Golang Prog.As方法代码示例

func readprog(b *bufio.Reader, p *liblink.Prog) {
	if !undef[p] {
		panic("double-def")
	}
	delete(undef, p)
	p.Pc = rdint(b)
	p.Lineno = int32(rdint(b))
	p.Link = rdprog(b)
	p.As = int16(rdint(b))
	p.Reg = uint8(rdint(b))
	p.Scond = uint8(rdint(b))
	p.Width = int8(rdint(b))
	readaddr(b, &p.From)
	readaddr(b, &p.To)
}

// Append code to p to load g into cx.
// Overwrites p with the first instruction (no first appendp).
// Overwriting p is unusual but it lets use this in both the
// prologue (caller must call appendp first) and in the epilogue.
// Returns last new instruction.
func load_g_cx(ctxt *liblink.Link, p *liblink.Prog) *liblink.Prog {

	var next *liblink.Prog

	p.As = AMOVL
	p.From.Type_ = D_INDIR + D_TLS
	p.From.Offset = 0
	p.To.Type_ = D_CX

	next = p.Link
	progedit(ctxt, p)
	for p.Link != next {
		p = p.Link
	}

	if p.From.Index == D_TLS {
		p.From.Scale = 2
	}

	return p
}

func progedit(ctxt *liblink.Link, p *liblink.Prog) {
	var literal string
	var s *liblink.LSym
	var tlsfallback *liblink.LSym

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

	// Rewrite B/BL to symbol as D_BRANCH.
	switch p.As {

	case AB,
		ABL,
		ADUFFZERO,
		ADUFFCOPY:
		if p.To.Type_ == D_OREG && (p.To.Name == D_EXTERN || p.To.Name == D_STATIC) && p.To.Sym != nil {
			p.To.Type_ = D_BRANCH
		}
		break
	}

	// Replace TLS register fetches on older ARM procesors.
	switch p.As {

	// Treat MRC 15, 0, <reg>, C13, C0, 3 specially.
	case AMRC:
		if p.To.Offset&0xffff0fff == 0xee1d0f70 {

			// Because the instruction might be rewriten to a BL which returns in R0
			// the register must be zero.
			if p.To.Offset&0xf000 != 0 {

				ctxt.Diag("%L: TLS MRC instruction must write to R0 as it might get translated into a BL instruction", p.Lineno)
			}

			if ctxt.Goarm < 7 {
				// Replace it with BL runtime.read_tls_fallback(SB) for ARM CPUs that lack the tls extension.
				if tlsfallback == nil {

					tlsfallback = liblink.Linklookup(ctxt, "runtime.read_tls_fallback", 0)
				}

				// MOVW	LR, R11
				p.As = AMOVW

				p.From.Type_ = D_REG
				p.From.Reg = REGLINK
				p.To.Type_ = D_REG
				p.To.Reg = REGTMP

				// BL	runtime.read_tls_fallback(SB)
				p = liblink.Appendp(ctxt, p)

				p.As = ABL
				p.To.Type_ = D_BRANCH
				p.To.Sym = tlsfallback
				p.To.Offset = 0

				// MOVW	R11, LR
				p = liblink.Appendp(ctxt, p)

				p.As = AMOVW
				p.From.Type_ = D_REG
				p.From.Reg = REGTMP
				p.To.Type_ = D_REG
				p.To.Reg = REGLINK
				break
			}
		}

		// Otherwise, MRC/MCR instructions need no further treatment.
		p.As = AWORD

		break
	}

	// Rewrite float constants to values stored in memory.
	switch p.As {

	case AMOVF:
		if p.From.Type_ == D_FCONST && chipfloat5(ctxt, p.From.U.Dval) < 0 && (chipzero5(ctxt, p.From.U.Dval) < 0 || p.Scond&C_SCOND != C_SCOND_NONE) {
			var i32 uint32
			var f32 float32
			f32 = float32(p.From.U.Dval)
			i32 = math.Float32bits(f32)
			literal = fmt.Sprintf("$f32.%08x", i32)
			s = liblink.Linklookup(ctxt, literal, 0)
			if s.Type_ == 0 {
				s.Type_ = liblink.SRODATA
				liblink.Adduint32(ctxt, s, i32)
				s.Reachable = 0
			}

			p.From.Type_ = D_OREG
			p.From.Sym = s
			p.From.Name = D_EXTERN
			p.From.Offset = 0
		}

	case AMOVD:
//.........这里部分代码省略.........

