gc: align structs according to max alignment of fields

cc: same
runtime: test cc alignment (required moving #define of offsetof to runtime.h)
fix bug260

Fixes #482.
Fixes #609.

R=ken2, r
CC=golang-dev
https://golang.org/cl/3563042

src/cmd/5c/swt.c

@@ -606,7 +606,7 @@ zaddr(char *bp, Adr *a, int s)
 }
 
 int32
-align(int32 i, Type *t, int op)
+align(int32 i, Type *t, int op, int32 *maxalign)
 {
 	int32 o;
 	Type *v;
@@ -620,7 +620,9 @@ align(int32 i, Type *t, int op)
 		break;
 
 	case Asu2:	/* padding at end of a struct */
-		w = SZ_LONG;
+		w = *maxalign;
+		if(w < 1)
+			w = 1;
 		if(packflg)
 			w = packflg;
 		break;
@@ -628,10 +630,16 @@ align(int32 i, Type *t, int op)
 	case Ael1:	/* initial align of struct element */
 		for(v=t; v->etype==TARRAY; v=v->link)
 			;
-		w = ewidth[v->etype];
-		if(w <= 0 || w >= SZ_LONG)
-			w = SZ_LONG;
-		if(packflg)
+		if(v->etype == TSTRUCT || v->etype == TUNION)
+			w = v->align;
+		else {
+			w = ewidth[v->etype];
+			if(w == 8)
+				w = 4;
+		}
+		if(w < 1 || w > SZ_LONG)
+			fatal(Z, "align");
+		if(packflg) 
 			w = packflg;
 		break;
 
@@ -641,8 +649,8 @@ align(int32 i, Type *t, int op)
 
 	case Aarg0:	/* initial passbyptr argument in arg list */
 		if(typesuv[t->etype]) {
-			o = align(o, types[TIND], Aarg1);
-			o = align(o, types[TIND], Aarg2);
+			o = align(o, types[TIND], Aarg1, nil);
+			o = align(o, types[TIND], Aarg2, nil);
 		}
 		break;
 
@@ -661,12 +669,14 @@ align(int32 i, Type *t, int op)
 		break;
 
 	case Aaut3:	/* total align of automatic */
-		o = align(o, t, Ael2);
-		o = align(o, t, Ael1);
+		o = align(o, t, Ael2, nil);
+		o = align(o, t, Ael1, nil);
 		w = SZ_LONG;	/* because of a pun in cc/dcl.c:contig() */
 		break;
 	}
 	o = xround(o, w);
+	if(maxalign != nil && *maxalign < w)
+		*maxalign = w;
 	if(debug['A'])
 		print("align %s %d %T = %d\n", bnames[op], i, t, o);
 	return o;

src/cmd/5c/txt.c

@@ -388,7 +388,7 @@ err:
 void
 regsalloc(Node *n, Node *nn)
 {
-	cursafe = align(cursafe, nn->type, Aaut3);
+	cursafe = align(cursafe, nn->type, Aaut3, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 	*n = *nodsafe;
 	n->xoffset = -(stkoff + cursafe);
@@ -402,22 +402,22 @@ regaalloc1(Node *n, Node *nn)
 {
 	nodreg(n, nn, REGARG);
 	reg[REGARG]++;
-	curarg = align(curarg, nn->type, Aarg1);
-	curarg = align(curarg, nn->type, Aarg2);
+	curarg = align(curarg, nn->type, Aarg1, nil);
+	curarg = align(curarg, nn->type, Aarg2, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 }
 
 void
 regaalloc(Node *n, Node *nn)
 {
-	curarg = align(curarg, nn->type, Aarg1);
+	curarg = align(curarg, nn->type, Aarg1, nil);
 	*n = *nn;
 	n->op = OINDREG;
 	n->reg = REGSP;
 	n->xoffset = curarg + SZ_LONG;
 	n->complex = 0;
 	n->addable = 20;
-	curarg = align(curarg, nn->type, Aarg2);
+	curarg = align(curarg, nn->type, Aarg2, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 }
 

