src/cmd/5l/pass.c - go - Git at Google

 // Inferno utils/5l/pass.c
 // http://code.google.com/p/inferno-os/source/browse/utils/5l/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.

 #include	"l.h"

 void
 dodata(void)
 {
 	int i, t;
 	Sym *s;
 	Prog *p;
 	int32 orig, v;

 	if(debug['v'])
 		Bprint(&bso, "%5.2f dodata\n", cputime());
 	Bflush(&bso);
 	for(p = datap; p != P; p = p->link) {
 		s = p->from.sym;
 		if(p->as == ADYNT || p->as == AINIT)
 			s->value = dtype;
 		if(s->type == SBSS)
 			s->type = SDATA;
 		if(s->type != SDATA)
 			diag("initialize non-data (%d): %s\n%P",
 				s->type, s->name, p);
 		v = p->from.offset + p->reg;
 		if(v > s->value)
 			diag("initialize bounds (%ld/%ld): %s\n%P",
 				v, s->value, s->name, p);
 		if((s->type == SBSS || s->type == SDATA) && (p->to.type == D_CONST || p->to.type == D_OCONST) && (p->to.name == D_EXTERN || p->to.name == D_STATIC)){
 			s = p->to.sym;
 			if(s != S && (s->type == STEXT || s->type == SLEAF || s->type == SCONST || s->type == SXREF))
 				s->fnptr = 1;
 		}
 	}

 	if(debug['t']) {
 		/*
 		 * pull out string constants
 		 */
 		for(p = datap; p != P; p = p->link) {
 			s = p->from.sym;
 			if(p->to.type == D_SCONST)
 				s->type = SSTRING;
 		}
 	}

 	/*
 	 * pass 1
 	 *	assign 'small' variables to data segment
 	 *	(rational is that data segment is more easily
 	 *	 addressed through offset on R12)
 	 */
 	orig = 0;
 	for(i=0; i<NHASH; i++)
 	for(s = hash[i]; s != S; s = s->link) {
 		t = s->type;
 		if(t != SDATA && t != SBSS)
 			continue;
 		v = s->value;
 		if(v == 0) {
 			diag("%s: no size", s->name);
 			v = 1;
 		}
 		while(v & 3)
 			v++;
 		s->value = v;
 		if(v > MINSIZ)
 			continue;
 		s->value = orig;
 		orig += v;
 		s->type = SDATA1;
 	}

 	/*
 	 * pass 2
 	 *	assign large 'data' variables to data segment
 	 */
 	for(i=0; i<NHASH; i++)
 	for(s = hash[i]; s != S; s = s->link) {
 		t = s->type;
 		if(t != SDATA) {
 			if(t == SDATA1)
 				s->type = SDATA;
 			continue;
 		}
 		v = s->value;
 		s->value = orig;
 		orig += v;
 	}

 	while(orig & 7)
 		orig++;
 	datsize = orig;

 	/*
 	 * pass 3
 	 *	everything else to bss segment
 	 */
 	for(i=0; i<NHASH; i++)
 	for(s = hash[i]; s != S; s = s->link) {
 		if(s->type != SBSS)
 			continue;
 		v = s->value;
 		s->value = orig;
 		orig += v;
 	}
 	while(orig & 7)
 		orig++;
 	bsssize = orig-datsize;

 	xdefine("setR12", SDATA, 0L+BIG);
 	xdefine("bdata", SDATA, 0L);
 	xdefine("data", SBSS, 0);
 	xdefine("edata", SDATA, datsize);
 	xdefine("end", SBSS, datsize+bsssize);
 	xdefine("etext", STEXT, 0L);
 }

 void
 undef(void)
 {
 	int i;
 	Sym *s;

 	for(i=0; i<NHASH; i++)
 	for(s = hash[i]; s != S; s = s->link)
 		if(s->type == SXREF)
 			diag("%s: not defined", s->name);
 }

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

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

 int
 relinv(int a)
 {
 	switch(a) {
 	case ABEQ:	return ABNE;
 	case ABNE:	return ABEQ;
 	case ABCS:	return ABCC;
 	case ABHS:	return ABLO;
 	case ABCC:	return ABCS;
 	case ABLO:	return ABHS;
 	case ABMI:	return ABPL;
 	case ABPL:	return ABMI;
 	case ABVS:	return ABVC;
 	case ABVC:	return ABVS;
 	case ABHI:	return ABLS;
 	case ABLS:	return ABHI;
 	case ABGE:	return ABLT;
 	case ABLT:	return ABGE;
 	case ABGT:	return ABLE;
 	case ABLE:	return ABGT;
 	}
 	diag("unknown relation: %s", anames[a]);
 	return a;
 }

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

 	firstp = prg();
 	lastp = firstp;
 	xfol(textp);

 	firstp = firstp->link;
 	lastp->link = P;
 }

 void
 xfol(Prog *p)
 {
 	Prog *q, *r;
 	int a, i;

 loop:
 	if(p == P)
 		return;
 	setarch(p);
 	a = p->as;
 	if(a == ATEXT)
 		curtext = p;
 	if(!curtext->from.sym->reachable) {
 		p = p->cond;
 		goto loop;
 	}
 	if(a == AB) {
 		q = p->cond;
 		if(q != P) {
 			p->mark |= FOLL;
 			p = q;
 			if(!(p->mark & FOLL))
 				goto loop;
 		}
 	}
 	if(p->mark & FOLL) {
 		for(i=0,q=p; i<4; i++,q=q->link) {
 			if(q == lastp)
 				break;
 			a = q->as;
 			if(a == ANOP) {
 				i--;
 				continue;
 			}
 			if(a == AB || (a == ARET && q->scond == 14) || a == ARFE)
 				goto copy;
 			if(!q->cond || (q->cond->mark&FOLL))
 				continue;
 			if(a != ABEQ && a != ABNE)
 				continue;
 		copy:
 			for(;;) {
 				r = prg();
 				*r = *p;
 				if(!(r->mark&FOLL))
 					print("cant happen 1\n");
 				r->mark |= FOLL;
 				if(p != q) {
 					p = p->link;
 					lastp->link = r;
 					lastp = r;
 					continue;
 				}
 				lastp->link = r;
 				lastp = r;
 				if(a == AB || (a == ARET && q->scond == 14) || a == ARFE)
 					return;
 				r->as = ABNE;
 				if(a == ABNE)
 					r->as = ABEQ;
 				r->cond = p->link;
 				r->link = p->cond;
 				if(!(r->link->mark&FOLL))
 					xfol(r->link);
 				if(!(r->cond->mark&FOLL))
 					print("cant happen 2\n");
 				return;
 			}
 		}
 		a = AB;
 		q = prg();
 		q->as = a;
 		q->line = p->line;
 		q->to.type = D_BRANCH;
 		q->to.offset = p->pc;
 		q->cond = p;
 		p = q;
 	}
 	p->mark |= FOLL;
 	lastp->link = p;
 	lastp = p;
 	if(a == AB || (a == ARET && p->scond == 14) || a == ARFE){
 		return;
 	}
 	if(p->cond != P)
 	if(a != ABL && a != ABX && p->link != P) {
 		q = brchain(p->link);
 		if(a != ATEXT && a != ABCASE)
 		if(q != P && (q->mark&FOLL)) {
 			p->as = relinv(a);
 			p->link = p->cond;
 			p->cond = q;
 		}
 		xfol(p->link);
 		q = brchain(p->cond);
 		if(q == P)
 			q = p->cond;
 		if(q->mark&FOLL) {
 			p->cond = q;
 			return;
 		}
 		p = q;
 		goto loop;
 	}
 	p = p->link;
 	goto loop;
 }