func softfloat(ctxt *liblink.Link, cursym *liblink.LSym) {
	var p *liblink.Prog
	var next *liblink.Prog
	var symsfloat *liblink.LSym
	var wasfloat int

	if ctxt.Goarm > 5 {
		return
	}

	symsfloat = liblink.Linklookup(ctxt, "_sfloat", 0)

	wasfloat = 0
	for p = cursym.Text; p != nil; p = p.Link {
		if p.Pcond != nil {
			p.Pcond.Mark |= LABEL
		}
	}
	for p = cursym.Text; p != nil; p = p.Link {
		switch p.As {
		case AMOVW:
			if p.To.Type_ == D_FREG || p.From.Type_ == D_FREG {
				goto soft
			}
			goto notsoft

		case AMOVWD,
			AMOVWF,
			AMOVDW,
			AMOVFW,
			AMOVFD,
			AMOVDF,
			AMOVF,
			AMOVD,
			ACMPF,
			ACMPD,
			AADDF,
			AADDD,
			ASUBF,
			ASUBD,
			AMULF,
			AMULD,
			ADIVF,
			ADIVD,
			ASQRTF,
			ASQRTD,
			AABSF,
			AABSD:
			goto soft

		default:
			goto notsoft
		}

	soft:
		if !(wasfloat != 0) || (p.Mark&LABEL != 0) {
			next = ctxt.Arch.Prg()
			*next = *p

			// BL _sfloat(SB)
			*p = zprg5

			p.Link = next
			p.As = ABL
			p.To.Type_ = D_BRANCH
			p.To.Sym = symsfloat
			p.Lineno = next.Lineno

			p = next
			wasfloat = 1
		}

		continue

	notsoft:
		wasfloat = 0
	}
}

func addstacksplit(ctxt *liblink.Link, cursym *liblink.LSym) {
	var p *liblink.Prog
	var pl *liblink.Prog
	var p1 *liblink.Prog
	var p2 *liblink.Prog
	var q *liblink.Prog
	var q1 *liblink.Prog
	var q2 *liblink.Prog
	var o int
	var autosize int32
	var autoffset int32

	autosize = 0

	if ctxt.Symmorestack[0] == nil {
		ctxt.Symmorestack[0] = liblink.Linklookup(ctxt, "runtime.morestack", 0)
		ctxt.Symmorestack[1] = liblink.Linklookup(ctxt, "runtime.morestack_noctxt", 0)
	}

	q = nil

	ctxt.Cursym = cursym

	if cursym.Text == nil || cursym.Text.Link == nil {
		return
	}

	softfloat(ctxt, cursym)

	p = cursym.Text
	autoffset = int32(p.To.Offset)
	if autoffset < 0 {
		autoffset = 0
	}
	cursym.Locals = autoffset
	cursym.Args = p.To.Offset2

	if ctxt.Debugzerostack != 0 {
		if autoffset != 0 && !(p.Reg&liblink.NOSPLIT != 0) {
			// MOVW $4(R13), R1
			p = liblink.Appendp(ctxt, p)

			p.As = AMOVW
			p.From.Type_ = D_CONST
			p.From.Reg = 13
			p.From.Offset = 4
			p.To.Type_ = D_REG
			p.To.Reg = 1

			// MOVW $n(R13), R2
			p = liblink.Appendp(ctxt, p)

			p.As = AMOVW
			p.From.Type_ = D_CONST
			p.From.Reg = 13
			p.From.Offset = 4 + int64(autoffset)
			p.To.Type_ = D_REG
			p.To.Reg = 2

			// MOVW $0, R3
			p = liblink.Appendp(ctxt, p)

			p.As = AMOVW
			p.From.Type_ = D_CONST
			p.From.Offset = 0
			p.To.Type_ = D_REG
			p.To.Reg = 3

			// L:
			//	MOVW.nil R3, 0(R1) +4
			//	CMP R1, R2
			//	BNE L
			pl = liblink.Appendp(ctxt, p)
			p = pl

			p.As = AMOVW
			p.From.Type_ = D_REG
			p.From.Reg = 3
			p.To.Type_ = D_OREG
			p.To.Reg = 1
			p.To.Offset = 4
			p.Scond |= C_PBIT

			p = liblink.Appendp(ctxt, p)
			p.As = ACMP
			p.From.Type_ = D_REG
			p.From.Reg = 1
			p.Reg = 2

			p = liblink.Appendp(ctxt, p)
			p.As = ABNE
			p.To.Type_ = D_BRANCH
			p.Pcond = pl
		}
	}

	/*
	 * find leaf subroutines
	 * strip NOPs
	 * expand RET
//.........这里部分代码省略.........

