cmd/internal/obj, cmd/link, runtime: lots of TLS cleanup

It's particularly nice to get rid of the android special cases in the linker.

Change-Id: I516363af7ce8a6b2f196fe49cb8887ac787a6dad
Reviewed-on: https://go-review.googlesource.com/14197
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/internal/obj/arm/asm5.go

@@ -739,9 +739,6 @@ func span5(ctxt *obj.Link, cursym *obj.LSym) {
 	 * code references to be relocated too, and then
 	 * perhaps we'd be able to parallelize the span loop above.
 	 */
-	if ctxt.Tlsg == nil {
-		ctxt.Tlsg = obj.Linklookup(ctxt, "runtime.tlsg", 0)
-	}
 
 	p = cursym.Text
 	ctxt.Autosize = int32(p.To.Offset + 4)
@@ -1646,19 +1643,7 @@ func asmout(ctxt *obj.Link, p *obj.Prog, o *Optab, out []uint32) {
 			rel.Sym = p.To.Sym
 			rel.Add = p.To.Offset
 
-			// runtime.tlsg is special.
-			// Its "address" is the offset from the TLS thread pointer
-			// to the thread-local g and m pointers.
-			// Emit a TLS relocation instead of a standard one if its
-			// type is not explicitly set by runtime. This assumes that
-			// all references to runtime.tlsg should be accompanied with
-			// its type declaration if necessary.
-			if rel.Sym == ctxt.Tlsg && ctxt.Tlsg.Type == 0 {
-				rel.Type = obj.R_TLS
-				if ctxt.Flag_shared != 0 {
-					rel.Add += ctxt.Pc - p.Rel.Pc - 8 - int64(rel.Siz)
-				}
-			} else if ctxt.Flag_shared != 0 {
+			if ctxt.Flag_shared != 0 {
 				rel.Type = obj.R_PCREL
 				rel.Add += ctxt.Pc - p.Rel.Pc - 8
 			} else {

src/cmd/internal/obj/arm/obj5.go

@@ -129,24 +129,6 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 			p.From.Offset = 0
 		}
 	}
-
-	if ctxt.Flag_shared != 0 {
-		// Shared libraries use R_ARM_TLS_IE32 instead of
-		// R_ARM_TLS_LE32, replacing the link time constant TLS offset in
-		// runtime.tlsg with an address to a GOT entry containing the
-		// offset. Rewrite $runtime.tlsg(SB) to runtime.tlsg(SB) to
-		// compensate.
-		if ctxt.Tlsg == nil {
-			ctxt.Tlsg = obj.Linklookup(ctxt, "runtime.tlsg", 0)
-		}
-
-		if p.From.Type == obj.TYPE_ADDR && p.From.Name == obj.NAME_EXTERN && p.From.Sym == ctxt.Tlsg {
-			p.From.Type = obj.TYPE_MEM
-		}
-		if p.To.Type == obj.TYPE_ADDR && p.To.Name == obj.NAME_EXTERN && p.To.Sym == ctxt.Tlsg {
-			p.To.Type = obj.TYPE_MEM
-		}
-	}
 }
 
 // Prog.mark

src/cmd/internal/obj/arm64/asm7.go

@@ -631,9 +631,6 @@ func span7(ctxt *obj.Link, cursym *obj.LSym) {
 	/*
 	 * lay out the code, emitting code and data relocations.
 	 */
-	if ctxt.Tlsg == nil {
-		ctxt.Tlsg = obj.Linklookup(ctxt, "runtime.tlsg", 0)
-	}
 	obj.Symgrow(ctxt, cursym, cursym.Size)
 	bp := cursym.P
 	psz := int32(0)

