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

// cmd/7l/noop.c, cmd/7l/obj.c, cmd/ld/pass.c from Vita Nuova.
// https://bitbucket.org/plan9-from-bell-labs/9-cc/src/master/
//
// 	Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
// 	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
// 	Portions Copyright © 1997-1999 Vita Nuova Limited
// 	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
// 	Portions Copyright © 2004,2006 Bruce Ellis
// 	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
// 	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
// 	Portions Copyright © 2009 The Go Authors. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package arm64

import (
	"cmd/internal/obj"
	"cmd/internal/objabi"
	"cmd/internal/src"
	"cmd/internal/sys"
	"internal/abi"
	"internal/buildcfg"
	"log"
	"math"
)

// zrReplace is the set of instructions for which $0 in the From operand
// should be replaced with REGZERO.
var zrReplace = map[obj.As]bool{
	AMOVD:  true,
	AMOVW:  true,
	AMOVWU: true,
	AMOVH:  true,
	AMOVHU: true,
	AMOVB:  true,
	AMOVBU: true,
	ASBC:   true,
	ASBCW:  true,
	ASBCS:  true,
	ASBCSW: true,
	AADC:   true,
	AADCW:  true,
	AADCS:  true,
	AADCSW: true,
	AFMOVD: true,
	AFMOVS: true,
	AMSR:   true,
}

func (c *ctxt7) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
	if c.ctxt.Flag_maymorestack != "" {
		p = c.cursym.Func().SpillRegisterArgs(p, c.newprog)

		// Save LR and make room for FP, REGCTXT. Leave room
		// for caller's saved FP.
		const frameSize = 32
		p = obj.Appendp(p, c.newprog)
		p.As = AMOVD
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGLINK
		p.To.Type = obj.TYPE_MEM
		p.Scond = C_XPRE
		p.To.Offset = -frameSize
		p.To.Reg = REGSP
		p.Spadj = frameSize

		// Save FP.
		p = obj.Appendp(p, c.newprog)
		p.As = AMOVD
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGFP
		p.To.Type = obj.TYPE_MEM
		p.To.Reg = REGSP
		p.To.Offset = -8

		p = obj.Appendp(p, c.newprog)
		p.As = ASUB
		p.From.Type = obj.TYPE_CONST
		p.From.Offset = 8
		p.Reg = REGSP
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REGFP

		// Save REGCTXT (for simplicity we do this whether or
		// not we need it.)
		p = obj.Appendp(p, c.newprog)
		p.As = AMOVD
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGCTXT
		p.To.Type = obj.TYPE_MEM
		p.To.Reg = REGSP
		p.To.Offset = 8

		// BL maymorestack
		p = obj.Appendp(p, c.newprog)
		p.As = ABL
		p.To.Type = obj.TYPE_BRANCH
		// See ../x86/obj6.go
		p.To.Sym = c.ctxt.LookupABI(c.ctxt.Flag_maymorestack, c.cursym.ABI())

		// Restore REGCTXT.
		p = obj.Appendp(p, c.newprog)
		p.As = AMOVD
		p.From.Type = obj.TYPE_MEM
		p.From.Reg = REGSP
		p.From.Offset = 8
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REGCTXT

		// Restore FP.
		p = obj.Appendp(p, c.newprog)
		p.As = AMOVD
		p.From.Type = obj.TYPE_MEM
		p.From.Reg = REGSP
		p.From.Offset = -8
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REGFP

		// Restore LR and SP.
		p = obj.Appendp(p, c.newprog)
		p.As = AMOVD
		p.From.Type = obj.TYPE_MEM
		p.Scond = C_XPOST
		p.From.Offset = frameSize
		p.From.Reg = REGSP
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REGLINK
		p.Spadj = -frameSize

		p = c.cursym.Func().UnspillRegisterArgs(p, c.newprog)
	}

	// Jump back to here after morestack returns.
	startPred := p

	// MOV	g_stackguard(g), RT1
	p = obj.Appendp(p, c.newprog)

	p.As = AMOVD
	p.From.Type = obj.TYPE_MEM
	p.From.Reg = REGG
	p.From.Offset = 2 * int64(c.ctxt.Arch.PtrSize) // G.stackguard0
	if c.cursym.CFunc() {
		p.From.Offset = 3 * int64(c.ctxt.Arch.PtrSize) // G.stackguard1
	}
	p.To.Type = obj.TYPE_REG
	p.To.Reg = REGRT1