func xfol(ctxt *liblink.Link, p *liblink.Prog, last **liblink.Prog) {
	var q *liblink.Prog
	var r *liblink.Prog
	var a int
	var i int

loop:
	if p == nil {
		return
	}
	a = int(p.As)
	if a == AB {
		q = p.Pcond
		if q != nil && q.As != ATEXT {
			p.Mark |= FOLL
			p = q
			if !(p.Mark&FOLL != 0) {
				goto loop
			}
		}
	}

	if p.Mark&FOLL != 0 {
		i = 0
		q = p
		for ; i < 4; (func() { i++; q = q.Link })() {
			if q == *last || q == nil {
				break
			}
			a = int(q.As)
			if a == ANOP {
				i--
				continue
			}

			if a == AB || (a == ARET && q.Scond == C_SCOND_NONE) || a == ARFE || a == AUNDEF {
				goto copy
			}
			if q.Pcond == nil || (q.Pcond.Mark&FOLL != 0) {
				continue
			}
			if a != ABEQ && a != ABNE {
				continue
			}

		copy:
			for {
				r = ctxt.Arch.Prg()
				*r = *p
				if !(r.Mark&FOLL != 0) {
					fmt.Printf("can't happen 1\n")
				}
				r.Mark |= FOLL
				if p != q {
					p = p.Link
					(*last).Link = r
					*last = r
					continue
				}

				(*last).Link = r
				*last = r
				if a == AB || (a == ARET && q.Scond == C_SCOND_NONE) || a == ARFE || a == AUNDEF {
					return
				}
				r.As = ABNE
				if a == ABNE {
					r.As = ABEQ
				}
				r.Pcond = p.Link
				r.Link = p.Pcond
				if !(r.Link.Mark&FOLL != 0) {
					xfol(ctxt, r.Link, last)
				}
				if !(r.Pcond.Mark&FOLL != 0) {
					fmt.Printf("can't happen 2\n")
				}
				return
			}
		}

		a = AB
		q = ctxt.Arch.Prg()
		q.As = int16(a)
		q.Lineno = p.Lineno
		q.To.Type_ = D_BRANCH
		q.To.Offset = p.Pc
		q.Pcond = p
		p = q
	}

	p.Mark |= FOLL
	(*last).Link = p
	*last = p
	if a == AB || (a == ARET && p.Scond == C_SCOND_NONE) || a == ARFE || a == AUNDEF {
		return
	}

	if p.Pcond != nil {
		if a != ABL && a != ABX && p.Link != nil {
//.........这里部分代码省略.........

func xfol(ctxt *liblink.Link, p *liblink.Prog, last **liblink.Prog) {
	var q *liblink.Prog
	var r *liblink.Prog
	var a int
	var b int
	var i int

loop:
	if p == nil {
		return
	}
	a = int(p.As)
	if a == ABR {
		q = p.Pcond
		if (p.Mark&NOSCHED != 0) || q != nil && (q.Mark&NOSCHED != 0) {
			p.Mark |= FOLL
			(*last).Link = p
			*last = p
			p = p.Link
			xfol(ctxt, p, last)
			p = q
			if p != nil && !(p.Mark&FOLL != 0) {
				goto loop
			}
			return
		}

		if q != nil {
			p.Mark |= FOLL
			p = q
			if !(p.Mark&FOLL != 0) {
				goto loop
			}
		}
	}

	if p.Mark&FOLL != 0 {
		i = 0
		q = p
		for ; i < 4; (func() { i++; q = q.Link })() {
			if q == *last || (q.Mark&NOSCHED != 0) {
				break
			}
			b = 0 /* set */
			a = int(q.As)
			if a == ANOP {
				i--
				continue
			}

			if a == ABR || a == ARETURN || a == ARFI || a == ARFCI || a == ARFID || a == AHRFID {
				goto copy
			}
			if !(q.Pcond != nil) || (q.Pcond.Mark&FOLL != 0) {
				continue
			}
			b = relinv(a)
			if !(b != 0) {
				continue
			}

		copy:
			for {
				r = ctxt.Arch.Prg()
				*r = *p
				if !(r.Mark&FOLL != 0) {
					fmt.Printf("cant happen 1\n")
				}
				r.Mark |= FOLL
				if p != q {
					p = p.Link
					(*last).Link = r
					*last = r
					continue
				}

				(*last).Link = r
				*last = r
				if a == ABR || a == ARETURN || a == ARFI || a == ARFCI || a == ARFID || a == AHRFID {
					return
				}
				r.As = int16(b)
				r.Pcond = p.Link
				r.Link = p.Pcond
				if !(r.Link.Mark&FOLL != 0) {
					xfol(ctxt, r.Link, last)
				}
				if !(r.Pcond.Mark&FOLL != 0) {
					fmt.Printf("cant happen 2\n")
				}
				return
			}
		}

		a = ABR
		q = ctxt.Arch.Prg()
		q.As = int16(a)
		q.Lineno = p.Lineno
		q.To.Type_ = D_BRANCH
		q.To.Offset = p.Pc
//.........这里部分代码省略.........

