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 = int(rdint(b))
	p.Link = rdprog(b)
	p.As = int(rdint(b))
	p.Reg = int(rdint(b))
	p.Scond = int(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.Typ = D_INDIR + D_TLS
	p.From.Offset = 0
	p.To.Typ = 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 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) {
		// 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.Typ == D_TLS && D_AX <= p.To.Typ && p.To.Typ <= D_R15 && ctxt.Headtype != liblink.Hsolaris {
			nopout(p)
		}
		if p.From.Index == D_TLS && D_INDIR+D_AX <= p.From.Typ && p.From.Typ <= D_INDIR+D_R15 {
			p.From.Typ = 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.Typ && p.To.Typ <= D_INDIR+D_R15 {
			p.To.Typ = 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.Typ == D_INDIR+D_TLS && D_AX <= p.To.Typ && p.To.Typ <= D_R15 {
			q = liblink.Appendp(ctxt, p)
			q.As = p.As
			q.From = p.From
			q.From.Typ = D_INDIR + p.To.Typ
			q.From.Index = D_TLS
			q.From.Scale = 2 // TODO: use 1
			q.To = p.To
			p.From.Typ = 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
		}
	}
	if ctxt.Headtype == liblink.Hnacl {
		nacladdr(ctxt, p, &p.From)
		nacladdr(ctxt, p, &p.To)
	}
	// Maintain information about code generation mode.
	if ctxt.Mode == 0 {
		ctxt.Mode = 64
	}
	p.Mode = ctxt.Mode
//.........这里部分代码省略.........

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

func addstacksplit(ctxt *liblink.Link, cursym *liblink.LSym) {
	var p *liblink.Prog
	var q *liblink.Prog
	var q1 *liblink.Prog
	var autoffset int64
	var deltasp int64
	var a int
	var pcsize int
	var i uint32
	var textstksiz int64
	var textarg int64
	if ctxt.Tlsg == nil {
		ctxt.Tlsg = liblink.Linklookup(ctxt, "runtime.tlsg", 0)
	}
	if ctxt.Symmorestack[0] == nil {
		if len(morename) > len(ctxt.Symmorestack) {
			log.Fatalf("Link.symmorestack needs at least %d elements", len(morename))
		}
		for i = 0; i < uint32(len(morename)); i++ {
			ctxt.Symmorestack[i] = liblink.Linklookup(ctxt, morename[i], 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
	parsetextconst(p.To.Offset, &textstksiz, &textarg)
	autoffset = textstksiz
	if autoffset < 0 {
		autoffset = 0
	}
	cursym.Args = int(p.To.Offset >> 32)
	cursym.Locals = textstksiz
	if autoffset < liblink.StackSmall && p.From.Scale&liblink.NOSPLIT == 0 {
		for q = p; q != nil; q = q.Link {
			if q.As == ACALL {
				goto noleaf
			}
			if (q.As == ADUFFCOPY || q.As == ADUFFZERO) && autoffset >= liblink.StackSmall-8 {
				goto noleaf
			}
		}
		p.From.Scale |= liblink.NOSPLIT
	noleaf:
	}
	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, textarg, bool2int(cursym.Text.From.Scale&liblink.NEEDCTXT == 0), &q) // emit split check
	}
	if autoffset != 0 {
		if autoffset%int64(ctxt.Arch.Regsize) != 0 {
			ctxt.Diag("unaligned stack size %d", autoffset)
		}
		p = liblink.Appendp(ctxt, p)
		p.As = AADJSP
		p.From.Typ = D_CONST
		p.From.Offset = 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 = -ctxt.Arch.Ptrsize
		p = liblink.Appendp(ctxt, p)
		p.As = ANOP
		p.Spadj = ctxt.Arch.Ptrsize
	}
	if q != nil {
		q.Pcond = p
	}
	deltasp = autoffset
	if cursym.Text.From.Scale&liblink.WRAPPER != 0 {
		// g->panicwrap += autoffset + ctxt->arch->regsize;
		p = liblink.Appendp(ctxt, p)
		p.As = AADDL
		p.From.Typ = D_CONST
		p.From.Offset = autoffset + int64(ctxt.Arch.Regsize)
		indir_cx(ctxt, &p.To)
		p.To.Offset = 2 * ctxt.Arch.Ptrsize
	}
	if ctxt.Debugstack > 1 && autoffset != 0 {
		// 6l -K -K means double-check for stack overflow
		// even after calling morestack and even if the
		// function is marked as nosplit.
