cmd/internal/obj: some platform independent bits of proper toolchain support for thread local storage

Also simplifies some silliness around making the .tbss section wrt internal
vs external linking. The "make TLS make sense" project has quite a few more
steps to go.

Issue #11270

Change-Id: Ia4fa135cb22d916728ead95bdbc0ebc1ae06f05c
Reviewed-on: https://go-review.googlesource.com/13990
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/obj/data.go

@@ -63,6 +63,9 @@ func savedata(ctxt *Link, s *LSym, p *Prog, pn string) {
 	if ctxt.Enforce_data_order != 0 && off < int32(len(s.P)) {
 		ctxt.Diag("data out of order (already have %d)\n%v", len(s.P), p)
 	}
+	if s.Type == SBSS || s.Type == STLSBSS {
+		ctxt.Diag("cannot supply data for BSS var")
+	}
 	Symgrow(ctxt, s, int64(off+siz))
 
 	switch int(p.To.Type) {

src/cmd/internal/obj/objfile.go

@@ -194,6 +194,8 @@ func Writeobjdirect(ctxt *Link, b *Biobuf) {
 					s.Type = SRODATA
 				} else if flag&NOPTR != 0 {
 					s.Type = SNOPTRBSS
+				} else if flag&TLSBSS != 0 {
+					s.Type = STLSBSS
 				}
 				edata = s
 				continue

src/cmd/internal/obj/textflag.go

@@ -35,4 +35,8 @@ const (
 
 	// When passed to ggloblsym, causes Local to be set to true on the LSym it creates.
 	LOCAL = 128
+
+	// Allocate a word of thread local storage and store the offset from the
+	// thread local base to the thread local storage in this variable.
+	TLSBSS = 256
 )

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

@@ -1401,26 +1401,25 @@ func dodata() {
 		Diag("data or bss segment too large")
 	}
 
-	if Iself && Linkmode == LinkExternal && s != nil && s.Type == obj.STLSBSS && HEADTYPE != obj.Hopenbsd {
-		sect := addsection(&Segdata, ".tbss", 06)
-		sect.Align = int32(Thearch.Ptrsize)
-		sect.Vaddr = 0
+	if s != nil && s.Type == obj.STLSBSS {
+		if Iself && (Linkmode == LinkExternal || Debug['d'] == 0) && HEADTYPE != obj.Hopenbsd {
+			sect = addsection(&Segdata, ".tbss", 06)
+			sect.Align = int32(Thearch.Ptrsize)
+			sect.Vaddr = 0
+		} else {
+			sect = nil
+		}
 		datsize = 0
+
 		for ; s != nil && s.Type == obj.STLSBSS; s = s.Next {
 			datsize = aligndatsize(datsize, s)
 			s.Sect = sect
-			s.Value = int64(uint64(datsize) - sect.Vaddr)
+			s.Value = datsize
 			growdatsize(&datsize, s)
 		}
 
-		sect.Length = uint64(datsize)
-	} else {
-		// Might be internal linking but still using cgo.
-		// In that case, the only possible STLSBSS symbol is runtime.tlsg.
-		// Give it offset 0, because it's the only thing here.
-		if s != nil && s.Type == obj.STLSBSS && s.Name == "runtime.tlsg" {
-			s.Value = 0
-			s = s.Next
+		if sect != nil {
+			sect.Length = uint64(datsize)
 		}
 	}
 
@@ -1690,8 +1689,11 @@ func address() {
 	var noptrbss *Section
 	var vlen int64
 	for s := Segdata.Sect; s != nil; s = s.Next {
+		if Iself && s.Name == ".tbss" {
+			continue
+		}
 		vlen = int64(s.Length)
-		if s.Next != nil {
+		if s.Next != nil && !(Iself && s.Next.Name == ".tbss") {
 			vlen = int64(s.Next.Vaddr - s.Vaddr)
 		}
 		s.Vaddr = va

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

@@ -1508,7 +1508,9 @@ func elfshbits(sect *Section) *ElfShdr {
 	}
 	sh.addralign = uint64(sect.Align)
 	sh.size = sect.Length
-	sh.off = sect.Seg.Fileoff + sect.Vaddr - sect.Seg.Vaddr
+	if sect.Name != ".tbss" || goos == "android" {
+		sh.off = sect.Seg.Fileoff + sect.Vaddr - sect.Seg.Vaddr
+	}
 
 	return sh
 }
@@ -2287,12 +2289,20 @@ func Asmbelf(symo int64) {
 		// Do not emit PT_TLS for OpenBSD since ld.so(1) does
 		// not currently support it. This is handled
 		// appropriately in runtime/cgo.
-		if Ctxt.Tlsoffset != 0 && HEADTYPE != obj.Hopenbsd {
-			ph := newElfPhdr()
-			ph.type_ = PT_TLS
-			ph.flags = PF_R
-			ph.memsz = uint64(-Ctxt.Tlsoffset)
-			ph.align = uint64(Thearch.Regsize)
+		if HEADTYPE != obj.Hopenbsd {
+			tlssize := uint64(0)
+			for sect := Segdata.Sect; sect != nil; sect = sect.Next {
+				if sect.Name == ".tbss" {
+					tlssize = sect.Length
+				}
+			}
+			if tlssize != 0 {
+				ph := newElfPhdr()
+				ph.type_ = PT_TLS
+				ph.flags = PF_R
+				ph.memsz = tlssize
+				ph.align = uint64(Thearch.Regsize)
+			}
 		}
 	}
 
@@ -2350,16 +2360,6 @@ elfobj:
 		sh.flags = 0
 	}
 
-	// generate .tbss section for dynamic internal linking (except for OpenBSD)
-	// external linking generates .tbss in data.c
-	if Linkmode == LinkInternal && Debug['d'] == 0 && HEADTYPE != obj.Hopenbsd {
-		sh := elfshname(".tbss")
-		sh.type_ = SHT_NOBITS
-		sh.addralign = uint64(Thearch.Regsize)
-		sh.size = uint64(-Ctxt.Tlsoffset)
-		sh.flags = SHF_ALLOC | SHF_TLS | SHF_WRITE
-	}
-
 	if Debug['s'] == 0 {
 		sh := elfshname(".symtab")
 		sh.type_ = SHT_SYMTAB

src/runtime/textflag.h

@@ -21,3 +21,6 @@
 #define WRAPPER 32
 // This function uses its incoming context register.
 #define NEEDCTXT 64
+// Allocate a word of thread local storage and store the offset from the
+// thread local base to the thread local storage in this variable.
+#define TLSBSS	256