 void
 patch(void)
 {
 	int32 c, vexit;
 	Prog *p, *q;
 	Sym *s, *s1;
 	int a;

 	if(debug['v'])
 		Bprint(&bso, "%5.2f patch\n", cputime());
 	Bflush(&bso);
 	mkfwd();
 	s = lookup("exit", 0);
 	vexit = s->value;
 	for(p = firstp; p != P; p = p->link) {
 		setarch(p);
 		a = p->as;
 		if(a == ATEXT)
 			curtext = p;
 		if(seenthumb && a == ABL){
 			// if((s = p->to.sym) != S && (s1 = curtext->from.sym) != S)
 			//	print("%s calls %s\n", s1->name, s->name);
 			 if((s = p->to.sym) != S && (s1 = curtext->from.sym) != S && s->thumb != s1->thumb)
 				s->foreign = 1;
 		}
 		if((a == ABL || a == ABX || a == AB || a == ARET) &&
 		   p->to.type != D_BRANCH && p->to.sym != S) {
 			s = p->to.sym;
 			switch(s->type) {
 			default:
 				diag("undefined: %s", s->name);
 				s->type = STEXT;
 				s->value = vexit;
 				continue;	// avoid more error messages
 			case STEXT:
 				p->to.offset = s->value;
 				p->to.type = D_BRANCH;
 				break;
 			case SUNDEF:
 				if(p->as != ABL)
 					diag("help: SUNDEF in AB || ARET");
 				p->to.offset = 0;
 				p->to.type = D_BRANCH;
 				p->cond = UP;
 				break;
 			}
 		}
 		if(p->to.type != D_BRANCH || p->cond == UP)
 			continue;
 		c = p->to.offset;
 		for(q = firstp; q != P;) {
 			if(q->forwd != P)
 			if(c >= q->forwd->pc) {
 				q = q->forwd;
 				continue;
 			}
 			if(c == q->pc)
 				break;
 			q = q->link;
 		}
 		if(q == P) {
 			diag("branch out of range %ld\n%P", c, p);
 			p->to.type = D_NONE;
 		}
 		p->cond = q;
 	}

 	for(p = firstp; p != P; p = p->link) {
 		setarch(p);
 		a = p->as;
 		if(p->as == ATEXT)
 			curtext = p;
 		if(seenthumb && a == ABL) {
 #ifdef CALLEEBX
 			if(0)
 				{}
 #else
 			if((s = p->to.sym) != S && (s->foreign || s->fnptr))
 				p->as = ABX;
 #endif
 			else if(p->to.type == D_OREG)
 				p->as = ABX;
 		}
 		if(p->cond != P && p->cond != UP) {
 			p->cond = brloop(p->cond);
 			if(p->cond != P)
 			if(p->to.type == D_BRANCH)
 				p->to.offset = p->cond->pc;
 		}
 	}
 }

 #define	LOG	5
 void
 mkfwd(void)
 {
 	Prog *p;
 	int32 dwn[LOG], cnt[LOG], i;
 	Prog *lst[LOG];

 	for(i=0; i<LOG; i++) {
 		if(i == 0)
 			cnt[i] = 1; else
 			cnt[i] = LOG * cnt[i-1];
 		dwn[i] = 1;
 		lst[i] = P;
 	}
 	i = 0;
 	for(p = firstp; p != P; p = p->link) {
 		if(p->as == ATEXT)
 			curtext = p;
 		i--;
 		if(i < 0)
 			i = LOG-1;
 		p->forwd = P;
 		dwn[i]--;
 		if(dwn[i] <= 0) {
 			dwn[i] = cnt[i];
 			if(lst[i] != P)
 				lst[i]->forwd = p;
 			lst[i] = p;
 		}
 	}
 }

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

 	for(c=0; p!=P;) {
 		if(p->as != AB)
 			return p;
 		q = p->cond;
 		if(q <= p) {
 			c++;
 			if(q == p || c > 5000)
 				break;
 		}
 		p = q;
 	}
 	return P;
 }

 int32
 atolwhex(char *s)
 {
 	int32 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;
 }

 int32
 rnd(int32 v, int32 r)
 {
 	int32 c;

 	if(r <= 0)
 		return v;
 	v += r - 1;
 	c = v % r;
 	if(c < 0)
 		c += r;
 	v -= c;
 	return v;
 }

 #define Reachable(n)	if((s = lookup(n, 0)) != nil) s->used++

 static void
 rused(Adr *a)
 {
 	Sym *s = a->sym;

 	if(s == S)
 		return;
 	if(a->type == D_OREG || a->type == D_OCONST || a->type == D_CONST){
 		if(a->name == D_EXTERN || a->name == D_STATIC){
 			if(s->used == 0)
 				s->used = 1;
 		}
 	}
 	else if(a->type == D_BRANCH){
 		if(s->used == 0)
 			s->used = 1;
 	}
 }

 void
 reachable()
 {
 	Prog *p, *prev, *prevt, *nextt, *q;
 	Sym *s, *s0;
 	int i, todo;
 	char *a;