	// Mark the stack bound check and morestack call async nonpreemptible.
	// If we get preempted here, when resumed the preemption request is
	// cleared, but we'll still call morestack, which will double the stack
	// unnecessarily. See issue #35470.
	p = c.ctxt.StartUnsafePoint(p, c.newprog)

	q := (*obj.Prog)(nil)
	if framesize <= abi.StackSmall {
		// small stack: SP < stackguard
		//	CMP	stackguard, SP

		p = obj.Appendp(p, c.newprog)
		p.As = ACMP
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGRT1
		p.Reg = REGSP
	} else if framesize <= abi.StackBig {
		// large stack: SP-framesize < stackguard-StackSmall
		//	SUB	$(framesize-StackSmall), SP, RT2
		//	CMP	stackguard, RT2
		p = obj.Appendp(p, c.newprog)

		p.As = ASUB
		p.From.Type = obj.TYPE_CONST
		p.From.Offset = int64(framesize) - abi.StackSmall
		p.Reg = REGSP
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REGRT2

		p = obj.Appendp(p, c.newprog)
		p.As = ACMP
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGRT1
		p.Reg = REGRT2
	} else {
		// Such a large stack we need to protect against underflow.
		// The runtime guarantees SP > objabi.StackBig, but
		// framesize is large enough that SP-framesize may
		// underflow, causing a direct comparison with the
		// stack guard to incorrectly succeed. We explicitly
		// guard against underflow.
		//
		//	SUBS	$(framesize-StackSmall), SP, RT2
		//	// On underflow, jump to morestack
		//	BLO	label_of_call_to_morestack
		//	CMP	stackguard, RT2

		p = obj.Appendp(p, c.newprog)
		p.As = ASUBS
		p.From.Type = obj.TYPE_CONST
		p.From.Offset = int64(framesize) - abi.StackSmall
		p.Reg = REGSP
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REGRT2

		p = obj.Appendp(p, c.newprog)
		q = p
		p.As = ABLO
		p.To.Type = obj.TYPE_BRANCH

		p = obj.Appendp(p, c.newprog)
		p.As = ACMP
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGRT1
		p.Reg = REGRT2
	}

	// BLS	do-morestack
	bls := obj.Appendp(p, c.newprog)
	bls.As = ABLS
	bls.To.Type = obj.TYPE_BRANCH

	end := c.ctxt.EndUnsafePoint(bls, c.newprog, -1)

	var last *obj.Prog
	for last = c.cursym.Func().Text; last.Link != nil; last = last.Link {
	}

	// Now we are at the end of the function, but logically
	// we are still in function prologue. We need to fix the
	// SP data and PCDATA.
	spfix := obj.Appendp(last, c.newprog)
	spfix.As = obj.ANOP
	spfix.Spadj = -framesize

	pcdata := c.ctxt.EmitEntryStackMap(c.cursym, spfix, c.newprog)
	pcdata = c.ctxt.StartUnsafePoint(pcdata, c.newprog)

	if q != nil {
		q.To.SetTarget(pcdata)
	}
	bls.To.SetTarget(pcdata)

	spill := c.cursym.Func().SpillRegisterArgs(pcdata, c.newprog)

	// MOV	LR, R3
	movlr := obj.Appendp(spill, c.newprog)
	movlr.As = AMOVD
	movlr.From.Type = obj.TYPE_REG
	movlr.From.Reg = REGLINK
	movlr.To.Type = obj.TYPE_REG
	movlr.To.Reg = REG_R3

	debug := movlr
	if false {
		debug = obj.Appendp(debug, c.newprog)
		debug.As = AMOVD
		debug.From.Type = obj.TYPE_CONST
		debug.From.Offset = int64(framesize)
		debug.To.Type = obj.TYPE_REG
		debug.To.Reg = REGTMP
	}