/*
// instruction scheduling
	if(debug['Q'] == 0)
		return;

	curtext = nil;
	q = nil;	// p - 1
	q1 = firstp;	// top of block
	o = 0;		// count of instructions
	for(p = firstp; p != nil; p = p1) {
		p1 = p->link;
		o++;
		if(p->mark & NOSCHED){
			if(q1 != p){
				sched(q1, q);
			}
			for(; p != nil; p = p->link){
				if(!(p->mark & NOSCHED))
					break;
				q = p;
			}
			p1 = p;
			q1 = p;
			o = 0;
			continue;
		}
		if(p->mark & (LABEL|SYNC)) {
			if(q1 != p)
				sched(q1, q);
			q1 = p;
			o = 1;
		}
		if(p->mark & (BRANCH|SYNC)) {
			sched(q1, p);
			q1 = p1;
			o = 0;
		}
		if(o >= NSCHED) {
			sched(q1, p);
			q1 = p1;
			o = 0;
		}
		q = p;
	}
*/
func stacksplit(ctxt *liblink.Link, p *liblink.Prog, framesize int32, noctxt int) *liblink.Prog {

	var q *liblink.Prog
	var q1 *liblink.Prog

	// MOVD	g_stackguard(g), R3
	p = liblink.Appendp(ctxt, p)

	p.As = AMOVD
	p.From.Type_ = D_OREG
	p.From.Reg = REGG
	p.From.Offset = 2 * int64(ctxt.Arch.Ptrsize) // G.stackguard0
	if ctxt.Cursym.Cfunc != 0 {
		p.From.Offset = 3 * int64(ctxt.Arch.Ptrsize) // G.stackguard1
	}
	p.To.Type_ = D_REG
	p.To.Reg = 3

	q = nil
	if framesize <= liblink.StackSmall {
		// small stack: SP < stackguard
		//	CMP	stackguard, SP
		p = liblink.Appendp(ctxt, p)

		p.As = ACMPU
		p.From.Type_ = D_REG
		p.From.Reg = 3
		p.To.Type_ = D_REG
		p.To.Reg = REGSP
	} else if framesize <= liblink.StackBig {
		// large stack: SP-framesize < stackguard-StackSmall
		//	ADD $-framesize, SP, R4
		//	CMP stackguard, R4
		p = liblink.Appendp(ctxt, p)

		p.As = AADD
		p.From.Type_ = D_CONST
		p.From.Offset = int64(-framesize)
		p.Reg = REGSP
		p.To.Type_ = D_REG
		p.To.Reg = 4

		p = liblink.Appendp(ctxt, p)
		p.As = ACMPU
		p.From.Type_ = D_REG
		p.From.Reg = 3
		p.To.Type_ = D_REG
		p.To.Reg = 4
	} else {

		// Such a large stack we need to protect against wraparound.
		// If SP is close to zero:
		//	SP-stackguard+StackGuard <= framesize + (StackGuard-StackSmall)
		// The +StackGuard on both sides is required to keep the left side positive:
		// SP is allowed to be slightly below stackguard. See stack.h.
//.........这里部分代码省略.........

func nopout(p *liblink.Prog) {
	p.As = ANOP
	p.From.Type_ = D_NONE
	p.To.Type_ = D_NONE
}

func addstacksplit(ctxt *liblink.Link, cursym *liblink.LSym) {
	var p *liblink.Prog
	var q *liblink.Prog
	var p1 *liblink.Prog
	var p2 *liblink.Prog
	var q1 *liblink.Prog
	var o int
	var mov int
	var aoffset int
	var textstksiz int64
	var textarg int64
	var autosize int32

	if ctxt.Symmorestack[0] == nil {
		ctxt.Symmorestack[0] = liblink.Linklookup(ctxt, "runtime.morestack", 0)
		ctxt.Symmorestack[1] = liblink.Linklookup(ctxt, "runtime.morestack_noctxt", 0)
	}

	// TODO(minux): add morestack short-cuts with small fixed frame-size.
	ctxt.Cursym = cursym

	if cursym.Text == nil || cursym.Text.Link == nil {
		return
	}

	p = cursym.Text
	parsetextconst(p.To.Offset, &textstksiz, &textarg)

	cursym.Args = int32(p.To.Offset >> 32)
	cursym.Locals = int32(textstksiz)