		p = liblink.Appendp(ctxt, p)
		p.As = AMOVQ
		indir_cx(ctxt, &p.From)
		p.From.Offset = 0
		p.To.Typ = D_BX
		p = liblink.Appendp(ctxt, p)
//.........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 = 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 = 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.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.Prg()
		q.As = a
		q.Lineno = p.Lineno
		q.To.Typ = 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 {
			q = liblink.Brchain(ctxt, p.Link)
			if a != ATEXT && a != ABCASE {
				if q != nil && (q.Mark&FOLL != 0) {
					p.As = relinv(a)
					p.Link = p.Pcond
					p.Pcond = q
				}
			}
//.........这里部分代码省略.........

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.Typ == D_OREG && (p.To.Name == D_EXTERN || p.To.Name == D_STATIC) && p.To.Sym != nil {
			p.To.Typ = D_BRANCH
		}
		break
	}
	// Replace TLS register fetches on older ARM procesors.
	switch p.As {
	// If the instruction matches MRC 15, 0, <reg>, C13, C0, 3, replace it.
	case AMRC:
		if ctxt.Goarm < 7 && p.To.Offset&0xffff0fff == 0xee1d0f70 {
			tlsfallback = liblink.Linklookup(ctxt, "runtime.read_tls_fallback", 0)
			// BL runtime.read_tls_fallback(SB)
			p.As = ABL
			p.To.Typ = D_BRANCH
			p.To.Sym = tlsfallback
			p.To.Offset = 0
		} else {
			// 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.Typ == 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("$f32.%08x", i32)
			s = liblink.Linklookup(ctxt, literal, 0)
			if s.Typ == 0 {
				s.Typ = liblink.SRODATA
				liblink.Adduint32(ctxt, s, i32)
				s.Reachable = 0
			}
			p.From.Typ = D_OREG
			p.From.Sym = s
			p.From.Name = D_EXTERN
			p.From.Offset = 0
		}
	case AMOVD:
		if p.From.Typ == D_FCONST && chipfloat5(ctxt, p.From.U.Dval) < 0 && (chipzero5(ctxt, p.From.U.Dval) < 0 || p.Scond&C_SCOND != C_SCOND_NONE) {
			var i64 uint64
			i64 = math.Float64bits(p.From.U.Dval)
			literal = fmt.Sprintf("$f64.%016x", uint64(i64))
			s = liblink.Linklookup(ctxt, literal, 0)
			if s.Typ == 0 {
				s.Typ = liblink.SRODATA
				liblink.Adduint64(ctxt, s, i64)
				s.Reachable = 0
			}
			p.From.Typ = D_OREG
			p.From.Sym = s
			p.From.Name = D_EXTERN
			p.From.Offset = 0
		}
		break
	}
	if ctxt.Flag_shared != 0 {
		// Shared libraries use R_ARM_TLS_IE32 instead of
		// R_ARM_TLS_LE32, replacing the link time constant TLS offset in
		// runtime.tlsg with an address to a GOT entry containing the
		// offset. Rewrite $runtime.tlsg(SB) to runtime.tlsg(SB) to
		// compensate.
		if ctxt.Tlsg == nil {
			ctxt.Tlsg = liblink.Linklookup(ctxt, "runtime.tlsg", 0)
		}
		if p.From.Typ == D_CONST && p.From.Name == D_EXTERN && p.From.Sym == ctxt.Tlsg {
			p.From.Typ = D_OREG
		}
		if p.To.Typ == D_CONST && p.To.Name == D_EXTERN && p.To.Sym == ctxt.Tlsg {
			p.To.Typ = D_OREG
		}
	}
}

func stacksplit(ctxt *liblink.Link, p *liblink.Prog, framesize int64, noctxt int) *liblink.Prog {
	var arg int
	// MOVW			g_stackguard(g), R1
	p = liblink.Appendp(ctxt, p)
	p.As = AMOVW
	p.From.Typ = D_OREG
	p.From.Reg = REGG
	p.To.Typ = D_REG
	p.To.Reg = 1
	if framesize <= liblink.StackSmall {
		// small stack: SP < stackguard
		//	CMP	stackguard, SP
		p = liblink.Appendp(ctxt, p)
		p.As = ACMP
		p.From.Typ = D_REG
		p.From.Reg = 1
		p.Reg = REGSP
	} else if framesize <= liblink.StackBig {
		// large stack: SP-framesize < stackguard-StackSmall
		//	MOVW $-framesize(SP), R2
		//	CMP stackguard, R2
		p = liblink.Appendp(ctxt, p)
		p.As = AMOVW
		p.From.Typ = D_CONST
		p.From.Reg = REGSP
		p.From.Offset = -framesize
		p.To.Typ = D_REG
		p.To.Reg = 2
		p = liblink.Appendp(ctxt, p)
		p.As = ACMP
		p.From.Typ = D_REG
		p.From.Reg = 1
		p.Reg = 2
	} 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.
