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://golang.org/cl/101510049

include/link.h

@@ -391,7 +391,7 @@ struct	Link
 	LSym*	sym_modu;
 	LSym*	symmorestack[20];
 	LSym*	tlsg;
-	LSym*	plan9tos;
+	LSym*	plan9privates;
 	Prog*	curp;
 	Prog*	printp;
 	Prog*	blitrl;

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 @@ doasm(Link *ctxt, Prog *p)
 		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;

src/liblink/asm8.c

@@ -2707,11 +2707,11 @@ doasm(Link *ctxt, Prog *p)
 			break;
 
 		case Hplan9:
-			if(ctxt->plan9tos == nil)
-				ctxt->plan9tos = linklookup(ctxt, "_tos", 0);
+			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->plan9tos;
+			pp.from.sym = ctxt->plan9privates;
 			pp.from.offset = 0;
 			pp.from.index = D_NONE;
 			*ctxt->andptr++ = 0x8B;

src/liblink/obj6.c

@@ -103,7 +103,7 @@ static int
 canuselocaltls(Link *ctxt)
 {
 	switch(ctxt->headtype) {
-//	case Hlinux:
+	case Hplan9:
 	case Hwindows:
 		return 0;
 	}
@@ -402,6 +402,10 @@ addstacksplit(Link *ctxt, LSym *cursym)
 		for(i=0; i<nelem(morename); i++)
 			ctxt->symmorestack[i] = linklookup(ctxt, morename[i], 0);
 	}
+
+	if(ctxt->headtype == Hplan9 && ctxt->plan9privates == nil)
+		ctxt->plan9privates = linklookup(ctxt, "_privates", 0);
+
 	ctxt->cursym = cursym;
 
 	if(cursym->text == nil || cursym->text->link == nil)

src/liblink/obj8.c

@@ -270,8 +270,8 @@ addstacksplit(Link *ctxt, LSym *cursym)
 		ctxt->symmorestack[1] = linklookup(ctxt, "runtime.morestack_noctxt", 0);
 	}
 
-	if(ctxt->headtype == Hplan9 && ctxt->plan9tos == nil)
-		ctxt->plan9tos = linklookup(ctxt, "_tos", 0);
+	if(ctxt->headtype == Hplan9 && ctxt->plan9privates == nil)
+		ctxt->plan9privates = linklookup(ctxt, "_privates", 0);
 
 	ctxt->cursym = cursym;
 

src/liblink/sym.c

@@ -128,8 +128,6 @@ linknew(LinkArch *arch)
 	default:
 		sysfatal("unknown thread-local storage offset for %s", headstr(ctxt->headtype));
 	case Hplan9:
-		ctxt->tlsoffset = -2*ctxt->arch->ptrsize;
-		break;
 	case Hwindows:
 		break;
 	case Hlinux:

src/pkg/runtime/arch_amd64.h

@@ -11,8 +11,12 @@ enum {
 #else
 #ifdef GOOS_windows
 	RuntimeGogoBytes = 80,
+#else
+#ifdef GOOS_plan9
+	RuntimeGogoBytes = 80,
 #else
 	RuntimeGogoBytes = 64,
+#endif	// Plan 9
 #endif	// Windows
 #endif	// Solaris
 	PhysPageSize = 4096,

src/pkg/runtime/defs_plan9_amd64.h

@@ -1,4 +1,4 @@
-#define PAGESIZE 0x200000ULL
+#define PAGESIZE 0x1000
 
 typedef struct Ureg Ureg;
 

src/pkg/runtime/memclr_plan9_amd64.s

@@ -5,44 +5,17 @@
 #include "../../cmd/ld/textflag.h"
 
