cmd/link: use path from "cc --print-prog-name ar" for c-archive buildmode

When external linking with -buildmode=c-archive, the Go linker
eventually invokes the "ar" tool to create the final archive library.
Prior to this patch, if the '-extar' flag was not in use, we would
just run "ar". This works well in most cases but breaks down if we're
doing cross-compilation targeting Windows (macos system "ar"
apparently doesn't create the windows symdef section correctly). To
fix the problem, capture the output of "cc --print-prog-name ar" and
invoke "ar" using the path returned by that command.

Fixes #59221.

Change-Id: I9de66e98947c42633b16fde7208c2958d62fe7cc
Reviewed-on: https://go-review.googlesource.com/c/go/+/479775
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index 02c6908407bdf408e2ca0c34632415932bec10a1..6500c810e04248ecf80fc95675ae2d7416f0e02c 100644 (file)
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -1316,7 +1316,12 @@ func (ctxt *Link) archive() {
        exitIfErrors()
 
        if *flagExtar == "" {
+               const printProgName = "--print-prog-name=ar"
+               cc := ctxt.extld()
                *flagExtar = "ar"
+               if linkerFlagSupported(ctxt.Arch, cc[0], "", printProgName) {
+                       *flagExtar = ctxt.findExtLinkTool("ar")
+               }
        }
 
        mayberemoveoutfile()
@@ -1875,22 +1880,8 @@ func (ctxt *Link) hostlink() {
 
        if combineDwarf {
                // Find "dsymutils" and "strip" tools using CC --print-prog-name.
-               var cc []string
-               cc = append(cc, ctxt.extld()...)
-               cc = append(cc, hostlinkArchArgs(ctxt.Arch)...)
-               cc = append(cc, "--print-prog-name", "dsymutil")
-               out, err := exec.Command(cc[0], cc[1:]...).CombinedOutput()
-               if err != nil {
-                       Exitf("%s: finding dsymutil failed: %v\n%s", os.Args[0], err, out)
-               }
-               dsymutilCmd := strings.TrimSuffix(string(out), "\n")
-
-               cc[len(cc)-1] = "strip"
-               out, err = exec.Command(cc[0], cc[1:]...).CombinedOutput()
-               if err != nil {
-                       Exitf("%s: finding strip failed: %v\n%s", os.Args[0], err, out)
-               }
-               stripCmd := strings.TrimSuffix(string(out), "\n")
+               dsymutilCmd := ctxt.findExtLinkTool("dsymutil")
+               stripCmd := ctxt.findExtLinkTool("dsymutil")
 
                dsym := filepath.Join(*flagTmpdir, "go.dwarf")
                if out, err := exec.Command(dsymutilCmd, "-f", *flagOutfile, "-o", dsym).CombinedOutput(); err != nil {
@@ -2763,3 +2754,19 @@ func captureHostObj(h *Hostobj) {
        fmt.Fprintf(os.Stderr, "link: info: captured host object %s to %s\n",
                h.file, opath)
 }
+
+// findExtLinkTool invokes the external linker CC with --print-prog-name
+// passing the name of the tool we're interested in, such as "strip",
+// "ar", or "dsymutil", and returns the path passed back from the command.
+func (ctxt *Link) findExtLinkTool(toolname string) string {
+       var cc []string
+       cc = append(cc, ctxt.extld()...)
+       cc = append(cc, hostlinkArchArgs(ctxt.Arch)...)
+       cc = append(cc, "--print-prog-name", toolname)
+       out, err := exec.Command(cc[0], cc[1:]...).CombinedOutput()
+       if err != nil {
+               Exitf("%s: finding %s failed: %v\n%s", os.Args[0], toolname, err, out)
+       }
+       cmdpath := strings.TrimSuffix(string(out), "\n")
+       return cmdpath
+}