Revert "cmd/internal/ld: put read-only relocated data into .data.rel.ro when making a shared object"

This reverts commit 2c2cbb69c8.

Broke darwin/arm64

Change-Id: Ibd2dea475d6ce6a8b4b40e2da19a83fc0514025d
Reviewed-on: https://go-review.googlesource.com/14301
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testcshared/test.bash

@@ -81,13 +81,6 @@ GOPATH=$(pwd) go install -buildmode=c-shared $suffix libgo
 GOPATH=$(pwd) go build -buildmode=c-shared $suffix -o libgo.$libext src/libgo/libgo.go
 binpush libgo.$libext
 
-if [ "$goos" == "linux" ]; then
-    if readelf -d libgo.$libext | grep TEXTREL >/dev/null; then
-        echo "libgo.$libext has TEXTREL set"
-        exit 1
-    fi
-fi
-
 # test0: exported symbols in shared lib are accessible.
 # TODO(iant): using _shared here shouldn't really be necessary.
 $(go env CC) $(go env GOGCCFLAGS) -I ${installdir} -o testp main0.c libgo.$libext

misc/cgo/testshared/shared_test.go

@@ -163,45 +163,6 @@ func TestSOBuilt(t *testing.T) {
 	}
 }
 
-func hasDynTag(f *elf.File, tag elf.DynTag) bool {
-	ds := f.SectionByType(elf.SHT_DYNAMIC)
-	if ds == nil {
-		return false
-	}
-	d, err := ds.Data()
-	if err != nil {
-		return false
-	}
-	for len(d) > 0 {
-		var t elf.DynTag
-		switch f.Class {
-		case elf.ELFCLASS32:
-			t = elf.DynTag(f.ByteOrder.Uint32(d[0:4]))
-			d = d[8:]
-		case elf.ELFCLASS64:
-			t = elf.DynTag(f.ByteOrder.Uint64(d[0:8]))
-			d = d[16:]
-		}
-		if t == tag {
-			return true
-		}
-	}
-	return false
-}
-
-// The shared library does not have relocations against the text segment.
-func TestNoTextrel(t *testing.T) {
-	sopath := filepath.Join(gorootInstallDir, soname)
-	f, err := elf.Open(sopath)
-	if err != nil {
-		t.Fatal("elf.Open failed: ", err)
-	}
-	defer f.Close()
-	if hasDynTag(f, elf.DT_TEXTREL) {
-		t.Errorf("%s has DT_TEXTREL set", soname)
-	}
-}
-
 // The install command should have created a "shlibname" file for the
 // listed packages (and runtime/cgo) indicating the name of the shared
 // library containing it.

src/cmd/internal/obj/link.go

@@ -334,7 +334,6 @@ const (
 	Sxxx = iota
 	STEXT
 	SELFRXSECT
-
 	STYPE
 	SSTRING
 	SGOSTRING
@@ -342,25 +341,6 @@ const (
 	SGCBITS
 	SRODATA
 	SFUNCTAB
-
-	// Types STYPE-SFUNCTAB above are written to the .rodata section by default.
-	// When linking a shared object, some conceptually "read only" types need to
-	// be written to by relocations and putting them in a section called
-	// ".rodata" interacts poorly with the system linkers. The GNU linkers
-	// support this situation by arranging for sections of the name
-	// ".data.rel.ro.XXX" to be mprotected read only by the dynamic linker after
-	// relocations have applied, so when the Go linker is creating a shared
-	// object it checks all objects of the above types and bumps any object that
-	// has a relocation to it to the corresponding type below, which are then
-	// written to sections with appropriate magic names.
-	STYPERELRO
-	SSTRINGRELRO
-	SGOSTRINGRELRO
-	SGOFUNCRELRO
-	SGCBITSRELRO
-	SRODATARELRO
-	SFUNCTABRELRO
-
 	STYPELINK
 	SSYMTAB
 	SPCLNTAB

