cmd/ld: fix symbol table sorting

runtime: double-check that symbol table is sorted

If the symbol table is unsorted, the binary search in findfunc
will not find its func, which will make stack traces stop early.
When the garbage collector starts using the stack tracer,
that would be a serious problem.

The unsorted symbol addresses came from from two things:

1. The symbols in an ELF object are not necessarily sorted,
   so sort them before adding them to the symbol list.

2. The __i686.get_pc_thunk.bx symbol is present in multiple
   object files and was having its address adjusted multiple
   times, producing an incorrect address in the symbol table.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7440044

src/cmd/ld/data.c

@@ -58,70 +58,73 @@ datcmp(Sym *s1, Sym *s2)
 }
 
 Sym*
-datsort(Sym *l)
+listsort(Sym *l, int (*cmp)(Sym*, Sym*), int off)
 {
 	Sym *l1, *l2, *le;
+	#define NEXT(l) (*(Sym**)((char*)(l)+off))
 
-	if(l == 0 || l->next == 0)
+	if(l == 0 || NEXT(l) == 0)
 		return l;
 
 	l1 = l;
 	l2 = l;
 	for(;;) {
-		l2 = l2->next;
+		l2 = NEXT(l2);
 		if(l2 == 0)
 			break;
-		l2 = l2->next;
+		l2 = NEXT(l2);
 		if(l2 == 0)
 			break;
-		l1 = l1->next;
+		l1 = NEXT(l1);
 	}
 
-	l2 = l1->next;
-	l1->next = 0;
-	l1 = datsort(l);
-	l2 = datsort(l2);
+	l2 = NEXT(l1);
+	NEXT(l1) = 0;
+	l1 = listsort(l, cmp, off);
+	l2 = listsort(l2, cmp, off);
 
 	/* set up lead element */
-	if(datcmp(l1, l2) < 0) {
+	if(cmp(l1, l2) < 0) {
 		l = l1;
-		l1 = l1->next;
+		l1 = NEXT(l1);
 	} else {
 		l = l2;
-		l2 = l2->next;
+		l2 = NEXT(l2);
 	}
 	le = l;
 
 	for(;;) {
 		if(l1 == 0) {
 			while(l2) {
-				le->next = l2;
+				NEXT(le) = l2;
 				le = l2;
-				l2 = l2->next;
+				l2 = NEXT(l2);
 			}
-			le->next = 0;
+			NEXT(le) = 0;
 			break;
 		}
 		if(l2 == 0) {
 			while(l1) {
-				le->next = l1;
+				NEXT(le) = l1;
 				le = l1;
-				l1 = l1->next;
+				l1 = NEXT(l1);
 			}
 			break;
 		}
-		if(datcmp(l1, l2) < 0) {
-			le->next = l1;
+		if(cmp(l1, l2) < 0) {
+			NEXT(le) = l1;
 			le = l1;
-			l1 = l1->next;
+			l1 = NEXT(l1);
 		} else {
-			le->next = l2;
+			NEXT(le) = l2;
 			le = l2;
-			l2 = l2->next;
+			l2 = NEXT(l2);
 		}
 	}
-	le->next = 0;
+	NEXT(le) = 0;
 	return l;
+	
+	#undef NEXT
 }
 
 Reloc*
@@ -1010,7 +1013,7 @@ dodata(void)
 				s->type = SDATARELRO;
 		}
 	}
-	datap = datsort(datap);
+	datap = listsort(datap, datcmp, offsetof(Sym, next));
 
 	/*
 	 * allocate sections.  list is sorted by type,

src/cmd/ld/ldelf.c

@@ -311,6 +311,16 @@ static int	map(ElfObj*, ElfSect*);
 static int	readsym(ElfObj*, int i, ElfSym*, int);
 static int	reltype(char*, int, uchar*);
 
+int
+valuecmp(Sym *a, Sym *b)
+{
+	if(a->value < b->value)
+		return -1;
+	if(a->value > b->value)
+		return +1;
+	return 0;
+}
+
 void
 ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 {
@@ -541,13 +551,6 @@ ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 		}
 		s->size = sect->size;
 		s->align = sect->align;
-		if(s->type == STEXT) {
-			if(etextp)
-				etextp->next = s;
-			else
-				textp = s;
-			etextp = s;
-		}
 		sect->sym = s;
 	}
 