src/cmd/internal/obj/link.go

@@ -414,23 +414,16 @@ const (
 	R_CALLPOWER
 	R_CONST
 	R_PCREL
-	// R_TLS (only used on arm currently, and not on android and darwin where tlsg is
-	// a regular variable) resolves to data needed to access the thread-local g. It is
-	// interpreted differently depending on toolchain flags to implement either the
-	// "local exec" or "inital exec" model for tls access.
-	// TODO(mwhudson): change to use R_TLS_LE or R_TLS_IE as appropriate, not having
-	// R_TLS do double duty.
-	R_TLS
-	// R_TLS_LE (only used on 386 and amd64 currently) resolves to the offset of the
-	// thread-local g from the thread local base and is used to implement the "local
-	// exec" model for tls access (r.Sym is not set by the compiler for this case but
-	// is set to Tlsg in the linker when externally linking).
+	// R_TLS_LE, used on 386, amd64, and ARM, resolves to the offset of the
+	// thread-local symbol from the thread local base and is used to implement the
+	// "local exec" model for tls access (r.Sym is not set on intel platforms but is
+	// set to a TLS symbol -- runtime.tlsg -- in the linker when externally linking).
 	R_TLS_LE
-	// R_TLS_IE (only used on 386 and amd64 currently) resolves to the PC-relative
-	// offset to a GOT slot containing the offset the thread-local g from the thread
-	// local base and is used to implemented the "initial exec" model for tls access
-	// (r.Sym is not set by the compiler for this case but is set to Tlsg in the
-	// linker when externally linking).
+	// R_TLS_IE, used 386, amd64, and ARM resolves to the PC-relative offset to a GOT
+	// slot containing the offset from the thread-local symbol from the thread local
+	// base and is used to implemented the "initial exec" model for tls access (r.Sym
+	// is not set on intel platforms but is set to a TLS symbol -- runtime.tlsg -- in
+	// the linker when externally linking).
 	R_TLS_IE
 	R_GOTOFF
 	R_PLT0
@@ -505,7 +498,6 @@ type Link struct {
 	Sym_divu           *LSym
 	Sym_mod            *LSym
 	Sym_modu           *LSym
-	Tlsg               *LSym
 	Plan9privates      *LSym
 	Curp               *Prog
 	Printp             *Prog

src/cmd/internal/obj/mips/asm0.go

@@ -504,9 +504,6 @@ func span9(ctxt *obj.Link, cursym *obj.LSym) {
 	/*
 	 * lay out the code, emitting code and data relocations.
 	 */
-	if ctxt.Tlsg == nil {
-		ctxt.Tlsg = obj.Linklookup(ctxt, "runtime.tlsg", 0)
-	}
 
 	obj.Symgrow(ctxt, cursym, cursym.Size)
 

src/cmd/internal/obj/ppc64/asm9.go

@@ -504,9 +504,6 @@ func span9(ctxt *obj.Link, cursym *obj.LSym) {
 	/*
 	 * lay out the code, emitting code and data relocations.
 	 */
-	if ctxt.Tlsg == nil {
-		ctxt.Tlsg = obj.Linklookup(ctxt, "runtime.tlsg", 0)
-	}
 
 	obj.Symgrow(ctxt, cursym, cursym.Size)
 

src/cmd/internal/obj/x86/obj6.go

@@ -435,10 +435,6 @@ func nacladdr(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) {
 }
 
 func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
-	if ctxt.Tlsg == nil {
-		ctxt.Tlsg = obj.Linklookup(ctxt, "runtime.tlsg", 0)
-	}
-
 	if ctxt.Headtype == obj.Hplan9 && ctxt.Plan9privates == nil {
 		ctxt.Plan9privates = obj.Linklookup(ctxt, "_privates", 0)
 	}

src/cmd/link/internal/arm/asm.go

@@ -223,17 +223,6 @@ func elfreloc1(r *ld.Reloc, sectoff int64) int {
 			return -1
 		}
 
-	case obj.R_TLS:
-		if r.Siz == 4 {
-			if ld.Buildmode == ld.BuildmodeCShared {
-				ld.Thearch.Lput(ld.R_ARM_TLS_IE32 | uint32(elfsym)<<8)
-			} else {
-				ld.Thearch.Lput(ld.R_ARM_TLS_LE32 | uint32(elfsym)<<8)
-			}
-		} else {
-			return -1
-		}
-
 	case obj.R_TLS_LE:
 		ld.Thearch.Lput(ld.R_ARM_TLS_LE32 | uint32(elfsym)<<8)
 