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

@@ -1207,31 +1207,6 @@ func dodata() {
 
 	*l = nil
 
-	if UseRelro() {
-		// "read only" data with relocations needs to go in its own section
-		// when building a shared library. We do this by boosting objects of
-		// type SXXX with relocations to type SXXXRELRO.
-		for s := datap; s != nil; s = s.Next {
-			if (s.Type >= obj.STYPE && s.Type <= obj.SFUNCTAB && len(s.R) > 0) || s.Type == obj.SGOSTRING {
-				s.Type += (obj.STYPERELRO - obj.STYPE)
-				if s.Outer != nil {
-					s.Outer.Type = s.Type
-				}
-			}
-		}
-		// Check that we haven't made two symbols with the same .Outer into
-		// different types (because references two symbols with non-nil Outer
-		// become references to the outer symbol + offset it's vital that the
-		// symbol and the outer end up in the same section).
-		for s := datap; s != nil; s = s.Next {
-			if s.Outer != nil && s.Outer.Type != s.Type {
-				Diag("inconsistent types for %s and its Outer %s (%d != %d)",
-					s.Name, s.Outer.Name, s.Type, s.Outer.Type)
-			}
-		}
-
-	}
-
 	datap = listsort(datap, datcmp, listnextp)
 
 	if Iself {
@@ -1490,12 +1465,12 @@ func dodata() {
 	/* read-only data */
 	sect = addsection(segro, ".rodata", 04)
 
-	sect.Align = maxalign(s, obj.STYPERELRO-1)
+	sect.Align = maxalign(s, obj.STYPELINK-1)
 	datsize = Rnd(datsize, int64(sect.Align))
 	sect.Vaddr = 0
 	Linklookup(Ctxt, "runtime.rodata", 0).Sect = sect
 	Linklookup(Ctxt, "runtime.erodata", 0).Sect = sect
-	for ; s != nil && s.Type < obj.STYPERELRO; s = s.Next {
+	for ; s != nil && s.Type < obj.STYPELINK; s = s.Next {
 		datsize = aligndatsize(datsize, s)
 		s.Sect = sect
 		s.Type = obj.SRODATA
@@ -1505,45 +1480,8 @@ func dodata() {
 
 	sect.Length = uint64(datsize) - sect.Vaddr
 
-	// There is some data that are conceptually read-only but are written to by
-	// relocations. On GNU systems, we can arrange for the dynamic linker to
-	// mprotect sections after relocations are applied by giving them write
-	// permissions in the object file and calling them ".data.rel.ro.FOO". We
-	// divide the .rodata section between actual .rodata and .data.rel.ro.rodata,
-	// but for the other sections that this applies to, we just write a read-only
-	// .FOO section or a read-write .data.rel.ro.FOO section depending on the
-	// situation.
-	// TODO(mwhudson): It would make sense to do this more widely, but it makes
-	// the system linker segfault on darwin.
-	relro_perms := 04
-	relro_prefix := ""
-
-	if UseRelro() {
-		relro_perms = 06
-		relro_prefix = ".data.rel.ro"
-		/* data only written by relocations */
-		sect = addsection(segro, ".data.rel.ro", 06)
-
-		sect.Align = maxalign(s, obj.STYPELINK-1)
-		datsize = Rnd(datsize, int64(sect.Align))
-		sect.Vaddr = 0
-		for ; s != nil && s.Type < obj.STYPELINK; s = s.Next {
-			datsize = aligndatsize(datsize, s)
-			if s.Outer != nil && s.Outer.Sect != nil && s.Outer.Sect != sect {
-				Diag("s.Outer (%s) in different section from s (%s)", s.Outer.Name, s.Name)
-			}
-			s.Sect = sect
-			s.Type = obj.SRODATA
-			s.Value = int64(uint64(datsize) - sect.Vaddr)
-			growdatsize(&datsize, s)
-		}
-
-		sect.Length = uint64(datsize) - sect.Vaddr
-
-	}
-
 	/* typelink */
-	sect = addsection(segro, relro_prefix+".typelink", relro_perms)
+	sect = addsection(segro, ".typelink", 04)
 
 	sect.Align = maxalign(s, obj.STYPELINK)
 	datsize = Rnd(datsize, int64(sect.Align))
@@ -1561,7 +1499,7 @@ func dodata() {
 	sect.Length = uint64(datsize) - sect.Vaddr
 
