cmd/internal/obj: add a flag to not write referenced symbol names in object file

The Go object file references (some of) symbols from other
packages by indices, not by names. The linker doesn't need the
symbol names to do the linking. The names are included in the
object file so it is self-contained and tools (objdump, nm) can
read the referenced symbol names. Including the names increases
object file size. Add a flag to disable it on demand (off by
default).

Change-Id: I143a0eb656997497c750b8eb1541341b2aee8f30
Reviewed-on: https://go-review.googlesource.com/c/go/+/404297
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index 2caff62702..d31afda703 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -269,17 +269,21 @@ func (w *writer) StringTable() {
 		w.AddString(pkg)
 	}
 	w.ctxt.traverseSyms(traverseAll, func(s *LSym) {
+		// Don't put names of builtins into the string table (to save
+		// space).
+		if s.PkgIdx == goobj.PkgIdxBuiltin {
+			return
+		}
 		// TODO: this includes references of indexed symbols from other packages,
 		// for which the linker doesn't need the name. Consider moving them to
 		// a separate block (for tools only).
+		if w.ctxt.Flag_noRefName && s.PkgIdx < goobj.PkgIdxSpecial {
+			// Don't include them if Flag_noRefName
+			return
+		}
 		if w.pkgpath != "" {
 			s.Name = strings.Replace(s.Name, "\"\".", w.pkgpath+".", -1)
 		}
-		// Don't put names of builtins into the string table (to save
-		// space).
-		if s.PkgIdx == goobj.PkgIdxBuiltin {
-			return
-		}
 		w.AddString(s.Name)
 	})
 
@@ -625,6 +629,9 @@ func (w *writer) refFlags() {
 // Emits names of referenced indexed symbols, used by tools (objdump, nm)
 // only.
 func (w *writer) refNames() {
+	if w.ctxt.Flag_noRefName {
+		return
+	}
 	seen := make(map[*LSym]bool)
 	w.ctxt.traverseSyms(traverseRefs, func(rs *LSym) { // only traverse refs, not auxs, as tools don't need auxs
 		switch rs.PkgIdx {