src/cmd/6c/cgen.c

@@ -1928,7 +1928,7 @@ vaddr(Node *n, int a)
 int32
 hi64v(Node *n)
 {
-	if(align(0, types[TCHAR], Aarg1))	/* isbigendian */
+	if(align(0, types[TCHAR], Aarg1, nil))	/* isbigendian */
 		return (int32)(n->vconst) & ~0L;
 	else
 		return (int32)((uvlong)n->vconst>>32) & ~0L;
@@ -1937,7 +1937,7 @@ hi64v(Node *n)
 int32
 lo64v(Node *n)
 {
-	if(align(0, types[TCHAR], Aarg1))	/* isbigendian */
+	if(align(0, types[TCHAR], Aarg1, nil))	/* isbigendian */
 		return (int32)((uvlong)n->vconst>>32) & ~0L;
 	else
 		return (int32)(n->vconst) & ~0L;

src/cmd/6c/swt.c

@@ -503,7 +503,7 @@ zaddr(Biobuf *b, Adr *a, int s)
 }
 
 int32
-align(int32 i, Type *t, int op)
+align(int32 i, Type *t, int op, int32 *maxalign)
 {
 	int32 o;
 	Type *v;
@@ -517,7 +517,9 @@ align(int32 i, Type *t, int op)
 		break;
 
 	case Asu2:	/* padding at end of a struct */
-		w = SZ_VLONG;
+		w = *maxalign;
+		if(w < 1)
+			w = 1;
 		if(packflg)
 			w = packflg;
 		break;
@@ -525,10 +527,13 @@ align(int32 i, Type *t, int op)
 	case Ael1:	/* initial align of struct element */
 		for(v=t; v->etype==TARRAY; v=v->link)
 			;
-		w = ewidth[v->etype];
-		if(w <= 0 || w >= SZ_VLONG)
-			w = SZ_VLONG;
-		if(packflg)
+		if(v->etype == TSTRUCT || v->etype == TUNION)
+			w = v->align;
+		else
+			w = ewidth[v->etype];
+		if(w < 1 || w > SZ_VLONG)
+			fatal(Z, "align");
+		if(packflg) 
 			w = packflg;
 		break;
 
@@ -538,8 +543,8 @@ align(int32 i, Type *t, int op)
 
 	case Aarg0:	/* initial passbyptr argument in arg list */
 		if(typesu[t->etype]) {
-			o = align(o, types[TIND], Aarg1);
-			o = align(o, types[TIND], Aarg2);
+			o = align(o, types[TIND], Aarg1, nil);
+			o = align(o, types[TIND], Aarg2, nil);
 		}
 		break;
 
@@ -560,11 +565,13 @@ align(int32 i, Type *t, int op)
 		break;
 
 	case Aaut3:	/* total align of automatic */
-		o = align(o, t, Ael1);
-		o = align(o, t, Ael2);
+		o = align(o, t, Ael1, nil);
+		o = align(o, t, Ael2, nil);
 		break;
 	}
 	o = xround(o, w);
+	if(maxalign && *maxalign < w)
+		*maxalign = w;
 	if(debug['A'])
 		print("align %s %d %T = %d\n", bnames[op], i, t, o);
 	return o;

src/cmd/6c/txt.c

@@ -424,7 +424,7 @@ err:
 void
 regsalloc(Node *n, Node *nn)
 {
-	cursafe = align(cursafe, nn->type, Aaut3);
+	cursafe = align(cursafe, nn->type, Aaut3, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 	*n = *nodsafe;
 	n->xoffset = -(stkoff + cursafe);
@@ -440,22 +440,22 @@ regaalloc1(Node *n, Node *nn)
 		diag(n, "regaalloc1 and REGARG<0");
 	nodreg(n, nn, REGARG);
 	reg[REGARG]++;
-	curarg = align(curarg, nn->type, Aarg1);
-	curarg = align(curarg, nn->type, Aarg2);
+	curarg = align(curarg, nn->type, Aarg1, nil);
+	curarg = align(curarg, nn->type, Aarg2, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 }
 