 	Reachable("_div");
 	Reachable("_divu");
 	Reachable("_mod");
 	Reachable("_modu");
 	a = INITENTRY;
 	if(*a >= '0' && *a <= '9')
 		return;
 	s = lookup(a, 0);
 	if(s == nil)
 		return;
 	if(s->type == 0){
 		s->used = 1;	// to stop asm complaining
 		for(p = firstp; p != P && p->as != ATEXT; p = p->link)
 			;
 		if(p == nil)
 			return;
 		s = p->from.sym;
 	}
 	s->used = 1;
 	do{
 		todo = 0;
 		for(p = firstp; p != P; p = p->link){
 			if(p->as == ATEXT && (s0 = p->from.sym)->used == 1){
 				todo = 1;
 				for(q = p->link; q != P && q->as != ATEXT; q = q->link){
 					rused(&q->from);
 					rused(&q->to);
 				}
 				s0->used = 2;
 			}
 		}
 		for(p = datap; p != P; p = p->link){
 			if((s0 = p->from.sym)->used == 1){
 				todo = 1;
 				for(q = p; q != P; q = q->link){	// data can be scattered
 					if(q->from.sym == s0)
 						rused(&q->to);
 				}
 				s0->used = 2;
 			}
 		}
 	}while(todo);
 	prev = nil;
 	prevt = nextt = nil;
 	for(p = firstp; p != P; ){
 		if(p->as == ATEXT){
 			prevt = nextt;
 			nextt = p;
 		}
 		if(p->as == ATEXT && (s0 = p->from.sym)->used == 0){
 			s0->type = SREMOVED;
 			for(q = p->link; q != P && q->as != ATEXT; q = q->link)
 				;
 			if(q != p->cond)
 				diag("bad ptr in reachable()");
 			if(prev == nil)
 				firstp = q;
 			else
 				prev->link = q;
 			if(q == nil)
 				lastp = prev;
 			if(prevt == nil)
 				textp = q;
 			else
 				prevt->cond = q;
 			if(q == nil)
 				etextp = prevt;
 			nextt = prevt;
 			if(debug['V'])
 				print("%s unused\n", s0->name);
 			p = q;
 		}
 		else{
 			prev = p;
 			p = p->link;
 		}
 	}
 	prevt = nil;
 	for(p = datap; p != nil; ){
 		if((s0 = p->from.sym)->used == 0){
 			s0->type = SREMOVED;
 			prev = prevt;
 			for(q = p; q != nil; q = q->link){
 				if(q->from.sym == s0){
 					if(prev == nil)
 						datap = q->link;
 					else
 						prev->link = q->link;
 				}
 				else
 					prev = q;
 			}
 			if(debug['V'])
 				print("%s unused (data)\n", s0->name);
 			p = prevt->link;
 		}
 		else{
 			prevt = p;
 			p = p->link;
 		}
 	}
 	for(i=0; i<NHASH; i++){
 		for(s = hash[i]; s != S; s = s->link){
 			if(s->used == 0)
 				s->type = SREMOVED;
 		}
 	}
 }

 static void
 fused(Adr *a, Prog *p, Prog *ct)
 {
 	Sym *s = a->sym;
 	Use *u;

 	if(s == S)
 		return;
 	if(a->type == D_OREG || a->type == D_OCONST || a->type == D_CONST){
 		if(a->name == D_EXTERN || a->name == D_STATIC){
 			u = malloc(sizeof(Use));
 			u->p = p;
 			u->ct = ct;
 			u->link = s->use;
 			s->use = u;
 		}
 	}
 	else if(a->type == D_BRANCH){
 		u = malloc(sizeof(Use));
 		u->p = p;
 		u->ct = ct;
 		u->link = s->use;
 		s->use = u;
 	}
 }

 static int
 ckfpuse(Prog *p, Prog *ct, Sym *fp, Sym *r)
 {
 	int reg;

 	USED(fp);
 	USED(ct);
 	if(p->from.sym == r && p->as == AMOVW && (p->from.type == D_CONST || p->from.type == D_OREG) && p->reg == NREG && p->to.type == D_REG){
 		reg = p->to.reg;
 		for(p = p->link; p != P && p->as != ATEXT; p = p->link){
 			if((p->as == ABL || p->as == ABX) && p->to.type == D_OREG && p->to.reg == reg)
 				return 1;
 			if(!debug['F'] && (isbranch(p) || p->as == ARET)){
 				// print("%s: branch %P in %s\n", fp->name, p, ct->from.sym->name);
 				return 0;
 			}
 			if((p->from.type == D_REG || p->from.type == D_OREG) && p->from.reg == reg){
 				if(!debug['F'] && p->to.type != D_REG){
 					// print("%s: store %P in %s\n", fp->name, p, ct->from.sym->name);
 					return 0;
 				}
 				reg = p->to.reg;
 			}
 		}
 	}
 	// print("%s: no MOVW O(R), R\n", fp->name);
 	return debug['F'];
 }

 static void
 setfpuse(Prog *p, Sym *fp, Sym *r)
 {
 	int reg;

 	if(p->from.sym == r && p->as == AMOVW && (p->from.type == D_CONST || p->from.type == D_OREG) && p->reg == NREG && p->to.type == D_REG){
 		reg = p->to.reg;
 		for(p = p->link; p != P && p->as != ATEXT; p = p->link){
 			if((p->as == ABL || p->as == ABX) && p->to.type == D_OREG && p->to.reg == reg){
 				fp->fnptr = 0;
 				p->as = ABL;	// safe to do so
 // print("simplified %s call\n", fp->name);
 				break;
 			}
 			if(!debug['F'] && (isbranch(p) || p->as == ARET))
 				diag("bad setfpuse call");
 			if((p->from.type == D_REG || p->from.type == D_OREG) && p->from.reg == reg){
 				if(!debug['F'] && p->to.type != D_REG)
 					diag("bad setfpuse call");
 				reg = p->to.reg;
 			}
 		}
 	}
 }

 static int
 cksymuse(Sym *s, int t)
 {
 	Prog *p;

 	for(p = datap; p != P; p = p->link){
 		if(p->from.sym == s && p->to.sym != nil && strcmp(p->to.sym->name, ".string") != 0 && p->to.sym->thumb != t){
 			// print("%s %s %d %d ", p->from.sym->name, p->to.sym->name, p->to.sym->thumb, t);
 			return 0;
 		}
 	}
 	return 1;
 }

