Revert "elf: Always call destructors in reverse constructor order (bug 30785)"

This reverts commit 02a67e102f.

Reason for revert: Incompatibility with existing applications.

NEWS

@@ -82,7 +82,6 @@ The following bugs are resolved with this release:
   [30305] x86_64: Fix asm constraints in feraiseexcept
   [30477] libc: [RISCV]: time64 does not work on riscv32
   [30515] _dl_find_object incorrectly returns 1 during early startup
-  [30785] Always call destructors in reverse constructor order
   [30804] F_GETLK, F_SETLK, and F_SETLKW value change for powerpc64 with
     -D_FILE_OFFSET_BITS=64
 

elf/dl-close.c

@@ -138,31 +138,30 @@ _dl_close_worker (struct link_map *map, bool force)
 
   bool any_tls = false;
   const unsigned int nloaded = ns->_ns_nloaded;
+  struct link_map *maps[nloaded];
 
-  /* Run over the list and assign indexes to the link maps.  */
+  /* Run over the list and assign indexes to the link maps and enter
+     them into the MAPS array.  */
   int idx = 0;
   for (struct link_map *l = ns->_ns_loaded; l != NULL; l = l->l_next)
     {
       l->l_map_used = 0;
       l->l_map_done = 0;
       l->l_idx = idx;
+      maps[idx] = l;
       ++idx;
     }
   assert (idx == nloaded);
 
-  /* Keep marking link maps until no new link maps are found.  */
+  /* Keep track of the lowest index link map we have covered already.  */
-  for (struct link_map *l = ns->_ns_loaded; l != NULL; )
+  int done_index = -1;
+  while (++done_index < nloaded)
     {
-      /* next is reset to earlier link maps for remarking.  */
+      struct link_map *l = maps[done_index];
-      struct link_map *next = l->l_next;
-      int next_idx = l->l_idx + 1; /* next->l_idx, but covers next == NULL.  */
 
       if (l->l_map_done)
-	{
+	/* Already handled.  */
-	  /* Already handled.  */
+	continue;
-	  l = next;
-	  continue;
-	}
 
       /* Check whether this object is still used.  */
       if (l->l_type == lt_loaded
@@ -172,10 +171,7 @@ _dl_close_worker (struct link_map *map, bool force)
 	     acquire is sufficient and correct.  */
 	  && atomic_load_acquire (&l->l_tls_dtor_count) == 0
 	  && !l->l_map_used)
-	{
+	continue;
-	  l = next;
-	  continue;
-	}
 
       /* We need this object and we handle it now.  */
       l->l_map_used = 1;
@@ -202,11 +198,8 @@ _dl_close_worker (struct link_map *map, bool force)
 			 already processed it, then we need to go back
 			 and process again from that point forward to
 			 ensure we keep all of its dependencies also.  */
-		      if ((*lp)->l_idx < next_idx)
+		      if ((*lp)->l_idx - 1 < done_index)
-			{
+			done_index = (*lp)->l_idx - 1;
-			  next = *lp;
-			  next_idx = next->l_idx;
-			}
 		    }
 		}
 
@@ -226,65 +219,44 @@ _dl_close_worker (struct link_map *map, bool force)
 		if (!jmap->l_map_used)
 		  {
 		    jmap->l_map_used = 1;
-		    if (jmap->l_idx < next_idx)
+		    if (jmap->l_idx - 1 < done_index)
-		      {
+		      done_index = jmap->l_idx - 1;
-			  next = jmap;
-			  next_idx = next->l_idx;
-		      }
 		  }
 	      }
 	  }
-
-      l = next;
     }
 
-  /* Call the destructors in reverse constructor order, and remove the
+  /* Sort the entries.  We can skip looking for the binary itself which is
-     closed link maps from the list.  */
+     at the front of the search list for the main namespace.  */
-  for (struct link_map **init_called_head = &_dl_init_called_list;
+  _dl_sort_maps (maps, nloaded, (nsid == LM_ID_BASE), true);
-       *init_called_head != NULL; )
-    {
-      struct link_map *imap = *init_called_head;
 
-      /* _dl_init_called_list is global, to produce a global odering.
+  /* Call all termination functions at once.  */
-	 Ignore the other namespaces (and link maps that are still used).  */
+  bool unload_any = false;
-      if (imap->l_ns != nsid || imap->l_map_used)
+  bool scope_mem_left = false;
-	init_called_head = &imap->l_init_called_next;
+  unsigned int unload_global = 0;
-      else
+  unsigned int first_loaded = ~0;
+  for (unsigned int i = 0; i < nloaded; ++i)
+    {
+      struct link_map *imap = maps[i];
+
+      /* All elements must be in the same namespace.  */
+      assert (imap->l_ns == nsid);
+
+      if (!imap->l_map_used)
 	{
 	  assert (imap->l_type == lt_loaded && !imap->l_nodelete_active);
 