	// BL	runtime.morestack(SB)
	call := obj.Appendp(debug, c.newprog)
	call.As = ABL
	call.To.Type = obj.TYPE_BRANCH
	morestack := "runtime.morestack"
	switch {
	case c.cursym.CFunc():
		morestack = "runtime.morestackc"
	case !c.cursym.Func().Text.From.Sym.NeedCtxt():
		morestack = "runtime.morestack_noctxt"
	}
	call.To.Sym = c.ctxt.Lookup(morestack)

	// The instructions which unspill regs should be preemptible.
	pcdata = c.ctxt.EndUnsafePoint(call, c.newprog, -1)
	unspill := c.cursym.Func().UnspillRegisterArgs(pcdata, c.newprog)

	// B	start
	jmp := obj.Appendp(unspill, c.newprog)
	jmp.As = AB
	jmp.To.Type = obj.TYPE_BRANCH
	jmp.To.SetTarget(startPred.Link)
	jmp.Spadj = +framesize

	return end
}

func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
	c := ctxt7{ctxt: ctxt, newprog: newprog}

	p.From.Class = 0
	p.To.Class = 0

	// Previously we rewrote $0 to ZR, but we have now removed this change.
	// In order to be compatible with some previous legal instruction formats,
	// reserve the previous conversion for some specific instructions.
	if p.From.Type == obj.TYPE_CONST && p.From.Offset == 0 && zrReplace[p.As] {
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGZERO
	}

	// Rewrite BR/BL to symbol as TYPE_BRANCH.
	switch p.As {
	case AB, ABL, obj.ARET:
		if p.To.Sym != nil {
			p.To.Type = obj.TYPE_BRANCH
		}
		break
	}

	// Rewrite float and vector constants to values stored in memory.
	switch p.As {
	case AVMOVS:
		if p.From.Type == obj.TYPE_CONST {
			p.From.Type = obj.TYPE_MEM
			p.From.Sym = c.ctxt.Int32Sym(p.From.Offset)
			p.From.Name = obj.NAME_EXTERN
			p.From.Offset = 0
		}

	case AVMOVD:
		if p.From.Type == obj.TYPE_CONST {
			p.From.Type = obj.TYPE_MEM
			p.From.Sym = c.ctxt.Int64Sym(p.From.Offset)
			p.From.Name = obj.NAME_EXTERN
			p.From.Offset = 0
		}

	case AVMOVQ:
		if p.From.Type == obj.TYPE_CONST {
			p.From.Type = obj.TYPE_MEM
			p.From.Sym = c.ctxt.Int128Sym(p.GetFrom3().Offset, p.From.Offset)
			p.From.Name = obj.NAME_EXTERN
			p.From.Offset = 0
			p.RestArgs = nil
		}

	case AFMOVS:
		if p.From.Type == obj.TYPE_FCONST {
			f64 := p.From.Val.(float64)
			f32 := float32(f64)
			if c.chipfloat7(f64) > 0 {
				break
			}
			if math.Float32bits(f32) == 0 {
				p.From.Type = obj.TYPE_REG
				p.From.Reg = REGZERO
				break
			}
			p.From.Type = obj.TYPE_MEM
			p.From.Sym = c.ctxt.Float32Sym(f32)
			p.From.Name = obj.NAME_EXTERN
			p.From.Offset = 0
		}

	case AFMOVD:
		if p.From.Type == obj.TYPE_FCONST {
			f64 := p.From.Val.(float64)
			if c.chipfloat7(f64) > 0 {
				break
			}
			if math.Float64bits(f64) == 0 {
				p.From.Type = obj.TYPE_REG
				p.From.Reg = REGZERO
				break
			}
			p.From.Type = obj.TYPE_MEM
			p.From.Sym = c.ctxt.Float64Sym(f64)
			p.From.Name = obj.NAME_EXTERN
			p.From.Offset = 0
		}
	}

	if c.ctxt.Flag_dynlink {
		c.rewriteToUseGot(p)
	}
}

// Rewrite p, if necessary, to access global data via the global offset table.
func (c *ctxt7) rewriteToUseGot(p *obj.Prog) {