 /* check the use of s at the given point */
 static int
 ckuse(Sym *s, Sym *s0, Use *u)
 {
 	Sym *s1;

 	s1 = u->p->from.sym;
 // print("ckuse %s %s %s\n", s->name, s0->name, s1 ? s1->name : "nil");
 	if(u->ct == nil){	/* in data area */
 		if(s0 == s && !cksymuse(s1, s0->thumb)){
 			// print("%s: cksymuse fails\n", s0->name);
 			return 0;
 		}
 		for(u = s1->use; u != U; u = u->link)
 			if(!ckuse(s1, s0, u))
 				return 0;
 	}
 	else{		/* in text area */
 		if(u->ct->from.sym->thumb != s0->thumb){
 			// print("%s(%d): foreign call %s(%d)\n", s0->name, s0->thumb, u->ct->from.sym->name, u->ct->from.sym->thumb);
 			return 0;
 		}
 		return ckfpuse(u->p, u->ct, s0, s);
 	}
 	return 1;
 }

 static void
 setuse(Sym *s, Sym *s0, Use *u)
 {
 	Sym *s1;

 	s1 = u->p->from.sym;
 	if(u->ct == nil){	/* in data area */
 		for(u = s1->use; u != U; u = u->link)
 			setuse(s1, s0, u);
 	}
 	else{		/* in text area */
 		setfpuse(u->p, s0, s);
 	}
 }

 /* detect BX O(R) which can be done as BL O(R) */
 void
 fnptrs()
 {
 	int i;
 	Sym *s;
 	Prog *p;
 	Use *u;

 	for(i=0; i<NHASH; i++){
 		for(s = hash[i]; s != S; s = s->link){
 			if(s->fnptr && (s->type == STEXT || s->type == SLEAF || s->type == SCONST)){
 				// print("%s : fnptr %d %d\n", s->name, s->thumb, s->foreign);
 			}
 		}
 	}
 	/* record use of syms */
 	for(p = firstp; p != P; p = p->link){
 		if(p->as == ATEXT)
 			curtext = p;
 		else{
 			fused(&p->from, p, curtext);
 			fused(&p->to, p, curtext);
 		}
 	}
 	for(p = datap; p != P; p = p->link)
 		fused(&p->to, p, nil);

 	/* now look for fn ptrs */
 	for(i=0; i<NHASH; i++){
 		for(s = hash[i]; s != S; s = s->link){
 			if(s->fnptr && (s->type == STEXT || s->type == SLEAF || s->type == SCONST)){
 				for(u = s->use; u != U; u = u->link){
 					if(!ckuse(s, s, u))
 						break;
 				}
 				if(u == U){		// can simplify
 					for(u = s->use; u != U; u = u->link)
 						setuse(s, s, u);
 				}
 			}
 		}
 	}

 	/*  now free Use structures */
 }

 void
 import(void)
 {
 	int i;
 	Sym *s;

 	for(i = 0; i < NHASH; i++)
 		for(s = hash[i]; s != S; s = s->link)
 			if(s->sig != 0 && s->type == SXREF && (nimports == 0 || s->subtype == SIMPORT)){
 				undefsym(s);
 				Bprint(&bso, "IMPORT: %s sig=%lux v=%ld\n", s->name, s->sig, s->value);
 			}
 }

 void
 ckoff(Sym *s, int32 v)
 {
 	if(v < 0 || v >= 1<<Roffset)
 		diag("relocation offset %ld for %s out of range", v, s->name);
 }

 Prog*
 newdata(Sym *s, int o, int w, int t)
 {
 	Prog *p;

 	p = prg();
 	p->link = datap;
 	datap = p;
 	p->as = ADATA;
 	p->reg = w;
 	p->from.type = D_OREG;
 	p->from.name = t;
 	p->from.sym = s;
 	p->from.offset = o;
 	p->to.type = D_CONST;
 	p->to.name = D_NONE;
 	s->data = p;
 	return p;
 }

 void
 export(void)
 {
 	int i, j, n, off, nb, sv, ne;
 	Sym *s, *et, *str, **esyms;
 	Prog *p;
 	char buf[NSNAME], *t;

 	n = 0;
 	for(i = 0; i < NHASH; i++)
 		for(s = hash[i]; s != S; s = s->link)
 			if(s->sig != 0 && s->type != SXREF && s->type != SUNDEF && (nexports == 0 || s->subtype == SEXPORT))
 				n++;
 	esyms = malloc(n*sizeof(Sym*));
 	ne = n;
 	n = 0;
 	for(i = 0; i < NHASH; i++)
 		for(s = hash[i]; s != S; s = s->link)
 			if(s->sig != 0 && s->type != SXREF && s->type != SUNDEF && (nexports == 0 || s->subtype == SEXPORT))
 				esyms[n++] = s;
 	for(i = 0; i < ne-1; i++)
 		for(j = i+1; j < ne; j++)
 			if(strcmp(esyms[i]->name, esyms[j]->name) > 0){
 				s = esyms[i];
 				esyms[i] = esyms[j];
 				esyms[j] = s;
 			}

 	nb = 0;
 	off = 0;
 	et = lookup(EXPTAB, 0);
 	if(et->type != 0 && et->type != SXREF)
 		diag("%s already defined", EXPTAB);
 	et->type = SDATA;
 	str = lookup(".string", 0);
 	if(str->type == 0)
 		str->type = SDATA;
 	sv = str->value;
 	for(i = 0; i < ne; i++){
 		s = esyms[i];
 		Bprint(&bso, "EXPORT: %s sig=%lux t=%d\n", s->name, s->sig, s->type);

 		/* signature */
 		p = newdata(et, off, sizeof(int32), D_EXTERN);
 		off += sizeof(int32);
 		p->to.offset = s->sig;

 		/* address */
 		p = newdata(et, off, sizeof(int32), D_EXTERN);
 		off += sizeof(int32);
 		p->to.name = D_EXTERN;
 		p->to.sym = s;

 		/* string */
 		t = s->name;
 		n = strlen(t)+1;
 		for(;;){
 			buf[nb++] = *t;
 			sv++;
 			if(nb >= NSNAME){
 				p = newdata(str, sv-NSNAME, NSNAME, D_STATIC);
 				p->to.type = D_SCONST;
 				p->to.sval = malloc(NSNAME);
 				memmove(p->to.sval, buf, NSNAME);
 				nb = 0;
 			}
 			if(*t++ == 0)
 				break;
 		}

 		/* name */
 		p = newdata(et, off, sizeof(int32), D_EXTERN);
 		off += sizeof(int32);
 		p->to.name = D_STATIC;
 		p->to.sym = str;
 		p->to.offset = sv-n;
 	}

 	if(nb > 0){
 		p = newdata(str, sv-nb, nb, D_STATIC);
 		p->to.type = D_SCONST;
 		p->to.sval = malloc(NSNAME);
 		memmove(p->to.sval, buf, nb);
 	}

 	for(i = 0; i < 3; i++){
 		newdata(et, off, sizeof(int32), D_EXTERN);
 		off += sizeof(int32);
 	}
 	et->value = off;
 	if(sv == 0)
 		sv = 1;
 	str->value = sv;
 	exports = ne;
 	free(esyms);
 }
	// Inferno utils/5l/pass.c
	// http://code.google.com/p/inferno-os/source/browse/utils/5l/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.