 // void runtime·memclr(void*, uintptr)
-TEXT runtime·memclr(SB), NOSPLIT, $0-16
-	MOVQ	ptr+0(FP), DI
-	MOVQ	n+8(FP), BX
-	XORQ	AX, AX
-
-clr_tail:
-	TESTQ	BX, BX
-	JEQ	clr_0
-	CMPQ	BX, $2
-	JBE	clr_1or2
-	CMPQ	BX, $4
-	JBE	clr_3or4
-	CMPQ	BX, $8
-	JBE	clr_5through8
-	CMPQ	BX, $16
-	JBE	clr_9through16
-	MOVQ	BX, CX
-	SHRQ	$2, CX
+TEXT runtime·memclr(SB),NOSPLIT,$0-16
+	MOVQ	addr+0(FP), DI
+	MOVQ	count+8(FP), CX
+	MOVQ	CX, BX
+	ANDQ	$7, BX
+	SHRQ	$3, CX
+	MOVQ	$0, AX
+	CLD
 	REP
 	STOSQ
-	ANDQ	$3, BX
-	JNE	clr_tail
-	RET
-
-clr_1or2:
-	MOVB	AX, (DI)
-	MOVB	AX, -1(DI)(BX*1)
-clr_0:
-	RET
-clr_3or4:
-	MOVW	AX, (DI)
-	MOVW	AX, -2(DI)(BX*1)
-	RET
-clr_5through8:
-	MOVL	AX, (DI)
-	MOVL	AX, -4(DI)(BX*1)
-	RET
-clr_9through16:
-	MOVQ	AX, (DI)
-	MOVQ	AX, -8(DI)(BX*1)
+	MOVQ	BX, CX
+	REP
+	STOSB
 	RET

src/pkg/runtime/os_plan9.c

@@ -146,6 +146,35 @@ runtime·usleep(uint32 µs)
 	runtime·sleep(ms);
 }
 
+#pragma textflag NOSPLIT
+int64
+runtime·nanotime(void)
+{
+	static int32 fd = -1;
+	byte b[8];
+	uint32 hi, lo;
+
+	// As long as all goroutines share the same file
+	// descriptor table we can get away with using
+	// just a static fd.  Without a lock the file can
+	// be opened twice but that's okay.
+	//
+	// Using /dev/bintime gives us a latency on the
+	// order of ten microseconds between two calls.
+	//
+	// The naïve implementation (without the cached
+	// file descriptor) is roughly four times slower
+	// in 9vx on a 2.16 GHz Intel Core 2 Duo.
+
+	if(fd < 0 && (fd = runtime·open("/dev/bintime", OREAD|OCEXEC, 0)) < 0)
+		return 0;
+	if(runtime·pread(fd, b, sizeof b, 0) != sizeof b)
+		return 0;
+	hi = b[0]<<24 | b[1]<<16 | b[2]<<8 | b[3];
+	lo = b[4]<<24 | b[5]<<16 | b[6]<<8 | b[7];
+	return (int64)hi<<32 | (int64)lo;
+}
+
 void
 time·now(int64 sec, int32 nsec)
 {

src/pkg/runtime/rt0_plan9_386.s

@@ -4,39 +4,20 @@
 
 #include "../../cmd/ld/textflag.h"
 
-TEXT _rt0_386_plan9(SB),NOSPLIT, $0
+TEXT _rt0_386_plan9(SB),NOSPLIT,$12
 	MOVL	AX, _tos(SB)
-
-	// move arguments down to make room for
-	// m and g at top of stack, right before Tos.
-	MOVL	SP, SI
-	SUBL	$8, SP
-	MOVL	SP, DI
-
-	MOVL	AX, CX
-	SUBL	SI, CX
-	CLD
-	REP; MOVSB
-
-	// adjust argv
-	SUBL	SI, DI
-	MOVL	newargc+0(SP), CX
-	LEAL	newargv+4(SP), BP
-argv_fix:
-	ADDL	DI, 0(BP)
-	ADDL	$4, BP
-	LOOP	argv_fix
-
+	LEAL	8(SP), AX
+	MOVL	AX, _privates(SB)
+	MOVL	$1, _nprivates(SB)
 	CALL	runtime·asminit(SB)
-
-	MOVL	0(SP), AX
-	LEAL	4(SP), BX
-	PUSHL	BX
-	PUSHL	AX
-	PUSHL	$-1
-
-	JMP	_rt0_go(SB)
+	MOVL	inargc-4(FP), AX
+	MOVL	AX, 0(SP)
+	LEAL	inargv+0(FP), AX
+	MOVL	AX, 4(SP)
+	CALL	_rt0_go(SB)
 
 DATA  runtime·isplan9(SB)/4, $1
 GLOBL runtime·isplan9(SB), $4
 GLOBL _tos(SB), $4
+GLOBL _privates(SB), $4
+GLOBL _nprivates(SB), $4

src/pkg/runtime/rt0_plan9_amd64.s

@@ -4,11 +4,18 @@
 
 #include "../../cmd/ld/textflag.h"
 