 void
 regaalloc(Node *n, Node *nn)
 {
-	curarg = align(curarg, nn->type, Aarg1);
+	curarg = align(curarg, nn->type, Aarg1, nil);
 	*n = *nn;
 	n->op = OINDREG;
 	n->reg = REGSP;
 	n->xoffset = curarg;
 	n->complex = 0;
 	n->addable = 20;
-	curarg = align(curarg, nn->type, Aarg2);
+	curarg = align(curarg, nn->type, Aarg2, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 }
 

src/cmd/8c/cgen64.c

@@ -57,7 +57,7 @@ vaddr(Node *n, int a)
 int32
 hi64v(Node *n)
 {
-	if(align(0, types[TCHAR], Aarg1))	/* isbigendian */
+	if(align(0, types[TCHAR], Aarg1, nil))	/* isbigendian */
 		return (int32)(n->vconst) & ~0L;
 	else
 		return (int32)((uvlong)n->vconst>>32) & ~0L;
@@ -66,7 +66,7 @@ hi64v(Node *n)
 int32
 lo64v(Node *n)
 {
-	if(align(0, types[TCHAR], Aarg1))	/* isbigendian */
+	if(align(0, types[TCHAR], Aarg1, nil))	/* isbigendian */
 		return (int32)((uvlong)n->vconst>>32) & ~0L;
 	else
 		return (int32)(n->vconst) & ~0L;

src/cmd/8c/swt.c

@@ -501,7 +501,7 @@ zaddr(Biobuf *b, Adr *a, int s)
 }
 
 int32
-align(int32 i, Type *t, int op)
+align(int32 i, Type *t, int op, int32 *maxalign)
 {
 	int32 o;
 	Type *v;
@@ -515,7 +515,9 @@ align(int32 i, Type *t, int op)
 		break;
 
 	case Asu2:	/* padding at end of a struct */
-		w = SZ_LONG;
+		w = *maxalign;
+		if(w < 1)
+			w = 1;
 		if(packflg)
 			w = packflg;
 		break;
@@ -523,10 +525,16 @@ align(int32 i, Type *t, int op)
 	case Ael1:	/* initial align of struct element */
 		for(v=t; v->etype==TARRAY; v=v->link)
 			;
-		w = ewidth[v->etype];
-		if(w <= 0 || w >= SZ_LONG)
-			w = SZ_LONG;
-		if(packflg)
+		if(v->etype == TSTRUCT || v->etype == TUNION)
+			w = v->align;
+		else {
+			w = ewidth[v->etype];
+			if(w == 8)
+				w = 4;
+		}
+		if(w < 1 || w > SZ_LONG)
+			fatal(Z, "align");
+		if(packflg) 
 			w = packflg;
 		break;
 
@@ -536,8 +544,8 @@ align(int32 i, Type *t, int op)
 
 	case Aarg0:	/* initial passbyptr argument in arg list */
 		if(typesuv[t->etype]) {
-			o = align(o, types[TIND], Aarg1);
-			o = align(o, types[TIND], Aarg2);
+			o = align(o, types[TIND], Aarg1, nil);
+			o = align(o, types[TIND], Aarg2, nil);
 		}
 		break;
 
@@ -558,11 +566,13 @@ align(int32 i, Type *t, int op)
 		break;
 
 	case Aaut3:	/* total align of automatic */
-		o = align(o, t, Ael1);
-		o = align(o, t, Ael2);
+		o = align(o, t, Ael1, nil);
+		o = align(o, t, Ael2, nil);
 		break;
 	}
 	o = xround(o, w);
+	if(maxalign && *maxalign < w)
+		*maxalign = w;
 	if(debug['A'])
 		print("align %s %d %T = %d\n", bnames[op], i, t, o);
 	return o;