-	  /* _dl_init_called_list is updated at the same time as
+	  /* Call its termination function.  Do not do it for
-	     l_init_called.  */
+	     half-cooked objects.  Temporarily disable exception
-	  assert (imap->l_init_called);
+	     handling, so that errors are fatal.  */
-
+	  if (imap->l_init_called)
-	  if (imap->l_info[DT_FINI_ARRAY] != NULL
-	      || imap->l_info[DT_FINI] != NULL)
 	    _dl_catch_exception (NULL, _dl_call_fini, imap);
 
 #ifdef SHARED
 	  /* Auditing checkpoint: we remove an object.  */
 	  _dl_audit_objclose (imap);
 #endif
-	  /* Unlink this link map.  */
-	  *init_called_head = imap->l_init_called_next;
-	}
-    }
 
-
-  bool unload_any = false;
-  bool scope_mem_left = false;
-  unsigned int unload_global = 0;
-
-  /* For skipping un-unloadable link maps in the second loop.  */
-  struct link_map *first_loaded = ns->_ns_loaded;
-
-  /* Iterate over the namespace to find objects to unload.  Some
-     unloadable objects may not be on _dl_init_called_list due to
-     dlopen failure.  */
-  for (struct link_map *imap = first_loaded; imap != NULL; imap = imap->l_next)
-    {
-      if (!imap->l_map_used)
-	{
 	  /* This object must not be used anymore.  */
 	  imap->l_removed = 1;
 
@@ -295,8 +267,8 @@ _dl_close_worker (struct link_map *map, bool force)
 	    ++unload_global;
 
 	  /* Remember where the first dynamically loaded object is.  */
-	  if (first_loaded == NULL)
+	  if (i < first_loaded)
-	      first_loaded = imap;
+	    first_loaded = i;
 	}
       /* Else imap->l_map_used.  */
       else if (imap->l_type == lt_loaded)
@@ -432,8 +404,8 @@ _dl_close_worker (struct link_map *map, bool force)
 	    imap->l_loader = NULL;
 
 	  /* Remember where the first dynamically loaded object is.  */
-	  if (first_loaded == NULL)
+	  if (i < first_loaded)
-	      first_loaded = imap;
+	    first_loaded = i;
 	}
     }
 
@@ -504,11 +476,10 @@ _dl_close_worker (struct link_map *map, bool force)
 
   /* Check each element of the search list to see if all references to
      it are gone.  */
-  for (struct link_map *imap = first_loaded; imap != NULL; )
+  for (unsigned int i = first_loaded; i < nloaded; ++i)
     {
-      if (imap->l_map_used)
+      struct link_map *imap = maps[i];
-	imap = imap->l_next;
+      if (!imap->l_map_used)
-      else
 	{
 	  assert (imap->l_type == lt_loaded);
 
@@ -719,9 +690,7 @@ _dl_close_worker (struct link_map *map, bool force)
 	  if (imap == GL(dl_initfirst))
 	    GL(dl_initfirst) = NULL;
 
-	  struct link_map *next = imap->l_next;
 	  free (imap);
-	  imap = next;
 	}
     }
 

elf/dl-fini.c

@@ -24,68 +24,116 @@
 void
 _dl_fini (void)
 {
-  /* Call destructors strictly in the reverse order of constructors.
+  /* Lots of fun ahead.  We have to call the destructors for all still
-     This causes fewer surprises than some arbitrary reordering based
+     loaded objects, in all namespaces.  The problem is that the ELF
-     on new (relocation) dependencies.  None of the objects are
+     specification now demands that dependencies between the modules
-     unmapped, so applications can deal with this if their DSOs remain
+     are taken into account.  I.e., the destructor for a module is
-     in a consistent state after destructors have run.  */
+     called before the ones for any of its dependencies.
 