	#include "l.h"

	void
	dodata(void)
	{
	int i, t;
	Sym *s;
	Prog *p;
	int32 orig, v;

	if(debug['v'])
	Bprint(&bso, "%5.2f dodata\n", cputime());
	Bflush(&bso);
	for(p = datap; p != P; p = p->link) {
	s = p->from.sym;
	if(p->as == ADYNT \|\| p->as == AINIT)
	s->value = dtype;
	if(s->type == SBSS)
	s->type = SDATA;
	if(s->type != SDATA)
	diag("initialize non-data (%d): %s\n%P",
	s->type, s->name, p);
	v = p->from.offset + p->reg;
	if(v > s->value)
	diag("initialize bounds (%ld/%ld): %s\n%P",
	v, s->value, s->name, p);
	if((s->type == SBSS \|\| s->type == SDATA) && (p->to.type == D_CONST \|\| p->to.type == D_OCONST) && (p->to.name == D_EXTERN \|\| p->to.name == D_STATIC)){
	s = p->to.sym;
	if(s != S && (s->type == STEXT \|\| s->type == SLEAF \|\| s->type == SCONST \|\| s->type == SXREF))
	s->fnptr = 1;
	}
	}

	if(debug['t']) {
	/*
	* pull out string constants
	*/
	for(p = datap; p != P; p = p->link) {
	s = p->from.sym;
	if(p->to.type == D_SCONST)
	s->type = SSTRING;
	}
	}

	/*
	* pass 1
	* assign 'small' variables to data segment
	* (rational is that data segment is more easily
	* addressed through offset on R12)
	*/
	orig = 0;
	for(i=0; i<NHASH; i++)
	for(s = hash[i]; s != S; s = s->link) {
	t = s->type;
	if(t != SDATA && t != SBSS)
	continue;
	v = s->value;
	if(v == 0) {
	diag("%s: no size", s->name);
	v = 1;
	}
	while(v & 3)
	v++;
	s->value = v;
	if(v > MINSIZ)
	continue;
	s->value = orig;
	orig += v;
	s->type = SDATA1;
	}

	/*
	* pass 2
	* assign large 'data' variables to data segment
	*/
	for(i=0; i<NHASH; i++)
	for(s = hash[i]; s != S; s = s->link) {
	t = s->type;
	if(t != SDATA) {
	if(t == SDATA1)
	s->type = SDATA;
	continue;
	}
	v = s->value;
	s->value = orig;
	orig += v;
	}

	while(orig & 7)
	orig++;
	datsize = orig;

	/*
	* pass 3
	* everything else to bss segment
	*/
	for(i=0; i<NHASH; i++)
	for(s = hash[i]; s != S; s = s->link) {
	if(s->type != SBSS)
	continue;
	v = s->value;
	s->value = orig;
	orig += v;
	}
	while(orig & 7)
	orig++;
	bsssize = orig-datsize;

	xdefine("setR12", SDATA, 0L+BIG);
	xdefine("bdata", SDATA, 0L);
	xdefine("data", SBSS, 0);
	xdefine("edata", SDATA, datsize);
	xdefine("end", SBSS, datsize+bsssize);
	xdefine("etext", STEXT, 0L);
	}

	void
	undef(void)
	{
	int i;
	Sym *s;

	for(i=0; i<NHASH; i++)
	for(s = hash[i]; s != S; s = s->link)
	if(s->type == SXREF)
	diag("%s: not defined", s->name);
	}

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

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

	int
	relinv(int a)
	{
	switch(a) {
	case ABEQ: return ABNE;
	case ABNE: return ABEQ;
	case ABCS: return ABCC;
	case ABHS: return ABLO;
	case ABCC: return ABCS;
	case ABLO: return ABHS;
	case ABMI: return ABPL;
	case ABPL: return ABMI;
	case ABVS: return ABVC;
	case ABVC: return ABVS;
	case ABHI: return ABLS;
	case ABLS: return ABHI;
	case ABGE: return ABLT;
	case ABLT: return ABGE;
	case ABGT: return ABLE;
	case ABLE: return ABGT;
	}
	diag("unknown relation: %s", anames[a]);
	return a;
	}

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

	firstp = prg();
	lastp = firstp;
	xfol(textp);

	firstp = firstp->link;
	lastp->link = P;
	}

	void
	xfol(Prog *p)
	{
	Prog q, r;
	int a, i;

	loop:
	if(p == P)
	return;
	setarch(p);
	a = p->as;
	if(a == ATEXT)
	curtext = p;
	if(!curtext->from.sym->reachable) {
	p = p->cond;
	goto loop;
	}
	if(a == AB) {
	q = p->cond;
	if(q != P) {
	p->mark \|= FOLL;
	p = q;
	if(!(p->mark & FOLL))
	goto loop;
	}
	}
	if(p->mark & FOLL) {
	for(i=0,q=p; i<4; i++,q=q->link) {
	if(q == lastp)
	break;
	a = q->as;
	if(a == ANOP) {
	i--;
	continue;
	}
	if(a == AB \|\| (a == ARET && q->scond == 14) \|\| a == ARFE)
	goto copy;
	if(!q->cond \|\| (q->cond->mark&FOLL))
	continue;
	if(a != ABEQ && a != ABNE)
	continue;
	copy:
	for(;;) {
	r = prg();
	r = p;
	if(!(r->mark&FOLL))
	print("cant happen 1\n");
	r->mark \|= FOLL;
	if(p != q) {
	p = p->link;
	lastp->link = r;
	lastp = r;
	continue;
	}
	lastp->link = r;
	lastp = r;
	if(a == AB \|\| (a == ARET && q->scond == 14) \|\| a == ARFE)
	return;
	r->as = ABNE;
	if(a == ABNE)
	r->as = ABEQ;
	r->cond = p->link;
	r->link = p->cond;
	if(!(r->link->mark&FOLL))
	xfol(r->link);
	if(!(r->cond->mark&FOLL))
	print("cant happen 2\n");
	return;
	}
	}
	a = AB;
	q = prg();
	q->as = a;
	q->line = p->line;
	q->to.type = D_BRANCH;
	q->to.offset = p->pc;
	q->cond = p;
	p = q;
	}
	p->mark \|= FOLL;
	lastp->link = p;
	lastp = p;
	if(a == AB \|\| (a == ARET && p->scond == 14) \|\| a == ARFE){
	return;
	}
	if(p->cond != P)
	if(a != ABL && a != ABX && p->link != P) {
	q = brchain(p->link);
	if(a != ATEXT && a != ABCASE)
	if(q != P && (q->mark&FOLL)) {
	p->as = relinv(a);
	p->link = p->cond;
	p->cond = q;
	}
	xfol(p->link);
	q = brchain(p->cond);
	if(q == P)
	q = p->cond;
	if(q->mark&FOLL) {
	p->cond = q;
	return;
	}
	p = q;
	goto loop;
	}
	p = p->link;
	goto loop;
	}

