cmd/internal/ld: prevent creation of .dynamic and .dynsym symbols when externally linking

This allows the removal of a fudge in data.go.

We have to defer the calls to adddynlib on non-Darwin until after we have
decided whether we are externally or internally linking.  The Macho/ELF
separation could do with some cleaning up, but: code freeze.

Fixing this once rather than per-arch is what inspired the previous CLs.

Change-Id: I0166f7078a045dc09827745479211247466c0c54
Reviewed-on: https://go-review.googlesource.com/10002
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/internal/ld/data.go

@@ -1127,13 +1127,7 @@ func proggenaddsym(g *ProgGen, s *LSym) {
 	proggenskip(g, g.pos, s.Value-g.pos)
 	g.pos = s.Value
 
-	// The test for names beginning with . here is meant
-	// to keep .dynamic and .dynsym from turning up as
-	// conservative symbols. They should be marked SELFSECT
-	// and not SDATA, but sometimes that doesn't happen.
-	// Leave debugging the SDATA issue for the Go rewrite.
-
-	if s.Gotype == nil && s.Size >= int64(Thearch.Ptrsize) && s.Name[0] != '.' {
+	if s.Gotype == nil && s.Size >= int64(Thearch.Ptrsize) {
 		Diag("missing Go type information for global symbol: %s size %d", s.Name, int(s.Size))
 		return
 	}

src/cmd/internal/ld/go.go

@@ -416,7 +416,11 @@ func loadcgo(file string, pkg string, p string) {
 				// to force a link of foo.so.
 				havedynamic = 1
 
-				adddynlib(lib)
+				if HEADTYPE == obj.Hdarwin {
+					Machoadddynlib(lib)
+				} else {
+					dynlib = append(dynlib, lib)
+				}
 				continue
 			}
 
@@ -537,7 +541,7 @@ err:
 var seenlib = make(map[string]bool)
 
 func adddynlib(lib string) {
-	if seenlib[lib] {
+	if seenlib[lib] || Linkmode == LinkExternal {
 		return
 	}
 	seenlib[lib] = true
@@ -548,15 +552,13 @@ func adddynlib(lib string) {
 			Addstring(s, "")
 		}
 		Elfwritedynent(Linklookup(Ctxt, ".dynamic", 0), DT_NEEDED, uint64(Addstring(s, lib)))
-	} else if HEADTYPE == obj.Hdarwin {
-		Machoadddynlib(lib)
 	} else {
 		Diag("adddynlib: unsupported binary format")
 	}
 }
 
 func Adddynsym(ctxt *Link, s *LSym) {
-	if s.Dynid >= 0 {
+	if s.Dynid >= 0 || Linkmode == LinkExternal {
 		return
 	}
 
@@ -774,8 +776,11 @@ func addexport() {
 		return
 	}
 
-	for i := 0; i < len(dynexp); i++ {
-		Adddynsym(Ctxt, dynexp[i])
+	for _, exp := range dynexp {
+		Adddynsym(Ctxt, exp)
+	}
+	for _, lib := range dynlib {
+		adddynlib(lib)
 	}
 }
 

src/cmd/internal/ld/lib.go

@@ -178,6 +178,7 @@ var (
 	Thelinkarch        *LinkArch
 	outfile            string
 	dynexp             []*LSym
+	dynlib             []string
 	ldflag             []string
 	havedynamic        int
 	Funcalign          int