cmd/go: elide -rpath when not applicable and used via LDFLAGS

Some linker flags should only be applied when performing the final
linking step for a shared library or executable, etc. In other
contexts, they're either invalid, or meaningless to apply (so should
not be specified).

When an external linker is used (either directly by Go or by the
compiler driver used by cgo), -rpath and -rpath-link should only be
specified in the final linking step.  On platforms such as Solaris,
ld(1) will reject its use in any other scenario (such as when linking
relocatable objects).

This change is necessary because Go does not currently offer a way to
specify LDFLAGS based on when they should be applied.

Fixes #12115

Change-Id: If35a18d8eee8ec7ddcca2d4ccd41ab6ffcf93b41
Reviewed-on: https://go-review.googlesource.com/14674Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/build.go

@@ -2943,7 +2943,9 @@ func (b *builder) cgo(p *Package, cgoExe, obj string, pcCFLAGS, pcLDFLAGS, cgofi
 	var linkobj []string
 
 	var bareLDFLAGS []string
-	// filter out -lsomelib, -l somelib, *.{so,dll,dylib}, and (on Darwin) -framework X
+	// When linking relocatable objects, various flags need to be
+	// filtered out as they are inapplicable and can cause some linkers
+	// to fail.
 	for i := 0; i < len(cgoLDFLAGS); i++ {
 		f := cgoLDFLAGS[i]
 		switch {
@@ -2959,7 +2961,6 @@ func (b *builder) cgo(p *Package, cgoExe, obj string, pcCFLAGS, pcLDFLAGS, cgofi
 		case strings.HasSuffix(f, ".dylib"),
 			strings.HasSuffix(f, ".so"),
 			strings.HasSuffix(f, ".dll"):
-			continue
 		// Remove any -fsanitize=foo flags.
 		// Otherwise the compiler driver thinks that we are doing final link
 		// and links sanitizer runtime into the object file. But we are not doing
@@ -2968,6 +2969,16 @@ func (b *builder) cgo(p *Package, cgoExe, obj string, pcCFLAGS, pcLDFLAGS, cgofi
 		// See issue 8788 for details.
 		case strings.HasPrefix(f, "-fsanitize="):
 			continue
+		// runpath flags not applicable unless building a shared
+		// object or executable; see issue 12115 for details.  This
+		// is necessary as Go currently does not offer a way to
+		// specify the set of LDFLAGS that only apply to shared
+		// objects.
+		case strings.HasPrefix(f, "-Wl,-rpath"):
+			if f == "-Wl,-rpath" || f == "-Wl,-rpath-link" {
+				// Skip following argument to -rpath* too.
+				i++
+			}
 		default:
 			bareLDFLAGS = append(bareLDFLAGS, f)
 		}