github.com/rohankumardubey/syslog-redirector-golang@v0.0.0-20140320174030-4859f03d829a/src/cmd/6l/pass.c

// Inferno utils/6l/pass.c
// http://code.google.com/p/inferno-os/source/browse/utils/6l/pass.c
//
//	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.

// Code and data passes.

#include	"l.h"
#include	"../ld/lib.h"
#include "../../pkg/runtime/stack.h"

static void xfol(Prog*, Prog**);

Prog*
brchain(Prog *p)
{
	int i;

	for(i=0; i<20; i++) {
		if(p == P || p->as != AJMP)
			return p;
		p = p->pcond;
	}
	return P;
}

void
follow(void)
{
	Prog *firstp, *lastp;

	if(debug['v'])
		Bprint(&bso, "%5.2f follow\n", cputime());
	Bflush(&bso);
	
	for(cursym = textp; cursym != nil; cursym = cursym->next) {
		firstp = prg();
		lastp = firstp;
		xfol(cursym->text, &lastp);
		lastp->link = nil;
		cursym->text = firstp->link;
	}
}

static int
nofollow(int a)
{
	switch(a) {
	case AJMP:
	case ARET:
	case AIRETL:
	case AIRETQ:
	case AIRETW:
	case ARETFL:
	case ARETFQ:
	case ARETFW:
	case AUNDEF:
		return 1;
	}
	return 0;
}

static int
pushpop(int a)
{
	switch(a) {
	case APUSHL:
	case APUSHFL:
	case APUSHQ:
	case APUSHFQ:
	case APUSHW:
	case APUSHFW:
	case APOPL:
	case APOPFL:
	case APOPQ:
	case APOPFQ:
	case APOPW:
	case APOPFW:
		return 1;
	}
	return 0;
}

static void
xfol(Prog *p, Prog **last)
{
	Prog *q;
	int i;
	enum as a;

loop:
	if(p == P)
		return;
	if(p->as == AJMP)
	if((q = p->pcond) != P && 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) {
		/* 
		 * p goes here, but already used it elsewhere.
		 * copy up to 4 instructions or else branch to other copy.
		 */
		for(i=0,q=p; i<4; i++,q=q->link) {
			if(q == P)
				break;
			if(q == *last)
				break;
			a = q->as;
			if(a == ANOP) {
				i--;
				continue;
			}
			if(nofollow(a) || pushpop(a))	
				break;	// NOTE(rsc): arm does goto copy
			if(q->pcond == P || q->pcond->mark)
				continue;
			if(a == ACALL || a == ALOOP)
				continue;
			for(;;) {
				if(p->as == ANOP) {
					p = p->link;
					continue;
				}
				q = copyp(p);
				p = p->link;
				q->mark = 1;
				(*last)->link = q;
				*last = q;
				if(q->as != a || q->pcond == P || q->pcond->mark)
					continue;

				q->as = relinv(q->as);
				p = q->pcond;
				q->pcond = q->link;
				q->link = p;
				xfol(q->link, last);
				p = q->link;
				if(p->mark)
					return;
				goto loop;
			}
		} /* */
		q = prg();
		q->as = AJMP;
		q->line = p->line;
		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 = p->as;

	/* continue loop with what comes after p */
	if(nofollow(a))
		return;
	if(p->pcond != P && a != ACALL) {
		/*
		 * some kind of conditional branch.
		 * recurse to follow one path.
		 * continue loop on the other.
		 */
		if((q = brchain(p->pcond)) != P)
			p->pcond = q;
		if((q = brchain(p->link)) != P)
			p->link = q;
		if(p->from.type == D_CONST) {
			if(p->from.offset == 1) {
				/*
				 * expect conditional jump to be taken.
				 * rewrite so that's the fall-through case.
				 */
				p->as = relinv(a);
				q = p->link;
				p->link = p->pcond;
				p->pcond = q;
			}
		} else {			
			q = p->link;
			if(q->mark)
			if(a != ALOOP) {
				p->as = relinv(a);
				p->link = p->pcond;
				p->pcond = q;
			}
		}
		xfol(p->link, last);
		if(p->pcond->mark)
			return;
		p = p->pcond;
		goto loop;
	}
	p = p->link;
	goto loop;
}

