ld: remove overlap of ELF sections on dynamic binaries

The dynamic ELF sections were pointing to the proper data,
but that data was already owned by the rodata and text sections.
Some ELF references explicitly prohibit multiple sections from
owning the same data, and strip behaves accordingly.

The data for these sections was moved out and their ranges are
now owned by their respective sections.  This change makes strip
happy both with and without -s being provided at link time.

A test was added in debug/elf to ensure there are no regressions
on this area in the future.

Fixes #1242.
Fixes #2022.

NOTE: Tested on Linux amd64/386/arm only.

R=rsc
CC=golang-dev
https://golang.org/cl/4808043

src/cmd/5l/asm.c

@@ -157,7 +157,7 @@ doelf(void)
 
 	/* predefine strings we need for section headers */
 	shstrtab = lookup(".shstrtab", 0);
-	shstrtab->type = SELFDATA;
+	shstrtab->type = SELFROSECT;
 	shstrtab->reachable = 1;
 
 	elfstr[ElfStrEmpty] = addstring(shstrtab, "");
@@ -186,19 +186,22 @@ doelf(void)
 		elfstr[ElfStrPlt] = addstring(shstrtab, ".plt");
 
 		/* interpreter string */
+		if(interpreter == nil)
+			interpreter = linuxdynld;
 		s = lookup(".interp", 0);
+		s->type = SELFROSECT;
 		s->reachable = 1;
-		s->type = SELFDATA;	// TODO: rodata
+		addstring(s, interpreter);
 
 		/* dynamic symbol table - first entry all zeros */
 		s = lookup(".dynsym", 0);
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		s->reachable = 1;
 		s->value += ELF32SYMSIZE;
 
 		/* dynamic string table */
 		s = lookup(".dynstr", 0);
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		s->reachable = 1;
 		if(s->size == 0)
 			addstring(s, "");
@@ -207,37 +210,37 @@ doelf(void)
 		/* relocation table */
 		s = lookup(".rel", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/* global offset table */
 		s = lookup(".got", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFSECT; // writable
 		
 		/* hash */
 		s = lookup(".hash", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/* got.plt */
 		s = lookup(".got.plt", 0);
 		s->reachable = 1;
-		s->type = SDATA;	// writable, so not SELFDATA
+		s->type = SELFSECT; // writable
 		
 		s = lookup(".plt", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		s = lookup(".rel.plt", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		
 		elfsetupplt();
 
 		/* define dynamic elf table */
 		s = lookup(".dynamic", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/*
 		 * .dynamic table
@@ -274,8 +277,11 @@ datoff(vlong addr)
 void
 shsym(Elf64_Shdr *sh, Sym *s)
 {
-	sh->addr = symaddr(s);
-	sh->off = datoff(sh->addr);
+	vlong addr;
+	addr = symaddr(s);
+	if(sh->flags&SHF_ALLOC)
+		sh->addr = addr;
+	sh->off = datoff(addr);
 	sh->size = s->size;
 }
 
@@ -331,7 +337,7 @@ asmb(void)
 	if(iself) {
 		/* index of elf text section; needed by asmelfsym, double-checked below */
 		/* !debug['d'] causes extra sections before the .text section */
-		elftextsh = 1;
+		elftextsh = 2;
 		if(!debug['d']) {
 			elftextsh += 10;
 			if(elfverneed)
@@ -486,9 +492,7 @@ asmb(void)
 			sh->type = SHT_PROGBITS;
 			sh->flags = SHF_ALLOC;
 			sh->addralign = 1;
-			if(interpreter == nil)
-				interpreter = linuxdynld;
-			elfinterp(sh, startva, interpreter);
+			shsym(sh, lookup(".interp", 0));
 
 			ph = newElfPhdr();
 			ph->type = PT_INTERP;
@@ -579,6 +583,11 @@ asmb(void)
 		ph->flags = PF_W+PF_R;
 		ph->align = 4;
 