	// We only care about global data: NAME_EXTERN means a global
	// symbol in the Go sense, and p.Sym.Local is true for a few
	// internally defined symbols.
	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; ADD <off>, Rx
		if p.As != AMOVD {
			c.ctxt.Diag("do not know how to handle TYPE_ADDR in %v with -dynlink", p)
		}
		if p.To.Type != obj.TYPE_REG {
			c.ctxt.Diag("do not know how to handle LEAQ-type insn to non-register in %v with -dynlink", p)
		}
		p.From.Type = obj.TYPE_MEM
		p.From.Name = obj.NAME_GOTREF
		if p.From.Offset != 0 {
			q := obj.Appendp(p, c.newprog)
			q.As = AADD
			q.From.Type = obj.TYPE_CONST
			q.From.Offset = p.From.Offset
			q.To = p.To
			p.From.Offset = 0
		}
	}
	if p.GetFrom3() != nil && p.GetFrom3().Name == obj.NAME_EXTERN {
		c.ctxt.Diag("don't know how to handle %v with -dynlink", p)
	}
	var source *obj.Addr
	// MOVx sym, Ry becomes MOVD sym@GOT, REGTMP; MOVx (REGTMP), Ry
	// MOVx Ry, sym becomes MOVD sym@GOT, REGTMP; MOVD Ry, (REGTMP)
	// 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() {
			c.ctxt.Diag("cannot handle NAME_EXTERN on both sides in %v with -dynlink", p)
		}
		source = &p.From
	} else if p.To.Name == obj.NAME_EXTERN && !p.To.Sym.Local() {
		source = &p.To
	} else {
		return
	}
	if p.As == obj.ATEXT || p.As == obj.AFUNCDATA || p.As == obj.ACALL || p.As == obj.ARET || p.As == obj.AJMP {
		return
	}
	if source.Sym.Type == objabi.STLSBSS {
		return
	}
	if source.Type != obj.TYPE_MEM {
		c.ctxt.Diag("don't know how to handle %v with -dynlink", p)
	}
	p1 := obj.Appendp(p, c.newprog)
	p2 := obj.Appendp(p1, c.newprog)
	p1.As = AMOVD
	p1.From.Type = obj.TYPE_MEM
	p1.From.Sym = source.Sym
	p1.From.Name = obj.NAME_GOTREF
	p1.To.Type = obj.TYPE_REG
	p1.To.Reg = REGTMP

	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.Name = obj.NAME_NONE
		p2.From.Sym = nil
	} else if p.To.Name == obj.NAME_EXTERN {
		p2.To.Reg = REGTMP
		p2.To.Name = obj.NAME_NONE
		p2.To.Sym = nil
	} else {
		return
	}
	obj.Nopout(p)
}

// SIMDSVEVectorLengthScaled marks a VL-scaled displacement ("#imm, mul vl").
const SIMDSVEVectorLengthScaled int16 = -32768

// sveStackAddr rewrites byte-scaled AUTO, PARAM and SP-relative memory
// operands of SVE pseudo loads/stores through REGTMP:
//
//	ZSTR Z0, 40(RSP)  ->  MOVD $40(RSP), R27; ZSTR Z0, (VL*0)(R27)
//
// SVE Z/P loads and stores only support VL-scaled immediate addressing, so
// a fixed byte frame offset - which is not a compile-time multiple of the
// runtime VL and can exceed the ±256-VL immediate range - must be reached
// through a register. VL-scaled operands are left untouched.
func (c *ctxt7) sveStackAddr(p *obj.Prog, a *obj.Addr) *obj.Prog {
	if a.Type != obj.TYPE_MEM || a.Scale < 0 || a.Index != 0 {
		return p
	}
	switch {
	case a.Name == obj.NAME_AUTO || a.Name == obj.NAME_PARAM:
	case a.Name == obj.NAME_NONE && a.Reg == REGSP && a.Sym == nil:
	default:
		return p
	}
	q := c.newprog()
	nocache(q)
	q.Pos = p.Pos
	q.As = p.As
	q.From = p.From
	q.To = p.To
	q.Link = p.Link
	p.Link = q

