cmd/ld: place read-only data in non-executable segment

R=golang-dev, dave, r
CC=golang-dev, nigeltao
https://golang.org/cl/10713043

src/cmd/5l/asm.c

@@ -550,13 +550,20 @@ asmb(void)
 	sect = segtext.sect;
 	cseek(sect->vaddr - segtext.vaddr + segtext.fileoff);
 	codeblk(sect->vaddr, sect->len);
-
-	/* output read-only data in text segment (rodata, gosymtab, pclntab, ...) */
 	for(sect = sect->next; sect != nil; sect = sect->next) {
 		cseek(sect->vaddr - segtext.vaddr + segtext.fileoff);
 		datblk(sect->vaddr, sect->len);
 	}
 
+	if(segrodata.filelen > 0) {
+		if(debug['v'])
+			Bprint(&bso, "%5.2f rodatblk\n", cputime());
+		Bflush(&bso);
+
+		cseek(segrodata.fileoff);
+		datblk(segrodata.vaddr, segrodata.filelen);
+	}
+
 	if(debug['v'])
 		Bprint(&bso, "%5.2f datblk\n", cputime());
 	Bflush(&bso);
@@ -587,7 +594,7 @@ asmb(void)
 			symo = HEADR+segtext.len+segdata.filelen;
 			break;
 		ElfSym:
-			symo = rnd(HEADR+segtext.filelen, INITRND)+segdata.filelen;
+			symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(HEADR+segrodata.filelen, INITRND)+segdata.filelen;
 			symo = rnd(symo, INITRND);
 			break;
 		}

src/cmd/6l/asm.c

@@ -625,13 +625,20 @@ asmb(void)
 	sect = segtext.sect;
 	cseek(sect->vaddr - segtext.vaddr + segtext.fileoff);
 	codeblk(sect->vaddr, sect->len);
-
-	/* output read-only data in text segment (rodata, gosymtab, pclntab, ...) */
 	for(sect = sect->next; sect != nil; sect = sect->next) {
 		cseek(sect->vaddr - segtext.vaddr + segtext.fileoff);
 		datblk(sect->vaddr, sect->len);
 	}
 
+	if(segrodata.filelen > 0) {
+		if(debug['v'])
+			Bprint(&bso, "%5.2f rodatblk\n", cputime());
+		Bflush(&bso);
+
+		cseek(segrodata.fileoff);
+		datblk(segrodata.vaddr, segrodata.filelen);
+	}
+
 	if(debug['v'])
 		Bprint(&bso, "%5.2f datblk\n", cputime());
 	Bflush(&bso);
@@ -696,7 +703,7 @@ asmb(void)
 		case Hfreebsd:
 		case Hnetbsd:
 		case Hopenbsd:
-			symo = rnd(HEADR+segtext.len, INITRND)+segdata.filelen;
+			symo = rnd(HEADR+segtext.len, INITRND)+rnd(segrodata.len, INITRND)+segdata.filelen;
 			symo = rnd(symo, INITRND);
 			break;
 		case Hwindows:

src/cmd/8l/asm.c

@@ -595,12 +595,19 @@ asmb(void)
 	sect = segtext.sect;
 	cseek(sect->vaddr - segtext.vaddr + segtext.fileoff);
 	codeblk(sect->vaddr, sect->len);
-
-	/* output read-only data in text segment (rodata, gosymtab, pclntab, ...) */
 	for(sect = sect->next; sect != nil; sect = sect->next) {
 		cseek(sect->vaddr - segtext.vaddr + segtext.fileoff);
 		datblk(sect->vaddr, sect->len);
 	}
+	
+	if(segrodata.filelen > 0) {
+		if(debug['v'])
+			Bprint(&bso, "%5.2f rodatblk\n", cputime());
+		Bflush(&bso);
+
+		cseek(segrodata.fileoff);
+		datblk(segrodata.vaddr, segrodata.filelen);
+	}
 
 	if(debug['v'])
 		Bprint(&bso, "%5.2f datblk\n", cputime());
@@ -655,7 +662,7 @@ asmb(void)
 			symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(segdata.filelen, INITRND)+machlink;
 			break;
 		Elfsym:
-			symo = rnd(HEADR+segtext.filelen, INITRND)+segdata.filelen;
+			symo = rnd(HEADR+segtext.filelen, INITRND)+rnd(HEADR+segrodata.filelen, INITRND)+segdata.filelen;
 			symo = rnd(symo, INITRND);
 			break;
 		case Hwindows:

src/cmd/ld/data.c

@@ -1040,6 +1040,7 @@ dodata(void)
 	int32 n;
 	vlong datsize;
 	Section *sect;
+	Segment *segro;
 	Sym *s, *last, **l;
 	Sym *gcdata1, *gcbss1;
 
