cmd/link: look at the R_AARCH64_RELATIVE relocs to find the gcdata on arm64

Change-Id: I5a1864a27ad917aa65c8e65a133f6cc0a980d05f
Reviewed-on: https://go-review.googlesource.com/13998Reviewed-by: Russ Cox <rsc@golang.org>

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

@@ -110,6 +110,14 @@ func decodetype_gcprog(s *LSym) []byte {
 }
 
 func decodetype_gcprog_shlib(s *LSym) uint64 {
+	if Thearch.Thechar == '7' {
+		for _, shlib := range Ctxt.Shlibs {
+			if shlib.Path == s.File {
+				return shlib.gcdata_addresses[s]
+			}
+		}
+		return 0
+	}
 	return decode_inuxi(s.P[2*int32(Thearch.Ptrsize)+8+1*int32(Thearch.Ptrsize):], Thearch.Ptrsize)
 }
 

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

@@ -1400,6 +1400,7 @@ func ldshlibsyms(shlib string) {
 		Diag("cannot read symbols from shared library: %s", libpath)
 		return
 	}
+	gcdata_locations := make(map[uint64]*LSym)
 	for _, elfsym := range syms {
 		if elf.ST_TYPE(elfsym.Info) == elf.STT_NOTYPE || elf.ST_TYPE(elfsym.Info) == elf.STT_SECTION {
 			continue
@@ -1428,6 +1429,32 @@ func ldshlibsyms(shlib string) {
 			// the type data.
 			if strings.HasPrefix(lsym.Name, "type.") && !strings.HasPrefix(lsym.Name, "type..") {
 				lsym.P = readelfsymboldata(f, &elfsym)
+				gcdata_locations[elfsym.Value+2*uint64(Thearch.Ptrsize)+8+1*uint64(Thearch.Ptrsize)] = lsym
+			}
+		}
+	}
+	gcdata_addresses := make(map[*LSym]uint64)
+	if Thearch.Thechar == '7' {
+		for _, sect := range f.Sections {
+			if sect.Type == elf.SHT_RELA {
+				var rela elf.Rela64
+				rdr := sect.Open()
+				for {
+					err := binary.Read(rdr, f.ByteOrder, &rela)
+					if err == io.EOF {
+						break
+					} else if err != nil {
+						Diag("reading relocation failed %v", err)
+						return
+					}
+					t := elf.R_AARCH64(rela.Info & 0xffff)
+					if t != elf.R_AARCH64_RELATIVE {
+						continue
+					}
+					if lsym, ok := gcdata_locations[rela.Off]; ok {
+						gcdata_addresses[lsym] = uint64(rela.Addend)
+					}
+				}
 			}
 		}
 	}
@@ -1459,7 +1486,7 @@ func ldshlibsyms(shlib string) {
 		Ctxt.Etextp = last
 	}
 
-	Ctxt.Shlibs = append(Ctxt.Shlibs, Shlib{Path: libpath, Hash: hash, Deps: deps, File: f})
+	Ctxt.Shlibs = append(Ctxt.Shlibs, Shlib{Path: libpath, Hash: hash, Deps: deps, File: f, gcdata_addresses: gcdata_addresses})
 }
 
 func mywhatsys() {

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

@@ -124,10 +124,11 @@ type Auto struct {
 }
 
 type Shlib struct {
-	Path string
-	Hash []byte
-	Deps []string
-	File *elf.File
+	Path             string
+	Hash             []byte
+	Deps             []string
+	File             *elf.File
+	gcdata_addresses map[*LSym]uint64
 }
 
 type Link struct {