diff --git a/src/cmd/5a/lex.c b/src/cmd/5a/lex.c
index cc02879b76..fbce6b771d 100644
--- a/src/cmd/5a/lex.c
+++ b/src/cmd/5a/lex.c
@@ -413,6 +413,8 @@ struct
 	"MULAWT",	LTYPEN, AMULAWT,
 	"MULAWB",	LTYPEN, AMULAWB,
 
+	"USEFIELD",	LTYPEN, AUSEFIELD,
+
 	0
 };
 
diff --git a/src/cmd/5g/gg.h b/src/cmd/5g/gg.h
index 80a5605f0c..ba9356edc3 100644
--- a/src/cmd/5g/gg.h
+++ b/src/cmd/5g/gg.h
@@ -142,6 +142,7 @@ void	datagostring(Strlit*, Addr*);
 void	split64(Node*, Node*, Node*);
 void	splitclean(void);
 Node*	ncon(uint32 i);
+void	gtrack(Sym*);
 
 /*
  * obj.c
diff --git a/src/cmd/5g/gsubr.c b/src/cmd/5g/gsubr.c
index c4961b80c6..0ab335e0bc 100644
--- a/src/cmd/5g/gsubr.c
+++ b/src/cmd/5g/gsubr.c
@@ -225,6 +225,17 @@ ggloblsym(Sym *s, int32 width, int dupok, int rodata)
 		p->reg |= RODATA;
 }
 
+void
+gtrack(Sym *s)
+{
+	Prog *p;
+	
+	p = gins(AUSEFIELD, N, N);
+	p->from.type = D_OREG;
+	p->from.name = D_EXTERN;
+	p->from.sym = s;
+}
+
 int
 isfat(Type *t)
 {
diff --git a/src/cmd/5l/5.out.h b/src/cmd/5l/5.out.h
index b9b0525701..c987001777 100644
--- a/src/cmd/5l/5.out.h
+++ b/src/cmd/5l/5.out.h
@@ -195,6 +195,8 @@ enum	as
 	AMULWB,
 	AMULAWT,
 	AMULAWB,
+	
+	AUSEFIELD,
 
 	ALAST,
 };
diff --git a/src/cmd/5l/l.h b/src/cmd/5l/l.h
index 36bf254e46..50531bb209 100644
--- a/src/cmd/5l/l.h
+++ b/src/cmd/5l/l.h
@@ -153,6 +153,8 @@ struct	Sym
 	Sym*	sub;	// in SSUB list
 	Sym*	outer;	// container of sub
 	Sym*	gotype;
+	Sym*	reachparent;
+	Sym*	queue;
 	char*	file;
 	char*	dynimpname;
 	char*	dynimplib;
diff --git a/src/cmd/5l/obj.c b/src/cmd/5l/obj.c
index 4c2603d28a..74ac6ecb47 100644
--- a/src/cmd/5l/obj.c
+++ b/src/cmd/5l/obj.c
@@ -147,6 +147,9 @@ main(int argc, char *argv[])
 		val = EARGF(usage());
 		addbuildinfo(val);
 		break;
+	case 'k':
+		tracksym = EARGF(usage());
+		break;
 	} ARGEND
 
 	USED(argc);
diff --git a/src/cmd/5l/optab.c b/src/cmd/5l/optab.c
index cb29cfd685..9e95c096de 100644
--- a/src/cmd/5l/optab.c
+++ b/src/cmd/5l/optab.c
@@ -242,5 +242,7 @@ Optab	optab[] =
 	{ AMULWT,	C_REG,	C_REG,	C_REG,		98, 4, 0 },
 	{ AMULAWT,	C_REG,	C_REG,	C_REGREG2,		99, 4, 0 },
 
+	{ AUSEFIELD,	C_ADDR,	C_NONE,	C_NONE, 	 0, 0, 0 },
+
 	{ AXXX,		C_NONE,	C_NONE,	C_NONE,		 0, 4, 0 },
 };
diff --git a/src/cmd/5l/span.c b/src/cmd/5l/span.c
index 7614c40185..59c0590b47 100644
--- a/src/cmd/5l/span.c
+++ b/src/cmd/5l/span.c
@@ -812,6 +812,7 @@ buildop(void)
 		case AMOVM:
 		case ARFE:
 		case ATEXT:
+		case AUSEFIELD:
 		case ACASE:
 		case ABCASE:
 			break;
diff --git a/src/cmd/6a/lex.c b/src/cmd/6a/lex.c
index 376a4b67e5..d65802a201 100644
--- a/src/cmd/6a/lex.c
+++ b/src/cmd/6a/lex.c
@@ -1014,7 +1014,8 @@ struct
 	"AESDECLAST",	LTYPE3, AAESDECLAST,
 	"AESIMC",	LTYPE3, AAESIMC,
 	"AESKEYGENASSIST", LTYPEX, AAESKEYGENASSIST,
-	"PSHUFD", LTYPEX, APSHUFD,
+	"PSHUFD",	LTYPEX, APSHUFD,
+	"USEFIELD",	LTYPEN, AUSEFIELD,
 
 	0
 };
diff --git a/src/cmd/6g/gg.h b/src/cmd/6g/gg.h
index 65ea7a4aa7..4045e9a2e2 100644
--- a/src/cmd/6g/gg.h
+++ b/src/cmd/6g/gg.h
@@ -125,6 +125,7 @@ void	sudoclean(void);
 int	sudoaddable(int, Node*, Addr*);
 void	afunclit(Addr*);
 void	nodfconst(Node*, Type*, Mpflt*);
+void	gtrack(Sym*);
 
 /*
  * cplx.c
diff --git a/src/cmd/6g/gsubr.c b/src/cmd/6g/gsubr.c
index 638ba4add6..b7ba420da1 100644
--- a/src/cmd/6g/gsubr.c
+++ b/src/cmd/6g/gsubr.c
@@ -205,6 +205,17 @@ ggloblnod(Node *nam, int32 width)
 		p->from.scale |= NOPTR;
 }
 
+void
+gtrack(Sym *s)
+{
+	Prog *p;
+	
+	p = gins(AUSEFIELD, N, N);
+	p->from.type = D_EXTERN;
+	p->from.index = D_NONE;
+	p->from.sym = s;
+}
+
 void
 ggloblsym(Sym *s, int32 width, int dupok, int rodata)
 {
diff --git a/src/cmd/6l/6.out.h b/src/cmd/6l/6.out.h
index 6acc1f459e..3946861de4 100644
--- a/src/cmd/6l/6.out.h
+++ b/src/cmd/6l/6.out.h
@@ -756,6 +756,8 @@ enum	as
 	AAESKEYGENASSIST,
 
 	APSHUFD,
+	
+	AUSEFIELD,
 
 	ALAST
 };
diff --git a/src/cmd/6l/l.h b/src/cmd/6l/l.h
index c2ae007790..91926a13a0 100644
--- a/src/cmd/6l/l.h
+++ b/src/cmd/6l/l.h
@@ -158,6 +158,8 @@ struct	Sym
 	Sym*	next;	// in text or data list
 	Sym*	sub;	// in SSUB list
 	Sym*	outer;	// container of sub
+	Sym*	reachparent;
+	Sym*	queue;
 	vlong	value;
 	vlong	size;
 	Sym*	gotype;
diff --git a/src/cmd/6l/obj.c b/src/cmd/6l/obj.c
index dad217cc86..08db03c4a3 100644
--- a/src/cmd/6l/obj.c
+++ b/src/cmd/6l/obj.c
@@ -144,6 +144,9 @@ main(int argc, char *argv[])
 		val = EARGF(usage());
 		addbuildinfo(val);
 		break;
+	case 'k':
+		tracksym = EARGF(usage());
+		break;
 	} ARGEND
 
 	if(argc != 1)
diff --git a/src/cmd/6l/optab.c b/src/cmd/6l/optab.c
index e81c1eda01..4f8406637c 100644
--- a/src/cmd/6l/optab.c
+++ b/src/cmd/6l/optab.c
@@ -1315,6 +1315,8 @@ Optab optab[] =
 