@@ -345,7 +334,7 @@ func archreloc(r *ld.Reloc, s *ld.LSym, val *int64) int {
 				rs = rs.Outer
 			}
 
-			if rs.Type != obj.SHOSTOBJ && rs.Sect == nil {
+			if rs.Type != obj.SHOSTOBJ && rs.Type != obj.SDYNIMPORT && rs.Sect == nil {
 				ld.Diag("missing section for %s", rs.Name)
 			}
 			r.Xsym = rs

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

@@ -362,11 +362,6 @@ func relocsym(s *LSym) {
 			Diag("unreachable sym in relocation: %s %s", s.Name, r.Sym.Name)
 		}
 
-		// Android emulates runtime.tlsg as a regular variable.
-		if r.Type == obj.R_TLS && goos == "android" {
-			r.Type = obj.R_ADDR
-		}
-
 		switch r.Type {
 		default:
 			switch siz {
@@ -385,26 +380,6 @@ func relocsym(s *LSym) {
 				Diag("unknown reloc %d", r.Type)
 			}
 
-		case obj.R_TLS:
-			if Linkmode == LinkExternal && Iself && HEADTYPE != obj.Hopenbsd {
-				r.Done = 0
-				r.Sym = Ctxt.Tlsg
-				r.Xsym = Ctxt.Tlsg
-				r.Xadd = r.Add
-				o = r.Add
-				break
-			}
-			if Linkmode == LinkInternal && Iself && Thearch.Thechar == '5' {
-				panic("should no longer get here")
-				break
-			}
-
-			r.Done = 0
-			o = 0
-			if Thearch.Thechar != '6' {
-				o = r.Add
-			}
-
 		case obj.R_TLS_LE:
 			if Linkmode == LinkExternal && Iself && HEADTYPE != obj.Hopenbsd {
 				r.Done = 0

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

@@ -1506,9 +1506,7 @@ func elfshbits(sect *Section) *ElfShdr {
 		sh.flags |= SHF_WRITE
 	}
 	if sect.Name == ".tbss" {
-		if goos != "android" {
-			sh.flags |= SHF_TLS // no TLS on android
-		}
+		sh.flags |= SHF_TLS
 		sh.type_ = SHT_NOBITS
 	}
 
@@ -1517,7 +1515,7 @@ func elfshbits(sect *Section) *ElfShdr {
 	}
 	sh.addralign = uint64(sect.Align)
 	sh.size = sect.Length
-	if sect.Name != ".tbss" || goos == "android" {
+	if sect.Name != ".tbss" {
 		sh.off = sect.Seg.Fileoff + sect.Vaddr - sect.Seg.Vaddr
 	}
 

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

@@ -307,7 +307,7 @@ func (mode *BuildMode) Set(s string) error {
 		}
 		*mode = BuildmodeCShared
 	case "shared":
-		if goos != "linux" || goarch != "amd64" {
+		if goos != "linux" || (goarch != "amd64" && goarch != "arm") {
 			return badmode()
 		}
 		*mode = BuildmodeShared
@@ -549,17 +549,14 @@ func loadlib() {
 
 	tlsg := Linklookup(Ctxt, "runtime.tlsg", 0)
 
-	// For most ports, runtime.tlsg is a placeholder symbol for TLS
-	// relocation. However, the Android and Darwin arm ports need it
-	// to be a real variable.
-	//
-	// TODO(crawshaw): android should require leaving the tlsg->type
-	// alone (as the runtime-provided SNOPTRBSS) just like darwin/arm.
-	// But some other part of the linker is expecting STLSBSS.
-	if tlsg.Type != obj.SDYNIMPORT && (goos != "darwin" || Thearch.Thechar != '5') {
+	// runtime.tlsg is used for external linking on platforms that do not define
+	// a variable to hold g in assembly (currently only intel).
+	if tlsg.Type == 0 {
 		tlsg.Type = obj.STLSBSS
+		tlsg.Size = int64(Thearch.Ptrsize)
+	} else if tlsg.Type != obj.SDYNIMPORT {
+		Diag("internal error: runtime declared tlsg variable %d", tlsg.Type)
 	}
-	tlsg.Size = int64(Thearch.Ptrsize)
 	tlsg.Reachable = true
 	Ctxt.Tlsg = tlsg
 