	/*
	 * find leaf subroutines
	 * strip NOPs
	 * expand RET
	 * expand BECOME pseudo
	 */
	if ctxt.Debugvlog != 0 {

		fmt.Fprintf(ctxt.Bso, "%5.2f noops\n", liblink.Cputime())
	}
	liblink.Bflush(ctxt.Bso)

	q = nil
	for p = cursym.Text; p != nil; p = p.Link {
		switch p.As {
		/* too hard, just leave alone */
		case ATEXT:
			q = p

			p.Mark |= LABEL | LEAF | SYNC
			if p.Link != nil {
				p.Link.Mark |= LABEL
			}

		case ANOR:
			q = p
			if p.To.Type_ == D_REG {
				if p.To.Reg == REGZERO {
					p.Mark |= LABEL | SYNC
				}
			}

		case ALWAR,
			ASTWCCC,
			AECIWX,
			AECOWX,
			AEIEIO,
			AICBI,
			AISYNC,
			ATLBIE,
			ATLBIEL,
			ASLBIA,
			ASLBIE,
			ASLBMFEE,
			ASLBMFEV,
			ASLBMTE,
			ADCBF,
			ADCBI,
			ADCBST,
			ADCBT,
			ADCBTST,
			ADCBZ,
			ASYNC,
			ATLBSYNC,
			APTESYNC,
			ATW,
			AWORD,
			ARFI,
			ARFCI,
			ARFID,
			AHRFID:
			q = p
			p.Mark |= LABEL | SYNC
			continue

		case AMOVW,
			AMOVWZ,
			AMOVD:
			q = p
//.........这里部分代码省略.........

func progedit(ctxt *liblink.Link, p *liblink.Prog) {
	var literal string
	var s *liblink.LSym
	var q *liblink.Prog

	// See obj6.c for discussion of TLS.
	if canuselocaltls(ctxt) != 0 {

		// Reduce TLS initial exec model to TLS local exec model.
		// Sequences like
		//	MOVL TLS, BX
		//	... off(BX)(TLS*1) ...
		// become
		//	NOP
		//	... off(TLS) ...
		if p.As == AMOVL && p.From.Type_ == D_TLS && D_AX <= p.To.Type_ && p.To.Type_ <= D_DI {

			p.As = ANOP
			p.From.Type_ = D_NONE
			p.To.Type_ = D_NONE
		}

		if p.From.Index == D_TLS && D_INDIR+D_AX <= p.From.Type_ && p.From.Type_ <= D_INDIR+D_DI {
			p.From.Type_ = D_INDIR + D_TLS
			p.From.Scale = 0
			p.From.Index = D_NONE
		}

		if p.To.Index == D_TLS && D_INDIR+D_AX <= p.To.Type_ && p.To.Type_ <= D_INDIR+D_DI {
			p.To.Type_ = D_INDIR + D_TLS
			p.To.Scale = 0
			p.To.Index = D_NONE
		}
	} else {

		// As a courtesy to the C compilers, rewrite TLS local exec load as TLS initial exec load.
		// The instruction
		//	MOVL off(TLS), BX
		// becomes the sequence
		//	MOVL TLS, BX
		//	MOVL off(BX)(TLS*1), BX
		// This allows the C compilers to emit references to m and g using the direct off(TLS) form.
		if p.As == AMOVL && p.From.Type_ == D_INDIR+D_TLS && D_AX <= p.To.Type_ && p.To.Type_ <= D_DI {

			q = liblink.Appendp(ctxt, p)
			q.As = p.As
			q.From = p.From
			q.From.Type_ = D_INDIR + p.To.Type_
			q.From.Index = D_TLS
			q.From.Scale = 2 // TODO: use 1
			q.To = p.To
			p.From.Type_ = D_TLS
			p.From.Index = D_NONE
			p.From.Offset = 0
		}
	}

	// TODO: Remove.
	if ctxt.Headtype == liblink.Hplan9 {

		if p.From.Scale == 1 && p.From.Index == D_TLS {
			p.From.Scale = 2
		}
		if p.To.Scale == 1 && p.To.Index == D_TLS {
			p.To.Scale = 2
		}
	}

	// Rewrite CALL/JMP/RET to symbol as D_BRANCH.
	switch p.As {

	case ACALL,
		AJMP,
		ARET:
		if (p.To.Type_ == D_EXTERN || p.To.Type_ == D_STATIC) && p.To.Sym != nil {
			p.To.Type_ = D_BRANCH
		}
		break
	}

	// Rewrite float constants to values stored in memory.
	switch p.As {

	// Convert AMOVSS $(0), Xx to AXORPS Xx, Xx
	case AMOVSS:
		if p.From.Type_ == D_FCONST {

			if p.From.U.Dval == 0 {
				if p.To.Type_ >= D_X0 {
					if p.To.Type_ <= D_X7 {
						p.As = AXORPS
						p.From.Type_ = p.To.Type_
						p.From.Index = p.To.Index
						break
					}
				}
			}
		}
		fallthrough