Prog*
byteq(int v)
{
	Prog *p;

	p = prg();
	p->as = ABYTE;
	p->from.type = D_CONST;
	p->from.offset = v&0xff;
	return p;
}

int
relinv(int a)
{

	switch(a) {
	case AJEQ:	return AJNE;
	case AJNE:	return AJEQ;
	case AJLE:	return AJGT;
	case AJLS:	return AJHI;
	case AJLT:	return AJGE;
	case AJMI:	return AJPL;
	case AJGE:	return AJLT;
	case AJPL:	return AJMI;
	case AJGT:	return AJLE;
	case AJHI:	return AJLS;
	case AJCS:	return AJCC;
	case AJCC:	return AJCS;
	case AJPS:	return AJPC;
	case AJPC:	return AJPS;
	case AJOS:	return AJOC;
	case AJOC:	return AJOS;
	}
	diag("unknown relation: %s in %s", anames[a], TNAME);
	errorexit();
	return a;
}

void
patch(void)
{
	int32 c;
	Prog *p, *q;
	Sym *s;
	int32 vexit;
	Sym *gmsym;

	if(debug['v'])
		Bprint(&bso, "%5.2f mkfwd\n", cputime());
	Bflush(&bso);
	mkfwd();
	if(debug['v'])
		Bprint(&bso, "%5.2f patch\n", cputime());
	Bflush(&bso);

	if(flag_shared) {
		s = lookup("init_array", 0);
		s->type = SINITARR;
		s->reachable = 1;
		s->hide = 1;
		addaddr(s, lookup(INITENTRY, 0));
	}

	gmsym = lookup("runtime.tlsgm", 0);
	if(linkmode != LinkExternal)
		gmsym->reachable = 0;
	s = lookup("exit", 0);
	vexit = s->value;
	for(cursym = textp; cursym != nil; cursym = cursym->next)
	for(p = cursym->text; p != P; p = p->link) {
		if(HEADTYPE == Hwindows) { 
			// Windows
			// Convert
			//   op	  n(GS), reg
			// to
			//   MOVL 0x28(GS), reg
			//   op	  n(reg), reg
			// The purpose of this patch is to fix some accesses
			// to extern register variables (TLS) on Windows, as
			// a different method is used to access them.
			if(p->from.type == D_INDIR+D_GS
			&& p->to.type >= D_AX && p->to.type <= D_DI 
			&& p->from.offset <= 8) {
				q = appendp(p);
				q->from = p->from;
				q->from.type = D_INDIR + p->to.type;
				q->to = p->to;
				q->as = p->as;
				p->as = AMOVQ;
				p->from.type = D_INDIR+D_GS;
				p->from.offset = 0x28;
			}
		}
		if(HEADTYPE == Hlinux || HEADTYPE == Hfreebsd
		|| HEADTYPE == Hopenbsd || HEADTYPE == Hnetbsd
		|| HEADTYPE == Hplan9x64 || HEADTYPE == Hdragonfly) {
			// ELF uses FS instead of GS.
			if(p->from.type == D_INDIR+D_GS)
				p->from.type = D_INDIR+D_FS;
			if(p->to.type == D_INDIR+D_GS)
				p->to.type = D_INDIR+D_FS;
			if(p->from.index == D_GS)
				p->from.index = D_FS;
			if(p->to.index == D_GS)
				p->to.index = D_FS;
		}
		if(!flag_shared) {
			// Convert g() or m() accesses of the form
			//   op n(reg)(GS*1), reg
			// to
			//   op n(GS*1), reg
			if(p->from.index == D_FS || p->from.index == D_GS) {
				p->from.type = D_INDIR + p->from.index;
				p->from.index = D_NONE;
			}
			// Convert g() or m() accesses of the form
			//   op reg, n(reg)(GS*1)
			// to
			//   op reg, n(GS*1)
			if(p->to.index == D_FS || p->to.index == D_GS) {
				p->to.type = D_INDIR + p->to.index;
				p->to.index = D_NONE;
			}
			// Convert get_tls access of the form
			//   op runtime.tlsgm(SB), reg
			// to
			//   NOP
			if(gmsym != S && p->from.sym == gmsym) {
				p->as = ANOP;
				p->from.type = D_NONE;
				p->to.type = D_NONE;
				p->from.sym = nil;
				p->to.sym = nil;
				continue;
			}
		} else {
			// Convert TLS reads of the form
			//   op n(GS), reg
			// to
			//   MOVQ $runtime.tlsgm(SB), reg
			//   op n(reg)(GS*1), reg
			if((p->from.type == D_INDIR+D_FS || p->from.type == D_INDIR + D_GS) && p->to.type >= D_AX && p->to.type <= D_DI) {
				q = appendp(p);
				q->to = p->to;
				q->as = p->as;
				q->from.type = D_INDIR+p->to.type;
				q->from.index = p->from.type - D_INDIR;
				q->from.scale = 1;
				q->from.offset = p->from.offset;
				p->as = AMOVQ;
				p->from.type = D_EXTERN;
				p->from.sym = gmsym;
				p->from.offset = 0;
			}
		}
		if(p->as == ACALL || (p->as == AJMP && p->to.type != D_BRANCH) || (p->as == ARET && p->to.sym != nil)) {
			s = p->to.sym;
			if(s) {
				if(debug['c'])
					Bprint(&bso, "%s calls %s\n", TNAME, s->name);
				if((s->type&SMASK) != STEXT) {
					/* diag prints TNAME first */
					diag("undefined: %s", s->name);
					s->type = STEXT;
					s->value = vexit;
					continue;	// avoid more error messages
				}
				if(s->text == nil)
					continue;
				p->to.type = D_BRANCH;
				p->to.offset = s->text->pc;
				p->pcond = s->text;
				continue;
			}
		}
		if(p->to.type != D_BRANCH)
			continue;
		c = p->to.offset;
		for(q = cursym->text; q != P;) {
			if(c == q->pc)
				break;
			if(q->forwd != P && c >= q->forwd->pc)
				q = q->forwd;
			else
				q = q->link;
		}
		if(q == P) {
			diag("branch out of range in %s (%#ux)\n%P [%s]",
				TNAME, c, p, p->to.sym ? p->to.sym->name : "<nil>");
			p->to.type = D_NONE;
		}
		p->pcond = q;
	}

