liblink, runtime: preliminary support for plan9/amd64

A TLS slot is reserved by _rt0_.*_plan9 as an automatic and
its address (which is static on Plan 9) is saved in the
global _privates symbol. The startup linkage now is exactly
like that from Plan 9 libc, and the way we access g is
exactly as if we'd have used privalloc(2).

Aside from making the code more standard, this change
drastically simplifies it, both for 386 and for amd64, and
makes the Plan 9 code in liblink common for both 386 and
amd64.

The amd64 runtime code was cleared of nxm assumptions, and
now runs on the standard Plan 9 kernel.

Note handling fixes will follow in a separate CL.

LGTM=rsc
R=golang-codereviews, rsc, bradfitz, dave
CC=0intro, ality, golang-codereviews, jas, minux.ma, mischief
https://codereview.appspot.com/101510049

Committer: Dave Cheney <dave@cheney.net>

1 files changed, 13 insertions, 1 deletions

diff --git a/src/liblink/asm6.c b/src/liblink/asm6.c
index 66afc7a12..751c97215 100644
--- a/src/liblink/asm6.c
+++ b/src/liblink/asm6.c
@@ -1901,7 +1901,6 @@ prefixof(Link *ctxt, Addr *a)
 		case Hlinux:
 		case Hnetbsd:
 		case Hopenbsd:
-		case Hplan9:
 		case Hsolaris:
 			return 0x64; // FS
 		case Hdarwin:
@@ -3365,6 +3364,19 @@ mfound:
 		default:
 			sysfatal("unknown TLS base location for %s", headstr(ctxt->headtype));
 
+		case Hplan9:
+			if(ctxt->plan9privates == nil)
+				ctxt->plan9privates = linklookup(ctxt, "_privates", 0);
+			memset(&pp.from, 0, sizeof pp.from);
+			pp.from.type = D_EXTERN;
+			pp.from.sym = ctxt->plan9privates;
+			pp.from.offset = 0;
+			pp.from.index = D_NONE;
+			ctxt->rexflag |= Pw;
+			*ctxt->andptr++ = 0x8B;
+			asmand(ctxt, &pp.from, &p->to);
+			break;
+
 		case Hsolaris: // TODO(rsc): Delete Hsolaris from list. Should not use this code. See progedit in obj6.c.
 			// TLS base is 0(FS).
 			pp.from = p->from;