 	{ APSHUFD,	yaes2,	Pq,	0x70,(0) },
 
+	{ AUSEFIELD,	ynop,	Px, 0,0 },
+
 	{ AEND },
 	0
 };
diff --git a/src/cmd/8a/lex.c b/src/cmd/8a/lex.c
index cebaa9e5f8..25c61d75c2 100644
--- a/src/cmd/8a/lex.c
+++ b/src/cmd/8a/lex.c
@@ -781,6 +781,7 @@ struct
 	"UNPCKLPS",	LTYPE3,	AUNPCKLPS,
 	"XORPD",	LTYPE3,	AXORPD,
 	"XORPS",	LTYPE3,	AXORPS,
+	"USEFIELD",	LTYPEN, AUSEFIELD,
 
 	0
 };
diff --git a/src/cmd/8g/gg.h b/src/cmd/8g/gg.h
index 09718855bd..e1d44c2300 100644
--- a/src/cmd/8g/gg.h
+++ b/src/cmd/8g/gg.h
@@ -147,6 +147,7 @@ void	afunclit(Addr*);
 void	split64(Node*, Node*, Node*);
 void	splitclean(void);
 void	nswap(Node*, Node*);
+void	gtrack(Sym*);
 
 /*
  * cplx.c
diff --git a/src/cmd/8g/gsubr.c b/src/cmd/8g/gsubr.c
index a94086e7c1..c5f6c22428 100644
--- a/src/cmd/8g/gsubr.c
+++ b/src/cmd/8g/gsubr.c
@@ -224,6 +224,17 @@ ggloblsym(Sym *s, int32 width, int dupok, int rodata)
 		p->from.scale |= RODATA;
 }
 
+void
+gtrack(Sym *s)
+{
+	Prog *p;
+	
+	p = gins(AUSEFIELD, N, N);
+	p->from.type = D_EXTERN;
+	p->from.index = D_NONE;
+	p->from.sym = s;
+}
+
 int
 isfat(Type *t)
 {
diff --git a/src/cmd/8l/8.out.h b/src/cmd/8l/8.out.h
index 27040be8bf..6a2d46c62e 100644
--- a/src/cmd/8l/8.out.h
+++ b/src/cmd/8l/8.out.h
@@ -566,6 +566,8 @@ enum	as
 	AUNPCKLPS,
 	AXORPD,
 	AXORPS,
+	
+	AUSEFIELD,
 
 	ALAST
 };
diff --git a/src/cmd/8l/l.h b/src/cmd/8l/l.h
index 8cf0fde3ac..96b425874d 100644
--- a/src/cmd/8l/l.h
+++ b/src/cmd/8l/l.h
@@ -143,6 +143,8 @@ struct	Sym
 	Sym*	sub;	// in sub list
 	Sym*	outer;	// container of sub
 	Sym*	gotype;
+	Sym*	reachparent;
+	Sym*	queue;
 	char*	file;
 	char*	dynimpname;
 	char*	dynimplib;
diff --git a/src/cmd/8l/obj.c b/src/cmd/8l/obj.c
index 19e351d998..eebf9fcfe5 100644
--- a/src/cmd/8l/obj.c
+++ b/src/cmd/8l/obj.c
@@ -149,6 +149,9 @@ main(int argc, char *argv[])
 		val = EARGF(usage());
 		addbuildinfo(val);
 		break;
+	case 'k':
+		tracksym = EARGF(usage());
+		break;
 	} ARGEND
 
 	if(argc != 1)
diff --git a/src/cmd/8l/optab.c b/src/cmd/8l/optab.c
index de87e22ecc..865871ce5c 100644
--- a/src/cmd/8l/optab.c
+++ b/src/cmd/8l/optab.c
@@ -960,5 +960,7 @@ Optab optab[] =
 	{ AXORPD,	yxm,	Pe, 0x57 },
 	{ AXORPS,	yxm,	Pm, 0x57 },
 
+	{ AUSEFIELD,	ynop,	Px, 0,0 },
+
 	0
 };
diff --git a/src/cmd/gc/dcl.c b/src/cmd/gc/dcl.c
index f7e52777fc..d20f64357b 100644
--- a/src/cmd/gc/dcl.c
+++ b/src/cmd/gc/dcl.c
@@ -1269,7 +1269,7 @@ methodname1(Node *n, Node *t)
  * n is fieldname, pa is base type, t is function type
  */
 void
-addmethod(Sym *sf, Type *t, int local)
+addmethod(Sym *sf, Type *t, int local, int nointerface)
 {
 	Type *f, *d, *pa;
 	Node *n;
@@ -1352,6 +1352,7 @@ addmethod(Sym *sf, Type *t, int local)
 	}
 
 	f = structfield(n);
+	f->nointerface = nointerface;
 
 	// during import unexported method names should be in the type's package
 	if(importpkg && f->sym && !exportname(f->sym->name) && f->sym->pkg != structpkg)
diff --git a/src/cmd/gc/export.c b/src/cmd/gc/export.c
index 7f977874a1..7db713e481 100644
--- a/src/cmd/gc/export.c
+++ b/src/cmd/gc/export.c
@@ -278,6 +278,8 @@ dumpexporttype(Type *t)
 			// currently that can leave unresolved ONONAMEs in import-dot-ed packages in the wrong package
 			if(debug['l'] < 2)
 				typecheckinl(f->type->nname);
+			if(f->nointerface)
+				Bprint(bout, "\t//go:nointerface\n");
 			Bprint(bout, "\tfunc (%#T) %#hhS%#hT { %#H }\n", getthisx(f->type)->type, f->sym, f->type, f->type->nname->inl);
 			reexportdeplist(f->type->nname->inl);
 		} else
diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index 06f6e34f3a..22718889a7 100644
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -137,6 +137,7 @@ typedef	struct	Label	Label;
 struct	Type
 {
 	uchar	etype;
+	uchar	nointerface;
 	uchar	chan;
 	uchar	trecur;		// to detect loops
 	uchar	printed;
@@ -175,6 +176,7 @@ struct	Type
 
 	// TFIELD
 	Type*	down;		// next struct field, also key type in TMAP
+	Type*	outer;		// outer struct
 	Strlit*	note;		// literal string annotation
 
 	// TARRAY
@@ -185,6 +187,9 @@ struct	Type
 	
 	// for TFORW, where to copy the eventual value to
 	NodeList	*copyto;
+	
+	// for usefield
+	Node	*lastfn;
 };
 #define	T	((Type*)0)
 
@@ -236,6 +241,7 @@ struct	Node
 	NodeList*	rlist;
 
 	uchar	op;
+	uchar	nointerface;
 	uchar	ullman;		// sethi/ullman number
 	uchar	addable;	// type of addressability - 0 is not addressable
 	uchar	trecur;		// to detect loops
@@ -284,7 +290,7 @@ struct	Node
 	Node*	defn;	// ONAME: initializing assignment; OLABEL: labeled statement
 	Node*	pack;	// real package for import . names
 	Node*	curfn;	// function for local variables
-	Type*	paramfld; // TFIELD for this PPARAM
+	Type*	paramfld; // TFIELD for this PPARAM; also for ODOT, curfn
 