	for(cursym = textp; cursym != nil; cursym = cursym->next)
	for(p = cursym->text; p != P; p = p->link) {
		p->mark = 0;	/* initialization for follow */
		if(p->pcond != P) {
			p->pcond = brloop(p->pcond);
			if(p->pcond != P)
			if(p->to.type == D_BRANCH)
				p->to.offset = p->pcond->pc;
		}
	}
}

Prog*
brloop(Prog *p)
{
	int c;
	Prog *q;

	c = 0;
	for(q = p; q != P; q = q->pcond) {
		if(q->as != AJMP)
			break;
		c++;
		if(c >= 5000)
			return P;
	}
	return q;
}

static char*
morename[] =
{
	"runtime.morestack00",
	"runtime.morestack10",
	"runtime.morestack01",
	"runtime.morestack11",

	"runtime.morestack8",
	"runtime.morestack16",
	"runtime.morestack24",
	"runtime.morestack32",
	"runtime.morestack40",
	"runtime.morestack48",
};
Prog*	pmorestack[nelem(morename)];
Sym*	symmorestack[nelem(morename)];
Sym*	gmsym;

static Prog*	load_g_cx(Prog*);
static Prog*	stacksplit(Prog*, int32, Prog**);

void
dostkoff(void)
{
	Prog *p, *q, *q1;
	int32 autoffset, deltasp;
	int a, pcsize;
	uint32 i;

	gmsym = lookup("runtime.tlsgm", 0);
	for(i=0; i<nelem(morename); i++) {
		symmorestack[i] = lookup(morename[i], 0);
		if(symmorestack[i]->type != STEXT)
			diag("morestack trampoline not defined - %s", morename[i]);
		pmorestack[i] = symmorestack[i]->text;
	}

	for(cursym = textp; cursym != nil; cursym = cursym->next) {
		if(cursym->text == nil || cursym->text->link == nil)
			continue;				

		p = cursym->text;
		parsetextconst(p->to.offset);
		autoffset = textstksiz;
		if(autoffset < 0)
			autoffset = 0;

		if(autoffset < StackSmall && !(p->from.scale & NOSPLIT)) {
			for(q = p; q != P; q = q->link)
				if(q->as == ACALL)
					goto noleaf;
			p->from.scale |= NOSPLIT;
		noleaf:;
		}

		if((p->from.scale & NOSPLIT) && autoffset >= StackSmall)
			diag("nosplit func likely to overflow stack");

		q = P;
		if(!(p->from.scale & NOSPLIT) || (p->from.scale & WRAPPER)) {
			p = appendp(p);
			p = load_g_cx(p); // load g into CX
		}
		if(!(cursym->text->from.scale & NOSPLIT))
			p = stacksplit(p, autoffset, &q); // emit split check