	p.As = AMOVD
	p.From = obj.Addr{Type: obj.TYPE_ADDR, Name: a.Name, Sym: a.Sym, Reg: a.Reg, Offset: a.Offset}
	p.To = obj.Addr{Type: obj.TYPE_REG, Reg: REGTMP}
	nocache(p)

	a = &q.To
	if q.As == AZLDR || q.As == APLDR {
		a = &q.From
	}
	a.Name = obj.NAME_NONE
	a.Sym = nil
	a.Reg = REGTMP
	a.Offset = 0
	a.Scale = SIMDSVEVectorLengthScaled
	return q
}

func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
	if cursym.Func().Text == nil || cursym.Func().Text.Link == nil {
		return
	}

	c := ctxt7{ctxt: ctxt, newprog: newprog, cursym: cursym}

	p := c.cursym.Func().Text
	textstksiz := p.To.Offset
	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)

	/*
	 * find leaf subroutines
	 */
	for p := c.cursym.Func().Text; p != nil; p = p.Link {
		switch p.As {
		case obj.ATEXT:
			p.Mark |= LEAF

		case ABL:
			c.cursym.Func().Text.Mark &^= LEAF
		}
	}

	var q *obj.Prog
	var q1 *obj.Prog
	for p := c.cursym.Func().Text; p != nil; p = p.Link {
		o := p.As
		switch o {
		case obj.ATEXT:
			c.cursym.Func().Text = p
			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 !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 {
				extrasize := int32(0)
				if c.autosize%16 == 8 {
					// Allocate extra 8 bytes on the frame top to save FP
					extrasize = 8
				} else if c.autosize&(16-1) == 0 {
					// Allocate extra 16 bytes to save FP for the old frame whose size is 8 mod 16
					extrasize = 16
				} else {
					c.ctxt.Diag("%v: unaligned frame size %d - must be 16 aligned", p, c.autosize-8)
				}
				c.autosize += extrasize
				c.cursym.Func().Locals += extrasize

				// low 32 bits for autosize
				// high 32 bits for extrasize
				p.To.Offset = int64(c.autosize) | int64(extrasize)<<32
			} else {
				// NOFRAME
				p.To.Offset = 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 cursym.Func().Text.Mark&LEAF != 0 {
				cursym.Set(obj.AttrLeaf, true)
				if p.From.Sym.NoFrame() {
					break
				}
			}

			if p.Mark&LEAF != 0 && c.autosize < abi.StackSmall {
				// A leaf function with a small stack can be marked
				// NOSPLIT, avoiding a stack check.
				p.From.Sym.Set(obj.AttrNoSplit, true)
			}

			if !p.From.Sym.NoSplit() {
				p = c.stacksplit(p, c.autosize) // emit split check
			}

			var prologueEnd *obj.Prog

			aoffset := c.autosize
			if aoffset > 0xf0 {
				// MOVD.W offset variant range is -0x100 to 0xf8, SP should be 16-byte aligned.
				// so the maximum aoffset value is 0xf0.
				aoffset = 0xf0
			}

			// Frame is non-empty. Make sure to save link register, even if
			// it is a leaf function, so that traceback works.
			q = p
			if c.autosize > aoffset {
				// Frame size is too large for a MOVD.W instruction. Store the frame pointer
				// register and link register before decrementing SP, so if a signal comes
				// during the execution of the function prologue, the traceback code will
				// not see a half-updated stack frame.