 	/* gosymtab */
-	sect = addsection(segro, relro_prefix+".gosymtab", relro_perms)
+	sect = addsection(segro, ".gosymtab", 04)
 
 	sect.Align = maxalign(s, obj.SPCLNTAB-1)
 	datsize = Rnd(datsize, int64(sect.Align))
@@ -1579,7 +1517,7 @@ func dodata() {
 	sect.Length = uint64(datsize) - sect.Vaddr
 
 	/* gopclntab */
-	sect = addsection(segro, relro_prefix+".gopclntab", relro_perms)
+	sect = addsection(segro, ".gopclntab", 04)
 
 	sect.Align = maxalign(s, obj.SELFROSECT-1)
 	datsize = Rnd(datsize, int64(sect.Align))
@@ -1785,11 +1723,6 @@ func address() {
 		rodata = text.Next
 	}
 	typelink := rodata.Next
-	if UseRelro() {
-		// There is another section (.data.rel.ro) when building a shared
-		// object on elf systems.
-		typelink = typelink.Next
-	}
 	symtab := typelink.Next
 	pclntab := symtab.Next
 

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

@@ -1690,18 +1690,9 @@ func doelf() {
 	}
 	Addstring(shstrtab, ".elfdata")
 	Addstring(shstrtab, ".rodata")
-	if Buildmode == BuildmodeShared || Buildmode == BuildmodeCShared {
-		Addstring(shstrtab, ".data.rel.ro")
-	}
-	// See the comment about data.rel.ro.FOO section names in data.go.
-	relro_prefix := ""
-
-	if UseRelro() {
-		relro_prefix = ".data.rel.ro"
-	}
-	Addstring(shstrtab, relro_prefix+".typelink")
-	Addstring(shstrtab, relro_prefix+".gosymtab")
-	Addstring(shstrtab, relro_prefix+".gopclntab")
+	Addstring(shstrtab, ".typelink")
+	Addstring(shstrtab, ".gosymtab")
+	Addstring(shstrtab, ".gopclntab")
 
 	if Linkmode == LinkExternal {
 		Debug['d'] = 1
@@ -1710,26 +1701,20 @@ func doelf() {
 		case '6', '7', '9':
 			Addstring(shstrtab, ".rela.text")
 			Addstring(shstrtab, ".rela.rodata")
-			Addstring(shstrtab, ".rela"+relro_prefix+".typelink")
-			Addstring(shstrtab, ".rela"+relro_prefix+".gosymtab")
-			Addstring(shstrtab, ".rela"+relro_prefix+".gopclntab")
+			Addstring(shstrtab, ".rela.typelink")
+			Addstring(shstrtab, ".rela.gosymtab")
+			Addstring(shstrtab, ".rela.gopclntab")
 			Addstring(shstrtab, ".rela.noptrdata")
 			Addstring(shstrtab, ".rela.data")
-			if UseRelro() {
-				Addstring(shstrtab, ".rela.data.rel.ro")
-			}
 
 		default:
 			Addstring(shstrtab, ".rel.text")
 			Addstring(shstrtab, ".rel.rodata")
-			Addstring(shstrtab, ".rel"+relro_prefix+".typelink")
-			Addstring(shstrtab, ".rel"+relro_prefix+".gosymtab")
-			Addstring(shstrtab, ".rel"+relro_prefix+".gopclntab")
+			Addstring(shstrtab, ".rel.typelink")
+			Addstring(shstrtab, ".rel.gosymtab")
+			Addstring(shstrtab, ".rel.gopclntab")
 			Addstring(shstrtab, ".rel.noptrdata")
 			Addstring(shstrtab, ".rel.data")
-			if UseRelro() {
-				Addstring(shstrtab, ".rel.data.rel.ro")
-			}
 		}
 