@@ -583,6 +586,12 @@ ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 			continue;
 		}
 		s = sym.sym;
+		if(s->outer != S) {
+			if(s->dupok)
+				continue;
+			diag("%s: duplicate symbol reference: %s in both %s and %s", pn, s->name, s->outer->name, sect->sym->name);
+			errorexit();
+		}
 		s->sub = sect->sym->sub;
 		sect->sym->sub = s;
 		s->type = sect->sym->type | (s->type&~SMASK) | SSUB;
@@ -611,7 +620,25 @@ ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 				p->link = nil;
 				p->pc = pc++;
 				s->text = p;
-
+			}
+		}
+	}
+	
+	// Sort outer lists by address, adding to textp.
+	// This keeps textp in increasing address order.
+	for(i=0; i<obj->nsect; i++) {
+		s = obj->sect[i].sym;
+		if(s == S)
+			continue;
+		if(s->sub)
+			s->sub = listsort(s->sub, valuecmp, offsetof(Sym, sub));
+		if(s->type == STEXT) {
+			if(etextp)
+				etextp->next = s;
+			else
+				textp = s;
+			etextp = s;
+			for(s = s->sub; s != S; s = s->sub) {
 				etextp->next = s;
 				etextp = s;
 			}
@@ -792,7 +819,7 @@ readsym(ElfObj *obj, int i, ElfSym *sym, int needSym)
 				// set dupok generally. See http://codereview.appspot.com/5823055/
 				// comment #5 for details.
 				if(s && sym->other == 2) {
-					s->type = SHIDDEN;
+					s->type |= SHIDDEN;
 					s->dupok = 1;
 				}
 			}
@@ -804,14 +831,14 @@ readsym(ElfObj *obj, int i, ElfSym *sym, int needSym)
 					// and should only reference by its index, not name, so we
 					// don't bother to add them into hash table
 					s = newsym(sym->name, version);
-					s->type = SHIDDEN;
+					s->type |= SHIDDEN;
 				}
 			break;
 		case ElfSymBindWeak:
 			if(needSym) {
 				s = newsym(sym->name, 0);
 				if(sym->other == 2)
-					s->type = SHIDDEN;
+					s->type |= SHIDDEN;
 			}
 			break;
 		default:

src/cmd/ld/ldmacho.c

@@ -593,13 +593,6 @@ ldmacho(Biobuf *f, char *pkg, int64 len, char *pn)
 			} else
 				s->type = SDATA;
 		}
-		if(s->type == STEXT) {
-			if(etextp)
-				etextp->next = s;
-			else
-				textp = s;
-			etextp = s;
-		}
 		sect->sym = s;
 	}
 	
@@ -631,6 +624,12 @@ ldmacho(Biobuf *f, char *pkg, int64 len, char *pn)
 			werrstr("reference to invalid section %s/%s", sect->segname, sect->name);
 			continue;
 		}
+		if(s->outer != S) {
+			if(s->dupok)
+				continue;
+			diag("%s: duplicate symbol reference: %s in both %s and %s", pn, s->name, s->outer->name, sect->sym->name);
+			errorexit();
+		}
 		s->type = outer->type | SSUB;
 		s->sub = outer->sub;
 		outer->sub = s;
@@ -661,11 +660,29 @@ ldmacho(Biobuf *f, char *pkg, int64 len, char *pn)
 			p->link = nil;
 			p->pc = pc++;
 			s->text = p;
+		}
+		sym->sym = s;
+	}
 
-			etextp->next = s;
+	// Sort outer lists by address, adding to textp.
+	// This keeps textp in increasing address order.
+	for(i=0; i<c->seg.nsect; i++) {
+		sect = &c->seg.sect[i];
+		if((s = sect->sym) == S)
+			continue;
+		if(s->sub)
+			s->sub = listsort(s->sub, valuecmp, offsetof(Sym, sub));
+		if(s->type == STEXT) {
+			if(etextp)
+				etextp->next = s;
+			else
+				textp = s;
 			etextp = s;
+			for(s = s->sub; s != S; s = s->sub) {
+				etextp->next = s;
+				etextp = s;
+			}
 		}
-		sym->sym = s;
 	}
 