@@ -1130,7 +1131,7 @@ dodata(void)
 		sect->vaddr = datsize;
 		s->sect = sect;
 		s->type = SDATA;
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		growdatsize(&datsize, s);
 		sect->len = datsize - sect->vaddr;
 	}
@@ -1146,7 +1147,7 @@ dodata(void)
 		datsize = aligndatsize(datsize, s);
 		s->sect = sect;
 		s->type = SDATA;
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		growdatsize(&datsize, s);
 	}
 	sect->len = datsize - sect->vaddr;
@@ -1163,7 +1164,7 @@ dodata(void)
 			datsize = aligndatsize(datsize, s);
 			s->sect = sect;
 			s->type = SDATA;
-			s->value = datsize;
+			s->value = datsize - sect->vaddr;
 			growdatsize(&datsize, s);
 		}
 		sect->len = datsize - sect->vaddr;
@@ -1184,7 +1185,7 @@ dodata(void)
 		s->sect = sect;
 		s->type = SDATA;
 		datsize = aligndatsize(datsize, s);
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		gcaddsym(gcdata1, s, datsize - sect->vaddr);  // gc
 		growdatsize(&datsize, s);
 	}
@@ -1203,7 +1204,7 @@ dodata(void)
 	for(; s != nil && s->type < SNOPTRBSS; s = s->next) {
 		s->sect = sect;
 		datsize = aligndatsize(datsize, s);
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		gcaddsym(gcbss1, s, datsize - sect->vaddr);  // gc
 		growdatsize(&datsize, s);
 	}
@@ -1222,7 +1223,7 @@ dodata(void)
 	for(; s != nil && s->type == SNOPTRBSS; s = s->next) {
 		datsize = aligndatsize(datsize, s);
 		s->sect = sect;
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		growdatsize(&datsize, s);
 	}
 	sect->len = datsize - sect->vaddr;
@@ -1241,7 +1242,7 @@ dodata(void)
 		for(; s != nil && s->type == STLSBSS; s = s->next) {
 			datsize = aligndatsize(datsize, s);
 			s->sect = sect;
-			s->value = datsize;
+			s->value = datsize - sect->vaddr;
 			growdatsize(&datsize, s);
 		}
 		sect->len = datsize;
@@ -1252,27 +1253,56 @@ dodata(void)
 		diag("unexpected symbol type %d for %s", s->type, s->name);
 	}
 
-	/* we finished segdata, begin segtext */
+	/*
+	 * We finished data, begin read-only data.
+	 * Not all systems support a separate read-only non-executable data section.
+	 * ELF systems do.
+	 * OS X and Plan 9 do not.
+	 * Windows PE may, but if so we have not implemented it.
+	 * And if we're using external linking mode, the point is moot,
+	 * since it's not our decision; that code expects the sections in
+	 * segtext.
+	 */
+	if(iself && linkmode == LinkInternal)
+		segro = &segrodata;
+	else
+		segro = &segtext;
+
 	s = datap;
+	
+	datsize = 0;
+	
+	/* read-only executable ELF, Mach-O sections */
+	for(; s != nil && s->type < STYPE; s = s->next) {
+		sect = addsection(&segtext, s->name, 04);
+		sect->align = symalign(s);
+		datsize = rnd(datsize, sect->align);
+		sect->vaddr = datsize;
+		s->sect = sect;
+		s->type = SRODATA;
+		s->value = datsize - sect->vaddr;
+		growdatsize(&datsize, s);
+		sect->len = datsize - sect->vaddr;
+	}
 
 	/* read-only data */
-	sect = addsection(&segtext, ".rodata", 04);
+	sect = addsection(segro, ".rodata", 04);
 	sect->align = maxalign(s, STYPELINK-1);
+	datsize = rnd(datsize, sect->align);
 	sect->vaddr = 0;
 	lookup("rodata", 0)->sect = sect;
 	lookup("erodata", 0)->sect = sect;
-	datsize = 0;
 	for(; s != nil && s->type < STYPELINK; s = s->next) {
 		datsize = aligndatsize(datsize, s);
 		s->sect = sect;
 		s->type = SRODATA;
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		growdatsize(&datsize, s);
 	}
 	sect->len = datsize - sect->vaddr;
 
