cmd/5l, cmd/ld: dynamic linking library support

        Part 1 of CL 5601044 (cgo: Linux/ARM support)
        Limitation: doesn't support thumb library yet.

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/5991065

src/cmd/5l/5.out.h

@@ -254,6 +254,12 @@ enum	as
 /* internal only */
 #define	D_SIZE		(D_NONE+40)
 #define	D_PCREL		(D_NONE+41)
+#define	D_GOTOFF	(D_NONE+42) // R_ARM_GOTOFF
+#define	D_PLT0		(D_NONE+43) // R_ARM_PLT32, 1st inst: add ip, pc, #0xNN00000
+#define	D_PLT1		(D_NONE+44) // R_ARM_PLT32, 2nd inst: add ip, ip, #0xNN000
+#define	D_PLT2		(D_NONE+45) // R_ARM_PLT32, 3rd inst: ldr pc, [ip, #0xNNN]!
+#define	D_PLT32 	(D_NONE+46) // R_ARM_PLT32, bl xxxxx
+#define	D_CALL		(D_NONE+47) // R_ARM_CALL, bl xxxxx
 
 /*
  * this is the ranlib header

src/cmd/5l/l.h

@@ -303,6 +303,7 @@ EXTERN	int	version;
 EXTERN	char	xcmp[C_GOK+1][C_GOK+1];
 EXTERN	Prog	zprg;
 EXTERN	int	dtype;
+EXTERN	int	tlsoffset;
 EXTERN	int	armsize;
 
 extern	char*	anames[];

src/cmd/5l/obj.c

@@ -205,7 +205,9 @@ main(int argc, char *argv[])
 			INITRND = 1024;
 		break;
 	case Hlinux:	/* arm elf */
-		debug['d'] = 1;	// no dynamic linking
+		debug['d'] = 0;	// with dynamic linking
+		tlsoffset = -8; // hardcoded number, first 4-byte word for g, and then 4-byte word for m
+		                // this number is known to ../../pkg/runtime/cgo/gcc_linux_arm.c
 		elfinit();
 		HEADR = ELFRESERVE;
 		if(INITTEXT == -1)
@@ -263,6 +265,8 @@ main(int argc, char *argv[])
 	noops();
 	dostkcheck();
 	span();
+	addexport();
+	// textaddress() functionality is handled in span()
 	pclntab();
 	symtab();
 	dodata();

src/cmd/5l/pass.c

@@ -215,7 +215,7 @@ patch(void)
 				s = p->to.sym;
 				if(s->text == nil)
 					continue;
-				switch(s->type) {
+				switch(s->type&~SSUB) {
 				default:
 					diag("undefined: %s", s->name);
 					s->type = STEXT;
@@ -231,7 +231,7 @@ patch(void)
 			if(p->to.type != D_BRANCH)
 				continue;
 			c = p->to.offset;
-			for(q = textp->text; q != P;) {
+			for(q = cursym->text; q != P;) {
 				if(c == q->pc)
 					break;
 				if(q->forwd != P && c >= q->forwd->pc)

src/cmd/5l/span.c

@@ -90,6 +90,7 @@ span(void)
 	int32 c, otxt, out[6];
 	Section *sect;
 	uchar *bp;
+	Sym *sub;
 
 	if(debug['v'])
 		Bprint(&bso, "%5.2f span\n", cputime());
@@ -100,6 +101,20 @@ span(void)
 	otxt = c;
 	for(cursym = textp; cursym != nil; cursym = cursym->next) {
 		p = cursym->text;
+		if(p == P || p->link == P) { // handle external functions and ELF section symbols
+			if(cursym->type & SSUB)
+				continue;
+			if(cursym->align != 0)
+				c = rnd(c, cursym->align);
+			cursym->value = 0;
+			for(sub = cursym; sub != S; sub = sub->sub) {
+				sub->value += c;
+				for(p = sub->text; p != P; p = p->link)
+					p->pc += sub->value;
+			}
+			c += cursym->size;
+			continue;
+		}
 		p->pc = c;
 		cursym->value = c;
 
@@ -160,6 +175,8 @@ span(void)
 		bflag = 0;
 		c = INITTEXT;
 		for(cursym = textp; cursym != nil; cursym = cursym->next) {
+			if(!cursym->text || !cursym->text->link)
+				continue;
 			cursym->value = c;
 			for(p = cursym->text; p != P; p = p->link) {
 				curp = p;
@@ -217,6 +234,8 @@ span(void)
 	 */
 	for(cursym = textp; cursym != nil; cursym = cursym->next) {
 		p = cursym->text;
+		if(p == P || p->link == P)
+		       continue;
 		autosize = p->to.offset + 4;
 		symgrow(cursym, cursym->size);
 	