 	// load relocations

src/cmd/ld/ldpe.c

@@ -236,13 +236,6 @@ ldpe(Biobuf *f, char *pkg, int64 len, char *pn)
 		s->p = sect->base;
 		s->np = sect->size;
 		s->size = sect->size;
-		if(s->type == STEXT) {
-			if(etextp)
-				etextp->next = s;
-			else
-				textp = s;
-			etextp = s;
-		}
 		sect->sym = s;
 		if(strcmp(sect->name, ".rsrc") == 0)
 			setpersrc(sect->sym);
@@ -327,6 +320,12 @@ ldpe(Biobuf *f, char *pkg, int64 len, char *pn)
 			goto bad;
 	
 		s = sym->sym;
+		if(s->outer != S) {
+			if(s->dupok)
+				continue;
+			diag("%s: duplicate symbol reference: %s in both %s and %s", pn, s->name, s->outer->name, sect->sym->name);
+			errorexit();
+		}
 		if(sym->sectnum == 0) {// extern
 			if(s->type == SDYNIMPORT)
 				s->plt = -2; // flag for dynimport in PE object files.
@@ -367,9 +366,27 @@ ldpe(Biobuf *f, char *pkg, int64 len, char *pn)
 			p->link = nil;
 			p->pc = pc++;
 			s->text = p;
-	
-			etextp->next = s;
+		}
+	}
+
+	// Sort outer lists by address, adding to textp.
+	// This keeps textp in increasing address order.
+	for(i=0; i<obj->nsect; i++) {
+		s = obj->sect[i].sym;
+		if(s == S)
+			continue;
+		if(s->sub)
+			s->sub = listsort(s->sub, valuecmp, offsetof(Sym, sub));
+		if(s->type == STEXT) {
+			if(etextp)
+				etextp->next = s;
+			else
+				textp = s;
 			etextp = s;
+			for(s = s->sub; s != S; s = s->sub) {
+				etextp->next = s;
+				etextp = s;
+			}
 		}
 	}
 

src/cmd/ld/lib.h

@@ -196,7 +196,6 @@ void	deadcode(void);
 Reloc*	addrel(Sym*);
 void	codeblk(int32, int32);
 void	datblk(int32, int32);
-Sym*	datsort(Sym*);
 void	reloc(void);
 void	relocsym(Sym*);
 void	savedata(Sym*, Prog*, char*);
@@ -238,6 +237,8 @@ void	setpersrc(Sym*);
 void	doversion(void);
 void	usage(void);
 void	setinterp(char*);
+Sym*	listsort(Sym*, int(*cmp)(Sym*, Sym*), int);
+int	valuecmp(Sym*, Sym*);
 
 int	pathchar(void);
 void*	mal(uint32);

src/pkg/runtime/symtab.c

@@ -195,12 +195,13 @@ static int32 nfname;
 
 static uint32 funcinit;
 static Lock funclock;
+static uintptr lastvalue;
 
 static void
 dofunc(Sym *sym)
 {
 	Func *f;
-
+	
 	switch(sym->symtype) {
 	case 't':
 	case 'T':
@@ -208,6 +209,11 @@ dofunc(Sym *sym)
 	case 'L':
 		if(runtime·strcmp(sym->name, (byte*)"etext") == 0)
 			break;
+		if(sym->value < lastvalue) {
+			runtime·printf("symbols out of order: %p before %p\n", lastvalue, sym->value);
+			runtime·throw("malformed symbol table");
+		}
+		lastvalue = sym->value;
 		if(func == nil) {
 			nfunc++;
 			break;
@@ -544,6 +550,7 @@ buildfuncs(void)
 	// count funcs, fnames
 	nfunc = 0;
 	nfname = 0;
+	lastvalue = 0;
 	walksymtab(dofunc);
 
 	// Initialize tables.
@@ -553,6 +560,7 @@ buildfuncs(void)
 	func[nfunc].entry = (uint64)etext;
 	fname = runtime·mallocgc(nfname*sizeof fname[0], FlagNoPointers, 0, 1);
 	nfunc = 0;
+	lastvalue = 0;
 	walksymtab(dofunc);
 
 	// split pc/ln table by func