		//	CMP $StackPreempt, R1
		//	MOVW.NE $StackGuard(SP), R2
		//	SUB.NE R1, R2
		//	MOVW.NE $(framesize+(StackGuard-StackSmall)), R3
		//	CMP.NE R3, R2
		p = liblink.Appendp(ctxt, p)
		p.As = ACMP
		p.From.Typ = D_CONST
		p.From.Offset = int64(uint32(liblink.StackPreempt & 0xFFFFFFFF))
		p.Reg = 1
		p = liblink.Appendp(ctxt, p)
		p.As = AMOVW
		p.From.Typ = D_CONST
		p.From.Reg = REGSP
		p.From.Offset = liblink.StackGuard
		p.To.Typ = D_REG
		p.To.Reg = 2
		p.Scond = C_SCOND_NE
		p = liblink.Appendp(ctxt, p)
		p.As = ASUB
		p.From.Typ = D_REG
		p.From.Reg = 1
		p.To.Typ = D_REG
		p.To.Reg = 2
		p.Scond = C_SCOND_NE
		p = liblink.Appendp(ctxt, p)
		p.As = AMOVW
		p.From.Typ = D_CONST
		p.From.Offset = framesize + (liblink.StackGuard - liblink.StackSmall)
		p.To.Typ = D_REG
		p.To.Reg = 3
		p.Scond = C_SCOND_NE
		p = liblink.Appendp(ctxt, p)
		p.As = ACMP
		p.From.Typ = D_REG
		p.From.Reg = 3
		p.Reg = 2
		p.Scond = C_SCOND_NE
	}
	// MOVW.LS		$framesize, R1
	p = liblink.Appendp(ctxt, p)
	p.As = AMOVW
	p.Scond = C_SCOND_LS
	p.From.Typ = D_CONST
	p.From.Offset = framesize
	p.To.Typ = D_REG
	p.To.Reg = 1
	// MOVW.LS		$args, R2
	p = liblink.Appendp(ctxt, p)
	p.As = AMOVW
	p.Scond = C_SCOND_LS
	p.From.Typ = D_CONST
	arg = ctxt.Cursym.Text.To.Offset2
	if arg == 1 { // special marker for known 0
		arg = 0
	}
	if arg&3 != 0 {
		ctxt.Diag("misaligned argument size in stack split")
	}
	p.From.Offset = int64(arg)
	p.To.Typ = D_REG
//.........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.Typ == D_FREG || p.From.Typ == 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.Prg()
			*next = *p
			// BL _sfloat(SB)
			*p = zprg_obj5
			p.Ctxt = ctxt
			p.Link = next
			p.As = ABL
			p.To.Typ = 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 q *liblink.Prog
	var q1 *liblink.Prog
	var q2 *liblink.Prog
	var o int
	var autosize int64
	var autoffset int64
	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 = 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.Typ = D_CONST
			p.From.Reg = 13
			p.From.Offset = 4
			p.To.Typ = D_REG
			p.To.Reg = 1
			// MOVW $n(R13), R2
			p = liblink.Appendp(ctxt, p)
			p.As = AMOVW
			p.From.Typ = D_CONST
			p.From.Reg = 13
			p.From.Offset = 4 + autoffset
			p.To.Typ = D_REG
			p.To.Reg = 2
			// MOVW $0, R3
			p = liblink.Appendp(ctxt, p)
			p.As = AMOVW
			p.From.Typ = D_CONST
			p.From.Offset = 0
			p.To.Typ = 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.Typ = D_REG
			p.From.Reg = 3
			p.To.Typ = D_OREG
			p.To.Reg = 1
			p.To.Offset = 4
			p.Scond |= C_PBIT
			p = liblink.Appendp(ctxt, p)
			p.As = ACMP
			p.From.Typ = D_REG
			p.From.Reg = 1
			p.Reg = 2
			p = liblink.Appendp(ctxt, p)