+		sh = newElfShstrtab(elfstr[ElfStrShstrtab]);
+		sh->type = SHT_STRTAB;
+		sh->addralign = 1;
+		shsym(sh, lookup(".shstrtab", 0));
+
 		if(elftextsh != eh->shnum)
 			diag("elftextsh = %d, want %d", elftextsh, eh->shnum);
 		for(sect=segtext.sect; sect!=nil; sect=sect->next)
@@ -604,11 +613,6 @@ asmb(void)
 			// dwarfaddelfheaders();
 		}
 
-		sh = newElfShstrtab(elfstr[ElfStrShstrtab]);
-		sh->type = SHT_STRTAB;
-		sh->addralign = 1;
-		shsym(sh, lookup(".shstrtab", 0));
-
 		/* Main header */
 		eh->ident[EI_MAG0] = '\177';
 		eh->ident[EI_MAG1] = 'E';
@@ -634,7 +638,7 @@ asmb(void)
 		a += elfwritephdrs();
 		a += elfwriteshdrs();
 		cflush();
-		if(a+elfwriteinterp() > ELFRESERVE)
+		if(a > ELFRESERVE)	
 			diag("ELFRESERVE too small: %d > %d", a, ELFRESERVE);
 		break;
 	}
@@ -1825,7 +1829,7 @@ genasmsym(void (*put)(Sym*, char*, int, vlong, vlong, int, Sym*))
 			case SCONST:
 			case SRODATA:
 			case SDATA:
-			case SELFDATA:
+			case SELFROSECT:
 			case STYPE:
 			case SSTRING:
 			case SGOSTRING:

src/cmd/5l/span.c

@@ -416,7 +416,7 @@ symaddr(Sym *s)
 		return 0;
 	
 	case STEXT:
-	case SELFDATA:
+	case SELFROSECT:
 	case SRODATA:
 	case SDATA:
 	case SBSS:

src/cmd/6l/asm.c

@@ -559,7 +559,7 @@ doelf(void)
 
 	/* predefine strings we need for section headers */
 	shstrtab = lookup(".shstrtab", 0);
-	shstrtab->type = SELFDATA;
+	shstrtab->type = SELFROSECT;
 	shstrtab->reachable = 1;
 
 	elfstr[ElfStrEmpty] = addstring(shstrtab, "");
@@ -591,15 +591,31 @@ doelf(void)
 		elfstr[ElfStrGnuVersion] = addstring(shstrtab, ".gnu.version");
 		elfstr[ElfStrGnuVersionR] = addstring(shstrtab, ".gnu.version_r");
 
+		/* interpreter string */
+		if(interpreter == nil) {
+			switch(HEADTYPE) {
+			case Hlinux:
+				interpreter = linuxdynld;
+				break;
+			case Hfreebsd:
+				interpreter = freebsddynld;
+				break;
+			}
+		}
+		s = lookup(".interp", 0);
+		s->type = SELFROSECT;
+		s->reachable = 1;
+		addstring(s, interpreter);
+
 		/* dynamic symbol table - first entry all zeros */
 		s = lookup(".dynsym", 0);
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		s->reachable = 1;
 		s->size += ELF64SYMSIZE;
 
 		/* dynamic string table */
 		s = lookup(".dynstr", 0);
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		s->reachable = 1;
 		if(s->size == 0)
 			addstring(s, "");
@@ -608,44 +624,44 @@ doelf(void)
 		/* relocation table */
 		s = lookup(".rela", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/* global offset table */
 		s = lookup(".got", 0);
 		s->reachable = 1;
-		s->type = SDATA;	// writable, so not SELFDATA
+		s->type = SELFSECT; // writable
 
 		/* hash */
 		s = lookup(".hash", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		s = lookup(".got.plt", 0);
 		s->reachable = 1;
-		s->type = SDATA;	// writable, not SELFDATA
+		s->type = SELFSECT; // writable
 
 		s = lookup(".plt", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		
 		elfsetupplt();
 		
 		s = lookup(".rela.plt", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		
 		s = lookup(".gnu.version", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		
 		s = lookup(".gnu.version_r", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/* define dynamic elf table */
 		s = lookup(".dynamic", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/*
 		 * .dynamic table
@@ -673,8 +689,11 @@ doelf(void)
 void
 shsym(ElfShdr *sh, Sym *s)
 {
-	sh->addr = symaddr(s);
-	sh->off = datoff(sh->addr);
+	vlong addr;
+	addr = symaddr(s);
+	if(sh->flags&SHF_ALLOC)
+		sh->addr = addr;
+	sh->off = datoff(addr);
 	sh->size = s->size;
 }
 