@@ -1821,13 +1818,7 @@ func genasmsym(put func(*LSym, string, int, int64, int64, int, *LSym)) {
 
 		case obj.STLSBSS:
 			if Linkmode == LinkExternal && HEADTYPE != obj.Hopenbsd {
-				var type_ int
-				if goos == "android" {
-					type_ = 'B'
-				} else {
-					type_ = 't'
-				}
-				put(s, s.Name, type_, Symaddr(s), s.Size, int(s.Version), s.Gotype)
+				put(s, s.Name, 't', Symaddr(s), s.Size, int(s.Version), s.Gotype)
 			}
 		}
 	}

src/runtime/asm_arm64.s

@@ -36,9 +36,9 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$0
 	MRS_TPIDR_R0			// load TLS base pointer
 	MOVD	R0, R3			// arg 3: TLS base pointer
 #ifdef TLSG_IS_VARIABLE
-	MOVD	$runtime·tls_g(SB), R2 	// arg 2: tlsg
+	MOVD	$runtime·tls_g(SB), R2 	// arg 2: &tls_g
 #else
-	MOVD	$0x10, R2		// arg 2: tlsg TODO(minux): hardcoded for linux
+	MOVD	0, R2		        // arg 2: not used when using platform's TLS
 #endif
 	MOVD	$setg_gcc<>(SB), R1	// arg 1: setg
 	MOVD	g, R0			// arg 0: G

src/runtime/tls_arm.s

@@ -58,9 +58,6 @@ TEXT runtime·load_g(SB),NOSPLIT,$0
 	// See save_g
 	MRC	15, 0, R0, C13, C0, 3 // fetch TLS base pointer
 	BIC $3, R0 // Darwin/ARM might return unaligned pointer
-	// $runtime.tlsg(SB) is a special linker symbol.
-	// It is the offset from the TLS base pointer to our
-	// thread-local storage for g.
 	MOVW	runtime·tls_g(SB), R11
 	ADD	R11, R0
 	MOVW	0(R0), g

src/runtime/tls_arm64.s

@@ -53,8 +53,5 @@ nocgo:
 	RET
 
 #ifdef TLSG_IS_VARIABLE
-// The runtime.tlsg name is being handled specially in the
-// linker. As we just need a regular variable here, don't
-// use that name.
 GLOBL runtime·tls_g+0(SB), NOPTR, $8
 #endif

src/runtime/tls_ppc64x.s

@@ -30,7 +30,7 @@ TEXT runtime·save_g(SB),NOSPLIT,$-8-0
 	// $runtime.tlsg(SB) is a special linker symbol.
 	// It is the offset from the start of TLS to our
 	// thread-local storage for g.
-	MOVD	$runtime·tlsg(SB), R31
+	MOVD	$runtime·tls_g(SB), R31
 	ADD	R13, R31
 	// The actual TLS base is 0x7000 below R13
 	SUB	$0x7000, R31
@@ -51,10 +51,12 @@ nocgo:
 //
 // NOTE: _cgo_topofstack assumes this only clobbers g (R30), and R31.
 TEXT runtime·load_g(SB),NOSPLIT,$-8-0
-	MOVD	$runtime·tlsg(SB), R31
+	MOVD	$runtime·tls_g(SB), R31
 	// R13 is the C ABI TLS base pointer + 0x7000
 	ADD	R13, R31
 	SUB	$0x7000, R31
 
 	MOVD	0(R31), g
 	RET
+
+GLOBL runtime·tls_g+0(SB), TLSBSS, $8