src/cmd/8c/txt.c

@@ -385,7 +385,7 @@ err:
 void
 regsalloc(Node *n, Node *nn)
 {
-	cursafe = align(cursafe, nn->type, Aaut3);
+	cursafe = align(cursafe, nn->type, Aaut3, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 	*n = *nodsafe;
 	n->xoffset = -(stkoff + cursafe);
@@ -399,22 +399,22 @@ regaalloc1(Node *n, Node *nn)
 {
 	nodreg(n, nn, REGARG);
 	reg[REGARG]++;
-	curarg = align(curarg, nn->type, Aarg1);
-	curarg = align(curarg, nn->type, Aarg2);
+	curarg = align(curarg, nn->type, Aarg1, nil);
+	curarg = align(curarg, nn->type, Aarg2, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 }
 
 void
 regaalloc(Node *n, Node *nn)
 {
-	curarg = align(curarg, nn->type, Aarg1);
+	curarg = align(curarg, nn->type, Aarg1, nil);
 	*n = *nn;
 	n->op = OINDREG;
 	n->reg = REGSP;
 	n->xoffset = curarg;
 	n->complex = 0;
 	n->addable = 20;
-	curarg = align(curarg, nn->type, Aarg2);
+	curarg = align(curarg, nn->type, Aarg2, nil);
 	maxargsafe = maxround(maxargsafe, cursafe+curarg);
 }
 

src/cmd/cc/cc.h

@@ -166,6 +166,7 @@ struct	Type
 	uchar	nbits;
 	uchar	etype;
 	uchar	garb;
+	uchar	align;
 };
 
 #define	T	((Type*)0)
@@ -785,7 +786,7 @@ int32	outlstring(ushort*, int32);
 void	sextern(Sym*, Node*, int32, int32);
 void	xcom(Node*);
 int32	exreg(Type*);
-int32	align(int32, Type*, int);
+int32	align(int32, Type*, int, int32*);
 int32	maxround(int32, int32);
 
 extern	schar	ewidth[];

src/cmd/cc/dcl.c

@@ -552,9 +552,10 @@ void
 sualign(Type *t)
 {
 	Type *l;
-	int32 o, w;
+	int32 o, w, maxal;
 
 	o = 0;
+	maxal = 0;
 	switch(t->etype) {
 
 	case TSTRUCT:
@@ -577,13 +578,14 @@ sualign(Type *t)
 							l->sym->name);
 					else
 						diag(Z, "incomplete structure element");
-				w = align(w, l, Ael1);
+				w = align(w, l, Ael1, &maxal);
 				l->offset = w;
-				w = align(w, l, Ael2);
+				w = align(w, l, Ael2, &maxal);
 			}
 		}
-		w = align(w, t, Asu2);
+		w = align(w, t, Asu2, &maxal);
 		t->width = w;
+		t->align = maxal;
 		acidtype(t);
 		pickletype(t);
 		return;
@@ -600,12 +602,13 @@ sualign(Type *t)
 					diag(Z, "incomplete union element");
 			l->offset = 0;
 			l->shift = 0;
-			o = align(align(0, l, Ael1), l, Ael2);
+			o = align(align(0, l, Ael1, &maxal), l, Ael2, &maxal);
 			if(o > w)
 				w = o;
 		}
-		w = align(w, t, Asu2);
+		w = align(w, t, Asu2, &maxal);
 		t->width = w;
+		t->align = maxal;
 		acidtype(t);
 		pickletype(t);
 		return;
@@ -663,7 +666,7 @@ argmark(Node *n, int pass)
 {
 	Type *t;
 
