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://codereview.appspot.com/7440044

1 files changed, 38 insertions, 11 deletions

diff --git a/src/cmd/ld/ldelf.c b/src/cmd/ld/ldelf.c
index 19c582b00..2bbf4f83e 100644
--- a/src/cmd/ld/ldelf.c
+++ b/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: