elf: Add a DTV setup test [BZ #27136]

The test dlopens a large number of modules with TLS, they are reused
from an existing test.

The test relies on the reuse of slotinfo entries after dlclose, without
bug 27135 fixed this needs a failing dlopen. With a slotinfo list that
has non-monotone increasing generation counters, bug 27136 can trigger.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

elf/Makefile

@@ -222,7 +222,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-audit14 tst-audit15 tst-audit16 \
 	 tst-single_threaded tst-single_threaded-pthread \
 	 tst-tls-ie tst-tls-ie-dlmopen argv0test \
-	 tst-glibc-hwcaps tst-glibc-hwcaps-prepend tst-glibc-hwcaps-mask
+	 tst-glibc-hwcaps tst-glibc-hwcaps-prepend tst-glibc-hwcaps-mask \
+	 tst-tls20
 #	 reldep9
 tests-internal += loadtest unload unload2 circleload1 \
 	 neededtest neededtest2 neededtest3 neededtest4 \
@@ -344,6 +345,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		libmarkermod2-1 libmarkermod2-2 \
 		libmarkermod3-1 libmarkermod3-2 libmarkermod3-3 \
 		libmarkermod4-1 libmarkermod4-2 libmarkermod4-3 libmarkermod4-4 \
+		tst-tls20mod-bad
 
 # Most modules build with _ISOMAC defined, but those filtered out
 # depend on internal headers.
@@ -1922,3 +1924,9 @@ $(objpfx)tst-rtld-help.out: $(objpfx)ld.so
 	fi; \
 	(exit $$status); \
 	$(evaluate-test)
+
+# Reuses tst-tls-many-dynamic-modules
+tst-tls20mod-bad.so-no-z-defs = yes
+$(objpfx)tst-tls20: $(libdl) $(shared-thread-library)
+$(objpfx)tst-tls20.out: $(objpfx)tst-tls20mod-bad.so \
+			$(tst-tls-many-dynamic-modules:%=$(objpfx)%.so)

elf/tst-tls20.c

@@ -0,0 +1,98 @@
+/* Test dtv setup if entries don't have monotone increasing generation.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <dlfcn.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/xdlfcn.h>
+#include <support/xthread.h>
+
+#define NMOD 100
+static void *mod[NMOD];
+
+static void
+load_fail (void)
+{
+  /* Expected to fail because of a missing symbol.  */
+  void *m = dlopen ("tst-tls20mod-bad.so", RTLD_NOW);
+  if (m != NULL)
+    FAIL_EXIT1 ("dlopen of tst-tls20mod-bad.so succeeded\n");
+}
+
+static void
+load_mod (int i)
+{
+  char *buf = xasprintf ("tst-tls-manydynamic%02dmod.so", i);
+  mod[i] = xdlopen (buf, RTLD_LAZY);
+  free (buf);
+}
+
+static void
+unload_mod (int i)
+{
+  if (mod[i] != NULL)
+    xdlclose (mod[i]);
+  mod[i] = NULL;
+}
+
+static void
+access (int i)
+{
+  char *buf = xasprintf ("tls_global_%02d", i);
+  dlerror ();
+  int *p = dlsym (mod[i], buf);
+  printf ("mod[%d]: &tls = %p\n", i, p);
+  if (p == NULL)
+    FAIL_EXIT1 ("dlsym failed: %s\n", dlerror ());
+  ++*p;
+  free (buf);
+}
+
+static void *
+start (void *a)
+{
+  for (int i = 0; i < NMOD; i++)
+    if (mod[i] != NULL)
+      access (i);
+  return 0;
+}
+
+static int
+do_test (void)
+{
+  int i;
+
+  for (i = 0; i < NMOD; i++)
+    {
+      load_mod (i);
+      /* Bump the generation of mod[0] without using new dtv slot.  */
+      unload_mod (0);
+      load_fail (); /* Ensure GL(dl_tls_dtv_gaps) is true: see bug 27135.  */
+      load_mod (0);
+      /* Access TLS in all loaded modules.  */
+      pthread_t t = xpthread_create (0, start, 0);
+      xpthread_join (t);
+    }
+  for (i = 0; i < NMOD; i++)
+    unload_mod (i);
+  return 0;
+}
+
+#include <support/test-driver.c>

elf/tst-tls20mod-bad.c

@@ -0,0 +1,2 @@
+void missing_symbol (void);
+void f (void) {missing_symbol ();}