cmd/internal/obj/s390x, runtime: fix breakpoint in s390x

Currently runtime.Breakpoint generates SIGSEGV in s390x.
The solution to this is add new asm instruction BRRK of
type FORMAT_E for the breakpoint exception.

Fixes #52103

Change-Id: I8358a56e428849a5d28d5ade141e1d7310bee084
Reviewed-on: https://go-review.googlesource.com/c/go/+/457456
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>

src/cmd/asm/internal/asm/testdata/s390x.s

@@ -410,6 +410,7 @@ TEXT main·foo(SB),DUPOK|NOSPLIT,$16-0 // TEXT main.foo(SB), DUPOK|NOSPLIT, $16-
 	TCDB	F15, $4095             // edf00fff0011
 
 	UNDEF                          // 00000000
+	BRRK			       // 0001
 	NOPH                           // 0700
 
 	SYNC                           // 07e0

src/cmd/internal/obj/s390x/a.out.go

@@ -994,6 +994,9 @@ const (
 	AWORD
 	ADWORD
 
+	// Breakpoint
+	ABRRK
+
 	// end marker
 	ALAST
 

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

@@ -716,5 +716,6 @@ var Anames = []string{
 	"BYTE",
 	"WORD",
 	"DWORD",
+	"BRRK",
 	"LAST",
 }

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

@@ -333,6 +333,9 @@ var optab = []Optab{
 	// undefined (deliberate illegal instruction)
 	{i: 78, as: obj.AUNDEF},
 
+	// Break point instruction(0x0001 opcode)
+	{i: 73, as: ABRRK},
+
 	// 2 byte no-operation
 	{i: 66, as: ANOPH},
 
@@ -2470,6 +2473,7 @@ const (
 	op_XSCH    uint32 = 0xB276 // FORMAT_S          CANCEL SUBCHANNEL
 	op_XY      uint32 = 0xE357 // FORMAT_RXY1       EXCLUSIVE OR (32)
 	op_ZAP     uint32 = 0xF800 // FORMAT_SS2        ZERO AND ADD
+	op_BRRK    uint32 = 0x0001 // FORMAT_E          BREAKPOINT
 
 	// added in z13
 	op_CXPT   uint32 = 0xEDAF // 	RSL-b	CONVERT FROM PACKED (to extended DFP)
@@ -3605,6 +3609,9 @@ func (c *ctxtz) asmout(p *obj.Prog, asm *[]byte) {
 			zSIL(opcode, uint32(r), uint32(d), uint32(v), asm)
 		}
 
+	case 73: //Illegal opcode with SIGTRAP Exception
+		zE(op_BRRK, asm)
+
 	case 74: // mov reg addr (including relocation)
 		i2 := c.regoff(&p.To)
 		switch p.As {

src/runtime/asm_s390x.s

@@ -163,7 +163,7 @@ DATA	runtime·mainPC+0(SB)/8,$runtime·main(SB)
 GLOBL	runtime·mainPC(SB),RODATA,$8
 
 TEXT runtime·breakpoint(SB),NOSPLIT|NOFRAME,$0-0
-	MOVD	$0, 2(R0)
+	BRRK
 	RET
 
 TEXT runtime·asminit(SB),NOSPLIT|NOFRAME,$0-0