cmd/internal/ld: support for -buildmode=shared

Change-Id: Id4997d611ced29397133f14def6abc88aa9e811e
Reviewed-on: https://go-review.googlesource.com/8252
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/6l/asm.go

@@ -313,7 +313,11 @@ func elfreloc1(r *ld.Reloc, sectoff int64) int {
 	case ld.R_CALL:
 		if r.Siz == 4 {
 			if r.Xsym.Type == ld.SDYNIMPORT {
-				ld.Thearch.Vput(ld.R_X86_64_GOTPCREL | uint64(elfsym)<<32)
+				if ld.DynlinkingGo() {
+					ld.Thearch.Vput(ld.R_X86_64_PLT32 | uint64(elfsym)<<32)
+				} else {
+					ld.Thearch.Vput(ld.R_X86_64_GOTPCREL | uint64(elfsym)<<32)
+				}
 			} else {
 				ld.Thearch.Vput(ld.R_X86_64_PC32 | uint64(elfsym)<<32)
 			}

src/cmd/6l/obj.go

@@ -91,7 +91,7 @@ func archinit() {
 		ld.Linkmode = ld.LinkInternal
 	}
 
-	if ld.Buildmode == ld.BuildmodeCShared {
+	if ld.Buildmode == ld.BuildmodeCShared || ld.DynlinkingGo() {
 		ld.Linkmode = ld.LinkExternal
 	}
 

src/cmd/internal/ld/data.go

@@ -333,8 +333,14 @@ func relocsym(s *LSym) {
 		}
 
 		if r.Sym != nil && (r.Sym.Type&(SMASK|SHIDDEN) == 0 || r.Sym.Type&SMASK == SXREF) {
-			Diag("%s: not defined", r.Sym.Name)
-			continue
+			// When putting the runtime but not main into a shared library
+			// these symbols are undefined and that's OK.
+			if Buildmode == BuildmodeShared && (r.Sym.Name == "main.main" || r.Sym.Name == "main.init") {
+				r.Sym.Type = SDYNIMPORT
+			} else {
+				Diag("%s: not defined", r.Sym.Name)
+				continue
+			}
 		}
 
 		if r.Type >= 256 {
@@ -344,8 +350,9 @@ func relocsym(s *LSym) {
 			continue
 		}
 
-		// Solaris needs the ability to reference dynimport symbols.
-		if HEADTYPE != Hsolaris && r.Sym != nil && r.Sym.Type == SDYNIMPORT {
+		// We need to be able to reference dynimport symbols when linking against
+		// shared libraries, and Solaris needs it always
+		if HEADTYPE != Hsolaris && r.Sym != nil && r.Sym.Type == SDYNIMPORT && !DynlinkingGo() {
 			Diag("unhandled relocation for %s (type %d rtype %d)", r.Sym.Name, r.Sym.Type, r.Type)
 		}
 		if r.Sym != nil && r.Sym.Type != STLSBSS && !r.Sym.Reachable {
@@ -1322,7 +1329,7 @@ func dodata() {
 	sect.Length = uint64(datsize) - sect.Vaddr
 
 	/* shared library initializer */
-	if Buildmode == BuildmodeCShared {
+	if Buildmode == BuildmodeCShared || DynlinkingGo() {
 		sect := addsection(&Segdata, ".init_array", 06)
 		sect.Align = maxalign(s, SINITARR)
 		datsize = Rnd(datsize, int64(sect.Align))
@@ -1728,10 +1735,12 @@ func address() {
 	xdefine("runtime.etypelink", SRODATA, int64(typelink.Vaddr+typelink.Length))
 
 	sym := Linklookup(Ctxt, "runtime.gcdata", 0)
+	sym.Local = true
 	xdefine("runtime.egcdata", SRODATA, Symaddr(sym)+sym.Size)
 	Linklookup(Ctxt, "runtime.egcdata", 0).Sect = sym.Sect
 
 	sym = Linklookup(Ctxt, "runtime.gcbss", 0)
+	sym.Local = true
 	xdefine("runtime.egcbss", SRODATA, Symaddr(sym)+sym.Size)
 	Linklookup(Ctxt, "runtime.egcbss", 0).Sect = sym.Sect
 

src/cmd/internal/ld/elf.go

@@ -1658,7 +1658,7 @@ func doelf() {
 		Addstring(shstrtab, ".note.GNU-stack")
 	}
 
-	if Buildmode == BuildmodeCShared {
+	if Buildmode == BuildmodeCShared || DynlinkingGo() {
 		Addstring(shstrtab, ".init_array")
 		switch Thearch.Thechar {
 		case '6', '7', '9':

src/cmd/internal/ld/go.go

@@ -619,47 +619,58 @@ func deadcode() {
 		fmt.Fprintf(&Bso, "%5.2f deadcode\n", obj.Cputime())
 	}
 