				// SUB $autosize, RSP, R20
				q1 = obj.Appendp(q, c.newprog)
				q1.Pos = p.Pos
				q1.As = ASUB
				q1.From.Type = obj.TYPE_CONST
				q1.From.Offset = int64(c.autosize)
				q1.Reg = REGSP
				q1.To.Type = obj.TYPE_REG
				q1.To.Reg = REG_R20

				prologueEnd = q1

				// STP (R29, R30), -8(R20)
				q1 = obj.Appendp(q1, c.newprog)
				q1.Pos = p.Pos
				q1.As = ASTP
				q1.From.Type = obj.TYPE_REGREG
				q1.From.Reg = REGFP
				q1.From.Offset = REGLINK
				q1.To.Type = obj.TYPE_MEM
				q1.To.Reg = REG_R20
				q1.To.Offset = -8

				// This is not async preemptible, as if we open a frame
				// at the current SP, it will clobber the saved LR.
				q1 = c.ctxt.StartUnsafePoint(q1, c.newprog)

				// MOVD R20, RSP
				q1 = obj.Appendp(q1, c.newprog)
				q1.Pos = p.Pos
				q1.As = AMOVD
				q1.From.Type = obj.TYPE_REG
				q1.From.Reg = REG_R20
				q1.To.Type = obj.TYPE_REG
				q1.To.Reg = REGSP
				q1.Spadj = c.autosize

				q1 = c.ctxt.EndUnsafePoint(q1, c.newprog, -1)

				if buildcfg.GOOS == "ios" {
					// iOS does not support SA_ONSTACK. We will run the signal handler
					// on the G stack. If we write below SP, it may be clobbered by
					// the signal handler. So we save FP and LR after decrementing SP.
					// STP (R29, R30), -8(RSP)
					q1 = obj.Appendp(q1, c.newprog)
					q1.Pos = p.Pos
					q1.As = ASTP
					q1.From.Type = obj.TYPE_REGREG
					q1.From.Reg = REGFP
					q1.From.Offset = REGLINK
					q1.To.Type = obj.TYPE_MEM
					q1.To.Reg = REGSP
					q1.To.Offset = -8
				}
			} else {
				// small frame, update SP and save LR in a single MOVD.W instruction.
				// So if a signal comes during the execution of the function prologue,
				// the traceback code will not see a half-updated stack frame.
				// Also, on Linux, in a cgo binary we may get a SIGSETXID signal
				// early on before the signal stack is set, as glibc doesn't allow
				// us to block SIGSETXID. So it is important that we don't write below
				// the SP until the signal stack is set.
				// Luckily, all the functions from thread entry to setting the signal
				// stack have small frames.
				q1 = obj.Appendp(q, c.newprog)
				q1.As = AMOVD
				q1.Pos = p.Pos
				q1.From.Type = obj.TYPE_REG
				q1.From.Reg = REGLINK
				q1.To.Type = obj.TYPE_MEM
				q1.Scond = C_XPRE
				q1.To.Offset = int64(-aoffset)
				q1.To.Reg = REGSP
				q1.Spadj = aoffset

				prologueEnd = q1

				// Frame pointer.
				q1 = obj.Appendp(q1, c.newprog)
				q1.Pos = p.Pos
				q1.As = AMOVD
				q1.From.Type = obj.TYPE_REG
				q1.From.Reg = REGFP
				q1.To.Type = obj.TYPE_MEM
				q1.To.Reg = REGSP
				q1.To.Offset = -8
			}

			prologueEnd.Pos = prologueEnd.Pos.WithXlogue(src.PosPrologueEnd)

			q1 = obj.Appendp(q1, c.newprog)
			q1.Pos = p.Pos
			q1.As = ASUB
			q1.From.Type = obj.TYPE_CONST
			q1.From.Offset = 8
			q1.Reg = REGSP
			q1.To.Type = obj.TYPE_REG
			q1.To.Reg = REGFP

		case obj.ARET:
			nocache(p)
			if p.From.Type == obj.TYPE_CONST {
				c.ctxt.Diag("using BECOME (%v) is not supported!", p)
				break
			}