	void
	patch(void)
	{
	int32 c, vexit;
	Prog p, q;
	Sym s, s1;
	int a;

	if(debug['v'])
	Bprint(&bso, "%5.2f patch\n", cputime());
	Bflush(&bso);
	mkfwd();
	s = lookup("exit", 0);
	vexit = s->value;
	for(p = firstp; p != P; p = p->link) {
	setarch(p);
	a = p->as;
	if(a == ATEXT)
	curtext = p;
	if(seenthumb && a == ABL){
	// if((s = p->to.sym) != S && (s1 = curtext->from.sym) != S)
	// print("%s calls %s\n", s1->name, s->name);
	if((s = p->to.sym) != S && (s1 = curtext->from.sym) != S && s->thumb != s1->thumb)
	s->foreign = 1;
	}
	if((a == ABL \|\| a == ABX \|\| a == AB \|\| a == ARET) &&
	p->to.type != D_BRANCH && p->to.sym != S) {
	s = p->to.sym;
	switch(s->type) {
	default:
	diag("undefined: %s", s->name);
	s->type = STEXT;
	s->value = vexit;
	continue; // avoid more error messages
	case STEXT:
	p->to.offset = s->value;
	p->to.type = D_BRANCH;
	break;
	case SUNDEF:
	if(p->as != ABL)
	diag("help: SUNDEF in AB \|\| ARET");
	p->to.offset = 0;
	p->to.type = D_BRANCH;
	p->cond = UP;
	break;
	}
	}
	if(p->to.type != D_BRANCH \|\| p->cond == UP)
	continue;
	c = p->to.offset;
	for(q = firstp; q != P;) {
	if(q->forwd != P)
	if(c >= q->forwd->pc) {
	q = q->forwd;
	continue;
	}
	if(c == q->pc)
	break;
	q = q->link;
	}
	if(q == P) {
	diag("branch out of range %ld\n%P", c, p);
	p->to.type = D_NONE;
	}
	p->cond = q;
	}

	for(p = firstp; p != P; p = p->link) {
	setarch(p);
	a = p->as;
	if(p->as == ATEXT)
	curtext = p;
	if(seenthumb && a == ABL) {
	#ifdef CALLEEBX
	if(0)
	{}
	#else
	if((s = p->to.sym) != S && (s->foreign \|\| s->fnptr))
	p->as = ABX;
	#endif
	else if(p->to.type == D_OREG)
	p->as = ABX;
	}
	if(p->cond != P && p->cond != UP) {
	p->cond = brloop(p->cond);
	if(p->cond != P)
	if(p->to.type == D_BRANCH)
	p->to.offset = p->cond->pc;
	}
	}
	}

	#define LOG 5
	void
	mkfwd(void)
	{
	Prog *p;
	int32 dwn[LOG], cnt[LOG], i;
	Prog *lst[LOG];

	for(i=0; i<LOG; i++) {
	if(i == 0)
	cnt[i] = 1; else
	cnt[i] = LOG * cnt[i-1];
	dwn[i] = 1;
	lst[i] = P;
	}
	i = 0;
	for(p = firstp; p != P; p = p->link) {
	if(p->as == ATEXT)
	curtext = p;
	i--;
	if(i < 0)
	i = LOG-1;
	p->forwd = P;
	dwn[i]--;
	if(dwn[i] <= 0) {
	dwn[i] = cnt[i];
	if(lst[i] != P)
	lst[i]->forwd = p;
	lst[i] = p;
	}
	}
	}

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

	for(c=0; p!=P;) {
	if(p->as != AB)
	return p;
	q = p->cond;
	if(q <= p) {
	c++;
	if(q == p \|\| c > 5000)
	break;
	}
	p = q;
	}
	return P;
	}

	int32
	atolwhex(char *s)
	{
	int32 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 = n16 + s++ - '0';
	else if(s >= 'a' && s <= 'f')
	n = n16 + s++ - 'a' + 10;
	else if(s >= 'A' && s <= 'F')
	n = n16 + s++ - 'A' + 10;
	else
	break;
	}
	} else
	while(s >= '0' && s <= '7')
	n = n8 + s++ - '0';
	} else
	while(s >= '0' && s <= '9')
	n = n10 + s++ - '0';
	if(f)
	n = -n;
	return n;
	}

	int32
	rnd(int32 v, int32 r)
	{
	int32 c;

	if(r <= 0)
	return v;
	v += r - 1;
	c = v % r;
	if(c < 0)
	c += r;
	v -= c;
	return v;
	}

	#define Reachable(n) if((s = lookup(n, 0)) != nil) s->used++

	static void
	rused(Adr *a)
	{
	Sym *s = a->sym;

	if(s == S)
	return;
	if(a->type == D_OREG \|\| a->type == D_OCONST \|\| a->type == D_CONST){
	if(a->name == D_EXTERN \|\| a->name == D_STATIC){
	if(s->used == 0)
	s->used = 1;
	}
	}
	else if(a->type == D_BRANCH){
	if(s->used == 0)
	s->used = 1;
	}
	}

	void
	reachable()
	{
	Prog p, prev, prevt, nextt, *q;
	Sym s, s0;
	int i, todo;
	char *a;