-TEXT _rt0_amd64_plan9(SB),NOSPLIT,$-8
-	LEAQ	8(SP), SI // argv
-	MOVQ	0(SP), DI // argc
+TEXT _rt0_amd64_plan9(SB),NOSPLIT,$24
+	MOVQ	AX, _tos(SB)
+	LEAQ	16(SP), AX
+	MOVQ	AX, _privates(SB)
+	MOVL	$1, _nprivates(SB)
+	MOVL	inargc-8(FP), DI
+	LEAQ	inargv+0(FP), SI
 	MOVQ	$_rt0_go(SB), AX
 	JMP	AX
 
 DATA runtime·isplan9(SB)/4, $1
 GLOBL runtime·isplan9(SB), $4
+GLOBL _tos(SB), $8
+GLOBL _privates(SB), $8
+GLOBL _nprivates(SB), $4

src/pkg/runtime/sys_plan9_386.s

@@ -101,7 +101,7 @@ TEXT runtime·rfork(SB),NOSPLIT,$0
 	MOVL	BX, g_m(DX)
 
 	// Initialize procid from TOS struct.
-	// TODO: Be explicit and insert a new MOVL _tos(SB), AX here.
+	MOVL	_tos(SB), AX
 	MOVL	48(AX), AX // procid
 	MOVL	AX, m_procid(BX)	// save pid as m->procid
 

src/pkg/runtime/sys_plan9_amd64.s

@@ -10,26 +10,22 @@ TEXT runtime·setldt(SB),NOSPLIT,$0
 	RET
 
 TEXT runtime·open(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$14, BP
 	SYSCALL
 	RET
 
 TEXT runtime·pread(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$50, BP
 	SYSCALL
 	RET
 
 TEXT runtime·pwrite(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$51, BP
 	SYSCALL
 	RET
 
 // int32 _seek(int64*, int32, int64, int32)
 TEXT _seek<>(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$39, BP
 	SYSCALL
 	RET
@@ -52,67 +48,51 @@ TEXT runtime·seek(SB),NOSPLIT,$56
 	RET
 
 TEXT runtime·close(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$4, BP
 	SYSCALL
 	RET
 
 TEXT runtime·exits(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$8, BP
 	SYSCALL
 	RET
 
 TEXT runtime·brk_(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$24, BP
 	SYSCALL
 	RET
 
 TEXT runtime·sleep(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$17, BP
 	SYSCALL
 	RET
 
 TEXT runtime·plan9_semacquire(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$37, BP
 	SYSCALL
 	RET
 
 TEXT runtime·plan9_tsemacquire(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$52, BP
 	SYSCALL
 	RET
 
 TEXT runtime·notify(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$28, BP
 	SYSCALL
 	RET
 
 TEXT runtime·noted(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$29, BP
 	SYSCALL
 	RET
 
 TEXT runtime·plan9_semrelease(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$38, BP
 	SYSCALL
 	RET
 
-TEXT runtime·nanotime(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
-	MOVQ	$60, BP
-	SYSCALL
-	RET
-
 TEXT runtime·rfork(SB),NOSPLIT,$0
-	MOVQ	$0x8000, AX
 	MOVQ	$19, BP // rfork
 	SYSCALL
 
@@ -135,8 +115,9 @@ TEXT runtime·rfork(SB),NOSPLIT,$0
 	MOVQ	DX, g(AX)
 	MOVQ	BX, g_m(DX)
 
-	// Initialize AX from pid in TLS.
-	MOVQ	0(FS), AX
+	// Initialize procid from TOS struct.
+	MOVQ	_tos(SB), AX
+	MOVQ	64(AX), AX
 	MOVQ	AX, m_procid(BX)	// save pid as m->procid
 
 	CALL	runtime·stackcheck(SB)	// smashes AX, CX
@@ -224,7 +205,6 @@ TEXT runtime·errstr(SB),NOSPLIT,$0
 	MOVQ	m_errstr(BX), CX
 	MOVQ	CX, 8(SP)
 	MOVQ	$ERRMAX, 16(SP)
-	MOVQ	$0x8000, AX
 	MOVQ	$41, BP
 	SYSCALL