@@ -746,7 +765,7 @@ asmb(void)
 		debug['8'] = 1;	/* 64-bit addresses */
 		/* index of elf text section; needed by asmelfsym, double-checked below */
 		/* !debug['d'] causes extra sections before the .text section */
-		elftextsh = 1;
+		elftextsh = 2;
 		if(!debug['d']) {
 			elftextsh += 10;
 			if(elfverneed)
@@ -890,7 +909,7 @@ asmb(void)
 					break;
 				}
 			}
-			elfinterp(sh, startva, interpreter);
+			shsym(sh, lookup(".interp", 0));
 
 			ph = newElfPhdr();
 			ph->type = PT_INTERP;
@@ -1014,6 +1033,11 @@ asmb(void)
 		ph->flags = PF_W+PF_R;
 		ph->align = 8;
 
+		sh = newElfShstrtab(elfstr[ElfStrShstrtab]);
+		sh->type = SHT_STRTAB;
+		sh->addralign = 1;
+		shsym(sh, lookup(".shstrtab", 0));
+
 		if(elftextsh != eh->shnum)
 			diag("elftextsh = %d, want %d", elftextsh, eh->shnum);
 		for(sect=segtext.sect; sect!=nil; sect=sect->next)
@@ -1039,11 +1063,6 @@ asmb(void)
 			dwarfaddelfheaders();
 		}
 
-		sh = newElfShstrtab(elfstr[ElfStrShstrtab]);
-		sh->type = SHT_STRTAB;
-		sh->addralign = 1;
-		shsym(sh, lookup(".shstrtab", 0));
-
 		/* Main header */
 		eh->ident[EI_MAG0] = '\177';
 		eh->ident[EI_MAG1] = 'E';
@@ -1069,7 +1088,7 @@ asmb(void)
 		a += elfwritephdrs();
 		a += elfwriteshdrs();
 		cflush();
-		if(a+elfwriteinterp() > ELFRESERVE)
+		if(a > ELFRESERVE)	
 			diag("ELFRESERVE too small: %d > %d", a, ELFRESERVE);
 		break;
 	case Hwindows:
@@ -1111,7 +1130,7 @@ genasmsym(void (*put)(Sym*, char*, int, vlong, vlong, int, Sym*))
 		case SCONST:
 		case SRODATA:
 		case SDATA:
-		case SELFDATA:
+		case SELFROSECT:
 		case SMACHOGOT:
 		case STYPE:
 		case SSTRING:

src/cmd/8l/asm.c

@@ -519,7 +519,7 @@ doelf(void)
 
 	/* predefine strings we need for section headers */
 	shstrtab = lookup(".shstrtab", 0);
-	shstrtab->type = SELFDATA;
+	shstrtab->type = SELFROSECT;
 	shstrtab->reachable = 1;
 
 	elfstr[ElfStrEmpty] = addstring(shstrtab, "");
@@ -552,20 +552,31 @@ doelf(void)
 		elfstr[ElfStrGnuVersionR] = addstring(shstrtab, ".gnu.version_r");
 
 		/* interpreter string */
+		if(interpreter == nil) {
+			switch(HEADTYPE) {
+			case Hlinux:
+				interpreter = linuxdynld;
+				break;
+			case Hfreebsd:
+				interpreter = freebsddynld;
+				break;
+			}
+		}
 		s = lookup(".interp", 0);
+		s->type = SELFROSECT;
 		s->reachable = 1;
-		s->type = SELFDATA;
+		addstring(s, interpreter);
 
 		/* dynamic symbol table - first entry all zeros */
 		s = lookup(".dynsym", 0);
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		s->reachable = 1;
 		s->size += ELF32SYMSIZE;
 