			p.As = ABNE
			p.To.Typ = D_BRANCH
			p.Pcond = pl
		}
	}
	/*
	 * find leaf subroutines
	 * strip NOPs
	 * expand RET
	 * expand BECOME pseudo
	 */
	for p = cursym.Text; p != nil; p = p.Link {
		switch p.As {
		case ACASE:
			if ctxt.Flag_shared != 0 {
				linkcase(p)
			}
		case ATEXT:
			p.Mark |= LEAF
		case ARET:
			break
		case ADIV,
			ADIVU,
			AMOD,
			AMODU:
			q = p
			if ctxt.Sym_div == nil {
				initdiv(ctxt)
			}
//.........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) {
		// 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.Typ == D_TLS && D_AX <= p.To.Typ && p.To.Typ <= D_DI {
			p.As = ANOP
			p.From.Typ = D_NONE
			p.To.Typ = D_NONE
		}
		if p.From.Index == D_TLS && D_INDIR+D_AX <= p.From.Typ && p.From.Typ <= D_INDIR+D_DI {
			p.From.Typ = 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.Typ && p.To.Typ <= D_INDIR+D_DI {
			p.To.Typ = 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.Typ == D_INDIR+D_TLS && D_AX <= p.To.Typ && p.To.Typ <= D_DI {
			q = liblink.Appendp(ctxt, p)
			q.As = p.As
			q.From = p.From
			q.From.Typ = D_INDIR + p.To.Typ
			q.From.Index = D_TLS
			q.From.Scale = 2 // TODO: use 1
			q.To = p.To
			p.From.Typ = 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.Typ == D_EXTERN || p.To.Typ == D_STATIC) && p.To.Sym != nil {
			p.To.Typ = D_BRANCH
		}
		break
	}
	// Rewrite float constants to values stored in memory.
	switch p.As {
	case AFMOVF,
		AFADDF,
		AFSUBF,
		AFSUBRF,
		AFMULF,
		AFDIVF,
		AFDIVRF,
		AFCOMF,
		AFCOMFP,
		AMOVSS,
		AADDSS,
		ASUBSS,
		AMULSS,
		ADIVSS,
		ACOMISS,
		AUCOMISS:
		if p.From.Typ == D_FCONST {
			var i32 uint32
			var f32 float32
			f32 = float32(p.From.U.Dval)
			i32 = math.Float32bits(f32)
			literal = fmt.Sprintf("$f32.%08x", uint32(i32))
			s = liblink.Linklookup(ctxt, literal, 0)
			if s.Typ == 0 {
				s.Typ = liblink.SRODATA
				liblink.Adduint32(ctxt, s, i32)
				s.Reachable = 0
			}
			p.From.Typ = D_EXTERN
			p.From.Sym = s
//.........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 = q.As
			if a == ANOP {
				i--
				continue
			}
			if nofollow(a) || 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 q.As != a || q.Pcond == nil || q.Pcond.Mark != 0 {
					continue
				}
				q.As = relinv(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.Prg()
		q.As = AJMP
		q.Lineno = p.Lineno
		q.To.Typ = D_BRANCH
		q.To.Offset = p.Pc
		q.Pcond = p
		p = q
	}
	/* emit p */
	p.Mark = 1
	(*last).Link = p
	*last = p
	a = p.As
	/* continue loop with what comes after p */
	if nofollow(a) {
		return
	}
	if p.Pcond != nil && a != ACALL {
		/*
		 * some kind of conditional branch.
		 * recurse to follow one path.
		 * continue loop on the other.
