cmd/internal/obj/arm64: support NOFRAME

In addition, this makes the arm64 prologue code generation much closer
to the pattern used on other platforms.

This passes toolstash -cmp with one exception: assembly functions that
were declared with a frame size of -8 used to record
locals=0xfffffffffffffff8 in the object file and now record
locals=0x0. This doesn't affect anything.

Change-Id: I0d15e81770e54222ae329ce4496da06016736770
Reviewed-on: https://go-review.googlesource.com/92040
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -443,7 +443,19 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 
 	p := c.cursym.Func.Text
 	textstksiz := p.To.Offset
-	aoffset := int32(textstksiz)
+	if textstksiz == -8 {
+		// Historical way to mark NOFRAME.
+		p.From.Sym.Set(obj.AttrNoFrame, true)
+		textstksiz = 0
+	}
+	if textstksiz < 0 {
+		c.ctxt.Diag("negative frame size %d - did you mean NOFRAME?", textstksiz)
+	}
+	if p.From.Sym.NoFrame() {
+		if textstksiz != 0 {
+			c.ctxt.Diag("NOFRAME functions must have a frame size of 0, not %d", textstksiz)
+		}
+	}
 
 	c.cursym.Func.Args = p.To.Val.(int32)
 	c.cursym.Func.Locals = int32(textstksiz)
@@ -521,14 +533,20 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		switch o {
 		case obj.ATEXT:
 			c.cursym.Func.Text = p
-			if textstksiz < 0 {
-				c.autosize = 0
-			} else {
-				c.autosize = int32(textstksiz + 8)
+			c.autosize = int32(textstksiz)
+
+			if p.Mark&LEAF != 0 && c.autosize == 0 {
+				// A leaf function with no locals has no frame.
+				p.From.Sym.Set(obj.AttrNoFrame, true)
 			}
-			if (c.cursym.Func.Text.Mark&LEAF != 0) && c.autosize <= 8 {
-				c.autosize = 0
-			} else if c.autosize&(16-1) != 0 {
+
+			if !p.From.Sym.NoFrame() {
+				// If there is a stack frame at all, it includes
+				// space to save the LR.
+				c.autosize += 8
+			}
+
+			if c.autosize != 0 && c.autosize&(16-1) != 0 {
 				// The frame includes an LR.
 				// If the frame size is 8, it's only an LR,
 				// so there's no potential for breaking references to
@@ -544,17 +562,19 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 					c.ctxt.Diag("%v: unaligned frame size %d - must be 8 mod 16 (or 0)", p, c.autosize-8)
 				}
 			}
-			p.To.Offset = int64(c.autosize) - 8
-			if c.autosize == 0 && !(c.cursym.Func.Text.Mark&LEAF != 0) {
+			if c.autosize == 0 && c.cursym.Func.Text.Mark&LEAF == 0 {
 				if c.ctxt.Debugvlog {
 					c.ctxt.Logf("save suppressed in: %s\n", c.cursym.Func.Text.From.Sym.Name)
 				}
 				c.cursym.Func.Text.Mark |= LEAF
 			}
 
-			if c.cursym.Func.Text.Mark&LEAF != 0 {
-				c.cursym.Set(obj.AttrLeaf, true)
-				if c.autosize == 0 {
+			// FP offsets need an updated p.To.Offset.
+			p.To.Offset = int64(c.autosize) - 8
+
+			if cursym.Func.Text.Mark&LEAF != 0 {
+				cursym.Set(obj.AttrLeaf, true)
+				if p.From.Sym.NoFrame() {
 					break
 				}
 			}
@@ -563,7 +583,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				p = c.stacksplit(p, c.autosize) // emit split check
 			}
 
-			aoffset = c.autosize
+			aoffset := c.autosize
 			if aoffset > 0xF0 {
 				aoffset = 0xF0
 			}
@@ -740,7 +760,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				}
 			} else {
 				/* want write-back pre-indexed SP+autosize -> SP, loading REGLINK*/
-				aoffset = c.autosize
+				aoffset := c.autosize
 
 				if aoffset > 0xF0 {
 					aoffset = 0xF0