 	// ONAME func param with PHEAP
 	Node*	heapaddr;	// temp holding heap address of param
@@ -849,6 +855,7 @@ EXTERN	Pkg*	stringpkg;	// fake package for C strings
 EXTERN	Pkg*	typepkg;	// fake package for runtime type info
 EXTERN	Pkg*	weaktypepkg;	// weak references to runtime type info
 EXTERN	Pkg*	unsafepkg;	// package unsafe
+EXTERN	Pkg*	trackpkg;	// fake package for field tracking
 EXTERN	Pkg*	phash[128];
 EXTERN	int	tptr;		// either TPTR32 or TPTR64
 extern	char*	runtimeimport;
@@ -929,6 +936,9 @@ EXTERN	int	typecheckok;
 EXTERN	int	compiling_runtime;
 EXTERN	int	compiling_wrappers;
 
+EXTERN	int	nointerface;
+EXTERN	int	fieldtrack_enabled;
+
 /*
  *	y.tab.c
  */
@@ -1004,7 +1014,7 @@ void	nodfconst(Node *n, Type *t, Mpflt* fval);
 /*
  *	dcl.c
  */
-void	addmethod(Sym *sf, Type *t, int local);
+void	addmethod(Sym *sf, Type *t, int local, int nointerface);
 void	addvar(Node *n, Type *t, int ctxt);
 NodeList*	checkarglist(NodeList *all, int input);
 Node*	colas(NodeList *left, NodeList *right, int32 lno);
@@ -1200,8 +1210,10 @@ void	dumptypestructs(void);
 Type*	methodfunc(Type *f, Type*);
 Node*	typename(Type *t);
 Sym*	typesym(Type *t);
+Sym*	tracksym(Type *t);
 Sym*	typesymprefix(char *prefix, Type *t);
 int	haspointers(Type *t);
+void	usefield(Node*);
 
 /*
  *	select.c
diff --git a/src/cmd/gc/go.y b/src/cmd/gc/go.y
index e9dcd506e7..0f2622c3b8 100644
--- a/src/cmd/gc/go.y
+++ b/src/cmd/gc/go.y
@@ -1275,6 +1275,7 @@ fndcl:
 		$$->nname = methodname1($$->shortname, rcvr->right);
 		$$->nname->defn = $$;
 		$$->nname->ntype = t;
+		$$->nname->nointerface = nointerface;
 		declare($$->nname, PFUNC);
 
 		funchdr($$);
@@ -1312,7 +1313,8 @@ hidden_fndcl:
 		$$->type = functype($2->n, $6, $8);
 
 		checkwidth($$->type);
-		addmethod($4, $$->type, 0);
+		addmethod($4, $$->type, 0, nointerface);
+		nointerface = 0;
 		funchdr($$);
 		
 		// inl.c's inlnode in on a dotmeth node expects to find the inlineable body as
@@ -1389,6 +1391,7 @@ xdcl_list:
 		$$ = concat($1, $2);
 		if(nsyntaxerrors == 0)
 			testdclstack();
+		nointerface = 0;
 	}
 
 vardcl_list:
diff --git a/src/cmd/gc/lex.c b/src/cmd/gc/lex.c
index 920de6f635..d31395c1d0 100644
--- a/src/cmd/gc/lex.c
+++ b/src/cmd/gc/lex.c
@@ -40,6 +40,7 @@ static struct {
 	int *val;
 } exper[] = {
 //	{"rune32", &rune32},
+	{"fieldtrack", &fieldtrack_enabled},
 	{nil, nil},
 };
 
@@ -199,9 +200,19 @@ main(int argc, char *argv[])
 
 	localpkg = mkpkg(strlit(""));
 	localpkg->prefix = "\"\"";
-
+	
+	// pseudo-package, for scoping
 	builtinpkg = mkpkg(strlit("go.builtin"));
 
+	// pseudo-package, accessed by import "unsafe"
+	unsafepkg = mkpkg(strlit("unsafe"));
+	unsafepkg->name = "unsafe";
+
+	// real package, referred to by generated runtime calls
+	runtimepkg = mkpkg(strlit("runtime"));
+	runtimepkg->name = "runtime";
+
+	// pseudo-packages used in symbol tables
 	gostringpkg = mkpkg(strlit("go.string"));
 	gostringpkg->name = "go.string";
 	gostringpkg->prefix = "go.string";	// not go%2estring
@@ -210,18 +221,16 @@ main(int argc, char *argv[])
 	itabpkg->name = "go.itab";
 	itabpkg->prefix = "go.itab";	// not go%2eitab
 
-	runtimepkg = mkpkg(strlit("runtime"));
-	runtimepkg->name = "runtime";
-
-	typepkg = mkpkg(strlit("type"));
-	typepkg->name = "type";
-
 	weaktypepkg = mkpkg(strlit("go.weak.type"));
 	weaktypepkg->name = "go.weak.type";
 	weaktypepkg->prefix = "go.weak.type";  // not go%2eweak%2etype
 
-	unsafepkg = mkpkg(strlit("unsafe"));
-	unsafepkg->name = "unsafe";
+	trackpkg = mkpkg(strlit("go.track"));
+	trackpkg->name = "go.track";
+	trackpkg->prefix = "go.track";  // not go%2etrack
+
+	typepkg = mkpkg(strlit("type"));
+	typepkg->name = "type";
 
 	goroot = getgoroot();
 	goos = getgoos();
@@ -1443,7 +1452,12 @@ getlinepragma(void)
 	char *cp, *ep, *linep;
 	Hist *h;
 
-	for(i=0; i<5; i++) {
+	c = getr();
+	if(c == 'g' && fieldtrack_enabled)
+		goto go;
+	if(c != 'l')	
+		goto out;
+	for(i=1; i<5; i++) {
 		c = getr();
 		if(c != "line "[i])
 			goto out;
@@ -1491,6 +1505,20 @@ getlinepragma(void)
 		}
 	}
 	linehist(strdup(lexbuf), n, 0);
+	goto out;
+
+go:
+	for(i=1; i<11; i++) {
+		c = getr();
+		if(c != "go:nointerface"[i])
+			goto out;
+	}
+	nointerface = 1;
+	for(;;) {
+		c = getr();
+		if(c == EOF || c == '\n')
+			break;
+	}
 
 out:
 	return c;
diff --git a/src/cmd/gc/pgen.c b/src/cmd/gc/pgen.c
index 46b763bf09..7be254fff1 100644
--- a/src/cmd/gc/pgen.c
+++ b/src/cmd/gc/pgen.c
@@ -83,6 +83,10 @@ compile(Node *fn)
 	afunclit(&ptxt->from);
 
 	ginit();
+
+	for(t=curfn->paramfld; t; t=t->down)
+		gtrack(tracksym(t->type));
+
 	genlist(curfn->enter);
 
 	retpc = nil;
@@ -115,6 +119,7 @@ compile(Node *fn)
 	gclean();
 	if(nerrors != 0)
 		goto ret;
+
 	pc->as = ARET;	// overwrite AEND
 	pc->lineno = lineno;
 
diff --git a/src/cmd/gc/reflect.c b/src/cmd/gc/reflect.c
index 8e4f0a4d27..00d6f5fe76 100644
--- a/src/cmd/gc/reflect.c
+++ b/src/cmd/gc/reflect.c
@@ -172,6 +172,8 @@ methods(Type *t)
 			fatal("non-method on %T method %S %T\n", mt, f->sym, f);
 		if (!getthisx(f->type)->type)
 			fatal("receiver with no type on %T method %S %T\n", mt, f->sym, f);
+		if(f->nointerface)
+			continue;
 
 		method = f->sym;
 		if(method == nil)
@@ -622,6 +624,18 @@ typesym(Type *t)
 	return s;
 }
 