		if(autoffset) {
			p = appendp(p);
			p->as = AADJSP;
			p->from.type = 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 = appendp(p);
			p->as = ANOP;
			p->spadj = -PtrSize;
			p = appendp(p);
			p->as = ANOP;
			p->spadj = PtrSize;
		}
		if(q != P)
			q->pcond = p;
		deltasp = autoffset;
		
		if(cursym->text->from.scale & WRAPPER) {
			// g->panicwrap += autoffset + PtrSize;
			p = appendp(p);
			p->as = AADDL;
			p->from.type = D_CONST;
			p->from.offset = autoffset + PtrSize;
			p->to.type = D_INDIR+D_CX;
			p->to.offset = 2*PtrSize;
		}

		if(debug['K'] > 1 && autoffset) {
			// 6l -KK means double-check for stack overflow
			// even after calling morestack and even if the
			// function is marked as nosplit.
			p = appendp(p);
			p->as = AMOVQ;
			p->from.type = D_INDIR+D_CX;
			p->from.offset = 0;
			p->to.type = D_BX;

			p = appendp(p);
			p->as = ASUBQ;
			p->from.type = D_CONST;
			p->from.offset = StackSmall+32;
			p->to.type = D_BX;

			p = appendp(p);
			p->as = ACMPQ;
			p->from.type = D_SP;
			p->to.type = D_BX;

			p = appendp(p);
			p->as = AJHI;
			p->to.type = D_BRANCH;
			q1 = p;

			p = appendp(p);
			p->as = AINT;
			p->from.type = D_CONST;
			p->from.offset = 3;

			p = appendp(p);
			p->as = ANOP;
			q1->pcond = p;
		}
		
		if(debug['Z'] && autoffset && !(cursym->text->from.scale&NOSPLIT)) {
			// 6l -Z means zero the stack frame on entry.
			// This slows down function calls but can help avoid
			// false positives in garbage collection.
			p = appendp(p);
			p->as = AMOVQ;
			p->from.type = D_SP;
			p->to.type = D_DI;
			
			p = appendp(p);
			p->as = AMOVQ;
			p->from.type = D_CONST;
			p->from.offset = autoffset/8;
			p->to.type = D_CX;
			
			p = appendp(p);
			p->as = AMOVQ;
			p->from.type = D_CONST;
			p->from.offset = 0;
			p->to.type = D_AX;
			
			p = appendp(p);
			p->as = AREP;
			
			p = appendp(p);
			p->as = ASTOSQ;
		}
		
		for(; p != P; p = p->link) {
			pcsize = p->mode/8;
			a = p->from.type;
			if(a == D_AUTO)
				p->from.offset += deltasp;
			if(a == D_PARAM)
				p->from.offset += deltasp + pcsize;
			a = p->to.type;
			if(a == D_AUTO)
				p->to.offset += deltasp;
			if(a == D_PARAM)
				p->to.offset += deltasp + pcsize;
	
			switch(p->as) {
			default:
				continue;
			case APUSHL:
			case APUSHFL:
				deltasp += 4;
				p->spadj = 4;
				continue;
			case APUSHQ:
			case APUSHFQ:
				deltasp += 8;
				p->spadj = 8;
				continue;
			case APUSHW:
			case APUSHFW:
				deltasp += 2;
				p->spadj = 2;
				continue;
			case APOPL:
			case APOPFL:
				deltasp -= 4;
				p->spadj = -4;
				continue;
			case APOPQ:
			case APOPFQ:
				deltasp -= 8;
				p->spadj = -8;
				continue;
			case APOPW:
			case APOPFW:
				deltasp -= 2;
				p->spadj = -2;
				continue;
			case ARET:
				break;
			}
	
			if(autoffset != deltasp)
				diag("unbalanced PUSH/POP");

			if(cursym->text->from.scale & WRAPPER) {
				p = load_g_cx(p);
				p = appendp(p);
				// g->panicwrap -= autoffset + PtrSize;
				p->as = ASUBL;
				p->from.type = D_CONST;
				p->from.offset = autoffset + PtrSize;
				p->to.type = D_INDIR+D_CX;
				p->to.offset = 2*PtrSize;
				p = appendp(p);
				p->as = ARET;
			}
	
			if(autoffset) {
				p->as = AADJSP;
				p->from.type = D_CONST;
				p->from.offset = -autoffset;
				p->spadj = -autoffset;
				p = appendp(p);
				p->as = ARET;
				// If there are instructions following
				// this ARET, they come from a branch
				// with the same stackframe, so undo
				// the cleanup.
				p->spadj = +autoffset;
			}
			if(p->to.sym) // retjmp
				p->as = AJMP;
		}
	}
}

