[PATCH v6] Remove Linuxism from tst-tls-atexit

["Siddhesh Poyarekar" <siddhesh at redhat dot com>]

The tst-tls-atexit test case searches for its module in /proc/PID/maps
to verify that it is unloaded, which is a Linux-specific test.  This
patch makes the test generic by trying to call foo (the symbol
obtained from dlsym) and traps SIGSEGV momentarily to see if the crash
occurred.

Verified that the test continues to succeed on x86_64.  There is a bug
in the test case where it calls dlclose once again, which is actually
incorrect but still manages to unload the DSO thanks to an existing
bug in __tls_call_dtors.  This will be fixed in a later patch which
also fixes up the __cxa_thread_atexit_impl implementation.  I have
added a FIXME comment to that call momentarily, which I will remove
when I fix the problem.

	* stdlib/tst-tls-atexit-lib.c (do_foo): Rename to reg_dtor.
	* stdlib/tst-tls-atexit.c: (is_loaded): New function.
	(load): Rename to reg_dtor_and_close.  Move dlopen to...
	(do_test): ... here.  Use IS_LOADED to test for its
	availability.
---
 stdlib/tst-tls-atexit-lib.c |  2 +-
 stdlib/tst-tls-atexit.c     | 84 +++++++++++++++++++++++----------------------
 2 files changed, 44 insertions(+), 42 deletions(-)

diff --git a/stdlib/tst-tls-atexit-lib.c b/stdlib/tst-tls-atexit-lib.c
index 2945379..2478d80 100644
--- a/stdlib/tst-tls-atexit-lib.c
+++ b/stdlib/tst-tls-atexit-lib.c
@@ -31,7 +31,7 @@ void A_dtor (void *obj)
   ((A *)obj)->val = obj;
 }
 
-void do_foo (void)
+void reg_dtor (void)
 {
   static __thread A b;
   __cxa_thread_atexit_impl (A_dtor, &b, __dso_handle);
diff --git a/stdlib/tst-tls-atexit.c b/stdlib/tst-tls-atexit.c
index 0c6c499..1947048 100644
--- a/stdlib/tst-tls-atexit.c
+++ b/stdlib/tst-tls-atexit.c
@@ -16,10 +16,11 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-/* There are two tests in this test case.  The first is implicit where it is
+/* There are two parts in this test case.  The first is implicit where it is
    assumed that the destructor call on exit of the LOAD function does not
    segfault.  The other is a verification that after the thread has exited, a
-   dlclose will unload the DSO.  */
+   dlclose will unload the DSO, which is done by calling into the DSO and
+   expecting that call to segfault.  */
 
 #include <dlfcn.h>
 #include <pthread.h>
@@ -27,32 +28,41 @@
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
+#include <link.h>
 
-void *handle;
+#define DSO_NAME "$ORIGIN/tst-tls-atexit-lib.so"
 
-void *
-load (void *u)
+/* Walk through the map in the _r_debug structure to see if our lib is still
+   loaded.  */
+static bool
+is_loaded (void)
 {
-  handle = dlopen ("$ORIGIN/tst-tls-atexit-lib.so", RTLD_LAZY);
-  if (handle == NULL)
-    {
-      printf ("Unable to load DSO: %s\n", dlerror ());
-      return (void *) (uintptr_t) 1;
-    }
+  struct link_map *lm = (struct link_map *) _r_debug.r_map;
+
+  for (; lm; lm = lm->l_next)
+    if (lm->l_type == lt_loaded && lm->l_name
+	&& strcmp (basename (DSO_NAME), basename (lm->l_name)) == 0)
+	  return true;
+  return false;
+}
 
-  void (*foo) (void) = (void (*) (void)) dlsym (handle, "do_foo");
+/* Accept a valid handle returned by DLOPEN, load the reg_dtor symbol to
+   register a destructor and then call dlclose on the handle.  The dlclose
+   should not unload the DSO since the destructor has not been called yet.  */
+static void *
+reg_dtor_and_close (void *h)
+{
+  void (*reg_dtor) (void) = (void (*) (void)) dlsym (h, "reg_dtor");
 
-  if (foo == NULL)
+  if (reg_dtor == NULL)
     {
       printf ("Unable to find symbol: %s\n", dlerror ());
-      exit (1);
+      return (void *) (uintptr_t) 1;
     }
 
-  foo ();
+  reg_dtor ();
 
-  /* This should not unload the DSO.  If it does, then the thread exit will
-     result in a segfault.  */
-  dlclose (handle);
+  dlclose (h);
 
   return NULL;
 }
@@ -64,7 +74,15 @@ do_test (void)
   int ret;
   void *thr_ret;
 
-  if ((ret = pthread_create (&t, NULL, load, NULL)) != 0)
+  /* Load the DSO.  */
+  void *handle = dlopen (DSO_NAME, RTLD_LAZY);
+  if (handle == NULL)
+    {
+      printf ("Unable to load DSO: %s\n", dlerror ());
+      return 1;
+    }
+
+  if ((ret = pthread_create (&t, NULL, reg_dtor_and_close, handle)) != 0)
     {
       printf ("pthread_create failed: %s\n", strerror (ret));
       return 1;
@@ -79,30 +97,14 @@ do_test (void)
   if (thr_ret != NULL)
     return 1;
 
-  /* Now this should unload the DSO.  */
+  /* Now this should unload the DSO.  FIXME: This is a bug, calling dlclose
+     like this is actually wrong, but it works because cxa_thread_atexit_impl
+     has a bug which results in dlclose allowing this to work.  */
   dlclose (handle);
 
-  /* Run through our maps and ensure that the DSO is unloaded.  */
-  FILE *f = fopen ("/proc/self/maps", "r");
-
-  if (f == NULL)
-    {
-      perror ("Failed to open /proc/self/maps");
-      fprintf (stderr, "Skipping verification of DSO unload\n");
-      return 0;
-    }
-
-  char *line = NULL;
-  size_t s = 0;
-  while (getline (&line, &s, f) > 0)
-    {
-      if (strstr (line, "tst-tls-atexit-lib.so"))
-        {
-	  printf ("DSO not unloaded yet:\n%s", line);
-	  return 1;
-	}
-    }
-  free (line);
+  /* Check link maps to ensure that the DSO has unloaded.  */
+  if (is_loaded ())
+    return 1;
 
   return 0;
 }
-- 
2.4.3