+Sym*
+tracksym(Type *t)
+{
+	char *p;
+	Sym *s;
+
+	p = smprint("%-T.%s", t->outer, t->sym->name);
+	s = pkglookup(p, trackpkg);
+	free(p);
+	return s;
+}
+
 Sym*
 typesymprefix(char *prefix, Type *t)
 {
@@ -1155,4 +1169,3 @@ dgcsym(Type *t)
 
 	return s;
 }
-
diff --git a/src/cmd/gc/subr.c b/src/cmd/gc/subr.c
index 8409a442a0..142921153d 100644
--- a/src/cmd/gc/subr.c
+++ b/src/cmd/gc/subr.c
@@ -3040,7 +3040,7 @@ implements(Type *t, Type *iface, Type **m, Type **samename, int *ptr)
 	for(im=iface->type; im; im=im->down) {
 		imtype = methodfunc(im->type, 0);
 		tm = ifacelookdot(im->sym, t, &followptr, 0);
-		if(tm == T || !eqtype(methodfunc(tm->type, 0), imtype)) {
+		if(tm == T || tm->nointerface || !eqtype(methodfunc(tm->type, 0), imtype)) {
 			if(tm == T)
 				tm = ifacelookdot(im->sym, t, &followptr, 1);
 			*m = im;
diff --git a/src/cmd/gc/typecheck.c b/src/cmd/gc/typecheck.c
index 6f3449eec3..b109d3a119 100644
--- a/src/cmd/gc/typecheck.c
+++ b/src/cmd/gc/typecheck.c
@@ -1833,6 +1833,7 @@ lookdot(Node *n, Type *t, int dostrcmp)
 			fatal("lookdot badwidth %T %p", f1, f1);
 		n->xoffset = f1->width;
 		n->type = f1->type;
+		n->paramfld = f1;
 		if(t->etype == TINTER) {
 			if(isptr[n->left->type->etype]) {
 				n->left = nod(OIND, n->left, N);	// implicitstar
@@ -2637,7 +2638,7 @@ typecheckfunc(Node *n)
 	t->nname = n->nname;
 	rcvr = getthisx(t)->type;
 	if(rcvr != nil && n->shortname != N && !isblank(n->shortname))
-		addmethod(n->shortname->sym, t, 1);
+		addmethod(n->shortname->sym, t, 1, n->nname->nointerface);
 }
 
 static void
diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 9e6d57c860..11c9c2f435 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -429,14 +429,19 @@ walkexpr(Node **np, NodeList **init)
 	case OCOM:
 	case OREAL:
 	case OIMAG:
-	case ODOT:
-	case ODOTPTR:
 	case ODOTMETH:
 	case ODOTINTER:
 	case OIND:
 		walkexpr(&n->left, init);
 		goto ret;
 
+	case ODOT:
+	case ODOTPTR:
+		usefield(n);
+		walkexpr(&n->left, init);
+		goto ret;
+		
+
 	case OEFACE:
 		walkexpr(&n->left, init);
 		walkexpr(&n->right, init);
@@ -2897,3 +2902,44 @@ bounded(Node *n, int64 max)
 	
 	return 0;
 }
+
+void
+usefield(Node *n)
+{
+	Type *field, *l;
+
+	if(!fieldtrack_enabled)
+		return;
+
+	switch(n->op) {
+	default:
+		fatal("usefield %O", n->op);
+	case ODOT:
+	case ODOTPTR:
+		break;
+	}
+	
+	field = n->paramfld;
+	if(field == T)
+		fatal("usefield %T %S without paramfld", n->left->type, n->right->sym);
+	if(field->note == nil || strstr(field->note->s, "go:\"track\"") == nil)
+		return;
+
+	// dedup on list
+	if(field->lastfn == curfn)
+		return;
+	field->lastfn = curfn;
+	field->outer = n->left->type;
+	if(isptr[field->outer->etype])
+		field->outer = field->outer->type;
+	if(field->outer->sym == S)
+		yyerror("tracked field must be in named struct type");
+	if(!exportname(field->sym->name))
+		yyerror("tracked field must be exported (upper case)");
+
+	l = typ(0);
+	l->type = field;
+	l->down = curfn->paramfld;
+	curfn->paramfld = l;
+}
+
diff --git a/src/cmd/gc/y.tab.c b/src/cmd/gc/y.tab.c
index 478b463486..b2ed8302ee 100644
--- a/src/cmd/gc/y.tab.c
+++ b/src/cmd/gc/y.tab.c
@@ -674,21 +674,21 @@ static const yytype_uint16 yyrline[] =
     1098,  1099,  1100,  1101,  1107,  1108,  1111,  1114,  1115,  1116,
     1117,  1118,  1121,  1122,  1135,  1139,  1144,  1149,  1154,  1158,
     1159,  1162,  1168,  1175,  1181,  1188,  1194,  1205,  1216,  1245,
-    1284,  1309,  1326,  1335,  1338,  1346,  1350,  1354,  1361,  1367,
-    1372,  1384,  1387,  1395,  1396,  1402,  1403,  1409,  1413,  1419,
-    1420,  1426,  1430,  1436,  1459,  1464,  1470,  1476,  1483,  1492,
-    1501,  1516,  1522,  1527,  1531,  1538,  1551,  1552,  1558,  1564,
-    1567,  1571,  1577,  1580,  1589,  1592,  1593,  1597,  1598,  1604,
-    1605,  1606,  1607,  1608,  1610,  1609,  1624,  1629,  1633,  1637,
-    1641,  1645,  1650,  1669,  1675,  1683,  1687,  1693,  1697,  1703,
-    1707,  1713,  1717,  1726,  1730,  1734,  1738,  1744,  1747,  1755,
-    1756,  1758,  1759,  1762,  1765,  1768,  1771,  1774,  1777,  1780,
-    1783,  1786,  1789,  1792,  1795,  1798,  1801,  1807,  1811,  1815,
-    1819,  1823,  1827,  1847,  1854,  1865,  1866,  1867,  1870,  1871,
-    1874,  1878,  1888,  1892,  1896,  1900,  1904,  1908,  1912,  1918,
-    1924,  1932,  1940,  1946,  1953,  1969,  1987,  1991,  1997,  2000,
-    2003,  2007,  2017,  2021,  2036,  2044,  2045,  2057,  2058,  2061,
-    2065,  2071,  2075,  2081,  2085
+    1285,  1310,  1328,  1337,  1340,  1348,  1352,  1356,  1363,  1369,
+    1374,  1386,  1389,  1398,  1399,  1405,  1406,  1412,  1416,  1422,
+    1423,  1429,  1433,  1439,  1462,  1467,  1473,  1479,  1486,  1495,
+    1504,  1519,  1525,  1530,  1534,  1541,  1554,  1555,  1561,  1567,
+    1570,  1574,  1580,  1583,  1592,  1595,  1596,  1600,  1601,  1607,
+    1608,  1609,  1610,  1611,  1613,  1612,  1627,  1632,  1636,  1640,
+    1644,  1648,  1653,  1672,  1678,  1686,  1690,  1696,  1700,  1706,
+    1710,  1716,  1720,  1729,  1733,  1737,  1741,  1747,  1750,  1758,
+    1759,  1761,  1762,  1765,  1768,  1771,  1774,  1777,  1780,  1783,
+    1786,  1789,  1792,  1795,  1798,  1801,  1804,  1810,  1814,  1818,
+    1822,  1826,  1830,  1850,  1857,  1868,  1869,  1870,  1873,  1874,
+    1877,  1881,  1891,  1895,  1899,  1903,  1907,  1911,  1915,  1921,
+    1927,  1935,  1943,  1949,  1956,  1972,  1990,  1994,  2000,  2003,
+    2006,  2010,  2020,  2024,  2039,  2047,  2048,  2060,  2061,  2064,
+    2068,  2074,  2078,  2084,  2088
 };
 #endif
 