			retJMP, retReg := p.To.Sym, p.To.Reg
			if retReg == 0 {
				retReg = REGLINK
			}
			p.To = obj.Addr{}
			aoffset := c.autosize
			if c.cursym.Func().Text.Mark&LEAF != 0 {
				if aoffset != 0 {
					// Restore frame pointer.
					// ADD $framesize-8, RSP, R29
					p.As = AADD
					p.From.Type = obj.TYPE_CONST
					p.From.Offset = int64(c.autosize) - 8
					p.Reg = REGSP
					p.To.Type = obj.TYPE_REG
					p.To.Reg = REGFP

					// Pop stack frame.
					// ADD $framesize, RSP, RSP
					p = obj.Appendp(p, c.newprog)
					p.As = AADD
					p.From.Type = obj.TYPE_CONST
					p.From.Offset = int64(c.autosize)
					p.To.Type = obj.TYPE_REG
					p.To.Reg = REGSP
					p.Spadj = -c.autosize
				}
			} else if aoffset <= 0xF0 {
				// small frame, restore LR and update SP in a single MOVD.P instruction.
				// There is no correctness issue to use a single LDP for LR and FP,
				// but the instructions are not pattern matched with the prologue's
				// MOVD.W and MOVD, which may cause performance issue in
				// store-forwarding.

				// MOVD -8(RSP), R29
				p.As = AMOVD
				p.From.Type = obj.TYPE_MEM
				p.From.Reg = REGSP
				p.From.Offset = -8
				p.To.Type = obj.TYPE_REG
				p.To.Reg = REGFP
				p = obj.Appendp(p, c.newprog)

				// MOVD.P offset(RSP), R30
				p.As = AMOVD
				p.From.Type = obj.TYPE_MEM
				p.Scond = C_XPOST
				p.From.Offset = int64(aoffset)
				p.From.Reg = REGSP
				p.To.Type = obj.TYPE_REG
				p.To.Reg = REGLINK
				p.Spadj = -aoffset
			} else {
				// LDP -8(RSP), (R29, R30)
				p.As = ALDP
				p.From.Type = obj.TYPE_MEM
				p.From.Offset = -8
				p.From.Reg = REGSP
				p.To.Type = obj.TYPE_REGREG
				p.To.Reg = REGFP
				p.To.Offset = REGLINK

				if aoffset < 1<<12 {
					// ADD $aoffset, RSP, RSP
					q = newprog()
					q.As = AADD
					q.From.Type = obj.TYPE_CONST
					q.From.Offset = int64(aoffset)
					q.To.Type = obj.TYPE_REG
					q.To.Reg = REGSP
					q.Spadj = -aoffset
					q.Pos = p.Pos
					q.Link = p.Link
					p.Link = q
					p = q
				} else {
					// Put frame size in a separate register and
					// add it in with a single instruction,
					// so we never have a partial frame during
					// the epilog. See issue 73259.

					// MOVD $aoffset, REGTMP
					q = newprog()
					q.As = AMOVD
					q.From.Type = obj.TYPE_CONST
					q.From.Offset = int64(aoffset)
					q.To.Type = obj.TYPE_REG
					q.To.Reg = REGTMP
					q.Pos = p.Pos
					q.Link = p.Link
					p.Link = q
					p = q
					// ADD REGTMP, RSP, RSP
					q = newprog()
					q.As = AADD
					q.From.Type = obj.TYPE_REG
					q.From.Reg = REGTMP
					q.To.Type = obj.TYPE_REG
					q.To.Reg = REGSP
					q.Spadj = -aoffset
					q.Pos = p.Pos
					q.Link = p.Link
					p.Link = q
					p = q
				}
			}