@@ -407,25 +426,9 @@ immhalf(int32 v)
 int32
 symaddr(Sym *s)
 {
-	int32 v;
-
-	v = s->value;
-	switch(s->type) {
-	default:
-		diag("unexpected type %d in symaddr(%s)", s->type, s->name);
-		return 0;
-	
-	case STEXT:
-	case SELFROSECT:
-	case SRODATA:
-	case SDATA:
-	case SBSS:
-	case SCONST:
-	case SNOPTRDATA:
-	case SNOPTRBSS:
-		break;
-	}
-	return v;
+	if(!s->reachable)
+		diag("unreachable symbol in symaddr - %s", s->name);
+	return s->value;
 }
 
 int

src/cmd/ld/data.c

@@ -282,7 +282,7 @@ dynrelocsym(Sym *s)
 	}
 
 	for(r=s->r; r<s->r+s->nr; r++)
-		if(r->sym->type == SDYNIMPORT || r->type >= 256)
+		if(r->sym != S && r->sym->type == SDYNIMPORT || r->type >= 256)
 			adddynrel(s, r);
 }
 

src/cmd/ld/elf.h

@@ -562,6 +562,8 @@ typedef struct {
 #define	R_ARM_GOTPC		25	/* Add PC-relative GOT table address. */
 #define	R_ARM_GOT32		26	/* Add PC-relative GOT offset. */
 #define	R_ARM_PLT32		27	/* Add PC-relative PLT offset. */
+#define	R_ARM_CALL		28
+#define	R_ARM_V4BX		40
 #define	R_ARM_GNU_VTENTRY	100
 #define	R_ARM_GNU_VTINHERIT	101
 #define	R_ARM_RSBREL32		250

src/cmd/ld/ldelf.c

@@ -588,6 +588,9 @@ ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 					p += 4;
 				}
 			}
+			if((info >> 32) == 0) { // absolute relocation, don't bother reading the null symbol
+				rp->sym = S;
+			} else {
 				if(readsym(obj, info>>32, &sym) < 0)
 					goto bad;
 				if(sym.sym == nil) {
@@ -596,6 +599,7 @@ ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 					goto bad;
 				}
 				rp->sym = sym.sym;
+			}
 			rp->type = reltype(pn, (uint32)info, &rp->siz);
 			if(rela)
 				rp->add = add;
@@ -633,6 +637,8 @@ ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 		}
 		if(sym.shndx >= obj->nsect || sym.shndx == 0)
 			continue;
+		if(thechar == '5' && (strcmp(sym.name, "$a") == 0 || strcmp(sym.name, "$d") == 0)) // binutils for arm generate these mapping symbols, skip these
+			continue;
 		sect = obj->sect+sym.shndx;
 		if(sect->sym == nil) {
 			diag("%s: sym#%d: ignoring %s in section %d (type %d)", pn, i, sym.name, sym.shndx, sym.type);
@@ -715,6 +721,9 @@ readsym(ElfObj *obj, int i, ElfSym *sym)
 		werrstr("invalid elf symbol index");
 		return -1;
 	}
+	if(i == 0) {
+		diag("readym: read null symbol!");
+	}
 
 	if(obj->is64) {
 		ElfSymBytes64 *b;
@@ -760,6 +769,7 @@ readsym(ElfObj *obj, int i, ElfSym *sym)
 			}
 			// fall through
 		case ElfSymBindLocal:
+			if(!(thechar == '5' && (strcmp(sym->name, "$a") == 0 || strcmp(sym->name, "$d") == 0))) // binutils for arm generate these mapping symbols, ignore these
 				s = lookup(sym->name, version);
 			break;
 		default:
@@ -797,6 +807,15 @@ reltype(char *pn, int elftype, uchar *siz)
 	switch(R(thechar, elftype)) {
 	default:
 		diag("%s: unknown relocation type %d; compiled without -fpic?", pn, elftype);
+	case R('5', R_ARM_ABS32):
+	case R('5', R_ARM_GOT32):
+	case R('5', R_ARM_PLT32):
+	case R('5', R_ARM_GOTOFF):
+	case R('5', R_ARM_GOTPC):
+	case R('5', R_ARM_THM_PC22):
+	case R('5', R_ARM_REL32):
+	case R('5', R_ARM_CALL):
+	case R('5', R_ARM_V4BX):
 	case R('6', R_X86_64_PC32):
 	case R('6', R_X86_64_PLT32):
 	case R('6', R_X86_64_GOTPCREL):