-  /* Protect against concurrent loads and unloads.  */
+     To make things more complicated, we cannot simply use the reverse
-  __rtld_lock_lock_recursive (GL(dl_load_lock));
+     order of the constructors.  Since the user might have loaded objects
+     using `dlopen' there are possibly several other modules with its
+     dependencies to be taken into account.  Therefore we have to start
+     determining the order of the modules once again from the beginning.  */
 
-  /* Ignore objects which are opened during shutdown.  */
+  /* We run the destructors of the main namespaces last.  As for the
-  struct link_map *local_init_called_list = _dl_init_called_list;
+     other namespaces, we pick run the destructors in them in reverse
-
+     order of the namespace ID.  */
-  for (struct link_map *l = local_init_called_list; l != NULL;
-       l = l->l_init_called_next)
-      /* Bump l_direct_opencount of all objects so that they
-	 are not dlclose()ed from underneath us.  */
-      ++l->l_direct_opencount;
-
-  /* After this point, everything linked from local_init_called_list
-     cannot be unloaded because of the reference counter update.  */
-  __rtld_lock_unlock_recursive (GL(dl_load_lock));
-
-  /* Perform two passes: One for non-audit modules, one for audit
-     modules.  This way, audit modules receive unload notifications
-     for non-audit objects, and the destructors for audit modules
-     still run.  */
 #ifdef SHARED
-  int last_pass = GLRO(dl_naudit) > 0;
+  int do_audit = 0;
-  Lmid_t last_ns = -1;
+ again:
-  for (int do_audit = 0; do_audit <= last_pass; ++do_audit)
 #endif
-    for (struct link_map *l = local_init_called_list; l != NULL;
+  for (Lmid_t ns = GL(dl_nns) - 1; ns >= 0; --ns)
-	 l = l->l_init_called_next)
+    {
-      {
+      /* Protect against concurrent loads and unloads.  */
-#ifdef SHARED
+      __rtld_lock_lock_recursive (GL(dl_load_lock));
-	if (GL(dl_ns)[l->l_ns]._ns_loaded->l_auditing != do_audit)
-	  continue;
 
-	/* Avoid back-to-back calls of _dl_audit_activity_nsid for the
+      unsigned int nloaded = GL(dl_ns)[ns]._ns_nloaded;
-	   same namespace.  */
+      /* No need to do anything for empty namespaces or those used for
-	if (last_ns != l->l_ns)
+	 auditing DSOs.  */
-	  {
+      if (nloaded == 0
-	    if (last_ns >= 0)
+#ifdef SHARED
-	      _dl_audit_activity_nsid (last_ns, LA_ACT_CONSISTENT);
+	  || GL(dl_ns)[ns]._ns_loaded->l_auditing != do_audit
-	    _dl_audit_activity_nsid (l->l_ns, LA_ACT_DELETE);
+#endif
-	    last_ns = l->l_ns;
+	  )
-	  }
+	__rtld_lock_unlock_recursive (GL(dl_load_lock));
+      else
+	{
+#ifdef SHARED
+	  _dl_audit_activity_nsid (ns, LA_ACT_DELETE);
 #endif
 
-	/* There is no need to re-enable exceptions because _dl_fini
+	  /* Now we can allocate an array to hold all the pointers and
-	   is not called from a context where exceptions are caught.  */
+	     copy the pointers in.  */
-	_dl_call_fini (l);
+	  struct link_map *maps[nloaded];
 
+	  unsigned int i;
+	  struct link_map *l;
+	  assert (nloaded != 0 || GL(dl_ns)[ns]._ns_loaded == NULL);
+	  for (l = GL(dl_ns)[ns]._ns_loaded, i = 0; l != NULL; l = l->l_next)
+	    /* Do not handle ld.so in secondary namespaces.  */
+	    if (l == l->l_real)
+	      {
+		assert (i < nloaded);
+
+		maps[i] = l;
+		l->l_idx = i;
+		++i;
+
+		/* Bump l_direct_opencount of all objects so that they
+		   are not dlclose()ed from underneath us.  */
+		++l->l_direct_opencount;
+	      }
+	  assert (ns != LM_ID_BASE || i == nloaded);
+	  assert (ns == LM_ID_BASE || i == nloaded || i == nloaded - 1);
+	  unsigned int nmaps = i;
+
+	  /* Now we have to do the sorting.  We can skip looking for the
+	     binary itself which is at the front of the search list for
+	     the main namespace.  */
+	  _dl_sort_maps (maps, nmaps, (ns == LM_ID_BASE), true);
+
+	  /* We do not rely on the linked list of loaded object anymore
+	     from this point on.  We have our own list here (maps).  The
+	     various members of this list cannot vanish since the open
+	     count is too high and will be decremented in this loop.  So
+	     we release the lock so that some code which might be called
+	     from a destructor can directly or indirectly access the
+	     lock.  */
+	  __rtld_lock_unlock_recursive (GL(dl_load_lock));
+
+	  /* 'maps' now contains the objects in the right order.  Now
+	     call the destructors.  We have to process this array from
+	     the front.  */
+	  for (i = 0; i < nmaps; ++i)
+	    {
+	      struct link_map *l = maps[i];
+
+	      if (l->l_init_called)
+		{
+		  _dl_call_fini (l);
 #ifdef SHARED
-	/* Auditing checkpoint: another object closed.  */
+		  /* Auditing checkpoint: another object closed.  */
-	_dl_audit_objclose (l);
+		  _dl_audit_objclose (l);
 #endif
-      }
+		}
+
+	      /* Correct the previous increment.  */
+	      --l->l_direct_opencount;
+	    }
 