 		/* dynamic string table */
 		s = lookup(".dynstr", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		if(s->size == 0)
 			addstring(s, "");
 		dynstr = s;
@@ -573,45 +584,45 @@ doelf(void)
 		/* relocation table */
 		s = lookup(".rel", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/* global offset table */
 		s = lookup(".got", 0);
 		s->reachable = 1;
-		s->type = SDATA;	// writable, so not SELFDATA
+		s->type = SELFSECT; // writable
 		
 		/* hash */
 		s = lookup(".hash", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/* got.plt */
 		s = lookup(".got.plt", 0);
 		s->reachable = 1;
-		s->type = SDATA;	// writable, so not SELFDATA
+		s->type = SELFSECT; // writable
 		
 		s = lookup(".plt", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		s = lookup(".rel.plt", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		
 		s = lookup(".gnu.version", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 		
 		s = lookup(".gnu.version_r", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		elfsetupplt();
 
 		/* define dynamic elf table */
 		s = lookup(".dynamic", 0);
 		s->reachable = 1;
-		s->type = SELFDATA;
+		s->type = SELFROSECT;
 
 		/*
 		 * .dynamic table
@@ -638,8 +649,11 @@ doelf(void)
 void
 shsym(Elf64_Shdr *sh, Sym *s)
 {
-	sh->addr = symaddr(s);
-	sh->off = datoff(sh->addr);
+	vlong addr;
+	addr = symaddr(s);
+	if(sh->flags&SHF_ALLOC)
+		sh->addr = addr;
+	sh->off = datoff(addr);
 	sh->size = s->size;
 }
 
@@ -696,7 +710,7 @@ asmb(void)
 	if(iself) {
 		/* index of elf text section; needed by asmelfsym, double-checked below */
 		/* !debug['d'] causes extra sections before the .text section */
-		elftextsh = 1;
+		elftextsh = 2;
 		if(!debug['d']) {
 			elftextsh += 10;
 			if(elfverneed)
@@ -950,17 +964,7 @@ asmb(void)
 			sh->type = SHT_PROGBITS;
 			sh->flags = SHF_ALLOC;
 			sh->addralign = 1;
-			if(interpreter == nil) {
-				switch(HEADTYPE) {
-				case Hlinux:
-					interpreter = linuxdynld;
-					break;
-				case Hfreebsd:
-					interpreter = freebsddynld;
-					break;
-				}
-			}
-			elfinterp(sh, startva, interpreter);
+			shsym(sh, lookup(".interp", 0));
 
 			ph = newElfPhdr();
 			ph->type = PT_INTERP;
@@ -1084,6 +1088,11 @@ asmb(void)
 		ph->flags = PF_W+PF_R;
 		ph->align = 4;
 
+		sh = newElfShstrtab(elfstr[ElfStrShstrtab]);
+		sh->type = SHT_STRTAB;
+		sh->addralign = 1;
+		shsym(sh, lookup(".shstrtab", 0));
+
 		if(elftextsh != eh->shnum)
 			diag("elftextsh = %d, want %d", elftextsh, eh->shnum);
 		for(sect=segtext.sect; sect!=nil; sect=sect->next)
@@ -1109,11 +1118,6 @@ asmb(void)
 			dwarfaddelfheaders();
 		}
 
-		sh = newElfShstrtab(elfstr[ElfStrShstrtab]);
-		sh->type = SHT_STRTAB;
-		sh->addralign = 1;
-		shsym(sh, lookup(".shstrtab", 0));
-
 		/* Main header */
 		eh->ident[EI_MAG0] = '\177';
 		eh->ident[EI_MAG1] = 'E';
@@ -1144,7 +1148,7 @@ asmb(void)
 		a += elfwritephdrs();
 		a += elfwriteshdrs();
 		cflush();
-		if(a+elfwriteinterp() > ELFRESERVE)
+		if(a > ELFRESERVE)	
 			diag("ELFRESERVE too small: %d > %d", a, ELFRESERVE);
 		break;
 