-	mark(Linklookup(Ctxt, INITENTRY, 0))
-	for i := 0; i < len(markextra); i++ {
-		mark(Linklookup(Ctxt, markextra[i], 0))
-	}
-
-	for i := 0; i < len(dynexp); i++ {
-		mark(dynexp[i])
-	}
+	if Buildmode == BuildmodeShared {
+		// Mark all symbols as reachable when building a
+		// shared library.
+		for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+			if s.Type != 0 {
+				mark(s)
+			}
+		}
+		mark(Linkrlookup(Ctxt, "main.main", 0))
+		mark(Linkrlookup(Ctxt, "main.init", 0))
+	} else {
+		mark(Linklookup(Ctxt, INITENTRY, 0))
+		for i := 0; i < len(markextra); i++ {
+			mark(Linklookup(Ctxt, markextra[i], 0))
+		}
 
-	markflood()
+		for i := 0; i < len(dynexp); i++ {
+			mark(dynexp[i])
+		}
+		markflood()
 
-	// keep each beginning with 'typelink.' if the symbol it points at is being kept.
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
-		if strings.HasPrefix(s.Name, "go.typelink.") {
-			s.Reachable = len(s.R) == 1 && s.R[0].Sym.Reachable
+		// keep each beginning with 'typelink.' if the symbol it points at is being kept.
+		for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+			if strings.HasPrefix(s.Name, "go.typelink.") {
+				s.Reachable = len(s.R) == 1 && s.R[0].Sym.Reachable
+			}
 		}
-	}
 
-	// remove dead text but keep file information (z symbols).
-	var last *LSym
+		// remove dead text but keep file information (z symbols).
+		var last *LSym
 
-	for s := Ctxt.Textp; s != nil; s = s.Next {
-		if !s.Reachable {
-			continue
+		for s := Ctxt.Textp; s != nil; s = s.Next {
+			if !s.Reachable {
+				continue
+			}
+
+			// NOTE: Removing s from old textp and adding to new, shorter textp.
+			if last == nil {
+				Ctxt.Textp = s
+			} else {
+				last.Next = s
+			}
+			last = s
 		}
 
-		// NOTE: Removing s from old textp and adding to new, shorter textp.
 		if last == nil {
-			Ctxt.Textp = s
+			Ctxt.Textp = nil
+			Ctxt.Etextp = nil
 		} else {
-			last.Next = s
+			last.Next = nil
+			Ctxt.Etextp = last
 		}
-		last = s
-	}
-
-	if last == nil {
-		Ctxt.Textp = nil
-		Ctxt.Etextp = nil
-	} else {
-		last.Next = nil
-		Ctxt.Etextp = last
 	}
 
 	for s := Ctxt.Allsym; s != nil; s = s.Allsym {

src/cmd/internal/ld/lib.go

@@ -150,6 +150,14 @@ type Section struct {
 	Rellen  uint64
 }
 
+// DynlinkingGo returns whether we are producing Go code that can live
+// in separate shared libraries linked together at runtime.
+func DynlinkingGo() bool {
+	// TODO(mwhudson): This is a bit silly for now, but it will need to have
+	// "|| Linkshared" appended when a subsequent change adds that flag.
+	return Buildmode == BuildmodeShared
+}
+
 var (
 	Thestring          string
 	Thelinkarch        *LinkArch
@@ -241,11 +249,15 @@ func Lflag(arg string) {
 //   "c-shared": build a main package, plus all packages that it imports, into a
 //     single C shared library. The only callable symbols will be those functions
 //     marked as exported.
+//   "shared": combine all packages passed on the command line, and their
+//     dependencies, into a single shared library that will be used when
+//     building with the -linkshared option.
 type BuildMode uint8
 
 const (
 	BuildmodeExe BuildMode = iota
 	BuildmodeCShared
+	BuildmodeShared
 )
 