 #ifdef SHARED
-  if (last_ns >= 0)
+	  _dl_audit_activity_nsid (ns, LA_ACT_CONSISTENT);
-    _dl_audit_activity_nsid (last_ns, LA_ACT_CONSISTENT);
+#endif
+	}
+    }
+
+#ifdef SHARED
+  if (! do_audit && GLRO(dl_naudit) > 0)
+    {
+      do_audit = 1;
+      goto again;
+    }
 
   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_STATISTICS))
     _dl_debug_printf ("\nruntime linker statistics:\n"

elf/dl-init.c

@@ -21,7 +21,6 @@
 #include <ldsodefs.h>
 #include <elf-initfini.h>
 
-struct link_map *_dl_init_called_list;
 
 static void
 call_init (struct link_map *l, int argc, char **argv, char **env)
@@ -43,21 +42,6 @@ call_init (struct link_map *l, int argc, char **argv, char **env)
      dependency.  */
   l->l_init_called = 1;
 
-  /* Help an already-running dlclose: The just-loaded object must not
-     be removed during the current pass.  (No effect if no dlclose in
-     progress.)  */
-  l->l_map_used = 1;
-
-  /* Record execution before starting any initializers.  This way, if
-     the initializers themselves call dlopen, their ELF destructors
-     will eventually be run before this object is destructed, matching
-     that their ELF constructors have run before this object was
-     constructed.  _dl_fini uses this list for audit callbacks, so
-     register objects on the list even if they do not have a
-     constructor.  */
-  l->l_init_called_next = _dl_init_called_list;
-  _dl_init_called_list = l;
-
   /* Check for object which constructors we do not run here.  */
   if (__builtin_expect (l->l_name[0], 'a') == '\0'
       && l->l_type == lt_executable)

elf/dso-sort-tests-1.def

@@ -53,14 +53,21 @@ tst-dso-ordering10: {}->a->b->c;soname({})=c
 output: b>a>{}<a<b
 
 # Complex example from Bugzilla #15311, under-linked and with circular
-# relocation(dynamic) dependencies. For both sorting algorithms, the
+# relocation(dynamic) dependencies. While this is technically unspecified, the
-# destruction order is the reverse of the construction order, and
+# presumed reasonable practical behavior is for the destructor order to respect
-# relocation dependencies are not taken into account.
+# the static DT_NEEDED links (here this means the a->b->c->d order).
+# The older dynamic_sort=1 algorithm does not achieve this, while the DFS-based
+# dynamic_sort=2 algorithm does, although it is still arguable whether going
+# beyond spec to do this is the right thing to do.
+# The below expected outputs are what the two algorithms currently produce
+# respectively, for regression testing purposes.
 tst-bz15311: {+a;+e;+f;+g;+d;%d;-d;-g;-f;-e;-a};a->b->c->d;d=>[ba];c=>a;b=>e=>a;c=>f=>b;d=>g=>c
-output: {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<g<f<e<a<b<c<d];}
+output(glibc.rtld.dynamic_sort=1): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<a<c<d<g<f<b<e];}
+output(glibc.rtld.dynamic_sort=2): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<g<f<a<b<c<d<e];}
 
 # Test that even in the presence of dependency loops involving dlopen'ed
 # object, that object is initialized last (and not unloaded prematurely).
-# Final destructor order is the opposite of constructor order.
+# Final destructor order is indeterminate due to the cycle.
 tst-bz28937: {+a;+b;-b;+c;%c};a->a1;a->a2;a2->a;b->b1;c->a1;c=>a1
-output: {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<c<a<a1<a2
+output(glibc.rtld.dynamic_sort=1): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a<a2<c<a1
+output(glibc.rtld.dynamic_sort=2): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a2<a<c<a1

elf/tst-audit23.c

@@ -98,8 +98,6 @@ do_test (int argc, char *argv[])
     char *lname;
     uintptr_t laddr;
     Lmid_t lmid;
-    uintptr_t cookie;
-    uintptr_t namespace;
     bool closed;
   } objs[max_objs] = { [0 ... max_objs-1] = { .closed = false } };
   size_t nobjs = 0;
@@ -119,9 +117,6 @@ do_test (int argc, char *argv[])
   size_t buffer_length = 0;
   while (xgetline (&buffer, &buffer_length, out))
     {
-      *strchrnul (buffer, '\n') = '\0';
-      printf ("info: subprocess output: %s\n", buffer);
-
       if (startswith (buffer, "la_activity: "))
 	{
 	  uintptr_t cookie;
@@ -130,26 +125,29 @@ do_test (int argc, char *argv[])
 			  &cookie);
 	  TEST_COMPARE (r, 2);
 
