cmd/link/internal/ld: consider alternative linkers in linkerFlagSupported

CL 235017 is about to change the default Android linker to lld. lld doesn't
support the --compress-debug-sections=zlib-gnu flag, but linkerFlagSupported
doesn't take any alternative linkers specified with -fuse-ld into account.

Updates #38838

Change-Id: I5f7422c06d40dedde2e4b070fc48398e8f822190
Reviewed-on: https://go-review.googlesource.com/c/go/+/235157
Run-TryBot: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 12 insertions, 6 deletions

diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index 3c60901124..523a7992bb 100644
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -1466,6 +1466,7 @@ func (ctxt *Link) hostlink() {
 		}
 	}
 
+	var altLinker string
 	if ctxt.IsELF && ctxt.DynlinkingGo() {
 		// We force all symbol resolution to be done at program startup
 		// because lazy PLT resolution can use large amounts of stack at
@@ -1486,7 +1487,7 @@ func (ctxt *Link) hostlink() {
 			// generating COPY relocations.
 			//
 			// In both cases, switch to gold.
-			argv = append(argv, "-fuse-ld=gold")
+			altLinker = "gold"
 
 			// If gold is not installed, gcc will silently switch
 			// back to ld.bfd. So we parse the version information
@@ -1499,10 +1500,9 @@ func (ctxt *Link) hostlink() {
 			}
 		}
 	}
-
 	if ctxt.Arch.Family == sys.ARM64 && objabi.GOOS == "freebsd" {
 		// Switch to ld.bfd on freebsd/arm64.
-		argv = append(argv, "-fuse-ld=bfd")
+		altLinker = "bfd"
 
 		// Provide a useful error if ld.bfd is missing.
 		cmd := exec.Command(*flagExtld, "-fuse-ld=bfd", "-Wl,--version")
@@ -1512,6 +1512,9 @@ func (ctxt *Link) hostlink() {
 			}
 		}
 	}
+	if altLinker != "" {
+		argv = append(argv, "-fuse-ld="+altLinker)
+	}
 
 	if ctxt.IsELF && len(buildinfo) > 0 {
 		argv = append(argv, fmt.Sprintf("-Wl,--build-id=0x%x", buildinfo))
@@ -1548,7 +1551,7 @@ func (ctxt *Link) hostlink() {
 	}
 
 	const compressDWARF = "-Wl,--compress-debug-sections=zlib-gnu"
-	if ctxt.compressDWARF && linkerFlagSupported(argv[0], compressDWARF) {
+	if ctxt.compressDWARF && linkerFlagSupported(argv[0], altLinker, compressDWARF) {
 		argv = append(argv, compressDWARF)
 	}
 
@@ -1638,7 +1641,7 @@ func (ctxt *Link) hostlink() {
 	if ctxt.BuildMode == BuildModeExe && !ctxt.linkShared {
 		// GCC uses -no-pie, clang uses -nopie.
 		for _, nopie := range []string{"-no-pie", "-nopie"} {
-			if linkerFlagSupported(argv[0], nopie) {
+			if linkerFlagSupported(argv[0], altLinker, nopie) {
 				argv = append(argv, nopie)
 				break
 			}
@@ -1739,7 +1742,7 @@ func (ctxt *Link) hostlink() {
 
 var createTrivialCOnce sync.Once
 
-func linkerFlagSupported(linker, flag string) bool {
+func linkerFlagSupported(linker, altLinker, flag string) bool {
 	createTrivialCOnce.Do(func() {
 		src := filepath.Join(*flagTmpdir, "trivial.c")
 		if err := ioutil.WriteFile(src, []byte("int main() { return 0; }"), 0666); err != nil {
@@ -1799,6 +1802,9 @@ func linkerFlagSupported(linker, flag string) bool {
 		}
 	}
 
+	if altLinker != "" {
+		flags = append(flags, "-fuse-ld="+altLinker)
+	}
 	flags = append(flags, flag, "trivial.c")
 
 	cmd := exec.Command(linker, flags...)