 func (mode *BuildMode) Set(s string) error {
@@ -260,6 +272,13 @@ func (mode *BuildMode) Set(s string) error {
 			return fmt.Errorf("not supported on %s", goarch)
 		}
 		*mode = BuildmodeCShared
+	case "shared":
+		goos := obj.Getgoos()
+		goarch := obj.Getgoarch()
+		if goos != "linux" || goarch != "amd64" {
+			return fmt.Errorf("not supported on %s/%s", goos, goarch)
+		}
+		*mode = BuildmodeShared
 	}
 	return nil
 }
@@ -270,6 +289,8 @@ func (mode *BuildMode) String() string {
 		return "exe"
 	case BuildmodeCShared:
 		return "c-shared"
+	case BuildmodeShared:
+		return "shared"
 	}
 	return fmt.Sprintf("BuildMode(%d)", uint8(*mode))
 }
@@ -321,12 +342,16 @@ func libinit() {
 			INITENTRY = fmt.Sprintf("_rt0_%s_%s_lib", goarch, goos)
 		case BuildmodeExe:
 			INITENTRY = fmt.Sprintf("_rt0_%s_%s", goarch, goos)
+		case BuildmodeShared:
+			// No INITENTRY for -buildmode=shared
 		default:
 			Diag("unknown INITENTRY for buildmode %v", Buildmode)
 		}
 	}
 
-	Linklookup(Ctxt, INITENTRY, 0).Type = SXREF
+	if !DynlinkingGo() {
+		Linklookup(Ctxt, INITENTRY, 0).Type = SXREF
+	}
 }
 
 func Errorexit() {
@@ -790,6 +815,16 @@ func hostlink() {
 	if Buildmode == BuildmodeCShared {
 		argv = append(argv, "-Wl,-Bsymbolic")
 		argv = append(argv, "-shared")
+	} else if Buildmode == BuildmodeShared {
+		// TODO(mwhudson): unless you do this, dynamic relocations fill
+		// out the findfunctab table and for some reason shared libraries
+		// and the executable both define a main function and putting the
+		// address of executable's main into the shared libraries
+		// findfunctab violates the assumptions of the runtime.  TBH, I
+		// think we may well end up wanting to use -Bsymbolic here
+		// anyway.
+		argv = append(argv, "-Wl,-Bsymbolic-functions")
+		argv = append(argv, "-shared")
 	}
 
 	argv = append(argv, "-o")
@@ -1162,7 +1197,8 @@ func stkcheck(up *Chain, depth int) int {
 		// external function.
 		// should never be called directly.
 		// only diagnose the direct caller.
-		if depth == 1 && s.Type != SXREF {
+		// TODO(mwhudson): actually think about this.
+		if depth == 1 && s.Type != SXREF && !DynlinkingGo() {
 			Diag("call to external function %s", s.Name)
 		}
 		return -1
@@ -1477,6 +1513,7 @@ func xdefine(p string, t int, v int64) {
 	s.Value = v
 	s.Reachable = true
 	s.Special = 1
+	s.Local = true
 }
 
 func datoff(addr int64) int64 {

src/cmd/internal/ld/link.go

@@ -74,6 +74,7 @@ type LSym struct {
 	Pcln        *Pcln
 	P           []byte
 	R           []Reloc
+	Local       bool
 }
 
 type Reloc struct {

src/cmd/internal/ld/objfile.go

@@ -327,12 +327,14 @@ func rdsym(ctxt *Link, f *Biobuf, pkg string) *LSym {
 			x, _ := strconv.ParseUint(s.Name[5:], 16, 32)
 			i32 := int32(x)
 			s.Type = SRODATA
+			s.Local = true
 			Adduint32(ctxt, s, uint32(i32))
 			s.Reachable = false
 		} else if strings.HasPrefix(s.Name, "$f64.") || strings.HasPrefix(s.Name, "$i64.") {
 			x, _ := strconv.ParseUint(s.Name[5:], 16, 64)
 			i64 := int64(x)
 			s.Type = SRODATA
+			s.Local = true
 			Adduint64(ctxt, s, uint64(i64))
 			s.Reachable = false
 		}

src/cmd/internal/ld/pcln.go

@@ -380,6 +380,7 @@ func findfunctab() {
 	t := Linklookup(Ctxt, "runtime.findfunctab", 0)
 	t.Type = SRODATA
 	t.Reachable = true
+	t.Local = true
 
 	// find min and max address
 	min := Ctxt.Textp.Value

src/cmd/internal/ld/pobj.go

@@ -152,7 +152,7 @@ func Ldmain() {
 		}
 	}
 
-	if flag.NArg() != 1 {
+	if Buildmode != BuildmodeShared && flag.NArg() != 1 {
 		usage()
 	}
 
@@ -181,7 +181,21 @@ func Ldmain() {
 	}
 	Bflush(&Bso)
 