+	  /* The cookie identifies the object at the head of the link map,
+	     so we only add a new namespace if it changes from the previous
+	     one.  This works since dlmopen is the last in the test body.  */
+	  if (cookie != last_act_cookie && last_act_cookie != -1)
+	    TEST_COMPARE (last_act, LA_ACT_CONSISTENT);
+
 	  if (this_act == LA_ACT_ADD && acts[nacts] != cookie)
 	    {
-	      /* The cookie identifies the object at the head of the
-		 link map, so we only add a new namespace if it
-		 changes from the previous one.  This works since
-		 dlmopen is the last in the test body.  */
-	      if (cookie != last_act_cookie && last_act_cookie != -1)
-		TEST_COMPARE (last_act, LA_ACT_CONSISTENT);
-
 	      acts[nacts++] = cookie;
 	      last_act_cookie = cookie;
 	    }
-	  /* LA_ACT_DELETE is called multiple times for each
+	  /* The LA_ACT_DELETE is called in the reverse order of LA_ACT_ADD
-	     namespace, depending on destruction order.  */
+	     at program termination (if the tests adds a dlclose or a library
+	     with extra dependencies this will need to be adapted).  */
 	  else if (this_act == LA_ACT_DELETE)
-	    last_act_cookie = cookie;
+	    {
+	      last_act_cookie = acts[--nacts];
+	      TEST_COMPARE (acts[nacts], cookie);
+	      acts[nacts] = 0;
+	    }
 	  else if (this_act == LA_ACT_CONSISTENT)
 	    {
 	      TEST_COMPARE (cookie, last_act_cookie);
-	      last_act_cookie = -1;
 
 	      /* LA_ACT_DELETE must always be followed by an la_objclose.  */
 	      if (last_act == LA_ACT_DELETE)
@@ -181,8 +179,6 @@ do_test (int argc, char *argv[])
 	  objs[nobjs].lname = lname;
 	  objs[nobjs].laddr = laddr;
 	  objs[nobjs].lmid = lmid;
-	  objs[nobjs].cookie = cookie;
-	  objs[nobjs].namespace = last_act_cookie;
 	  objs[nobjs].closed = false;
 	  nobjs++;
 
@@ -205,12 +201,6 @@ do_test (int argc, char *argv[])
 	      if (strcmp (lname, objs[i].lname) == 0 && lmid == objs[i].lmid)
 		{
 		  TEST_COMPARE (objs[i].closed, false);
-		  TEST_COMPARE (objs[i].cookie, cookie);
-		  if (objs[i].namespace == -1)
-		    /* No LA_ACT_ADD before the first la_objopen call.  */
-		    TEST_COMPARE (acts[0], last_act_cookie);
-		  else
-		    TEST_COMPARE (objs[i].namespace, last_act_cookie);
 		  objs[i].closed = true;
 		  break;
 		}
@@ -219,7 +209,11 @@ do_test (int argc, char *argv[])
 	  /* la_objclose should be called after la_activity(LA_ACT_DELETE) for
 	     the closed object's namespace.  */
 	  TEST_COMPARE (last_act, LA_ACT_DELETE);
-	  seen_first_objclose = true;
+	  if (!seen_first_objclose)
+	    {
+	      TEST_COMPARE (last_act_cookie, cookie);
+	      seen_first_objclose = true;
+	    }
 	}
     }
 

sysdeps/generic/ldsodefs.h

@@ -1120,10 +1120,6 @@ extern int _dl_check_map_versions (struct link_map *map, int verbose,
 extern void _dl_init (struct link_map *main_map, int argc, char **argv,
 		      char **env) attribute_hidden;
 
-/* List of ELF objects in reverse order of their constructor
-   invocation.  */
-extern struct link_map *_dl_init_called_list attribute_hidden;
-
 /* Call the finalizer functions of all shared objects whose
    initializer functions have completed.  */
 extern void _dl_fini (void) attribute_hidden;