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.

Issue golang#11270

Change-Id: Ia4fa135cb22d916728ead95bdbc0ebc1ae06f05c

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 this 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
-		datsize = 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
+			datsize = 0
+		} else {
+			sect = nil
+		}
+
 		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)
 		}
 	}
 

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

@@ -2287,11 +2287,12 @@ 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 {
+		tlssize := elfshname(".tbss").size
+		if tlssize != 0 && HEADTYPE != obj.Hopenbsd {
 			ph := newElfPhdr()
 			ph.type_ = PT_TLS
 			ph.flags = PF_R
-			ph.memsz = uint64(-Ctxt.Tlsoffset)
+			ph.memsz = tlssize
 			ph.align = uint64(Thearch.Regsize)
 		}
 	}
@@ -2350,16 +2351,6 @@ 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 this storage in this variable.
+#define TLSBSS	256