ld: align ELF data sections

fixes #2506

R=rsc, iant
CC=golang-dev
https://golang.org/cl/5440066

src/cmd/5l/l.h

@@ -143,6 +143,7 @@ struct	Sym
 	int32	value;
 	int32	sig;
 	int32	size;
+	int32	align;	// if non-zero, required alignment in bytes
 	uchar	special;
 	uchar	fnptr;	// used as fn ptr
 	Sym*	hash;	// in hash table

src/cmd/6l/l.h

@@ -133,6 +133,7 @@ struct	Sym
 	int32	sig;
 	int32	plt;
 	int32	got;
+	int32	align;	// if non-zero, required alignment in bytes
 	Sym*	hash;	// in hash table
 	Sym*	allsym;	// in all symbol list
 	Sym*	next;	// in text or data list

src/cmd/8l/l.h

@@ -134,6 +134,7 @@ struct	Sym
 	int32	dynid;
 	int32	plt;
 	int32	got;
+	int32	align;	// if non-zero, required alignment in bytes
 	Sym*	hash;	// in hash table
 	Sym*	allsym;	// in all symbol list
 	Sym*	next;	// in text or data list

src/cmd/ld/data.c

@@ -824,6 +824,8 @@ dodata(void)
 	datsize = 0;
 	s = datap;
 	for(; s != nil && s->type < SSYMTAB; s = s->next) {
+		if(s->align != 0)
+			datsize = rnd(datsize, s->align);
 		s->type = SRODATA;
 		s->value = datsize;
 		datsize += rnd(s->size, PtrSize);
@@ -855,6 +857,8 @@ dodata(void)
 	/* read-only ELF sections */
 	for(; s != nil && s->type < SELFSECT; s = s->next) {
 		sect = addsection(&segtext, s->name, 04);
+		if(s->align != 0)
+			datsize = rnd(datsize, s->align);
 		sect->vaddr = datsize;
 		s->type = SRODATA;
 		s->value = datsize;
@@ -866,6 +870,8 @@ dodata(void)
 	datsize = 0;
 	for(; s != nil && s->type < SDATA; s = s->next) {
 		sect = addsection(&segdata, s->name, 06);
+		if(s->align != 0)
+			datsize = rnd(datsize, s->align);
 		sect->vaddr = datsize;
 		s->type = SDATA;
 		s->value = datsize;
@@ -887,7 +893,9 @@ dodata(void)
 			t = rnd(t, PtrSize);
 		else if(t > 2)
 			t = rnd(t, 4);
-		if(t & 1) {
+		if(s->align != 0)
+			datsize = rnd(datsize, s->align);
+		else if(t & 1) {
 			;
 		} else if(t & 2)
 			datsize = rnd(datsize, 2);
@@ -913,7 +921,9 @@ dodata(void)
 			t = rnd(t, PtrSize);
 		else if(t > 2)
 			t = rnd(t, 4);
-		if(t & 1) {
+		if(s->align != 0)
+			datsize = rnd(datsize, s->align);
+		else if(t & 1) {
 			;
 		} else if(t & 2)
 			datsize = rnd(datsize, 2);
@@ -947,6 +957,8 @@ textaddress(void)
 	for(sym = textp; sym != nil; sym = sym->next) {
 		if(sym->type & SSUB)
 			continue;
+		if(sym->align != 0)
+			va = rnd(va, sym->align);
 		sym->value = 0;
 		for(sub = sym; sub != S; sub = sub->sub) {
 			sub->value += va;

src/cmd/ld/ldelf.c

@@ -538,6 +538,7 @@ ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 			s->np = sect->size;
 		}
 		s->size = sect->size;
+		s->align = sect->align;
 		if(s->type == STEXT) {
 			if(etextp)
 				etextp->next = s;