//.........这里部分代码省略.........

func xfol(ctxt *liblink.Link, p *liblink.Prog, last **liblink.Prog) {
	var q *liblink.Prog
	var i int
	var a int

loop:
	if p == nil {
		return
	}
	if p.As == AJMP {
		q = p.Pcond
		if q != nil && q.As != ATEXT {
			/* mark instruction as done and continue layout at target of jump */
			p.Mark = 1

			p = q
			if p.Mark == 0 {
				goto loop
			}
		}
	}

	if p.Mark != 0 {
		/*
		 * p goes here, but already used it elsewhere.
		 * copy up to 4 instructions or else branch to other copy.
		 */
		i = 0
		q = p
		for ; i < 4; (func() { i++; q = q.Link })() {

			if q == nil {
				break
			}
			if q == *last {
				break
			}
			a = int(q.As)
			if a == ANOP {
				i--
				continue
			}

			if nofollow(a) != 0 || pushpop(a) != 0 {
				break // NOTE(rsc): arm does goto copy
			}
			if q.Pcond == nil || q.Pcond.Mark != 0 {
				continue
			}
			if a == ACALL || a == ALOOP {
				continue
			}
			for {
				if p.As == ANOP {
					p = p.Link
					continue
				}

				q = liblink.Copyp(ctxt, p)
				p = p.Link
				q.Mark = 1
				(*last).Link = q
				*last = q
				if int(q.As) != a || q.Pcond == nil || q.Pcond.Mark != 0 {
					continue
				}

				q.As = int16(relinv(int(q.As)))
				p = q.Pcond
				q.Pcond = q.Link
				q.Link = p
				xfol(ctxt, q.Link, last)
				p = q.Link
				if p.Mark != 0 {
					return
				}
				goto loop
				/* */
			}
		}
		q = ctxt.Arch.Prg()
		q.As = AJMP
		q.Lineno = p.Lineno
		q.To.Type_ = D_BRANCH
		q.To.Offset = p.Pc
		q.Pcond = p
		p = q
	}

	/* emit p */
	p.Mark = 1

	(*last).Link = p
	*last = p
	a = int(p.As)

	/* continue loop with what comes after p */
	if nofollow(a) != 0 {

		return
//.........这里部分代码省略.........

// Append code to p to check for stack split.
// Appends to (does not overwrite) p.
// Assumes g is in CX.
// Returns last new instruction.
// On return, *jmpok is the instruction that should jump
// to the stack frame allocation if no split is needed.
func stacksplit(ctxt *liblink.Link, p *liblink.Prog, framesize int32, noctxt int, jmpok **liblink.Prog) *liblink.Prog {

	var q *liblink.Prog
	var q1 *liblink.Prog

	if ctxt.Debugstack != 0 {
		// 8l -K means check not only for stack
		// overflow but stack underflow.
		// On underflow, INT 3 (breakpoint).
		// Underflow itself is rare but this also
		// catches out-of-sync stack guard info.
		p = liblink.Appendp(ctxt, p)

		p.As = ACMPL
		p.From.Type_ = D_INDIR + D_CX
		p.From.Offset = 4
		p.To.Type_ = D_SP

		p = liblink.Appendp(ctxt, p)
		p.As = AJCC
		p.To.Type_ = D_BRANCH
		p.To.Offset = 4
		q1 = p

		p = liblink.Appendp(ctxt, p)
		p.As = AINT
		p.From.Type_ = D_CONST
		p.From.Offset = 3

		p = liblink.Appendp(ctxt, p)
		p.As = ANOP
		q1.Pcond = p
	}

	q1 = nil

	if framesize <= liblink.StackSmall {
		// small stack: SP <= stackguard
		//	CMPL SP, stackguard
		p = liblink.Appendp(ctxt, p)

		p.As = ACMPL
		p.From.Type_ = D_SP
		p.To.Type_ = D_INDIR + D_CX
		p.To.Offset = 2 * int64(ctxt.Arch.Ptrsize) // G.stackguard0
		if ctxt.Cursym.Cfunc != 0 {
			p.To.Offset = 3 * int64(ctxt.Arch.Ptrsize) // G.stackguard1
		}
	} else if framesize <= liblink.StackBig {
		// large stack: SP-framesize <= stackguard-StackSmall
		//	LEAL -(framesize-StackSmall)(SP), AX
		//	CMPL AX, stackguard
		p = liblink.Appendp(ctxt, p)

		p.As = ALEAL
		p.From.Type_ = D_INDIR + D_SP
		p.From.Offset = -(int64(framesize) - liblink.StackSmall)
		p.To.Type_ = D_AX

		p = liblink.Appendp(ctxt, p)
		p.As = ACMPL
		p.From.Type_ = D_AX
		p.To.Type_ = D_INDIR + D_CX
		p.To.Offset = 2 * int64(ctxt.Arch.Ptrsize) // G.stackguard0
		if ctxt.Cursym.Cfunc != 0 {
			p.To.Offset = 3 * int64(ctxt.Arch.Ptrsize) // G.stackguard1
		}
	} else {