 	/* typelink */
-	sect = addsection(&segtext, ".typelink", 04);
+	sect = addsection(segro, ".typelink", 04);
 	sect->align = maxalign(s, STYPELINK);
 	datsize = rnd(datsize, sect->align);
 	sect->vaddr = datsize;
@@ -1282,13 +1312,13 @@ dodata(void)
 		datsize = aligndatsize(datsize, s);
 		s->sect = sect;
 		s->type = SRODATA;
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		growdatsize(&datsize, s);
 	}
 	sect->len = datsize - sect->vaddr;
 
 	/* gosymtab */
-	sect = addsection(&segtext, ".gosymtab", 04);
+	sect = addsection(segro, ".gosymtab", 04);
 	sect->align = maxalign(s, SPCLNTAB-1);
 	datsize = rnd(datsize, sect->align);
 	sect->vaddr = datsize;
@@ -1298,13 +1328,13 @@ dodata(void)
 		datsize = aligndatsize(datsize, s);
 		s->sect = sect;
 		s->type = SRODATA;
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		growdatsize(&datsize, s);
 	}
 	sect->len = datsize - sect->vaddr;
 
 	/* gopclntab */
-	sect = addsection(&segtext, ".gopclntab", 04);
+	sect = addsection(segro, ".gopclntab", 04);
 	sect->align = maxalign(s, SELFROSECT-1);
 	datsize = rnd(datsize, sect->align);
 	sect->vaddr = datsize;
@@ -1314,33 +1344,35 @@ dodata(void)
 		datsize = aligndatsize(datsize, s);
 		s->sect = sect;
 		s->type = SRODATA;
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		growdatsize(&datsize, s);
 	}
 	sect->len = datsize - sect->vaddr;
 
 	/* read-only ELF, Mach-O sections */
 	for(; s != nil && s->type < SELFSECT; s = s->next) {
-		sect = addsection(&segtext, s->name, 04);
+		sect = addsection(segro, s->name, 04);
 		sect->align = symalign(s);
 		datsize = rnd(datsize, sect->align);
 		sect->vaddr = datsize;
 		s->sect = sect;
 		s->type = SRODATA;
-		s->value = datsize;
+		s->value = datsize - sect->vaddr;
 		growdatsize(&datsize, s);
 		sect->len = datsize - sect->vaddr;
 	}
 
 	// 6g uses 4-byte relocation offsets, so the entire segment must fit in 32 bits.
 	if(datsize != (uint32)datsize) {
-		diag("text segment too large");
+		diag("read-only data segment too large");
 	}
 	
 	/* number the sections */
 	n = 1;
 	for(sect = segtext.sect; sect != nil; sect = sect->next)
 		sect->extnum = n++;
+	for(sect = segrodata.sect; sect != nil; sect = sect->next)
+		sect->extnum = n++;
 	for(sect = segdata.sect; sect != nil; sect = sect->next)
 		sect->extnum = n++;
 }
@@ -1402,6 +1434,7 @@ address(void)
 	segtext.vaddr = va;
 	segtext.fileoff = HEADR;
 	for(s=segtext.sect; s != nil; s=s->next) {
+//print("%s at %#llux + %#llux\n", s->name, va, (vlong)s->len);
 		va = rnd(va, s->align);
 		s->vaddr = va;
 		va += s->len;
@@ -1409,8 +1442,25 @@ address(void)
 	segtext.len = va - INITTEXT;
 	segtext.filelen = segtext.len;
 
-	va = rnd(va, INITRND);
+	if(segrodata.sect != nil) {
+		// align to page boundary so as not to mix
+		// rodata and executable text.
+		va = rnd(va, INITRND);
+
+		segrodata.rwx = 04;
+		segrodata.vaddr = va;
+		segrodata.fileoff = va - segtext.vaddr + segtext.fileoff;
+		segrodata.filelen = 0;
+		for(s=segrodata.sect; s != nil; s=s->next) {
+			va = rnd(va, s->align);
+			s->vaddr = va;
+			va += s->len;
+		}
+		segrodata.len = va - segrodata.vaddr;
+		segrodata.filelen = segrodata.len;
+	}
 
