,10 @@ func (s byChildIndex) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
 // current extld.
 // AIX ld doesn't support DWARF with -bnoobjreorder with version
 // prior to 7.2.2.
-func IsDWARFEnabledOnAIXLd(extld string) (bool, error) {
+func IsDWARFEnabledOnAIXLd(extld []string) (bool, error) {
-	out, err := exec.Command(extld, "-Wl,-V").CombinedOutput()
+	name, args := extld[0], extld[1:]
+	args = append(args, "-Wl,-V")
+	out, err := exec.Command(name, args...).CombinedOutput()
 	if err != nil {
 		// The normal output should display ld version and
 		// then fails because ".main" is not defined:

src/cmd/link/dwarf_test.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	cmddwarf "cmd/internal/dwarf"
 	"cmd/internal/objfile"
+	"cmd/internal/str"
 	"debug/dwarf"
 	"internal/testenv"
 	"os"
@@ -67,8 +68,11 @@ func testDWARF(t *testing.T, buildmode string, expectDWARF bool, env ...string)
 			if extld == "" {
 				extld = "gcc"
 			}
-			var err error
+			extldArgs, err := str.SplitQuotedFields(extld)
-			expectDWARF, err = cmddwarf.IsDWARFEnabledOnAIXLd(extld)
+			if err != nil {
+				t.Fatal(err)
+			}
+			expectDWARF, err = cmddwarf.IsDWARFEnabledOnAIXLd(extldArgs)
 			if err != nil {
 				t.Fatal(err)
 			}

src/cmd/link/internal/ld/lib.go

@@ -464,23 +464,24 @@ func loadinternal(ctxt *Link, name string) *sym.Library {
 }
 
 // extld returns the current external linker.
-func (ctxt *Link) extld() string {
+func (ctxt *Link) extld() []string {
-	if *flagExtld == "" {
+	if len(flagExtld) == 0 {
-		*flagExtld = "gcc"
+		flagExtld = []string{"gcc"}
 	}
-	return *flagExtld
+	return flagExtld
 }
 
 // findLibPathCmd uses cmd command to find gcc library libname.
 // It returns library full path if found, or "none" if not found.
 func (ctxt *Link) findLibPathCmd(cmd, libname string) string {
 	extld := ctxt.extld()
-	args := hostlinkArchArgs(ctxt.Arch)
+	name, args := extld[0], extld[1:]
+	args = append(args, hostlinkArchArgs(ctxt.Arch)...)
 	args = append(args, cmd)
 	if ctxt.Debugvlog != 0 {
 		ctxt.Logf("%s %v\n", extld, args)
 	}
-	out, err := exec.Command(extld, args...).Output()
+	out, err := exec.Command(name, args...).Output()
 	if err != nil {
 		if ctxt.Debugvlog != 0 {
 			ctxt.Logf("not using a %s file because compiler failed\n%v\n%s\n", libname, err, out)
@@ -1240,7 +1241,7 @@ func (ctxt *Link) hostlink() {
 	}
 
 	var argv []string
-	argv = append(argv, ctxt.extld())
+	argv = append(argv, ctxt.extld()...)
 	argv = append(argv, hostlinkArchArgs(ctxt.Arch)...)
 
 	if *FlagS || debug_s {
@@ -1401,7 +1402,9 @@ func (ctxt *Link) hostlink() {
 			// If gold is not installed, gcc will silently switch
 			// back to ld.bfd. So we parse the version information
 			// and provide a useful error if gold is missing.
-			cmd := exec.Command(*flagExtld, "-fuse-ld=gold", "-Wl,--version")
+			name, args := flagExtld[0], flagExtld[1:]
+			args = append(args, "-fuse-ld=gold", "-Wl,--version")
+			cmd := exec.Command(name, args...)
 			if out, err := cmd.CombinedOutput(); err == nil {
 				if !bytes.Contains(out, []byte("GNU gold")) {
 					log.Fatalf("ARM external linker must be gold (issue #15696), but is not: %s", out)
@@ -1414,7 +1417,9 @@ func (ctxt *Link) hostlink() {
 		altLinker = "bfd"
 
