[dev.link] cmd/link: remove Sub field from sym.Symbol

Remove 'Sub' field from sym.Symbol, replacing uses (those downstream of
loadlibfull) with loader method calls.

NB: removing the Outer field will have to wait for now; it is accessed
in archreloc methods that don't have access to link ctxt or loader
currently.

Change-Id: I2abe5906fc169c64b2ab7d5ad213619bea5a17c7
Reviewed-on: https://go-review.googlesource.com/c/go/+/230617
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/link/internal/ld/elf.go

@@ -2026,7 +2026,7 @@ func Asmbelf(ctxt *Link, symo int64) {
 		// sh.info is the index of first non-local symbol (number of local symbols)
 		s := ctxt.Syms.Lookup(".dynsym", 0)
 		i := uint32(0)
-		for sub := s; sub != nil; sub = sub.Sub {
+		for sub := s; sub != nil; sub = symSub(ctxt, sub) {
 			i++
 			if !sub.Attr.Local() {
 				break

src/cmd/link/internal/ld/lib.go

@@ -2929,12 +2929,19 @@ func ElfSymForReloc(ctxt *Link, s *sym.Symbol) int32 {
 	}
 }
 
+func symSub(ctxt *Link, s *sym.Symbol) *sym.Symbol {
+	if lsub := ctxt.loader.SubSym(loader.Sym(s.SymIdx)); lsub != 0 {
+		return ctxt.loader.Syms[lsub]
+	}
+	return nil
+}
+
 func (ctxt *Link) dumpsyms() {
 	for _, s := range ctxt.loader.Syms {
 		if s == nil {
 			continue
 		}
-		fmt.Printf("%s %s reachable=%v onlist=%v outer=%v sub=%v\n", s, s.Type, s.Attr.Reachable(), s.Attr.OnList(), s.Outer, s.Sub)
+		fmt.Printf("%s %s reachable=%v onlist=%v outer=%v sub=%v\n", s, s.Type, s.Attr.Reachable(), s.Attr.OnList(), s.Outer, symSub(ctxt, s))
 		for i := range s.R {
 			fmt.Println("\t", s.R[i].Type, s.R[i].Sym)
 		}

src/cmd/link/internal/loader/loader.go

@@ -2544,13 +2544,10 @@ func (l *Loader) migrateAttributes(src Sym, dst *sym.Symbol) {
 	dst.Attr.Set(sym.AttrCgoExportStatic, l.AttrCgoExportStatic(src))
 	dst.Attr.Set(sym.AttrReadOnly, l.AttrReadOnly(src))
 
-	// Convert outer/sub relationships
+	// Convert outer relationship
 	if outer, ok := l.outer[src]; ok {
 		dst.Outer = l.Syms[outer]
 	}
-	if sub, ok := l.sub[src]; ok {
-		dst.Sub = l.Syms[sub]
-	}
 
 	// Set sub-symbol attribute. See the comment on the AttrSubSymbol
 	// method for more on this, there is some tricky stuff here.

src/cmd/link/internal/sym/sizeof_test.go

@@ -21,7 +21,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Symbol{}, 84, 136},
+		{Symbol{}, 80, 128},
 	}
 
 	for _, tt := range tests {

src/cmd/link/internal/sym/symbol.go

@@ -23,7 +23,6 @@ type Symbol struct {
 	Align   int32
 	Value   int64
 	Size    int64
-	Sub     *Symbol
 	Outer   *Symbol
 	SymIdx  LoaderSym
 	auxinfo *AuxSymbol