			// If enabled, this code emits 'MOV PC, R27' before every 'MOV LR, PC',
			// so that if you are debugging a low-level crash where PC and LR are zero,
			// you can look at R27 to see what jumped to the zero.
			// This is useful when bringing up Go on a new system.
			// (There is similar code in ../ppc64/obj9.go:/if.false.)
			const debugRETZERO = false
			if debugRETZERO {
				if p.As != obj.ARET {
					q = newprog()
					q.Pos = p.Pos
					q.Link = p.Link
					p.Link = q
					p = q
				}
				p.As = AADR
				p.From.Type = obj.TYPE_BRANCH
				p.From.Offset = 0
				p.To.Type = obj.TYPE_REG
				p.To.Reg = REGTMP

			}

			if p.As != obj.ARET {
				q = newprog()
				q.Pos = p.Pos
				q.Link = p.Link
				p.Link = q
				p = q
			}

			if retJMP != nil {
				p.As = AB
				p.To.Type = obj.TYPE_BRANCH
				p.To.Sym = retJMP
				p.Spadj = +c.autosize
				break
			}

			p.As = obj.ARET
			p.To.Type = obj.TYPE_MEM
			p.To.Offset = 0
			p.To.Reg = retReg
			p.Spadj = +c.autosize

		case AADD, ASUB:
			if p.To.Type == obj.TYPE_REG && p.To.Reg == REGSP && p.From.Type == obj.TYPE_CONST {
				if p.As == AADD {
					p.Spadj = int32(-p.From.Offset)
				} else {
					p.Spadj = int32(+p.From.Offset)
				}
			}

		case AZSTR, APSTR:
			p = c.sveStackAddr(p, &p.To)

		case AZLDR, APLDR:
			p = c.sveStackAddr(p, &p.From)

		case obj.AGETCALLERPC:
			if cursym.Leaf() {
				/* MOVD LR, Rd */
				p.As = AMOVD
				p.From.Type = obj.TYPE_REG
				p.From.Reg = REGLINK
			} else {
				/* MOVD (RSP), Rd */
				p.As = AMOVD
				p.From.Type = obj.TYPE_MEM
				p.From.Reg = REGSP
			}
		}
		if p.To.Type == obj.TYPE_REG && p.To.Reg == REGSP && p.Spadj == 0 {
			f := c.cursym.Func()
			if f.FuncFlag&abi.FuncFlagSPWrite == 0 {
				c.cursym.Func().FuncFlag |= abi.FuncFlagSPWrite
				if ctxt.Debugvlog || !ctxt.IsAsm {
					ctxt.Logf("auto-SPWRITE: %s %v\n", c.cursym.Name, p)
					if !ctxt.IsAsm {
						ctxt.Diag("invalid auto-SPWRITE in non-assembly")
						ctxt.DiagFlush()
						log.Fatalf("bad SPWRITE")
					}
				}
			}
		}
		if p.From.Type == obj.TYPE_SHIFT && (p.To.Reg == REG_RSP || p.Reg == REG_RSP) {
			offset := p.From.Offset
			op := offset & (3 << 22)
			if op != SHIFT_LL {
				ctxt.Diag("illegal combination: %v", p)
			}
			r := (offset >> 16) & 31
			shift := (offset >> 10) & 63
			if shift > 4 {
				// the shift amount is out of range, in order to avoid repeated error
				// reportings, don't call ctxt.Diag, because asmout case 27 has the
				// same check.
				shift = 7
			}
			p.From.Type = obj.TYPE_REG
			p.From.Reg = int16(REG_LSL + r + (shift&7)<<5)
			p.From.Offset = 0
		}
	}
}

func nocache(p *obj.Prog) {
	p.Optab = 0
	p.From.Class = 0
	p.To.Class = 0
}

var unaryDst = map[obj.As]bool{
	AWORD:  true,
	ADWORD: true,
	ABL:    true,
	AB:     true,
	ACLREX: true,
}

var Linkarm64 = obj.LinkArch{
	Arch:           sys.ArchARM64,
	Init:           buildop,
	Preprocess:     preprocess,
	Assemble:       span7,
	Progedit:       progedit,
	UnaryDst:       unaryDst,
	DWARFRegisters: ARM64DWARFRegisters,
}