// 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.
static Prog*
load_g_cx(Prog *p)
{
	if(flag_shared) {
		// Load TLS offset with MOVQ $runtime.tlsgm(SB), CX
		p->as = AMOVQ;
		p->from.type = D_EXTERN;
		p->from.sym = gmsym;
		p->to.type = D_CX;
		p = appendp(p);
	}
	p->as = AMOVQ;
	if(HEADTYPE == Hlinux || HEADTYPE == Hfreebsd
	|| HEADTYPE == Hopenbsd || HEADTYPE == Hnetbsd
	|| HEADTYPE == Hplan9x64 || HEADTYPE == Hdragonfly)
		// ELF uses FS
		p->from.type = D_INDIR+D_FS;
	else
		p->from.type = D_INDIR+D_GS;
	if(flag_shared) {
		// Add TLS offset stored in CX
		p->from.index = p->from.type - D_INDIR;
		p->from.type = D_INDIR + D_CX;
	}
	p->from.offset = tlsoffset+0;
	p->to.type = D_CX;
	if(HEADTYPE == Hwindows) {
		// movq %gs:0x28, %rcx
		// movq (%rcx), %rcx
		p->as = AMOVQ;
		p->from.type = D_INDIR+D_GS;
		p->from.offset = 0x28;
		p->to.type = D_CX;

		p = appendp(p);
		p->as = AMOVQ;
		p->from.type = D_INDIR+D_CX;
		p->from.offset = 0;
		p->to.type = D_CX;
	}
	return p;
}

// 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.
static Prog*
stacksplit(Prog *p, int32 framesize, Prog **jmpok)
{
	Prog *q, *q1;
	uint32 moreconst1, moreconst2, i;

	if(debug['K']) {
		// 6l -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 = appendp(p);
		p->as = ACMPQ;
		p->from.type = D_INDIR+D_CX;
		p->from.offset = 8;
		p->to.type = D_SP;

		p = appendp(p);
		p->as = AJHI;
		p->to.type = D_BRANCH;
		p->to.offset = 4;
		q1 = p;

		p = appendp(p);
		p->as = AINT;
		p->from.type = D_CONST;
		p->from.offset = 3;

		p = appendp(p);
		p->as = ANOP;
		q1->pcond = p;
	}

	q = P;
	q1 = P;
	if(framesize <= StackSmall) {
		// small stack: SP <= stackguard
		//	CMPQ SP, stackguard
		p = appendp(p);
		p->as = ACMPQ;
		p->from.type = D_SP;
		p->to.type = D_INDIR+D_CX;
	} else if(framesize <= StackBig) {
		// large stack: SP-framesize <= stackguard-StackSmall
		//	LEAQ -xxx(SP), AX
		//	CMPQ AX, stackguard
		p = appendp(p);
		p->as = ALEAQ;
		p->from.type = D_INDIR+D_SP;
		p->from.offset = -(framesize-StackSmall);
		p->to.type = D_AX;

		p = appendp(p);
		p->as = ACMPQ;
		p->from.type = D_AX;
		p->to.type = 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.
		//	MOVQ	stackguard, CX
		//	CMPQ	CX, $StackPreempt
		//	JEQ	label-of-call-to-morestack
		//	LEAQ	StackGuard(SP), AX
		//	SUBQ	CX, AX
		//	CMPQ	AX, $(framesize+(StackGuard-StackSmall))

		p = appendp(p);
		p->as = AMOVQ;
		p->from.type = D_INDIR+D_CX;
		p->from.offset = 0;
		p->to.type = D_SI;

		p = appendp(p);
		p->as = ACMPQ;
		p->from.type = D_SI;
		p->to.type = D_CONST;
		p->to.offset = StackPreempt;

		p = appendp(p);
		p->as = AJEQ;
		p->to.type = D_BRANCH;
		q1 = p;

		p = appendp(p);
		p->as = ALEAQ;
		p->from.type = D_INDIR+D_SP;
		p->from.offset = StackGuard;
		p->to.type = D_AX;
		
		p = appendp(p);
		p->as = ASUBQ;
		p->from.type = D_SI;
		p->to.type = D_AX;
		
		p = appendp(p);
		p->as = ACMPQ;
		p->from.type = D_AX;
		p->to.type = D_CONST;
		p->to.offset = framesize+(StackGuard-StackSmall);
	}					

