cmd/compile: fix large global variables in -linkshared mode on s390x

When rewriting loads and stores accessing global variables to use the
GOT we were making use of REGTMP (R10). Unfortunately loads and stores
with large offsets (larger than 20-bits) were also using REGTMP,
causing it to be clobbered and subsequently a segmentation fault.

This can be fixed by using REGTMP2 (R11) for the rewrite. This is fine
because REGTMP2 only has a couple of uses in the assembler (division,
high multiplication and storage-to-storage instructions). We didn't
use REGTMP2 originally because it used to be used more frequently,
in particular for stores of constants to memory. However we have now
eliminated those uses.

This was found while writing a test case for CL 63030. That test case
is included in this CL.

Change-Id: I13956f1f3ca258a7c8a7ff0a7570d2848adf7f68
Reviewed-on: https://go-review.googlesource.com/65011Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/cgo/testshared/shared_test.go

@@ -841,3 +841,12 @@ func TestInterface(t *testing.T) {
 	goCmd(t, "install", "-linkshared", "iface")
 	run(t, "running type/itab uniqueness tester", "./bin/iface")
 }
+
+// Access a global variable from a library.
+func TestGlobal(t *testing.T) {
+	goCmd(t, "install", "-buildmode=shared", "-linkshared", "globallib")
+	goCmd(t, "install", "-linkshared", "global")
+	run(t, "global executable", "./bin/global")
+	AssertIsLinkedTo(t, "./bin/global", soname)
+	AssertHasRPath(t, "./bin/global", gorootInstallDir)
+}

misc/cgo/testshared/src/global/main.go

+// Copyright 2017 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.
+
+package main
+
+import (
+	"globallib"
+)
+
+//go:noinline
+func testLoop() {
+	for i, s := range globallib.Data {
+		if s != int64(i) {
+			panic("testLoop: mismatch")
+		}
+	}
+}
+
+//go:noinline
+func ptrData() *[1<<20 + 10]int64 {
+	return &globallib.Data
+}
+
+//go:noinline
+func testMediumOffset() {
+	for i, s := range globallib.Data[1<<16-2:] {
+		if s != int64(i)+1<<16-2 {
+			panic("testMediumOffset: index mismatch")
+		}
+	}
+
+	x := globallib.Data[1<<16-1]
+	if x != 1<<16-1 {
+		panic("testMediumOffset: direct mismatch")
+	}
+
+	y := &globallib.Data[1<<16-3]
+	if y != &ptrData()[1<<16-3] {
+		panic("testMediumOffset: address mismatch")
+	}
+}
+
+//go:noinline
+func testLargeOffset() {
+	for i, s := range globallib.Data[1<<20:] {
+		if s != int64(i)+1<<20 {
+			panic("testLargeOffset: index mismatch")
+		}
+	}
+
+	x := globallib.Data[1<<20+1]
+	if x != 1<<20+1 {
+		panic("testLargeOffset: direct mismatch")
+	}
+
+	y := &globallib.Data[1<<20+2]
+	if y != &ptrData()[1<<20+2] {
+		panic("testLargeOffset: address mismatch")
+	}
+}
+
+func main() {
+	testLoop()
+
+	// SSA rules commonly merge offsets into addresses. These
+	// tests access global data in different ways to try
+	// and exercise different SSA rules.
+	testMediumOffset()
+	testLargeOffset()
+}

misc/cgo/testshared/src/globallib/global.go

+// Copyright 2017 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.
+
+package globallib
+
+// Data is large enough to that offsets into it do not fit into
+// 16-bit or 20-bit immediates. Ideally we'd also try and overrun
+// 32-bit immediates, but that requires the test machine to have
+// too much memory.
+var Data [1<<20 + 10]int64
+
+func init() {
+	for i := range Data {
+		Data[i] = int64(i)
+	}
+}

src/cmd/internal/obj/s390x/objz.go

@@ -126,7 +126,7 @@ func (c *ctxtz) rewriteToUseGot(p *obj.Prog) {
 	// ADD instruction.
 	if p.From.Type == obj.TYPE_ADDR && p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local() {
 		// MOVD $sym, Rx becomes MOVD sym@GOT, Rx
-		// MOVD $sym+<off>, Rx becomes MOVD sym@GOT, Rx; MOVD $<off>(Rx or REGTMP2), Rx
+		// MOVD $sym+<off>, Rx becomes MOVD sym@GOT, Rx or REGTMP2; MOVD $<off>(Rx or REGTMP2), Rx
 		if p.To.Type != obj.TYPE_REG || p.As != AMOVD {
 			c.ctxt.Diag("do not know how to handle LEA-type insn to non-register in %v with -dynlink", p)
 		}
@@ -154,8 +154,8 @@ func (c *ctxtz) rewriteToUseGot(p *obj.Prog) {
 		c.ctxt.Diag("don't know how to handle %v with -dynlink", p)
 	}
 	var source *obj.Addr
-	// MOVD sym, Ry becomes MOVD sym@GOT, REGTMP; MOVD (REGTMP), Ry
-	// MOVD Ry, sym becomes MOVD sym@GOT, REGTMP; MOVD Ry, (REGTMP)
+	// MOVD sym, Ry becomes MOVD sym@GOT, REGTMP2; MOVD (REGTMP2), Ry
+	// MOVD Ry, sym becomes MOVD sym@GOT, REGTMP2; MOVD Ry, (REGTMP2)
 	// An addition may be inserted between the two MOVs if there is an offset.
 	if p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local() {
 		if p.To.Name == obj.NAME_EXTERN && !p.To.Sym.Local() {
@@ -184,17 +184,17 @@ func (c *ctxtz) rewriteToUseGot(p *obj.Prog) {
 	p1.From.Sym = source.Sym
 	p1.From.Name = obj.NAME_GOTREF
 	p1.To.Type = obj.TYPE_REG
-	p1.To.Reg = REGTMP
+	p1.To.Reg = REGTMP2
 
 	p2.As = p.As
 	p2.From = p.From
 	p2.To = p.To
 	if p.From.Name == obj.NAME_EXTERN {
-		p2.From.Reg = REGTMP
+		p2.From.Reg = REGTMP2
 		p2.From.Name = obj.NAME_NONE
 		p2.From.Sym = nil
 	} else if p.To.Name == obj.NAME_EXTERN {
-		p2.To.Reg = REGTMP
+		p2.To.Reg = REGTMP2
 		p2.To.Name = obj.NAME_NONE
 		p2.To.Sym = nil
 	} else {