	Reachable("_div");
	Reachable("_divu");
	Reachable("_mod");
	Reachable("_modu");
	a = INITENTRY;
	if(a >= '0' && a <= '9')
	return;
	s = lookup(a, 0);
	if(s == nil)
	return;
	if(s->type == 0){
	s->used = 1; // to stop asm complaining
	for(p = firstp; p != P && p->as != ATEXT; p = p->link)
	;
	if(p == nil)
	return;
	s = p->from.sym;
	}
	s->used = 1;
	do{
	todo = 0;
	for(p = firstp; p != P; p = p->link){
	if(p->as == ATEXT && (s0 = p->from.sym)->used == 1){
	todo = 1;
	for(q = p->link; q != P && q->as != ATEXT; q = q->link){
	rused(&q->from);
	rused(&q->to);
	}
	s0->used = 2;
	}
	}
	for(p = datap; p != P; p = p->link){
	if((s0 = p->from.sym)->used == 1){
	todo = 1;
	for(q = p; q != P; q = q->link){ // data can be scattered
	if(q->from.sym == s0)
	rused(&q->to);
	}
	s0->used = 2;
	}
	}
	}while(todo);
	prev = nil;
	prevt = nextt = nil;
	for(p = firstp; p != P; ){
	if(p->as == ATEXT){
	prevt = nextt;
	nextt = p;
	}
	if(p->as == ATEXT && (s0 = p->from.sym)->used == 0){
	s0->type = SREMOVED;
	for(q = p->link; q != P && q->as != ATEXT; q = q->link)
	;
	if(q != p->cond)
	diag("bad ptr in reachable()");
	if(prev == nil)
	firstp = q;
	else
	prev->link = q;
	if(q == nil)
	lastp = prev;
	if(prevt == nil)
	textp = q;
	else
	prevt->cond = q;
	if(q == nil)
	etextp = prevt;
	nextt = prevt;
	if(debug['V'])
	print("%s unused\n", s0->name);
	p = q;
	}
	else{
	prev = p;
	p = p->link;
	}
	}
	prevt = nil;
	for(p = datap; p != nil; ){
	if((s0 = p->from.sym)->used == 0){
	s0->type = SREMOVED;
	prev = prevt;
	for(q = p; q != nil; q = q->link){
	if(q->from.sym == s0){
	if(prev == nil)
	datap = q->link;
	else
	prev->link = q->link;
	}
	else
	prev = q;
	}
	if(debug['V'])
	print("%s unused (data)\n", s0->name);
	p = prevt->link;
	}
	else{
	prevt = p;
	p = p->link;
	}
	}
	for(i=0; i<NHASH; i++){
	for(s = hash[i]; s != S; s = s->link){
	if(s->used == 0)
	s->type = SREMOVED;
	}
	}
	}

	static void
	fused(Adr a, Prog p, Prog *ct)
	{
	Sym *s = a->sym;
	Use *u;

	if(s == S)
	return;
	if(a->type == D_OREG \|\| a->type == D_OCONST \|\| a->type == D_CONST){
	if(a->name == D_EXTERN \|\| a->name == D_STATIC){
	u = malloc(sizeof(Use));
	u->p = p;
	u->ct = ct;
	u->link = s->use;
	s->use = u;
	}
	}
	else if(a->type == D_BRANCH){
	u = malloc(sizeof(Use));
	u->p = p;
	u->ct = ct;
	u->link = s->use;
	s->use = u;
	}
	}

	static int
	ckfpuse(Prog p, Prog ct, Sym fp, Sym r)
	{
	int reg;

	USED(fp);
	USED(ct);
	if(p->from.sym == r && p->as == AMOVW && (p->from.type == D_CONST \|\| p->from.type == D_OREG) && p->reg == NREG && p->to.type == D_REG){
	reg = p->to.reg;
	for(p = p->link; p != P && p->as != ATEXT; p = p->link){
	if((p->as == ABL \|\| p->as == ABX) && p->to.type == D_OREG && p->to.reg == reg)
	return 1;
	if(!debug['F'] && (isbranch(p) \|\| p->as == ARET)){
	// print("%s: branch %P in %s\n", fp->name, p, ct->from.sym->name);
	return 0;
	}
	if((p->from.type == D_REG \|\| p->from.type == D_OREG) && p->from.reg == reg){
	if(!debug['F'] && p->to.type != D_REG){
	// print("%s: store %P in %s\n", fp->name, p, ct->from.sym->name);
	return 0;
	}
	reg = p->to.reg;
	}
	}
	}
	// print("%s: no MOVW O(R), R\n", fp->name);
	return debug['F'];
	}

	static void
	setfpuse(Prog p, Sym fp, Sym *r)
	{
	int reg;

	if(p->from.sym == r && p->as == AMOVW && (p->from.type == D_CONST \|\| p->from.type == D_OREG) && p->reg == NREG && p->to.type == D_REG){
	reg = p->to.reg;
	for(p = p->link; p != P && p->as != ATEXT; p = p->link){
	if((p->as == ABL \|\| p->as == ABX) && p->to.type == D_OREG && p->to.reg == reg){
	fp->fnptr = 0;
	p->as = ABL; // safe to do so
	// print("simplified %s call\n", fp->name);
	break;
	}
	if(!debug['F'] && (isbranch(p) \|\| p->as == ARET))
	diag("bad setfpuse call");
	if((p->from.type == D_REG \|\| p->from.type == D_OREG) && p->from.reg == reg){
	if(!debug['F'] && p->to.type != D_REG)
	diag("bad setfpuse call");
	reg = p->to.reg;
	}
	}
	}
	}

	static int
	cksymuse(Sym *s, int t)
	{
	Prog *p;

	for(p = datap; p != P; p = p->link){
	if(p->from.sym == s && p->to.sym != nil && strcmp(p->to.sym->name, ".string") != 0 && p->to.sym->thumb != t){
	// print("%s %s %d %d ", p->from.sym->name, p->to.sym->name, p->to.sym->thumb, t);
	return 0;
	}
	}
	return 1;
	}