-	autoffset = align(0, thisfn->link, Aarg0);
+	autoffset = align(0, thisfn->link, Aarg0, nil);
 	stkoff = 0;
 	for(; n->left != Z; n = n->left) {
 		if(n->op != OFUNC || n->left->op != ONAME)
@@ -745,9 +748,9 @@ loop:
 				firstarg = s;
 				firstargtype = s->type;
 			}
-			autoffset = align(autoffset, s->type, Aarg1);
+			autoffset = align(autoffset, s->type, Aarg1, nil);
 			s->offset = autoffset;
-			autoffset = align(autoffset, s->type, Aarg2);
+			autoffset = align(autoffset, s->type, Aarg2, nil);
 		} else
 			dodecl(pdecl, CXXX, types[TINT], n);
 		break;
@@ -1275,7 +1278,7 @@ adecl(int c, Type *t, Sym *s)
 	}
 	switch(c) {
 	case CAUTO:
-		autoffset = align(autoffset, t, Aaut3);
+		autoffset = align(autoffset, t, Aaut3, nil);
 		stkoff = maxround(stkoff, autoffset);
 		s->offset = -autoffset;
 		break;
@@ -1285,10 +1288,10 @@ adecl(int c, Type *t, Sym *s)
 			firstarg = s;
 			firstargtype = t;
 		}
-		autoffset = align(autoffset, t, Aarg1);
+		autoffset = align(autoffset, t, Aarg1, nil);
 		if(s)
 			s->offset = autoffset;
-		autoffset = align(autoffset, t, Aarg2);
+		autoffset = align(autoffset, t, Aarg2, nil);
 		break;
 	}
 }
@@ -1587,7 +1590,7 @@ contig(Sym *s, Node *n, int32 v)
 		if(v != 0)
 			diag(n, "automatic adjustable array: %s", s->name);
 		v = s->offset;
-		autoffset = align(autoffset, s->type, Aaut3);
+		autoffset = align(autoffset, s->type, Aaut3, nil);
 		s->offset = -autoffset;
 		stkoff = maxround(stkoff, autoffset);
 		symadjust(s, n, v - s->offset);

src/cmd/cc/pgen.c

@@ -37,7 +37,7 @@ argsize(void)
 	int32 s;
 
 //print("t=%T\n", thisfn);
-	s = align(0, thisfn->link, Aarg0);
+	s = align(0, thisfn->link, Aarg0, nil);
 	for(t=thisfn->down; t!=T; t=t->down) {
 		switch(t->etype) {
 		case TVOID:
@@ -47,8 +47,8 @@ argsize(void)
 			s += 64;
 			break;
 		default:
-			s = align(s, t, Aarg1);
-			s = align(s, t, Aarg2);
+			s = align(s, t, Aarg1, nil);
+			s = align(s, t, Aarg2, nil);
 			break;
 		}
 //print("	%d %T\n", s, t);
@@ -99,7 +99,7 @@ codgen(Node *n, Node *nn)
 			nod1 = *nodret->left;
 			nod1.sym = firstarg;
 			nod1.type = firstargtype;
-			nod1.xoffset = align(0, firstargtype, Aarg1);
+			nod1.xoffset = align(0, firstargtype, Aarg1, nil);
 			nod1.etype = firstargtype->etype;
 			nodreg(&nod, &nod1, REGARG);
 			gmove(&nod, &nod1);

src/cmd/cc/pswt.c

@@ -115,7 +115,7 @@ outlstring(ushort *s, int32 n)
 	r = nstring;
 	while(n > 0) {
 		c = *s++;
-		if(align(0, types[TCHAR], Aarg1)) {
+		if(align(0, types[TCHAR], Aarg1, nil)) {
 			buf[0] = c>>8;
 			buf[1] = c;
 		} else {

src/cmd/gc/align.c

@@ -49,8 +49,8 @@ widstruct(Type *t, uint32 o, int flag)
 		if(f->etype != TFIELD)
 			fatal("widstruct: not TFIELD: %lT", f);
 		dowidth(f->type);
-		if(f->align > maxalign)
-			maxalign = f->align;
+		if(f->type->align > maxalign)
+			maxalign = f->type->align;
 		if(f->type->width < 0)
 			fatal("invalid width %lld", f->type->width);
 		w = f->type->width;
@@ -248,9 +248,11 @@ dowidth(Type *t)
 	case TSTRUCT:
 		if(t->funarg)
 			fatal("dowidth fn struct %T", t);
-		w = widstruct(t, 0, widthptr);
+		w = widstruct(t, 0, 1);
 		if(w == 0)
 			w = 1;
+		//if(t->align < widthptr)
+		//	warn("align %d: %T\n", t->align, t);
 		break;
 
