cmd/internal/obj: consolidate emitting entry stack map

The obj package needs to emit the PCDATA to select the entry stack map
before calling morestack. Currently this is copied for every
architecture. Since we're about to change how this works, consolidate
all of these copies into a single helper function.

For #24543.

Change-Id: Ia92d94de78f8e23fd06dba747c43e03e5989f67b
Reviewed-on: https://go-review.googlesource.com/109346
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/internal/obj/arm/obj5.go

@@ -768,13 +768,7 @@ func (c *ctxt5) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
 	spfix.As = obj.ANOP
 	spfix.Spadj = -framesize
 
-	pcdata := obj.Appendp(spfix, c.newprog)
-	pcdata.Pos = c.cursym.Func.Text.Pos
-	pcdata.As = obj.APCDATA
-	pcdata.From.Type = obj.TYPE_CONST
-	pcdata.From.Offset = objabi.PCDATA_StackMapIndex
-	pcdata.To.Type = obj.TYPE_CONST
-	pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
+	pcdata := c.ctxt.EmitEntryLiveness(c.cursym, spfix, c.newprog)
 
 	// MOVW	LR, R3
 	movw := obj.Appendp(pcdata, c.newprog)

src/cmd/internal/obj/arm64/obj7.go

@@ -167,13 +167,7 @@ func (c *ctxt7) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
 	spfix.As = obj.ANOP
 	spfix.Spadj = -framesize
 
-	pcdata := obj.Appendp(spfix, c.newprog)
-	pcdata.Pos = c.cursym.Func.Text.Pos
-	pcdata.As = obj.APCDATA
-	pcdata.From.Type = obj.TYPE_CONST
-	pcdata.From.Offset = objabi.PCDATA_StackMapIndex
-	pcdata.To.Type = obj.TYPE_CONST
-	pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
+	pcdata := c.ctxt.EmitEntryLiveness(c.cursym, spfix, c.newprog)
 
 	// MOV	LR, R3
 	movlr := obj.Appendp(pcdata, c.newprog)

src/cmd/internal/obj/mips/obj0.go

@@ -790,6 +790,8 @@ func (c *ctxt0) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
 		p.Mark |= LABEL
 	}
 
+	p = c.ctxt.EmitEntryLiveness(c.cursym, p, c.newprog)
+
 	// JAL	runtime.morestack(SB)
 	p = obj.Appendp(p, c.newprog)
 

src/cmd/internal/obj/plist.go

@@ -190,3 +190,18 @@ func (ctxt *Link) Globl(s *LSym, size int64, flag int) {
 		s.Type = objabi.STLSBSS
 	}
 }
+
+// EmitEntryLiveness generates PCDATA Progs after p to switch to the
+// liveness map active at the entry of function s. It returns the last
+// Prog generated.
+func (ctxt *Link) EmitEntryLiveness(s *LSym, p *Prog, newprog ProgAlloc) *Prog {
+	pcdata := Appendp(p, newprog)
+	pcdata.Pos = s.Func.Text.Pos
+	pcdata.As = APCDATA
+	pcdata.From.Type = TYPE_CONST
+	pcdata.From.Offset = objabi.PCDATA_StackMapIndex
+	pcdata.To.Type = TYPE_CONST
+	pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
+
+	return pcdata
+}

src/cmd/internal/obj/ppc64/obj9.go

@@ -966,6 +966,8 @@ func (c *ctxt9) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
 		q.Pcond = p
 	}
 
+	p = c.ctxt.EmitEntryLiveness(c.cursym, p, c.newprog)
+
 	var morestacksym *obj.LSym
 	if c.cursym.CFunc() {
 		morestacksym = c.ctxt.Lookup("runtime.morestackc")

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

@@ -679,13 +679,7 @@ func (c *ctxtz) stacksplitPost(p *obj.Prog, pPre *obj.Prog, pPreempt *obj.Prog,
 	spfix.As = obj.ANOP
 	spfix.Spadj = -framesize
 
-	pcdata := obj.Appendp(spfix, c.newprog)
-	pcdata.Pos = c.cursym.Func.Text.Pos
-	pcdata.As = obj.APCDATA
-	pcdata.From.Type = obj.TYPE_CONST
-	pcdata.From.Offset = objabi.PCDATA_StackMapIndex
-	pcdata.To.Type = obj.TYPE_CONST
-	pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
+	pcdata := c.ctxt.EmitEntryLiveness(c.cursym, spfix, c.newprog)
 
 	// MOVD	LR, R5
 	p = obj.Appendp(pcdata, c.newprog)

src/cmd/internal/obj/x86/obj6.go

@@ -1150,13 +1150,7 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
 	spfix.As = obj.ANOP
 	spfix.Spadj = -framesize
 
-	pcdata := obj.Appendp(spfix, newprog)
-	pcdata.Pos = cursym.Func.Text.Pos
-	pcdata.As = obj.APCDATA
-	pcdata.From.Type = obj.TYPE_CONST
-	pcdata.From.Offset = objabi.PCDATA_StackMapIndex
-	pcdata.To.Type = obj.TYPE_CONST
-	pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
+	pcdata := ctxt.EmitEntryLiveness(cursym, spfix, newprog)
 
 	call := obj.Appendp(pcdata, newprog)
 	call.Pos = cursym.Func.Text.Pos