 		// Provide a useful error if ld.bfd is missing.
-		cmd := exec.Command(*flagExtld, "-fuse-ld=bfd", "-Wl,--version")
+		name, args := flagExtld[0], flagExtld[1:]
+		args = append(args, "-fuse-ld=bfd", "-Wl,--version")
+		cmd := exec.Command(name, args...)
 		if out, err := cmd.CombinedOutput(); err == nil {
 			if !bytes.Contains(out, []byte("GNU ld")) {
 				log.Fatalf("ARM64 external linker must be ld.bfd (issue #35197), please install devel/binutils")
@@ -1482,10 +1487,11 @@ func (ctxt *Link) hostlink() {
 		argv = append(argv, "/lib/crt0_64.o")
 
 		extld := ctxt.extld()
+		name, args := extld[0], extld[1:]
 		// Get starting files.
 		getPathFile := func(file string) string {
-			args := []string{"-maix64", "--print-file-name=" + file}
+			args := append(args, "-maix64", "--print-file-name="+file)
-			out, err := exec.Command(extld, args...).CombinedOutput()
+			out, err := exec.Command(name, args...).CombinedOutput()
 			if err != nil {
 				log.Fatalf("running %s failed: %v\n%s", extld, err, out)
 			}
@@ -1567,14 +1573,18 @@ func (ctxt *Link) hostlink() {
 		}
 	}
 
-	for _, p := range strings.Fields(*flagExtldflags) {
+	for _, p := range flagExtldflags {
 		argv = append(argv, p)
 		checkStatic(p)
 	}
 	if ctxt.HeadType == objabi.Hwindows {
 		// Determine which linker we're using. Add in the extldflags in
 		// case used has specified "-fuse-ld=...".
-		cmd := exec.Command(*flagExtld, *flagExtldflags, "-Wl,--version")
+		extld := ctxt.extld()
+		name, args := extld[0], extld[1:]
+		args = append(args, flagExtldflags...)
+		args = append(args, "-Wl,--version")
+		cmd := exec.Command(name, args...)
 		usingLLD := false
 		if out, err := cmd.CombinedOutput(); err == nil {
 			if bytes.Contains(out, []byte("LLD ")) {
@@ -1718,8 +1728,7 @@ func linkerFlagSupported(arch *sys.Arch, linker, altLinker, flag string) bool {
 	flags := hostlinkArchArgs(arch)
 	keep := false
 	skip := false
-	extldflags := strings.Fields(*flagExtldflags)
+	for _, f := range append(flagExtldflags, ldflag...) {
-	for _, f := range append(extldflags, ldflag...) {
 		if keep {
 			flags = append(flags, f)
 			keep = false

src/cmd/link/internal/ld/main.go

@@ -34,6 +34,7 @@ import (
 	"bufio"
 	"cmd/internal/goobj"
 	"cmd/internal/objabi"
+	"cmd/internal/str"
 	"cmd/internal/sys"
 	"cmd/link/internal/benchmark"
 	"flag"
@@ -53,6 +54,8 @@ var (
 
 func init() {
 	flag.Var(&rpath, "r", "set the ELF dynamic linker search `path` to dir1:dir2:...")
+	flag.Var(&flagExtld, "extld", "use `linker` when linking in external mode")
+	flag.Var(&flagExtldflags, "extldflags", "pass `flags` to external linker")
 }
 
 // Flags used by the linker. The exported flags are used by the architecture-specific packages.
@@ -72,8 +75,8 @@ var (
 	flagLibGCC     = flag.String("libgcc", "", "compiler support lib for internal linking; use \"none\" to disable")
 	flagTmpdir     = flag.String("tmpdir", "", "use `directory` for temporary files")
 
-	flagExtld      = flag.String("extld", "", "use `linker` when linking in external mode")
+	flagExtld      str.QuotedStringListFlag
-	flagExtldflags = flag.String("extldflags", "", "pass `flags` to external linker")
+	flagExtldflags str.QuotedStringListFlag
 	flagExtar      = flag.String("extar", "", "archive program for buildmode=c-archive")
 
 	flagA             = flag.Bool("a", false, "no-op (deprecated)")