@@ -3731,6 +3731,7 @@ yyreduce:
 		(yyval.node)->nname = methodname1((yyval.node)->shortname, rcvr->right);
 		(yyval.node)->nname->defn = (yyval.node);
 		(yyval.node)->nname->ntype = t;
+		(yyval.node)->nname->nointerface = nointerface;
 		declare((yyval.node)->nname, PFUNC);
 
 		funchdr((yyval.node));
@@ -3738,7 +3739,7 @@ yyreduce:
     break;
 
   case 200:
-#line 1285 "go.y"
+#line 1286 "go.y"
     {
 		Sym *s;
 		Type *t;
@@ -3766,13 +3767,14 @@ yyreduce:
     break;
 
   case 201:
-#line 1310 "go.y"
+#line 1311 "go.y"
     {
 		(yyval.node) = methodname1(newname((yyvsp[(4) - (8)].sym)), (yyvsp[(2) - (8)].list)->n->right); 
 		(yyval.node)->type = functype((yyvsp[(2) - (8)].list)->n, (yyvsp[(6) - (8)].list), (yyvsp[(8) - (8)].list));
 
 		checkwidth((yyval.node)->type);
-		addmethod((yyvsp[(4) - (8)].sym), (yyval.node)->type, 0);
+		addmethod((yyvsp[(4) - (8)].sym), (yyval.node)->type, 0, nointerface);
+		nointerface = 0;
 		funchdr((yyval.node));
 		
 		// inl.c's inlnode in on a dotmeth node expects to find the inlineable body as
@@ -3784,7 +3786,7 @@ yyreduce:
     break;
 
   case 202:
-#line 1327 "go.y"
+#line 1329 "go.y"
     {
 		(yyvsp[(3) - (5)].list) = checkarglist((yyvsp[(3) - (5)].list), 1);
 		(yyval.node) = nod(OTFUNC, N, N);
@@ -3794,14 +3796,14 @@ yyreduce:
     break;
 
   case 203:
-#line 1335 "go.y"
+#line 1337 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 204:
-#line 1339 "go.y"
+#line 1341 "go.y"
     {
 		(yyval.list) = (yyvsp[(2) - (3)].list);
 		if((yyval.list) == nil)
@@ -3810,21 +3812,21 @@ yyreduce:
     break;
 
   case 205:
-#line 1347 "go.y"
+#line 1349 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 206:
-#line 1351 "go.y"
+#line 1353 "go.y"
     {
 		(yyval.list) = list1(nod(ODCLFIELD, N, (yyvsp[(1) - (1)].node)));
 	}
     break;
 
   case 207:
-#line 1355 "go.y"
+#line 1357 "go.y"
     {
 		(yyvsp[(2) - (3)].list) = checkarglist((yyvsp[(2) - (3)].list), 0);
 		(yyval.list) = (yyvsp[(2) - (3)].list);
@@ -3832,14 +3834,14 @@ yyreduce:
     break;
 
   case 208:
-#line 1362 "go.y"
+#line 1364 "go.y"
     {
 		closurehdr((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 209:
-#line 1368 "go.y"
+#line 1370 "go.y"
     {
 		(yyval.node) = closurebody((yyvsp[(3) - (4)].list));
 		fixlbrace((yyvsp[(2) - (4)].i));
@@ -3847,79 +3849,80 @@ yyreduce:
     break;
 
   case 210:
-#line 1373 "go.y"
+#line 1375 "go.y"
     {
 		(yyval.node) = closurebody(nil);
 	}
     break;
 
   case 211:
-#line 1384 "go.y"
+#line 1386 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 212:
-#line 1388 "go.y"
+#line 1390 "go.y"
     {
 		(yyval.list) = concat((yyvsp[(1) - (3)].list), (yyvsp[(2) - (3)].list));
 		if(nsyntaxerrors == 0)
 			testdclstack();
+		nointerface = 0;
 	}
     break;
 
   case 214:
-#line 1397 "go.y"
+#line 1400 "go.y"
     {
 		(yyval.list) = concat((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].list));
 	}
     break;
 
   case 216:
-#line 1404 "go.y"
+#line 1407 "go.y"
     {
 		(yyval.list) = concat((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].list));
 	}
     break;
 
   case 217:
-#line 1410 "go.y"
+#line 1413 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 218:
-#line 1414 "go.y"
+#line 1417 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 220:
-#line 1421 "go.y"
+#line 1424 "go.y"
     {
 		(yyval.list) = concat((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].list));
 	}
     break;
 
   case 221:
-#line 1427 "go.y"
+#line 1430 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 222:
-#line 1431 "go.y"
+#line 1434 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 223:
-#line 1437 "go.y"
+#line 1440 "go.y"
     {
 		NodeList *l;
 
@@ -3945,7 +3948,7 @@ yyreduce:
     break;
 
   case 224:
-#line 1460 "go.y"
+#line 1463 "go.y"
     {
 		(yyvsp[(1) - (2)].node)->val = (yyvsp[(2) - (2)].val);
 		(yyval.list) = list1((yyvsp[(1) - (2)].node));
@@ -3953,7 +3956,7 @@ yyreduce:
     break;
 
   case 225:
-#line 1465 "go.y"
+#line 1468 "go.y"
     {
 		(yyvsp[(2) - (4)].node)->val = (yyvsp[(4) - (4)].val);
 		(yyval.list) = list1((yyvsp[(2) - (4)].node));
@@ -3962,7 +3965,7 @@ yyreduce:
     break;
 
   case 226:
-#line 1471 "go.y"
+#line 1474 "go.y"
     {
 		(yyvsp[(2) - (3)].node)->right = nod(OIND, (yyvsp[(2) - (3)].node)->right, N);
 		(yyvsp[(2) - (3)].node)->val = (yyvsp[(3) - (3)].val);
@@ -3971,7 +3974,7 @@ yyreduce:
     break;
 
   case 227:
-#line 1477 "go.y"
+#line 1480 "go.y"
     {
 		(yyvsp[(3) - (5)].node)->right = nod(OIND, (yyvsp[(3) - (5)].node)->right, N);
 		(yyvsp[(3) - (5)].node)->val = (yyvsp[(5) - (5)].val);
@@ -3981,7 +3984,7 @@ yyreduce:
     break;
 
   case 228:
-#line 1484 "go.y"
+#line 1487 "go.y"
     {
 		(yyvsp[(3) - (5)].node)->right = nod(OIND, (yyvsp[(3) - (5)].node)->right, N);
 		(yyvsp[(3) - (5)].node)->val = (yyvsp[(5) - (5)].val);
@@ -3991,7 +3994,7 @@ yyreduce:
     break;
 
   case 229:
-#line 1493 "go.y"
+#line 1496 "go.y"
     {
 		Node *n;
 
@@ -4003,7 +4006,7 @@ yyreduce:
     break;
 
   case 230:
-#line 1502 "go.y"
+#line 1505 "go.y"
     {
 		Pkg *pkg;
 