@@ -1200,7 +1204,7 @@ genasmsym(void (*put)(Sym*, char*, int, vlong, vlong, int, Sym*))
 			case SCONST:
 			case SRODATA:
 			case SDATA:
-			case SELFDATA:
+			case SELFROSECT:
 			case SMACHO:
 			case SMACHOGOT:
 			case STYPE:

src/cmd/ld/data.c

@@ -821,9 +821,8 @@ dodata(void)
 	s = datap;
 	for(; s != nil && s->type < SSYMTAB; s = s->next) {
 		s->type = SRODATA;
-		t = rnd(s->size, PtrSize);
 		s->value = datsize;
-		datsize += t;
+		datsize += rnd(s->size, PtrSize);
 	}
 	sect->len = datsize - sect->vaddr;
 
@@ -836,19 +835,41 @@ dodata(void)
 		datsize += s->size;
 	}
 	sect->len = datsize - sect->vaddr;
+	datsize = rnd(datsize, PtrSize);
 
 	/* gopclntab */
 	sect = addsection(&segtext, ".gopclntab", 04);
 	sect->vaddr = datsize;
-	for(; s != nil && s->type < SDATA; s = s->next) {
+	for(; s != nil && s->type < SELFROSECT; s = s->next) {
 		s->type = SRODATA;
 		s->value = datsize;
 		datsize += s->size;
 	}
 	sect->len = datsize - sect->vaddr;
+	datsize = rnd(datsize, PtrSize);
 
-	/* data */
+	/* read-only ELF sections */
+	for(; s != nil && s->type < SELFSECT; s = s->next) {
+		sect = addsection(&segtext, s->name, 04);
+		sect->vaddr = datsize;
+		s->type = SRODATA;
+		s->value = datsize;
+		datsize += rnd(s->size, PtrSize);
+		sect->len = datsize - sect->vaddr;
+	}
+
+	/* writable ELF sections */
 	datsize = 0;
+	for(; s != nil && s->type < SDATA; s = s->next) {
+		sect = addsection(&segdata, s->name, 06);
+		sect->vaddr = datsize;
+		s->type = SDATA;
+		s->value = datsize;
+		datsize += rnd(s->size, PtrSize);
+		sect->len = datsize - sect->vaddr;
+	}
+
+	/* data */
 	sect = addsection(&segdata, ".data", 06);
 	sect->vaddr = 0;
 	for(; s != nil && s->type < SBSS; s = s->next) {
@@ -950,38 +971,43 @@ address(void)
 	segtext.fileoff = HEADR;
 	for(s=segtext.sect; s != nil; s=s->next) {
 		s->vaddr = va;
-		va += s->len;
-		segtext.len = va - INITTEXT;
-		va = rnd(va, INITRND);
+		va += rnd(s->len, PtrSize);
 	}
+	segtext.len = va - INITTEXT;
 	segtext.filelen = segtext.len;
 
+	va = rnd(va, INITRND);
+
 	segdata.rwx = 06;
 	segdata.vaddr = va;
 	segdata.fileoff = va - segtext.vaddr + segtext.fileoff;
+	segdata.filelen = 0;
 	if(HEADTYPE == Hwindows)
 		segdata.fileoff = segtext.fileoff + rnd(segtext.len, PEFILEALIGN);
 	if(HEADTYPE == Hplan9x32)
 		segdata.fileoff = segtext.fileoff + segtext.filelen;
+	data = nil;
 	for(s=segdata.sect; s != nil; s=s->next) {
 		s->vaddr = va;
 		va += s->len;
+		segdata.filelen += s->len;
 		segdata.len = va - segdata.vaddr;
+		if(strcmp(s->name, ".data") == 0)
+			data = s;
 	}
-	segdata.filelen = segdata.sect->len;	// assume .data is first
-	
+	segdata.filelen -= data->next->len; // deduct .bss
+
 	text = segtext.sect;
 	rodata = text->next;
 	symtab = rodata->next;
 	pclntab = symtab->next;
-	data = segdata.sect;
 
 	for(sym = datap; sym != nil; sym = sym->next) {
 		cursym = sym;
 		if(sym->type < SDATA)
 			sym->value += rodata->vaddr;
 		else
-			sym->value += data->vaddr;
+			sym->value += segdata.sect->vaddr;
 		for(sub = sym->sub; sub != nil; sub = sub->sub)
 			sub->value += sym->value;
 	}

src/cmd/ld/elf.c

@@ -19,7 +19,6 @@ static	int	elf64;
 static	ElfEhdr	hdr;
 static	ElfPhdr	*phdr[NSECT];
 static	ElfShdr	*shdr[NSECT];
-static	char	*interp;
 
 typedef struct Elfstring Elfstring;
 struct Elfstring
@@ -304,32 +303,6 @@ elfwritedynentsymsize(Sym *s, int tag, Sym *t)
 	addsize(s, t);
 }
 