 	case TFUNC:
@@ -272,6 +274,8 @@ dowidth(Type *t)
 		w = widstruct(*getinarg(t1), w, widthptr);
 		w = widstruct(*getoutarg(t1), w, widthptr);
 		t1->argwid = w;
+		if(w%widthptr)
+			warn("bad type %T %d\n", t1, w);
 		t->align = 1;
 		break;
 	}

src/cmd/gc/typecheck.c

@@ -1124,7 +1124,7 @@ reswitch:
 	case OPRINT:
 	case OPRINTN:
 		ok |= Etop;
-		typechecklist(n->list, Erv);
+		typechecklist(n->list, Erv | Eindir);  // Eindir: address does not escape
 		goto ret;
 
 	case OPANIC:

src/pkg/reflect/value.go

@@ -730,8 +730,6 @@ type tiny struct {
 // Call calls the function fv with input parameters in.
 // It returns the function's output parameters as Values.
 func (fv *FuncValue) Call(in []Value) []Value {
-	var structAlign = Typeof((*tiny)(nil)).(*PtrType).Elem().Size()
-
 	t := fv.Type().(*FuncType)
 	nin := len(in)
 	if fv.first != nil && !fv.isInterface {
@@ -757,7 +755,7 @@ func (fv *FuncValue) Call(in []Value) []Value {
 		size = (size + a - 1) &^ (a - 1)
 		size += tv.Size()
 	}
-	size = (size + structAlign - 1) &^ (structAlign - 1)
+	size = (size + ptrSize - 1) &^ (ptrSize - 1)
 	for i := 0; i < nout; i++ {
 		tv := t.Out(i)
 		a := uintptr(tv.Align())
@@ -767,9 +765,9 @@ func (fv *FuncValue) Call(in []Value) []Value {
 
 	// size must be > 0 in order for &args[0] to be valid.
 	// the argument copying is going to round it up to
-	// a multiple of 8 anyway, so make it 8 to begin with.
-	if size < 8 {
-		size = 8
+	// a multiple of ptrSize anyway, so make it ptrSize to begin with.
+	if size < ptrSize {
+		size = ptrSize
 	}
 
 	// round to pointer size
@@ -811,7 +809,7 @@ func (fv *FuncValue) Call(in []Value) []Value {
 		memmove(addr(ptr+off), v.getAddr(), n)
 		off += n
 	}
-	off = (off + structAlign - 1) &^ (structAlign - 1)
+	off = (off + ptrSize - 1) &^ (ptrSize - 1)
 
 	// Call
 	call(*(**byte)(fv.addr), (*byte)(addr(ptr)), uint32(size))

src/pkg/runtime/debug.go

@@ -4,6 +4,8 @@
 
 package runtime
 
+import "unsafe"
+
 // Breakpoint() executes a breakpoint trap.
 func Breakpoint()
 
@@ -73,6 +75,15 @@ type MemStatsType struct {
 	}
 }
 
+var sizeof_C_MStats int // filled in by malloc.goc
+
+func init() {
+	if sizeof_C_MStats != unsafe.Sizeof(MemStats) {
+		println(sizeof_C_MStats, unsafe.Sizeof(MemStats))
+		panic("MStats vs MemStatsType size mismatch")
+	}
+}
+
 // MemStats holds statistics about the memory system.
 // The statistics are only approximate, as they are not interlocked on update.
 var MemStats MemStatsType

src/pkg/runtime/hashmap.h

@@ -64,7 +64,6 @@
  */
 
 #define	malloc		runtime·mal
-#define	offsetof(s,m)	(uint32)(&(((s*)0)->m))
 #define	memset(a,b,c)	runtime·memclr((byte*)(a), (uint32)(c))
 #define	memcpy(a,b,c)	runtime·mcpy((byte*)(a),(byte*)(b),(uint32)(c))
 #define	assert(a)	if(!(a)) runtime·throw("assert")