@@ -4019,14 +4022,14 @@ yyreduce:
     break;
 
   case 231:
-#line 1517 "go.y"
+#line 1520 "go.y"
     {
 		(yyval.node) = embedded((yyvsp[(1) - (1)].sym));
 	}
     break;
 
   case 232:
-#line 1523 "go.y"
+#line 1526 "go.y"
     {
 		(yyval.node) = nod(ODCLFIELD, (yyvsp[(1) - (2)].node), (yyvsp[(2) - (2)].node));
 		ifacedcl((yyval.node));
@@ -4034,14 +4037,14 @@ yyreduce:
     break;
 
   case 233:
-#line 1528 "go.y"
+#line 1531 "go.y"
     {
 		(yyval.node) = nod(ODCLFIELD, N, oldname((yyvsp[(1) - (1)].sym)));
 	}
     break;
 
   case 234:
-#line 1532 "go.y"
+#line 1535 "go.y"
     {
 		(yyval.node) = nod(ODCLFIELD, N, oldname((yyvsp[(2) - (3)].sym)));
 		yyerror("cannot parenthesize embedded type");
@@ -4049,7 +4052,7 @@ yyreduce:
     break;
 
   case 235:
-#line 1539 "go.y"
+#line 1542 "go.y"
     {
 		// without func keyword
 		(yyvsp[(2) - (4)].list) = checkarglist((yyvsp[(2) - (4)].list), 1);
@@ -4060,7 +4063,7 @@ yyreduce:
     break;
 
   case 237:
-#line 1553 "go.y"
+#line 1556 "go.y"
     {
 		(yyval.node) = nod(ONONAME, N, N);
 		(yyval.node)->sym = (yyvsp[(1) - (2)].sym);
@@ -4069,7 +4072,7 @@ yyreduce:
     break;
 
   case 238:
-#line 1559 "go.y"
+#line 1562 "go.y"
     {
 		(yyval.node) = nod(ONONAME, N, N);
 		(yyval.node)->sym = (yyvsp[(1) - (2)].sym);
@@ -4078,56 +4081,56 @@ yyreduce:
     break;
 
   case 240:
-#line 1568 "go.y"
+#line 1571 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 241:
-#line 1572 "go.y"
+#line 1575 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 242:
-#line 1577 "go.y"
+#line 1580 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 243:
-#line 1581 "go.y"
+#line 1584 "go.y"
     {
 		(yyval.list) = (yyvsp[(1) - (2)].list);
 	}
     break;
 
   case 244:
-#line 1589 "go.y"
+#line 1592 "go.y"
     {
 		(yyval.node) = N;
 	}
     break;
 
   case 246:
-#line 1594 "go.y"
+#line 1597 "go.y"
     {
 		(yyval.node) = liststmt((yyvsp[(1) - (1)].list));
 	}
     break;
 
   case 248:
-#line 1599 "go.y"
+#line 1602 "go.y"
     {
 		(yyval.node) = N;
 	}
     break;
 
   case 254:
-#line 1610 "go.y"
+#line 1613 "go.y"
     {
 		(yyvsp[(1) - (2)].node) = nod(OLABEL, (yyvsp[(1) - (2)].node), N);
 		(yyvsp[(1) - (2)].node)->sym = dclstack;  // context, for goto restrictions
@@ -4135,7 +4138,7 @@ yyreduce:
     break;
 
   case 255:
-#line 1615 "go.y"
+#line 1618 "go.y"
     {
 		NodeList *l;
 
@@ -4148,7 +4151,7 @@ yyreduce:
     break;
 
   case 256:
-#line 1625 "go.y"
+#line 1628 "go.y"
     {
 		// will be converted to OFALL
 		(yyval.node) = nod(OXFALL, N, N);
@@ -4156,35 +4159,35 @@ yyreduce:
     break;
 
   case 257:
-#line 1630 "go.y"
+#line 1633 "go.y"
     {
 		(yyval.node) = nod(OBREAK, (yyvsp[(2) - (2)].node), N);
 	}
     break;
 
   case 258:
-#line 1634 "go.y"
+#line 1637 "go.y"
     {
 		(yyval.node) = nod(OCONTINUE, (yyvsp[(2) - (2)].node), N);
 	}
     break;
 
   case 259:
-#line 1638 "go.y"
+#line 1641 "go.y"
     {
 		(yyval.node) = nod(OPROC, (yyvsp[(2) - (2)].node), N);
 	}
     break;
 
   case 260:
-#line 1642 "go.y"
+#line 1645 "go.y"
     {
 		(yyval.node) = nod(ODEFER, (yyvsp[(2) - (2)].node), N);
 	}
     break;
 
   case 261:
-#line 1646 "go.y"
+#line 1649 "go.y"
     {
 		(yyval.node) = nod(OGOTO, (yyvsp[(2) - (2)].node), N);
 		(yyval.node)->sym = dclstack;  // context, for goto restrictions
@@ -4192,7 +4195,7 @@ yyreduce:
     break;
 
   case 262:
-#line 1651 "go.y"
+#line 1654 "go.y"
     {
 		(yyval.node) = nod(ORETURN, N, N);
 		(yyval.node)->list = (yyvsp[(2) - (2)].list);
@@ -4212,7 +4215,7 @@ yyreduce:
     break;
 
   case 263:
-#line 1670 "go.y"
+#line 1673 "go.y"
     {
 		(yyval.list) = nil;
 		if((yyvsp[(1) - (1)].node) != N)
@@ -4221,7 +4224,7 @@ yyreduce:
     break;
 
   case 264:
-#line 1676 "go.y"
+#line 1679 "go.y"
     {
 		(yyval.list) = (yyvsp[(1) - (3)].list);
 		if((yyvsp[(3) - (3)].node) != N)
@@ -4230,189 +4233,189 @@ yyreduce:
     break;
 
   case 265:
-#line 1684 "go.y"
+#line 1687 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 266:
-#line 1688 "go.y"
+#line 1691 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 267:
-#line 1694 "go.y"
+#line 1697 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 268:
-#line 1698 "go.y"
+#line 1701 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 269:
-#line 1704 "go.y"
+#line 1707 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 270:
-#line 1708 "go.y"
+#line 1711 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 271:
-#line 1714 "go.y"
+#line 1717 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 272:
-#line 1718 "go.y"
+#line 1721 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 273:
-#line 1727 "go.y"
+#line 1730 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 274:
-#line 1731 "go.y"
+#line 1734 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 275:
-#line 1735 "go.y"
+#line 1738 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 276:
-#line 1739 "go.y"
+#line 1742 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 277:
-#line 1744 "go.y"
+#line 1747 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 278:
-#line 1748 "go.y"
+#line 1751 "go.y"
     {
 		(yyval.list) = (yyvsp[(1) - (2)].list);
 	}
     break;
 
   case 283:
-#line 1762 "go.y"
+#line 1765 "go.y"
     {
 		(yyval.node) = N;
 	}
     break;
 
   case 285:
-#line 1768 "go.y"
+#line 1771 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 287:
-#line 1774 "go.y"
+#line 1777 "go.y"
     {
 		(yyval.node) = N;
 	}
     break;
 
   case 289:
-#line 1780 "go.y"
+#line 1783 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 291:
-#line 1786 "go.y"
+#line 1789 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 293:
-#line 1792 "go.y"
+#line 1795 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 295:
-#line 1798 "go.y"
+#line 1801 "go.y"
     {
 		(yyval.val).ctype = CTxxx;
 	}
     break;
 
   case 297:
-#line 1808 "go.y"
+#line 1811 "go.y"
     {
 		importimport((yyvsp[(2) - (4)].sym), (yyvsp[(3) - (4)].val).u.sval);
 	}
     break;
 