+	va = rnd(va, INITRND);
 	segdata.rwx = 06;
 	segdata.vaddr = va;
 	segdata.fileoff = va - segtext.vaddr + segtext.fileoff;
@@ -1445,17 +1495,17 @@ address(void)
 	segdata.filelen = bss->vaddr - segdata.vaddr;
 
 	text = segtext.sect;
-	rodata = text->next;
+	if(segrodata.sect)
+		rodata = segrodata.sect;
+	else
+		rodata = text->next;
 	typelink = rodata->next;
 	symtab = typelink->next;
 	pclntab = symtab->next;
 
 	for(sym = datap; sym != nil; sym = sym->next) {
 		cursym = sym;
-		if(sym->type < SNOPTRDATA)
-			sym->value += rodata->vaddr;
-		else
-			sym->value += segdata.sect->vaddr;
+		sym->value += sym->sect->vaddr;
 		for(sub = sym->sub; sub != nil; sub = sub->sub)
 			sub->value += sym->value;
 	}

src/cmd/ld/elf.c

@@ -864,6 +864,8 @@ elfemitreloc(void)
 	elfrelocsect(segtext.sect, textp);
 	for(sect=segtext.sect->next; sect!=nil; sect=sect->next)
 		elfrelocsect(sect, datap);	
+	for(sect=segrodata.sect; sect!=nil; sect=sect->next)
+		elfrelocsect(sect, datap);	
 	for(sect=segdata.sect; sect!=nil; sect=sect->next)
 		elfrelocsect(sect, datap);	
 }
@@ -1001,7 +1003,7 @@ doelf(void)
 
 		s = lookup(".plt", 0);
 		s->reachable = 1;
-		s->type = SELFROSECT;
+		s->type = SELFRXSECT;
 		
 		elfsetupplt();
 		
@@ -1105,6 +1107,8 @@ asmbelfsetup(void)
 	
 	for(sect=segtext.sect; sect!=nil; sect=sect->next)
 		elfshalloc(sect);
+	for(sect=segrodata.sect; sect!=nil; sect=sect->next)
+		elfshalloc(sect);
 	for(sect=segdata.sect; sect!=nil; sect=sect->next)
 		elfshalloc(sect);
 }
@@ -1232,6 +1236,8 @@ asmbelf(vlong symo)
 	USED(resoff);
 
 	elfphload(&segtext);
+	if(segrodata.sect != nil)
+		elfphload(&segrodata);
 	elfphload(&segdata);
 
 	/* Dynamic linking sections */
@@ -1397,12 +1403,16 @@ elfobj:
 
 	for(sect=segtext.sect; sect!=nil; sect=sect->next)
 		elfshbits(sect);
+	for(sect=segrodata.sect; sect!=nil; sect=sect->next)
+		elfshbits(sect);
 	for(sect=segdata.sect; sect!=nil; sect=sect->next)
 		elfshbits(sect);
 
 	if(linkmode == LinkExternal) {
 		for(sect=segtext.sect; sect!=nil; sect=sect->next)
 			elfshreloc(sect);
+		for(sect=segrodata.sect; sect!=nil; sect=sect->next)
+			elfshreloc(sect);
 		for(sect=segdata.sect; sect!=nil; sect=sect->next)
 			elfshreloc(sect);
 		// add a .note.GNU-stack section to mark the stack as non-executable

src/cmd/ld/lib.c

@@ -36,6 +36,13 @@
 
 #include	<ar.h>
 
+enum
+{
+	// Whether to assume that the external linker is "gold"
+	// (http://sourceware.org/ml/binutils/2008-03/msg00162.html).
+	AssumeGoldLinker = 0,
+};
+
 int iconv(Fmt*);
 
 char	symname[]	= SYMDEF;
@@ -676,6 +683,10 @@ hostlink(void)
 	}
 	if(HEADTYPE == Hdarwin)
 		argv[argc++] = "-Wl,-no_pie,-pagezero_size,4000000";
+	
+	if(iself && AssumeGoldLinker)
+		argv[argc++] = "-Wl,--rosegment";
+
 	argv[argc++] = "-o";
 	argv[argc++] = outfile;
 	

src/cmd/ld/lib.h

@@ -33,7 +33,11 @@ enum
 	Sxxx,
 
 	/* order here is order in output file */
+	/* readonly, executable */
 	STEXT,
+	SELFRXSECT,
+	
+	/* readonly, non-executable */
 	STYPE,
 	SSTRING,
 	SGOSTRING,
@@ -42,6 +46,8 @@ enum
 	SSYMTAB,
 	SPCLNTAB,
 	SELFROSECT,
+	
+	/* writable, non-executable */
 	SMACHOPLT,
 	SELFSECT,
 	SMACHO,	/* Mach-O __nl_symbol_ptr */
@@ -54,6 +60,7 @@ enum
 	SNOPTRBSS,
 	STLSBSS,
 
+	/* not mapped */
 	SXREF,
 	SMACHOSYMSTR,
 	SMACHOSYMTAB,
@@ -177,6 +184,7 @@ enum
 };
 
 EXTERN	Segment	segtext;
+EXTERN	Segment	segrodata;
 EXTERN	Segment	segdata;
 EXTERN	Segment	segdwarf;