 		// add a .note.GNU-stack section to mark the stack as non-executable

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

@@ -174,12 +174,6 @@ func DynlinkingGo() bool {
 	return Buildmode == BuildmodeShared || Linkshared
 }
 
-// UseRelro returns whether to make use of "read only relocations" aka
-// relro.
-func UseRelro() bool {
-	return (Buildmode == BuildmodeCShared || Buildmode == BuildmodeShared) && Iself
-}
-
 var (
 	Thestring          string
 	Thelinkarch        *LinkArch
@@ -986,9 +980,6 @@ func hostlink() {
 			argv = append(argv, "-dynamiclib")
 		} else {
 			argv = append(argv, "-Wl,-Bsymbolic")
-			if UseRelro() {
-				argv = append(argv, "-Wl,-z,relro")
-			}
 			argv = append(argv, "-shared")
 		}
 	case BuildmodeShared:
@@ -1000,10 +991,7 @@ func hostlink() {
 		// think we may well end up wanting to use -Bsymbolic here
 		// anyway.
 		argv = append(argv, "-Wl,-Bsymbolic-functions")
-		if UseRelro() {
-			argv = append(argv, "-shared")
-		}
-		argv = append(argv, "-Wl,-z,relro")
+		argv = append(argv, "-shared")
 	}
 
 	if Linkshared && Iself {
@@ -1783,12 +1771,6 @@ func genasmsym(put func(*LSym, string, int, int64, int64, int, *LSym)) {
 			obj.SGOSTRING,
 			obj.SGOFUNC,
 			obj.SGCBITS,
-			obj.STYPERELRO,
-			obj.SSTRINGRELRO,
-			obj.SGOSTRINGRELRO,
-			obj.SGOFUNCRELRO,
-			obj.SGCBITSRELRO,
-			obj.SRODATARELRO,
 			obj.SWINDOWS:
 			if !s.Reachable {
 				continue

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

@@ -350,29 +350,13 @@ func symtab() {
 
 	// pseudo-symbols to mark locations of type, string, and go string data.
 	var symtype *LSym
-	var symtyperel *LSym
-	if UseRelro() && Buildmode == BuildmodeCShared {
+	if !DynlinkingGo() {
 		s = Linklookup(Ctxt, "type.*", 0)
 
 		s.Type = obj.STYPE
 		s.Size = 0
 		s.Reachable = true
 		symtype = s
-
-		s = Linklookup(Ctxt, "typerel.*", 0)
-
-		s.Type = obj.STYPERELRO
-		s.Size = 0
-		s.Reachable = true
-		symtyperel = s
-	} else if !DynlinkingGo() {
-		s = Linklookup(Ctxt, "type.*", 0)
-
-		s.Type = obj.STYPE
-		s.Size = 0
-		s.Reachable = true
-		symtype = s
-		symtyperel = s
 	}
 
 	s = Linklookup(Ctxt, "go.string.*", 0)
@@ -397,7 +381,6 @@ func symtab() {
 	symgcbits := s
 
 	symtypelink := Linklookup(Ctxt, "runtime.typelink", 0)
-	symtypelink.Type = obj.STYPELINK
 
 	symt = Linklookup(Ctxt, "runtime.symtab", 0)
 	symt.Local = true
@@ -417,14 +400,9 @@ func symtab() {
 		}
 
 		if strings.HasPrefix(s.Name, "type.") && !DynlinkingGo() {
+			s.Type = obj.STYPE
 			s.Hide = 1
-			if UseRelro() && len(s.R) > 0 {
-				s.Type = obj.STYPERELRO
-				s.Outer = symtyperel
-			} else {
-				s.Type = obj.STYPE
-				s.Outer = symtype
-			}
+			s.Outer = symtype
 		}
 
 		if strings.HasPrefix(s.Name, "go.typelink.") {