   case 298:
-#line 1812 "go.y"
+#line 1815 "go.y"
     {
 		importvar((yyvsp[(2) - (4)].sym), (yyvsp[(3) - (4)].type));
 	}
     break;
 
   case 299:
-#line 1816 "go.y"
+#line 1819 "go.y"
     {
 		importconst((yyvsp[(2) - (5)].sym), types[TIDEAL], (yyvsp[(4) - (5)].node));
 	}
     break;
 
   case 300:
-#line 1820 "go.y"
+#line 1823 "go.y"
     {
 		importconst((yyvsp[(2) - (6)].sym), (yyvsp[(3) - (6)].type), (yyvsp[(5) - (6)].node));
 	}
     break;
 
   case 301:
-#line 1824 "go.y"
+#line 1827 "go.y"
     {
 		importtype((yyvsp[(2) - (4)].type), (yyvsp[(3) - (4)].type));
 	}
     break;
 
   case 302:
-#line 1828 "go.y"
+#line 1831 "go.y"
     {
 		if((yyvsp[(2) - (4)].node) == N) {
 			dclcontext = PEXTERN;  // since we skip the funcbody below
@@ -4433,7 +4436,7 @@ yyreduce:
     break;
 
   case 303:
-#line 1848 "go.y"
+#line 1851 "go.y"
     {
 		(yyval.sym) = (yyvsp[(1) - (1)].sym);
 		structpkg = (yyval.sym)->pkg;
@@ -4441,7 +4444,7 @@ yyreduce:
     break;
 
   case 304:
-#line 1855 "go.y"
+#line 1858 "go.y"
     {
 		(yyval.type) = pkgtype((yyvsp[(1) - (1)].sym));
 		importsym((yyvsp[(1) - (1)].sym), OTYPE);
@@ -4449,14 +4452,14 @@ yyreduce:
     break;
 
   case 310:
-#line 1875 "go.y"
+#line 1878 "go.y"
     {
 		(yyval.type) = pkgtype((yyvsp[(1) - (1)].sym));
 	}
     break;
 
   case 311:
-#line 1879 "go.y"
+#line 1882 "go.y"
     {
 		// predefined name like uint8
 		(yyvsp[(1) - (1)].sym) = pkglookup((yyvsp[(1) - (1)].sym)->name, builtinpkg);
@@ -4469,49 +4472,49 @@ yyreduce:
     break;
 
   case 312:
-#line 1889 "go.y"
+#line 1892 "go.y"
     {
 		(yyval.type) = aindex(N, (yyvsp[(3) - (3)].type));
 	}
     break;
 
   case 313:
-#line 1893 "go.y"
+#line 1896 "go.y"
     {
 		(yyval.type) = aindex(nodlit((yyvsp[(2) - (4)].val)), (yyvsp[(4) - (4)].type));
 	}
     break;
 
   case 314:
-#line 1897 "go.y"
+#line 1900 "go.y"
     {
 		(yyval.type) = maptype((yyvsp[(3) - (5)].type), (yyvsp[(5) - (5)].type));
 	}
     break;
 
   case 315:
-#line 1901 "go.y"
+#line 1904 "go.y"
     {
 		(yyval.type) = tostruct((yyvsp[(3) - (4)].list));
 	}
     break;
 
   case 316:
-#line 1905 "go.y"
+#line 1908 "go.y"
     {
 		(yyval.type) = tointerface((yyvsp[(3) - (4)].list));
 	}
     break;
 
   case 317:
-#line 1909 "go.y"
+#line 1912 "go.y"
     {
 		(yyval.type) = ptrto((yyvsp[(2) - (2)].type));
 	}
     break;
 
   case 318:
-#line 1913 "go.y"
+#line 1916 "go.y"
     {
 		(yyval.type) = typ(TCHAN);
 		(yyval.type)->type = (yyvsp[(2) - (2)].type);
@@ -4520,7 +4523,7 @@ yyreduce:
     break;
 
   case 319:
-#line 1919 "go.y"
+#line 1922 "go.y"
     {
 		(yyval.type) = typ(TCHAN);
 		(yyval.type)->type = (yyvsp[(3) - (4)].type);
@@ -4529,7 +4532,7 @@ yyreduce:
     break;
 
   case 320:
-#line 1925 "go.y"
+#line 1928 "go.y"
     {
 		(yyval.type) = typ(TCHAN);
 		(yyval.type)->type = (yyvsp[(3) - (3)].type);
@@ -4538,7 +4541,7 @@ yyreduce:
     break;
 
   case 321:
-#line 1933 "go.y"
+#line 1936 "go.y"
     {
 		(yyval.type) = typ(TCHAN);
 		(yyval.type)->type = (yyvsp[(3) - (3)].type);
@@ -4547,14 +4550,14 @@ yyreduce:
     break;
 
   case 322:
-#line 1941 "go.y"
+#line 1944 "go.y"
     {
 		(yyval.type) = functype(nil, (yyvsp[(3) - (5)].list), (yyvsp[(5) - (5)].list));
 	}
     break;
 
   case 323:
-#line 1947 "go.y"
+#line 1950 "go.y"
     {
 		(yyval.node) = nod(ODCLFIELD, N, typenod((yyvsp[(2) - (3)].type)));
 		if((yyvsp[(1) - (3)].sym))
@@ -4564,7 +4567,7 @@ yyreduce:
     break;
 
   case 324:
-#line 1954 "go.y"
+#line 1957 "go.y"
     {
 		Type *t;
 	
@@ -4581,7 +4584,7 @@ yyreduce:
     break;
 
   case 325:
-#line 1970 "go.y"
+#line 1973 "go.y"
     {
 		Sym *s;
 
@@ -4600,49 +4603,49 @@ yyreduce:
     break;
 
   case 326:
-#line 1988 "go.y"
+#line 1991 "go.y"
     {
 		(yyval.node) = nod(ODCLFIELD, newname((yyvsp[(1) - (5)].sym)), typenod(functype(fakethis(), (yyvsp[(3) - (5)].list), (yyvsp[(5) - (5)].list))));
 	}
     break;
 
   case 327:
-#line 1992 "go.y"
+#line 1995 "go.y"
     {
 		(yyval.node) = nod(ODCLFIELD, N, typenod((yyvsp[(1) - (1)].type)));
 	}
     break;
 
   case 328:
-#line 1997 "go.y"
+#line 2000 "go.y"
     {
 		(yyval.list) = nil;
 	}
     break;
 
   case 330:
-#line 2004 "go.y"
+#line 2007 "go.y"
     {
 		(yyval.list) = (yyvsp[(2) - (3)].list);
 	}
     break;
 
   case 331:
-#line 2008 "go.y"
+#line 2011 "go.y"
     {
 		(yyval.list) = list1(nod(ODCLFIELD, N, typenod((yyvsp[(1) - (1)].type))));
 	}
     break;
 
   case 332:
-#line 2018 "go.y"
+#line 2021 "go.y"
     {
 		(yyval.node) = nodlit((yyvsp[(1) - (1)].val));
 	}
     break;
 
   case 333:
-#line 2022 "go.y"
+#line 2025 "go.y"
     {
 		(yyval.node) = nodlit((yyvsp[(2) - (2)].val));
 		switch((yyval.node)->val.ctype){
@@ -4660,7 +4663,7 @@ yyreduce:
     break;
 
   case 334:
-#line 2037 "go.y"
+#line 2040 "go.y"
     {
 		(yyval.node) = oldname(pkglookup((yyvsp[(1) - (1)].sym)->name, builtinpkg));
 		if((yyval.node)->op != OLITERAL)
@@ -4669,7 +4672,7 @@ yyreduce:
     break;
 
