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nptl_db: Support different libpthread/ld.so load orders (bug 27744)
libthread_db is loaded once GDB encounters libpthread, and at this
point, ld.so may not have been processed by GDB yet. As a result,
_rtld_global cannot be accessed by regular means from libthread_db.
To make this work until GDB can be fixed, acess _rtld_global through
a pointer stored in libpthread.
The new test does not reproduce bug 27744 with
--disable-hardcoded-path-in-tests, but is still a valid smoke test.
With --enable-hardcoded-path-in-tests, it is necessary to avoid
add-symbol-file because this can tickle a GDB bug.
Fixes commit 1daccf403b ("nptl: Move
stack list variables into _rtld_global").
Tested-by: Emil Velikov <emil.velikov@collabora.com>
This commit is contained in:
Florian Weimer
143
nptl/tst-pthread-gdb-attach.c
Normal file
143
nptl/tst-pthread-gdb-attach.c
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@@ -0,0 +1,143 @@
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/* Smoke testing GDB process attach with thread-local variable access.
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Copyright (C) 2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* This test runs GDB against a forked copy of itself, to check
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whether libthread_db can be loaded, and that access to thread-local
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variables works. */
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#include <errno.h>
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#include <stdlib.h>
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#include <support/check.h>
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#include <support/support.h>
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#include <support/temp_file.h>
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#include <support/test-driver.h>
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#include <support/xstdio.h>
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#include <support/xthread.h>
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#include <support/xunistd.h>
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#include <unistd.h>
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/* Starts out as zero, changed to 1 or 2 by the debugger, depending on
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the thread. */
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__thread volatile int altered_by_debugger;
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/* Writes the GDB script to run the test to PATH. */
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static void
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write_gdbscript (const char *path, int tested_pid)
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{
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FILE *fp = xfopen (path, "w");
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fprintf (fp,
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"set trace-commands on\n"
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"set debug libthread-db 1\n"
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#if DO_ADD_SYMBOL_FILE
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/* Do not do this unconditionally to work around a GDB
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assertion failure: ../../gdb/symtab.c:6404:
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internal-error: CORE_ADDR get_msymbol_address(objfile*,
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const minimal_symbol*): Assertion `(objf->flags &
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OBJF_MAINLINE) == 0' failed. */
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"add-symbol-file %1$s/nptl/tst-pthread-gdb-attach\n"
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#endif
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"set auto-load safe-path %1$s/nptl_db\n"
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"set libthread-db-search-path %1$s/nptl_db\n"
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"attach %2$d\n",
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support_objdir_root, tested_pid);
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fputs ("break debugger_inspection_point\n"
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"continue\n"
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"thread 1\n"
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"print altered_by_debugger\n"
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"print altered_by_debugger = 1\n"
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"thread 2\n"
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"print altered_by_debugger\n"
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"print altered_by_debugger = 2\n"
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"continue\n",
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fp);
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xfclose (fp);
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}
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/* The test sets a breakpoint on this function and alters the
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altered_by_debugger thread-local variable. */
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void __attribute__ ((weak))
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debugger_inspection_point (void)
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{
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}
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/* Thread function for the test thread in the subprocess. */
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static void *
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subprocess_thread (void *closure)
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{
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/* Wait until altered_by_debugger changes the value away from 0. */
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while (altered_by_debugger == 0)
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{
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usleep (100 * 1000);
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debugger_inspection_point ();
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}
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TEST_COMPARE (altered_by_debugger, 2);
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return NULL;
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}
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/* This function implements the subprocess under test. It creates a
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second thread, waiting for its value to change to 2, and checks
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that the main thread also changed its value to 1. */
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static void
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in_subprocess (void)
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{
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pthread_t thr = xpthread_create (NULL, subprocess_thread, NULL);
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TEST_VERIFY (xpthread_join (thr) == NULL);
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TEST_COMPARE (altered_by_debugger, 1);
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_exit (0);
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}
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static int
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do_test (void)
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{
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pid_t tested_pid = xfork ();
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if (tested_pid == 0)
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in_subprocess ();
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char *tested_pid_string = xasprintf ("%d", tested_pid);
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char *gdbscript;
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xclose (create_temp_file ("tst-pthread-gdb-attach-", &gdbscript));
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write_gdbscript (gdbscript, tested_pid);
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pid_t gdb_pid = xfork ();
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if (gdb_pid == 0)
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{
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clearenv ();
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xdup2 (STDOUT_FILENO, STDERR_FILENO);
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execlp ("gdb", "gdb", "-nx", "-batch", "-x", gdbscript, NULL);
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if (errno == ENOENT)
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_exit (EXIT_UNSUPPORTED);
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else
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_exit (1);
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}
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int status;
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TEST_COMPARE (xwaitpid (gdb_pid, &status, 0), gdb_pid);
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if (WIFEXITED (status) && WEXITSTATUS (status) == EXIT_UNSUPPORTED)
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/* gdb is not installed. */
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return EXIT_UNSUPPORTED;
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TEST_COMPARE (status, 0);
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TEST_COMPARE (xwaitpid (tested_pid, &status, 0), tested_pid);
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TEST_COMPARE (status, 0);
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free (tested_pid_string);
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free (gdbscript);
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return 0;
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}
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#include <support/test-driver.c>
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