		// Such a large stack we need to protect against wraparound
		// if SP is close to zero.
		//	SP-stackguard+StackGuard <= framesize + (StackGuard-StackSmall)
		// The +StackGuard on both sides is required to keep the left side positive:
		// SP is allowed to be slightly below stackguard. See stack.h.
		//
		// Preemption sets stackguard to StackPreempt, a very large value.
		// That breaks the math above, so we have to check for that explicitly.
		//	MOVL	stackguard, CX
		//	CMPL	CX, $StackPreempt
		//	JEQ	label-of-call-to-morestack
		//	LEAL	StackGuard(SP), AX
		//	SUBL	stackguard, AX
		//	CMPL	AX, $(framesize+(StackGuard-StackSmall))
		p = liblink.Appendp(ctxt, p)

		p.As = AMOVL
		p.From.Type_ = D_INDIR + D_CX
		p.From.Offset = 0
		p.From.Offset = 2 * int64(ctxt.Arch.Ptrsize) // G.stackguard0
		if ctxt.Cursym.Cfunc != 0 {
			p.From.Offset = 3 * int64(ctxt.Arch.Ptrsize) // G.stackguard1
		}
		p.To.Type_ = D_SI

//.........这里部分代码省略.........

func addstacksplit(ctxt *liblink.Link, cursym *liblink.LSym) {
	var p *liblink.Prog
	var q *liblink.Prog
	var p1 *liblink.Prog
	var p2 *liblink.Prog
	var autoffset int32
	var deltasp int32
	var a int

	if ctxt.Symmorestack[0] == nil {
		ctxt.Symmorestack[0] = liblink.Linklookup(ctxt, "runtime.morestack", 0)
		ctxt.Symmorestack[1] = liblink.Linklookup(ctxt, "runtime.morestack_noctxt", 0)
	}

	if ctxt.Headtype == liblink.Hplan9 && ctxt.Plan9privates == nil {
		ctxt.Plan9privates = liblink.Linklookup(ctxt, "_privates", 0)
	}

	ctxt.Cursym = cursym

	if cursym.Text == nil || cursym.Text.Link == nil {
		return
	}

	p = cursym.Text
	autoffset = int32(p.To.Offset)
	if autoffset < 0 {
		autoffset = 0
	}

	cursym.Locals = autoffset
	cursym.Args = p.To.Offset2

	q = nil

	if !(p.From.Scale&liblink.NOSPLIT != 0) || (p.From.Scale&liblink.WRAPPER != 0) {
		p = liblink.Appendp(ctxt, p)
		p = load_g_cx(ctxt, p) // load g into CX
	}

	if !(cursym.Text.From.Scale&liblink.NOSPLIT != 0) {
		p = stacksplit(ctxt, p, autoffset, bool2int(!(cursym.Text.From.Scale&liblink.NEEDCTXT != 0)), &q) // emit split check
	}

	if autoffset != 0 {

		p = liblink.Appendp(ctxt, p)
		p.As = AADJSP
		p.From.Type_ = D_CONST
		p.From.Offset = int64(autoffset)
		p.Spadj = autoffset
	} else {

		// zero-byte stack adjustment.
		// Insert a fake non-zero adjustment so that stkcheck can
		// recognize the end of the stack-splitting prolog.
		p = liblink.Appendp(ctxt, p)

		p.As = ANOP
		p.Spadj = int32(-ctxt.Arch.Ptrsize)
		p = liblink.Appendp(ctxt, p)
		p.As = ANOP
		p.Spadj = int32(ctxt.Arch.Ptrsize)
	}

	if q != nil {
		q.Pcond = p
	}
	deltasp = autoffset

	if cursym.Text.From.Scale&liblink.WRAPPER != 0 {
		// if(g->panic != nil && g->panic->argp == FP) g->panic->argp = bottom-of-frame
		//
		//	MOVL g_panic(CX), BX
		//	TESTL BX, BX
		//	JEQ end
		//	LEAL (autoffset+4)(SP), DI
		//	CMPL panic_argp(BX), DI
		//	JNE end
		//	MOVL SP, panic_argp(BX)
		// end:
		//	NOP
		//
		// The NOP is needed to give the jumps somewhere to land.
		// It is a liblink NOP, not an x86 NOP: it encodes to 0 instruction bytes.