-int
-elfwriteinterp(void)
-{
-	int n;
-	
-	if(interp == nil)
-		return 0;
-
-	n = strlen(interp)+1;
-	cseek(ELFRESERVE-n);
-	cwrite(interp, n);
-	return n;
-}
-
-void
-elfinterp(ElfShdr *sh, uint64 startva, char *p)
-{
-	int n;
-	
-	interp = p;
-	n = strlen(interp)+1;
-	sh->addr = startva + ELFRESERVE - n;
-	sh->off = ELFRESERVE - n;
-	sh->size = n;
-}
-
 extern int nelfsym;
 int elfverneed;
 
@@ -393,7 +366,7 @@ elfdynhash(void)
 
 	nsym = nelfsym;
 	s = lookup(".hash", 0);
-	s->type = SELFDATA;
+	s->type = SELFROSECT;
 	s->reachable = 1;
 
 	i = nsym;
@@ -539,6 +512,12 @@ elfshbits(Section *sect)
 	return nil;
 
 found:
+	for(i=0; i<hdr.shnum; i++) {
+		sh = shdr[i];
+		if(sh->name == off)
+			return sh;
+	}
+
 	sh = newElfShdr(off);
 	if(sect->vaddr < sect->seg->vaddr + sect->seg->filelen)
 		sh->type = SHT_PROGBITS;

src/cmd/ld/lib.h

@@ -34,7 +34,6 @@ enum
 	
 	/* order here is order in output file */
 	STEXT,
-	SELFDATA,
 	SMACHOPLT,
 	STYPE,
 	SSTRING,
@@ -42,6 +41,8 @@ enum
 	SRODATA,
 	SSYMTAB,
 	SPCLNTAB,
+	SELFROSECT,
+	SELFSECT,
 	SDATA,
 	SMACHO,	/* Mach-O __nl_symbol_ptr */
 	SMACHOGOT,

src/cmd/ld/pe.c

@@ -396,7 +396,7 @@ dope(void)
 	/* relocation table */
 	rel = lookup(".rel", 0);
 	rel->reachable = 1;
-	rel->type = SELFDATA;
+	rel->type = SELFROSECT;
 
 	initdynimport();
 	initdynexport();

src/pkg/debug/elf/file_test.go

@@ -7,7 +7,10 @@ package elf
 import (
 	"debug/dwarf"
 	"encoding/binary"
+	"net"
+	"os"
 	"reflect"
+	"runtime"
 	"testing"
 )
 
@@ -210,3 +213,29 @@ func TestDWARFRelocations(t *testing.T) {
 		}
 	}
 }
+
+func TestNoSectionOverlaps(t *testing.T) {
+	// Ensure 6l outputs sections without overlaps.
+	if runtime.GOOS != "linux" && runtime.GOOS != "freebsd" {
+		return // not ELF
+	}
+	_ = net.ResolveIPAddr // force dynamic linkage
+	f, err := Open(os.Args[0])
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	for i, si := range f.Sections {
+		sih := si.SectionHeader
+		for j, sj := range f.Sections {
+			sjh := sj.SectionHeader
+			if i == j || sjh.Type == SHT_NOBITS || sih.Offset == sjh.Offset && sih.Size == 0 {
+				continue
+			}
+			if sih.Offset >= sjh.Offset && sih.Offset < sjh.Offset+sjh.Size {
+				t.Errorf("ld produced ELF with section %s within %s: 0x%x <= 0x%x..0x%x < 0x%x",
+					sih.Name, sjh.Name, sjh.Offset, sih.Offset, sih.Offset+sih.Size, sjh.Offset+sjh.Size)
+			}
+		}
+	}
+}