-	addlibpath(Ctxt, "command line", "command line", flag.Arg(0), "main")
+	if Buildmode == BuildmodeShared {
+		for i := 0; i < flag.NArg(); i++ {
+			arg := flag.Arg(i)
+			parts := strings.SplitN(arg, "=", 2)
+			var pkgpath, file string
+			if len(parts) == 1 {
+				pkgpath, file = "main", arg
+			} else {
+				pkgpath, file = parts[0], parts[1]
+			}
+			addlibpath(Ctxt, "command line", "command line", file, pkgpath)
+		}
+	} else {
+		addlibpath(Ctxt, "command line", "command line", flag.Arg(0), "main")
+	}
 	loadlib()
 
 	if Thearch.Thechar == '5' {

src/cmd/internal/ld/symtab.go

@@ -40,8 +40,13 @@ func putelfstr(s string) int {
 		putelfstr("")
 	}
 
-	// Rewrite · to . for ASCII-only tools like DTrace (sigh)
-	s = strings.Replace(s, "·", ".", -1)
+	// When dynamically linking, we create LSym's by reading the names from
+	// the symbol tables of the shared libraries and so the names need to
+	// match exactly.  Tools like DTrace will have to wait for now.
+	if !DynlinkingGo() {
+		// Rewrite · to . for ASCII-only tools like DTrace (sigh)
+		s = strings.Replace(s, "·", ".", -1)
+	}
 
 	n := len(s) + 1
 	for len(Elfstrdat)+n > cap(Elfstrdat) {
@@ -130,7 +135,7 @@ func putelfsym(x *LSym, s string, t int, addr int64, size int64, ver int, go_ *L
 	// maybe one day STB_WEAK.
 	bind := STB_GLOBAL
 
-	if ver != 0 || (x.Type&SHIDDEN != 0) {
+	if ver != 0 || (x.Type&SHIDDEN != 0) || x.Local {
 		bind = STB_LOCAL
 	}
 
@@ -138,7 +143,8 @@ func putelfsym(x *LSym, s string, t int, addr int64, size int64, ver int, go_ *L
 	// to get the exported symbols put into the dynamic symbol table.
 	// To avoid filling the dynamic table with lots of unnecessary symbols,
 	// mark all Go symbols local (not global) in the final executable.
-	if Linkmode == LinkExternal && x.Cgoexport&CgoExportStatic == 0 && elfshnum != SHN_UNDEF {
+	// But when we're dynamically linking, we need all those global symbols.
+	if !DynlinkingGo() && Linkmode == LinkExternal && x.Cgoexport&CgoExportStatic == 0 && elfshnum != SHN_UNDEF {
 		bind = STB_LOCAL
 	}
 
@@ -322,21 +328,26 @@ func symtab() {
 	xdefine("runtime.egcbss", SRODATA, 0)
 
 	// pseudo-symbols to mark locations of type, string, and go string data.
-	s = Linklookup(Ctxt, "type.*", 0)
-
-	s.Type = STYPE
-	s.Size = 0
-	s.Reachable = true
-	symtype := s
+	var symtype *LSym
+	if !DynlinkingGo() {
+		s = Linklookup(Ctxt, "type.*", 0)
+
+		s.Type = STYPE
+		s.Size = 0
+		s.Reachable = true
+		symtype = s
+	}
 
 	s = Linklookup(Ctxt, "go.string.*", 0)
 	s.Type = SGOSTRING
+	s.Local = true
 	s.Size = 0
 	s.Reachable = true
 	symgostring := s
 
 	s = Linklookup(Ctxt, "go.func.*", 0)
 	s.Type = SGOFUNC
+	s.Local = true
 	s.Size = 0
 	s.Reachable = true
 	symgofunc := s
@@ -344,6 +355,7 @@ func symtab() {
 	symtypelink := Linklookup(Ctxt, "runtime.typelink", 0)
 
 	symt = Linklookup(Ctxt, "runtime.symtab", 0)
+	symt.Local = true
 	symt.Type = SSYMTAB
 	symt.Size = 0
 	symt.Reachable = true
@@ -358,7 +370,7 @@ func symtab() {
 		if !s.Reachable || s.Special != 0 || s.Type != SRODATA {
 			continue
 		}
-		if strings.HasPrefix(s.Name, "type.") {
+		if strings.HasPrefix(s.Name, "type.") && !DynlinkingGo() {
 			s.Type = STYPE
 			s.Hide = 1
 			s.Outer = symtype
@@ -400,6 +412,7 @@ func symtab() {
 	moduledata.Type = SNOPTRDATA
 	moduledata.Size = 0 // truncate symbol back to 0 bytes to reinitialize
 	moduledata.Reachable = true
+	moduledata.Local = true
 	// The pclntab slice
 	Addaddr(Ctxt, moduledata, Linklookup(Ctxt, "runtime.pclntab", 0))
 	adduint(Ctxt, moduledata, uint64(Linklookup(Ctxt, "runtime.pclntab", 0).Size))