		p = liblink.Appendp(ctxt, p)

		p.As = AMOVL
		p.From.Type_ = D_INDIR + D_CX
		p.From.Offset = 4 * int64(ctxt.Arch.Ptrsize) // G.panic
		p.To.Type_ = D_BX

		p = liblink.Appendp(ctxt, p)
		p.As = ATESTL
		p.From.Type_ = D_BX
		p.To.Type_ = D_BX

		p = liblink.Appendp(ctxt, p)
		p.As = AJEQ
//.........这里部分代码省略.........

func progedit(ctxt *liblink.Link, p *liblink.Prog) {
	var literal string
	var s *liblink.LSym
	var q *liblink.Prog

	// Thread-local storage references use the TLS pseudo-register.
	// As a register, TLS refers to the thread-local storage base, and it
	// can only be loaded into another register:
	//
	//         MOVQ TLS, AX
	//
	// An offset from the thread-local storage base is written off(reg)(TLS*1).
	// Semantically it is off(reg), but the (TLS*1) annotation marks this as
	// indexing from the loaded TLS base. This emits a relocation so that
	// if the linker needs to adjust the offset, it can. For example:
	//
	//         MOVQ TLS, AX
	//         MOVQ 8(AX)(TLS*1), CX // load m into CX
	//
	// On systems that support direct access to the TLS memory, this
	// pair of instructions can be reduced to a direct TLS memory reference:
	//
	//         MOVQ 8(TLS), CX // load m into CX
	//
	// The 2-instruction and 1-instruction forms correspond roughly to
	// ELF TLS initial exec mode and ELF TLS local exec mode, respectively.
	//
	// We applies this rewrite on systems that support the 1-instruction form.
	// The decision is made using only the operating system (and probably
	// the -shared flag, eventually), not the link mode. If some link modes
	// on a particular operating system require the 2-instruction form,
	// then all builds for that operating system will use the 2-instruction
	// form, so that the link mode decision can be delayed to link time.
	//
	// In this way, all supported systems use identical instructions to
	// access TLS, and they are rewritten appropriately first here in
	// liblink and then finally using relocations in the linker.

	if canuselocaltls(ctxt) != 0 {

		// Reduce TLS initial exec model to TLS local exec model.
		// Sequences like
		//	MOVQ TLS, BX
		//	... off(BX)(TLS*1) ...
		// become
		//	NOP
		//	... off(TLS) ...
		//
		// TODO(rsc): Remove the Hsolaris special case. It exists only to
		// guarantee we are producing byte-identical binaries as before this code.
		// But it should be unnecessary.
		if (p.As == AMOVQ || p.As == AMOVL) && p.From.Type_ == D_TLS && D_AX <= p.To.Type_ && p.To.Type_ <= D_R15 && ctxt.Headtype != liblink.Hsolaris {

			nopout(p)
		}
		if p.From.Index == D_TLS && D_INDIR+D_AX <= p.From.Type_ && p.From.Type_ <= D_INDIR+D_R15 {
			p.From.Type_ = D_INDIR + D_TLS
			p.From.Scale = 0
			p.From.Index = D_NONE
		}

		if p.To.Index == D_TLS && D_INDIR+D_AX <= p.To.Type_ && p.To.Type_ <= D_INDIR+D_R15 {
			p.To.Type_ = D_INDIR + D_TLS
			p.To.Scale = 0
			p.To.Index = D_NONE
		}
	} else {

		// As a courtesy to the C compilers, rewrite TLS local exec load as TLS initial exec load.
		// The instruction
		//	MOVQ off(TLS), BX
		// becomes the sequence
		//	MOVQ TLS, BX
		//	MOVQ off(BX)(TLS*1), BX
		// This allows the C compilers to emit references to m and g using the direct off(TLS) form.
		if (p.As == AMOVQ || p.As == AMOVL) && p.From.Type_ == D_INDIR+D_TLS && D_AX <= p.To.Type_ && p.To.Type_ <= D_R15 {

			q = liblink.Appendp(ctxt, p)
			q.As = p.As
			q.From = p.From
			q.From.Type_ = D_INDIR + p.To.Type_
			q.From.Index = D_TLS
			q.From.Scale = 2 // TODO: use 1
			q.To = p.To
			p.From.Type_ = D_TLS
			p.From.Index = D_NONE
			p.From.Offset = 0
		}
	}

	// TODO: Remove.
	if ctxt.Headtype == liblink.Hwindows || ctxt.Headtype == liblink.Hplan9 {

		if p.From.Scale == 1 && p.From.Index == D_TLS {
			p.From.Scale = 2
		}
		if p.To.Scale == 1 && p.To.Index == D_TLS {
			p.To.Scale = 2
		}
	}
//.........这里部分代码省略.........