src/pkg/runtime/malloc.goc

@@ -244,6 +244,8 @@ runtime·allocmcache(void)
 	return c;
 }
 
+int32 runtime·sizeof_C_MStats = sizeof(MStats);
+
 void
 runtime·mallocinit(void)
 {

src/pkg/runtime/runtime.c

@@ -258,6 +258,13 @@ runtime·check(void)
 	float64 j;
 	void* k;
 	uint16* l;
+	struct x1 {
+		byte x;
+	};
+	struct y1 {
+		struct x1 x1;
+		byte y;
+	};
 
 	if(sizeof(a) != 1) runtime·throw("bad a");
 	if(sizeof(b) != 1) runtime·throw("bad b");
@@ -271,7 +278,9 @@ runtime·check(void)
 	if(sizeof(j) != 8) runtime·throw("bad j");
 	if(sizeof(k) != sizeof(uintptr)) runtime·throw("bad k");
 	if(sizeof(l) != sizeof(uintptr)) runtime·throw("bad l");
-//	prints(1"check ok\n");
+	if(sizeof(struct x1) != 1) runtime·throw("bad sizeof x1");
+	if(offsetof(struct y1, y) != 1) runtime·throw("bad offsetof y1.y");
+	if(sizeof(struct y1) != 2) runtime·throw("bad sizeof y1");
 
 	uint32 z;
 	z = 1;

src/pkg/runtime/runtime.h

@@ -306,6 +306,7 @@ enum {
  */
 #define	nelem(x)	(sizeof(x)/sizeof((x)[0]))
 #define	nil		((void*)0)
+#define	offsetof(s,m)	(uint32)(&(((s*)0)->m))
 
 /*
  * known to compiler

test/bugs/bug260.go → test/fixedbugs/bug260.go

@@ -10,9 +10,15 @@ import (
 	"strconv"
 )
 
-type T1 struct { x uint8 }
-type T2 struct { x uint16 }
-type T4 struct { x uint32 }
+type T1 struct {
+	x uint8
+}
+type T2 struct {
+	x uint16
+}
+type T4 struct {
+	x uint32
+}
 
 func main() {
 	report := len(os.Args) > 1
@@ -20,7 +26,7 @@ func main() {
 	var b1 [10]T1
 	a0, _ := strconv.Btoui64(fmt.Sprintf("%p", &b1[0])[2:], 16)
 	a1, _ := strconv.Btoui64(fmt.Sprintf("%p", &b1[1])[2:], 16)
-	if a1 != a0 + 1 {
+	if a1 != a0+1 {
 		fmt.Println("FAIL")
 		if report {
 			fmt.Println("alignment should be 1, is", a1-a0)
@@ -30,7 +36,7 @@ func main() {
 	var b2 [10]T2
 	a0, _ = strconv.Btoui64(fmt.Sprintf("%p", &b2[0])[2:], 16)
 	a1, _ = strconv.Btoui64(fmt.Sprintf("%p", &b2[1])[2:], 16)
-	if a1 != a0 + 2 {
+	if a1 != a0+2 {
 		if status == 0 {
 			fmt.Println("FAIL")
 			status = 1
@@ -42,7 +48,7 @@ func main() {
 	var b4 [10]T4
 	a0, _ = strconv.Btoui64(fmt.Sprintf("%p", &b4[0])[2:], 16)
 	a1, _ = strconv.Btoui64(fmt.Sprintf("%p", &b4[1])[2:], 16)
-	if a1 != a0 + 4 {
+	if a1 != a0+4 {
 		if status == 0 {
 			fmt.Println("FAIL")
 			status = 1

test/golden.out

@@ -173,7 +173,3 @@ panic: interface conversion: interface is main.T, not main.T
 panic PC=xxx
 
 == bugs/
-
-=========== bugs/bug260.go
-FAIL
-BUG: bug260 failed