   case 336:
-#line 2046 "go.y"
+#line 2049 "go.y"
     {
 		if((yyvsp[(2) - (5)].node)->val.ctype == CTRUNE && (yyvsp[(4) - (5)].node)->val.ctype == CTINT) {
 			(yyval.node) = (yyvsp[(2) - (5)].node);
@@ -4683,42 +4686,42 @@ yyreduce:
     break;
 
   case 339:
-#line 2062 "go.y"
+#line 2065 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 340:
-#line 2066 "go.y"
+#line 2069 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 341:
-#line 2072 "go.y"
+#line 2075 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 342:
-#line 2076 "go.y"
+#line 2079 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
     break;
 
   case 343:
-#line 2082 "go.y"
+#line 2085 "go.y"
     {
 		(yyval.list) = list1((yyvsp[(1) - (1)].node));
 	}
     break;
 
   case 344:
-#line 2086 "go.y"
+#line 2089 "go.y"
     {
 		(yyval.list) = list((yyvsp[(1) - (3)].list), (yyvsp[(3) - (3)].node));
 	}
@@ -4726,7 +4729,7 @@ yyreduce:
 
 
 /* Line 1267 of yacc.c.  */
-#line 4731 "y.tab.c"
+#line 4734 "y.tab.c"
       default: break;
     }
   YY_SYMBOL_PRINT ("-> $$ =", yyr1[yyn], &yyval, &yyloc);
@@ -4940,7 +4943,7 @@ yyreturn:
 }
 
 
-#line 2090 "go.y"
+#line 2093 "go.y"
 
 
 static void
diff --git a/src/cmd/ld/data.c b/src/cmd/ld/data.c
index e551f72903..8fe1773047 100644
--- a/src/cmd/ld/data.c
+++ b/src/cmd/ld/data.c
@@ -602,11 +602,15 @@ addstrdata(char *name, char *value)
 	addstring(sp, value);
 
 	s = lookup(name, 0);
+	s->size = 0;
 	s->dupok = 1;
 	addaddr(s, sp);
 	adduint32(s, strlen(value));
 	if(PtrSize == 8)
 		adduint32(s, 0);  // round struct to pointer width
+
+	// in case reachability has already been computed
+	sp->reachable = s->reachable;
 }
 
 vlong
diff --git a/src/cmd/ld/go.c b/src/cmd/ld/go.c
index aebb225b01..81ae71d736 100644
--- a/src/cmd/ld/go.c
+++ b/src/cmd/ld/go.c
@@ -431,10 +431,16 @@ parsemethod(char **pp, char *ep, char **methp)
 	if(p == ep)
 		return 0;
 
+	// might be a comment about the method
+	if(p + 2 < ep && strncmp(p, "//", 2) == 0)
+		goto useline;
+	
 	// if it says "func (", it's a method
-	if(p + 6 >= ep || strncmp(p, "func (", 6) != 0)
-		return 0;
+	if(p + 6 < ep && strncmp(p, "func (", 6) == 0)
+		goto useline;
+	return 0;
 
+useline:
 	// definition to end of line
 	*methp = p;
 	while(p < ep && *p != '\n')
@@ -612,50 +618,56 @@ err:
 	nerrors++;
 }
 
-static int markdepth;
+static Sym *markq;
+static Sym *emarkq;
 
 static void
-marktext(Sym *s)
+mark1(Sym *s, Sym *parent)
 {
-	Auto *a;
-	Prog *p;
-
-	if(s == S)
-		return;
-	markdepth++;
-	if(debug['v'] > 1)
-		Bprint(&bso, "%d marktext %s\n", markdepth, s->name);
-	for(a=s->autom; a; a=a->link)
-		mark(a->gotype);
-	for(p=s->text; p != P; p=p->link) {
-		if(p->from.sym)
-			mark(p->from.sym);
-		if(p->to.sym)
-			mark(p->to.sym);
-	}
-	markdepth--;
-}
-
-void
-mark(Sym *s)
-{
-	int i;
-
 	if(s == S || s->reachable)
 		return;
 	if(strncmp(s->name, "go.weak.", 8) == 0)
 		return;
 	s->reachable = 1;
-	if(s->text)
-		marktext(s);
-	for(i=0; i<s->nr; i++)
-		mark(s->r[i].sym);
-	if(s->gotype)
-		mark(s->gotype);
-	if(s->sub)
-		mark(s->sub);
-	if(s->outer)
-		mark(s->outer);
+	s->reachparent = parent;
+	if(markq == nil)
+		markq = s;
+	else
+		emarkq->queue = s;
+	emarkq = s;
+}
+
+void
+mark(Sym *s)
+{
+	mark1(s, nil);
+}
+
+static void
+markflood(void)
+{
+	Auto *a;
+	Prog *p;
+	Sym *s;
+	int i;
+	
+	for(s=markq; s!=S; s=s->queue) {
+		if(s->text) {
+			if(debug['v'] > 1)
+				Bprint(&bso, "marktext %s\n", s->name);
+			for(a=s->autom; a; a=a->link)
+				mark1(a->gotype, s);
+			for(p=s->text; p != P; p=p->link) {
+				mark1(p->from.sym, s);
+				mark1(p->to.sym, s);
+			}
+		}
+		for(i=0; i<s->nr; i++)
+			mark1(s->r[i].sym, s);
+		mark1(s->gotype, s);
+		mark1(s->sub, s);
+		mark1(s->outer, s);
+	}
 }
 
 static char*
@@ -712,8 +724,9 @@ void
 deadcode(void)
 {
 	int i;
-	Sym *s, *last;
+	Sym *s, *last, *p;
 	Auto *z;
+	Fmt fmt;
 
 	if(debug['v'])
 		Bprint(&bso, "%5.2f deadcode\n", cputime());
@@ -724,6 +737,8 @@ deadcode(void)
 
 	for(i=0; i<ndynexp; i++)
 		mark(dynexp[i]);
+
+	markflood();
 	
 	// remove dead text but keep file information (z symbols).
 	last = nil;
@@ -756,6 +771,29 @@ deadcode(void)
 			s->reachable = 1;
 			s->hide = 1;
 		}
+
+	// record field tracking references
+	fmtstrinit(&fmt);
+	for(s = allsym; s != S; s = s->allsym) {
+		if(strncmp(s->name, "go.track.", 9) == 0) {
+			s->special = 1;  // do not lay out in data segment
+			s->hide = 1;
+			if(s->reachable) {
+				fmtprint(&fmt, "%s", s->name+9);
+				for(p=s->reachparent; p; p=p->reachparent)
+					fmtprint(&fmt, "\t%s", p->name);
+				fmtprint(&fmt, "\n");
+			}
+			s->type = SCONST;
+			s->value = 0;
+		}
+	}
+	if(tracksym == nil)
+		return;
+	s = lookup(tracksym, 0);
+	if(!s->reachable)
+		return;
+	addstrdata(tracksym, fmtstrflush(&fmt));
 }
 
 void
diff --git a/src/cmd/ld/lib.h b/src/cmd/ld/lib.h
index 162e16180f..c2bac60102 100644
--- a/src/cmd/ld/lib.h
+++ b/src/cmd/ld/lib.h
@@ -132,6 +132,7 @@ EXTERN	char*	thestring;
 EXTERN	int	ndynexp;
 EXTERN	int	havedynamic;
 EXTERN	int	iscgo;
+EXTERN	char*	tracksym;
 
 EXTERN	Segment	segtext;
 EXTERN	Segment	segdata;