runtime: set up C TLS and save g to it on ppc64

Cgo will need this for calls from C to Go and for handling signals
that may occur in C code.

Change-Id: I50cc4caf17cd142bff501e7180a1e27721463ada
Reviewed-on: https://go-review.googlesource.com/2008Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/arch1_ppc64.go

@@ -8,7 +8,7 @@ const (
 	thechar           = '9'
 	_BigEndian        = 1
 	_CacheLineSize    = 64
-	_RuntimeGogoBytes = 64
+	_RuntimeGogoBytes = 72
 	_PhysPageSize     = 65536
 	_PCQuantum        = 4
 	_Int64Align       = 8

src/runtime/arch1_ppc64le.go

@@ -8,7 +8,7 @@ const (
 	thechar           = '9'
 	_BigEndian        = 0
 	_CacheLineSize    = 64
-	_RuntimeGogoBytes = 64
+	_RuntimeGogoBytes = 72
 	_PhysPageSize     = 65536
 	_PCQuantum        = 4
 	_Int64Align       = 8

src/runtime/asm_ppc64x.s

@@ -10,6 +10,8 @@
 #include "textflag.h"
 
 TEXT runtime·rt0_go(SB),NOSPLIT,$0
+	// R1 = stack; R3 = argc; R4 = argv; R13 = C TLS base pointer
+
 	// initialize essential registers
 	BL	runtime·reginit(SB)
 
@@ -102,6 +104,8 @@ TEXT runtime·gosave(SB), NOSPLIT, $-8-8
 TEXT runtime·gogo(SB), NOSPLIT, $-8-8
 	MOVD	buf+0(FP), R5
 	MOVD	gobuf_g(R5), g	// make sure g is not nil
+	BL	runtime·save_g(SB)
+
 	MOVD	0(g), R4
 	MOVD	gobuf_sp(R5), R1
 	MOVD	gobuf_lr(R5), R31
@@ -133,6 +137,7 @@ TEXT runtime·mcall(SB), NOSPLIT, $-8-8
 	MOVD	g, R3
 	MOVD	g_m(g), R8
 	MOVD	m_g0(R8), g
+	BL	runtime·save_g(SB)
 	CMP	g, R3
 	BNE	2(PC)
 	BR	runtime·badmcall(SB)
@@ -191,6 +196,7 @@ switch:
 
 	// switch to g0
 	MOVD	R5, g
+	BL	runtime·save_g(SB)
 	MOVD	(g_sched+gobuf_sp)(g), R3
 	// make it look like mstart called systemstack on g0, to stop traceback
 	SUB	$8, R3
@@ -206,6 +212,7 @@ switch:
 	// switch back to g
 	MOVD	g_m(g), R3
 	MOVD	m_curg(R3), g
+	BL	runtime·save_g(SB)
 	MOVD	(g_sched+gobuf_sp)(g), R1
 	MOVD	R0, (g_sched+gobuf_sp)(g)
 	RETURN
@@ -259,6 +266,7 @@ TEXT runtime·morestack(SB),NOSPLIT,$-8-0
 
 	// Call newstack on m->g0's stack.
 	MOVD	m_g0(R7), g
+	BL	runtime·save_g(SB)
 	MOVD	(g_sched+gobuf_sp)(g), R1
 	BL	runtime·newstack(SB)
 

src/runtime/rt0_linux_ppc64le.s

@@ -6,6 +6,8 @@ TEXT _rt0_ppc64le_linux(SB),NOSPLIT,$0
 TEXT _main<>(SB),NOSPLIT,$-8
 	MOVD 0(R1), R3 // argc
 	ADD $8, R1, R4 // argv
+	MOVD	$runtime·tls0(SB), R13 // TLS
+	ADD	$0x7000, R13
 	BR main(SB)
 
 TEXT main(SB),NOSPLIT,$-8

src/runtime/tls_ppc64x.s

+// Copyright 2014 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ppc64 ppc64le
+
+#include "go_asm.h"
+#include "go_tls.h"
+#include "funcdata.h"
+#include "textflag.h"
+
+// We have to resort to TLS variable to save g (R30).
+// One reason is that external code might trigger
+// SIGSEGV, and our runtime.sigtramp don't even know we
+// are in external code, and will continue to use R30,
+// this might well result in another SIGSEGV.
+
+// save_g saves the g register into pthread-provided
+// thread-local memory, so that we can call externally compiled
+// ppc64 code that will overwrite this register.
+//
+// If !iscgo, this is a no-op.
+TEXT runtime·save_g(SB),NOSPLIT,$-8-0
+	MOVB	runtime·iscgo(SB), R31
+	CMP	R31, $0
+	BEQ	nocgo
+
+	// $runtime.tlsg(SB) is a special linker symbol.
+	// It is the offset from the start of TLS to our
+	// thread-local storage for g.
+	MOVD	$runtime·tlsg(SB), R31
+	ADD	R13, R31
+	// The actual TLS base is 0x7000 below R13
+	SUB	$0x7000, R31
+
+	// Store g in TLS
+	MOVD	g, 0(R31)
+
+nocgo:
+	RET
+
+// load_g loads the g register from pthread-provided
+// thread-local memory, for use after calling externally compiled
+// ppc64 code that overwrote those registers.
+//
+// This is never called directly from C code (it doesn't have to
+// follow the C ABI), but it may be called from a C context, where the
+// usual Go registers aren't set up.
+TEXT runtime·load_g(SB),NOSPLIT,$-8-0
+	MOVD	$runtime·tlsg(SB), R31
+	// R13 is the C ABI TLS base pointer + 0x7000
+	ADD	R13, R31
+	SUB	$0x7000, R31
+
+	MOVD	0(R31), g
+	RET