	/* check the use of s at the given point */
	static int
	ckuse(Sym s, Sym s0, Use *u)
	{
	Sym *s1;

	s1 = u->p->from.sym;
	// print("ckuse %s %s %s\n", s->name, s0->name, s1 ? s1->name : "nil");
	if(u->ct == nil){ /* in data area */
	if(s0 == s && !cksymuse(s1, s0->thumb)){
	// print("%s: cksymuse fails\n", s0->name);
	return 0;
	}
	for(u = s1->use; u != U; u = u->link)
	if(!ckuse(s1, s0, u))
	return 0;
	}
	else{ /* in text area */
	if(u->ct->from.sym->thumb != s0->thumb){
	// print("%s(%d): foreign call %s(%d)\n", s0->name, s0->thumb, u->ct->from.sym->name, u->ct->from.sym->thumb);
	return 0;
	}
	return ckfpuse(u->p, u->ct, s0, s);
	}
	return 1;
	}

	static void
	setuse(Sym s, Sym s0, Use *u)
	{
	Sym *s1;

	s1 = u->p->from.sym;
	if(u->ct == nil){ /* in data area */
	for(u = s1->use; u != U; u = u->link)
	setuse(s1, s0, u);
	}
	else{ /* in text area */
	setfpuse(u->p, s0, s);
	}
	}

	/* detect BX O(R) which can be done as BL O(R) */
	void
	fnptrs()
	{
	int i;
	Sym *s;
	Prog *p;
	Use *u;

	for(i=0; i<NHASH; i++){
	for(s = hash[i]; s != S; s = s->link){
	if(s->fnptr && (s->type == STEXT \|\| s->type == SLEAF \|\| s->type == SCONST)){
	// print("%s : fnptr %d %d\n", s->name, s->thumb, s->foreign);
	}
	}
	}
	/* record use of syms */
	for(p = firstp; p != P; p = p->link){
	if(p->as == ATEXT)
	curtext = p;
	else{
	fused(&p->from, p, curtext);
	fused(&p->to, p, curtext);
	}
	}
	for(p = datap; p != P; p = p->link)
	fused(&p->to, p, nil);

	/* now look for fn ptrs */
	for(i=0; i<NHASH; i++){
	for(s = hash[i]; s != S; s = s->link){
	if(s->fnptr && (s->type == STEXT \|\| s->type == SLEAF \|\| s->type == SCONST)){
	for(u = s->use; u != U; u = u->link){
	if(!ckuse(s, s, u))
	break;
	}
	if(u == U){ // can simplify
	for(u = s->use; u != U; u = u->link)
	setuse(s, s, u);
	}
	}
	}
	}

	/* now free Use structures */
	}

	void
	import(void)
	{
	int i;
	Sym *s;

	for(i = 0; i < NHASH; i++)
	for(s = hash[i]; s != S; s = s->link)
	if(s->sig != 0 && s->type == SXREF && (nimports == 0 \|\| s->subtype == SIMPORT)){
	undefsym(s);
	Bprint(&bso, "IMPORT: %s sig=%lux v=%ld\n", s->name, s->sig, s->value);
	}
	}

	void
	ckoff(Sym *s, int32 v)
	{
	if(v < 0 \|\| v >= 1<<Roffset)
	diag("relocation offset %ld for %s out of range", v, s->name);
	}

	Prog*
	newdata(Sym *s, int o, int w, int t)
	{
	Prog *p;

	p = prg();
	p->link = datap;
	datap = p;
	p->as = ADATA;
	p->reg = w;
	p->from.type = D_OREG;
	p->from.name = t;
	p->from.sym = s;
	p->from.offset = o;
	p->to.type = D_CONST;
	p->to.name = D_NONE;
	s->data = p;
	return p;
	}

	void
	export(void)
	{
	int i, j, n, off, nb, sv, ne;
	Sym s, et, str, *esyms;
	Prog *p;
	char buf[NSNAME], *t;

	n = 0;
	for(i = 0; i < NHASH; i++)
	for(s = hash[i]; s != S; s = s->link)
	if(s->sig != 0 && s->type != SXREF && s->type != SUNDEF && (nexports == 0 \|\| s->subtype == SEXPORT))
	n++;
	esyms = malloc(nsizeof(Sym));
	ne = n;
	n = 0;
	for(i = 0; i < NHASH; i++)
	for(s = hash[i]; s != S; s = s->link)
	if(s->sig != 0 && s->type != SXREF && s->type != SUNDEF && (nexports == 0 \|\| s->subtype == SEXPORT))
	esyms[n++] = s;
	for(i = 0; i < ne-1; i++)
	for(j = i+1; j < ne; j++)
	if(strcmp(esyms[i]->name, esyms[j]->name) > 0){
	s = esyms[i];
	esyms[i] = esyms[j];
	esyms[j] = s;
	}

	nb = 0;
	off = 0;
	et = lookup(EXPTAB, 0);
	if(et->type != 0 && et->type != SXREF)
	diag("%s already defined", EXPTAB);
	et->type = SDATA;
	str = lookup(".string", 0);
	if(str->type == 0)
	str->type = SDATA;
	sv = str->value;
	for(i = 0; i < ne; i++){
	s = esyms[i];
	Bprint(&bso, "EXPORT: %s sig=%lux t=%d\n", s->name, s->sig, s->type);

	/* signature */
	p = newdata(et, off, sizeof(int32), D_EXTERN);
	off += sizeof(int32);
	p->to.offset = s->sig;

	/* address */
	p = newdata(et, off, sizeof(int32), D_EXTERN);
	off += sizeof(int32);
	p->to.name = D_EXTERN;
	p->to.sym = s;

	/* string */
	t = s->name;
	n = strlen(t)+1;
	for(;;){
	buf[nb++] = *t;
	sv++;
	if(nb >= NSNAME){
	p = newdata(str, sv-NSNAME, NSNAME, D_STATIC);
	p->to.type = D_SCONST;
	p->to.sval = malloc(NSNAME);
	memmove(p->to.sval, buf, NSNAME);
	nb = 0;
	}
	if(*t++ == 0)
	break;
	}

	/* name */
	p = newdata(et, off, sizeof(int32), D_EXTERN);
	off += sizeof(int32);
	p->to.name = D_STATIC;
	p->to.sym = str;
	p->to.offset = sv-n;
	}

	if(nb > 0){
	p = newdata(str, sv-nb, nb, D_STATIC);
	p->to.type = D_SCONST;
	p->to.sval = malloc(NSNAME);
	memmove(p->to.sval, buf, nb);
	}

	for(i = 0; i < 3; i++){
	newdata(et, off, sizeof(int32), D_EXTERN);
	off += sizeof(int32);
	}
	et->value = off;
	if(sv == 0)
	sv = 1;
	str->value = sv;
	exports = ne;
	free(esyms);
	}