		 */
		q = liblink.Brchain(ctxt, p.Pcond)
		if q != nil {
			p.Pcond = q
		}
		q = liblink.Brchain(ctxt, p.Link)
//.........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 int64, noctxt int, jmpok **liblink.Prog) *liblink.Prog {
	var q *liblink.Prog
	var q1 *liblink.Prog
	var arg int
	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.Typ = D_INDIR + D_CX
		p.From.Offset = 4
		p.To.Typ = D_SP
		p = liblink.Appendp(ctxt, p)
		p.As = AJCC
		p.To.Typ = D_BRANCH
		p.To.Offset = 4
		q1 = p
		p = liblink.Appendp(ctxt, p)
		p.As = AINT
		p.From.Typ = 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.Typ = D_SP
		p.To.Typ = D_INDIR + D_CX
	} 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.Typ = D_INDIR + D_SP
		p.From.Offset = -(framesize - liblink.StackSmall)
		p.To.Typ = D_AX
		p = liblink.Appendp(ctxt, p)
		p.As = ACMPL
		p.From.Typ = D_AX
		p.To.Typ = D_INDIR + D_CX
	} 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.Typ = D_INDIR + D_CX
		p.From.Offset = 0
		p.To.Typ = D_SI
		p = liblink.Appendp(ctxt, p)
		p.As = ACMPL
		p.From.Typ = D_SI
		p.To.Typ = D_CONST
		p.To.Offset = int64(uint32(liblink.StackPreempt & 0xFFFFFFFF))
		p = liblink.Appendp(ctxt, p)
		p.As = AJEQ
		p.To.Typ = D_BRANCH
		q1 = p
		p = liblink.Appendp(ctxt, p)
		p.As = ALEAL
		p.From.Typ = D_INDIR + D_SP
		p.From.Offset = liblink.StackGuard
		p.To.Typ = D_AX
		p = liblink.Appendp(ctxt, p)
		p.As = ASUBL
		p.From.Typ = D_SI
		p.From.Offset = 0
		p.To.Typ = D_AX
		p = liblink.Appendp(ctxt, p)
		p.As = ACMPL
		p.From.Typ = D_AX
		p.To.Typ = D_CONST
		p.To.Offset = framesize + (liblink.StackGuard - liblink.StackSmall)
	}
//.........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 autoffset int64
	var deltasp int64
	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 = 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.Typ = D_CONST
		p.From.Offset = 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 = -ctxt.Arch.Ptrsize
		p = liblink.Appendp(ctxt, p)
		p.As = ANOP
		p.Spadj = ctxt.Arch.Ptrsize
	}
	if q != nil {
		q.Pcond = p
	}
	deltasp = autoffset
	if cursym.Text.From.Scale&liblink.WRAPPER != 0 {
		// g->panicwrap += autoffset + ctxt->arch->ptrsize;
		p = liblink.Appendp(ctxt, p)
		p.As = AADDL
		p.From.Typ = D_CONST
		p.From.Offset = autoffset + ctxt.Arch.Ptrsize
		p.To.Typ = D_INDIR + D_CX
		p.To.Offset = 2 * ctxt.Arch.Ptrsize
	}
	if ctxt.Debugzerostack != 0 && autoffset != 0 && cursym.Text.From.Scale&liblink.NOSPLIT == 0 {
		// 8l -Z means zero the stack frame on entry.
		// This slows down function calls but can help avoid
		// false positives in garbage collection.
		p = liblink.Appendp(ctxt, p)
		p.As = AMOVL
		p.From.Typ = D_SP
		p.To.Typ = D_DI
		p = liblink.Appendp(ctxt, p)
		p.As = AMOVL
		p.From.Typ = D_CONST
		p.From.Offset = autoffset / 4
		p.To.Typ = D_CX
		p = liblink.Appendp(ctxt, p)
		p.As = AMOVL
		p.From.Typ = D_CONST
		p.From.Offset = 0
		p.To.Typ = D_AX
		p = liblink.Appendp(ctxt, p)
		p.As = AREP
		p = liblink.Appendp(ctxt, p)
		p.As = ASTOSL
	}
	for ; p != nil; p = p.Link {
		a = p.From.Typ
		if a == D_AUTO {
			p.From.Offset += deltasp
		}
		if a == D_PARAM {
			p.From.Offset += deltasp + 4
		}
		a = p.To.Typ
		if a == D_AUTO {
			p.To.Offset += deltasp
		}
		if a == D_PARAM {
			p.To.Offset += deltasp + 4
		}
//.........这里部分代码省略.........