cmd/internal/obj/x86: implement -shared computation of TLS base

Somehow, terribly embarrassingly, I lost part of the "re-enable
-shared on amd64" patch when rebasing before it got submitted.
This restores it and also fixes the addend to be the necessary -4.

Now updated so that Git will not put the new case into the wrong
switch.

Change-Id: I1d628232771a6d6ce6d085adf379f94a377822c5
Reviewed-on: https://go-review.googlesource.com/7126
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index ae4780124958446042e15a6f826039ea07a7f5e9..3bcec5de64a3dd4c94337a0450b43482d27bb6d2 100644 (file)
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -3801,6 +3801,32 @@ func doasm(ctxt *obj.Link, p *obj.Prog) {
                                        default:
                                                log.Fatalf("unknown TLS base location for %s", obj.Headstr(ctxt.Headtype))
 
+                                       case obj.Hlinux:
+                                               if ctxt.Flag_shared == 0 {
+                                                       log.Fatalf("unknown TLS base location for linux without -shared")
+                                               }
+                                               // Note that this is not generating the same insn as the other cases.
+                                               //     MOV TLS, R_to
+                                               // becomes
+                                               //     movq g@gottpoff(%rip), R_to
+                                               // which is encoded as
+                                               //     movq 0(%rip), R_to
+                                               // and a R_TLS_IE reloc. This all assumes the only tls variable we access
+                                               // is g, which we can't check here, but will when we assemble the second
+                                               // instruction.
+                                               ctxt.Rexflag = Pw | (regrex[p.To.Reg] & Rxr)
+
+                                               ctxt.Andptr[0] = 0x8B
+                                               ctxt.Andptr = ctxt.Andptr[1:]
+                                               ctxt.Andptr[0] = byte(0x05 | (reg[p.To.Reg] << 3))
+                                               ctxt.Andptr = ctxt.Andptr[1:]
+                                               r = obj.Addrel(ctxt.Cursym)
+                                               r.Off = int32(p.Pc + int64(-cap(ctxt.Andptr)+cap(ctxt.And[:])))
+                                               r.Type = obj.R_TLS_IE
+                                               r.Siz = 4
+                                               r.Add = -4
+                                               put4(ctxt, 0)
+
                                        case obj.Hplan9:
                                                if ctxt.Plan9privates == nil {
                                                        ctxt.Plan9privates = obj.Linklookup(ctxt, "_privates", 0)