	// common
	p = appendp(p);
	p->as = AJHI;
	p->to.type = D_BRANCH;
	q = p;

	// If we ask for more stack, we'll get a minimum of StackMin bytes.
	// We need a stack frame large enough to hold the top-of-stack data,
	// the function arguments+results, our caller's PC, our frame,
	// a word for the return PC of the next call, and then the StackLimit bytes
	// that must be available on entry to any function called from a function
	// that did a stack check.  If StackMin is enough, don't ask for a specific
	// amount: then we can use the custom functions and save a few
	// instructions.
	moreconst1 = 0;
	if(StackTop + textarg + PtrSize + framesize + PtrSize + StackLimit >= StackMin)
		moreconst1 = framesize;
	moreconst2 = textarg;
	if(moreconst2 == 1) // special marker
		moreconst2 = 0;
	if((moreconst2&7) != 0)
		diag("misaligned argument size in stack split");
	// 4 varieties varieties (const1==0 cross const2==0)
	// and 6 subvarieties of (const1==0 and const2!=0)
	p = appendp(p);
	if(moreconst1 == 0 && moreconst2 == 0) {
		p->as = ACALL;
		p->to.type = D_BRANCH;
		p->pcond = pmorestack[0];
		p->to.sym = symmorestack[0];
	} else
	if(moreconst1 != 0 && moreconst2 == 0) {
		p->as = AMOVL;
		p->from.type = D_CONST;
		p->from.offset = moreconst1;
		p->to.type = D_AX;

		p = appendp(p);
		p->as = ACALL;
		p->to.type = D_BRANCH;
		p->pcond = pmorestack[1];
		p->to.sym = symmorestack[1];
	} else
	if(moreconst1 == 0 && moreconst2 <= 48 && moreconst2%8 == 0) {
		i = moreconst2/8 + 3;
		p->as = ACALL;
		p->to.type = D_BRANCH;
		p->pcond = pmorestack[i];
		p->to.sym = symmorestack[i];
	} else
	if(moreconst1 == 0 && moreconst2 != 0) {
		p->as = AMOVL;
		p->from.type = D_CONST;
		p->from.offset = moreconst2;
		p->to.type = D_AX;

		p = appendp(p);
		p->as = ACALL;
		p->to.type = D_BRANCH;
		p->pcond = pmorestack[2];
		p->to.sym = symmorestack[2];
	} else {
		p->as = AMOVQ;
		p->from.type = D_CONST;
		p->from.offset = (uint64)moreconst2 << 32;
		p->from.offset |= moreconst1;
		p->to.type = D_AX;

		p = appendp(p);
		p->as = ACALL;
		p->to.type = D_BRANCH;
		p->pcond = pmorestack[3];
		p->to.sym = symmorestack[3];
	}
	
	p = appendp(p);
	p->as = AJMP;
	p->to.type = D_BRANCH;
	p->pcond = cursym->text->link;
	
	if(q != P)
		q->pcond = p->link;
	if(q1 != P)
		q1->pcond = q->link;

	*jmpok = q;
	return p;
}

vlong
atolwhex(char *s)
{
	vlong n;
	int f;

	n = 0;
	f = 0;
	while(*s == ' ' || *s == '\t')
		s++;
	if(*s == '-' || *s == '+') {
		if(*s++ == '-')
			f = 1;
		while(*s == ' ' || *s == '\t')
			s++;
	}
	if(s[0]=='0' && s[1]){
		if(s[1]=='x' || s[1]=='X'){
			s += 2;
			for(;;){
				if(*s >= '0' && *s <= '9')
					n = n*16 + *s++ - '0';
				else if(*s >= 'a' && *s <= 'f')
					n = n*16 + *s++ - 'a' + 10;
				else if(*s >= 'A' && *s <= 'F')
					n = n*16 + *s++ - 'A' + 10;
				else
					break;
			}
		} else
			while(*s >= '0' && *s <= '7')
				n = n*8 + *s++ - '0';
	} else
		while(*s >= '0' && *s <= '9')
			n = n*10 + *s++ - '0';
	if(f)
		n = -n;
	return n;
}