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 2021-04-21 11:50:43 +02:00
parent aaa23c3507
commit a64afc2252
7 changed files with 180 additions and 11 deletions

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@ -313,7 +313,8 @@ tests = tst-attr2 tst-attr3 tst-default-attr \
tst-thread-affinity-sched \
tst-pthread-defaultattr-free \
tst-pthread-attr-sigmask \
tst-pthread-timedlock-lockloop
tst-pthread-timedlock-lockloop \
tst-pthread-gdb-attach tst-pthread-gdb-attach-static
tests-container = tst-pthread-getattr
@ -359,6 +360,19 @@ CPPFLAGS-test-cond-printers.c := $(CFLAGS-printers-tests)
CPPFLAGS-test-rwlockattr-printers.c := $(CFLAGS-printers-tests)
CPPFLAGS-test-rwlock-printers.c := $(CFLAGS-printers-tests)
# Reuse the CFLAGS setting for the GDB attaching test. It needs
# debugging information.
CFLAGS-tst-pthread-gdb-attach.c := $(CFLAGS-printers-tests)
CPPFLAGS-tst-pthread-gdb-attach.c := $(CFLAGS-printers-tests)
ifeq ($(build-shared)$(build-hardcoded-path-in-tests),yesno)
CPPFLAGS-tst-pthread-gdb-attach.c += -DDO_ADD_SYMBOL_FILE=1
else
CPPFLAGS-tst-pthread-gdb-attach.c += -DDO_ADD_SYMBOL_FILE=0
endif
CFLAGS-tst-pthread-gdb-attach-static.c := $(CFLAGS-printers-tests)
CPPFLAGS-tst-pthread-gdb-attach-static.c := \
$(CFLAGS-printers-tests) -DDO_ADD_SYMBOL_FILE=0
ifeq ($(build-shared),yes)
tests-printers-libs := $(shared-thread-library)
else
@ -430,7 +444,8 @@ link-libc-static := $(common-objpfx)libc.a $(static-gnulib) \
tests-static += tst-stackguard1-static \
tst-cancel24-static \
tst-mutex8-static tst-mutexpi8-static tst-sem11-static \
tst-sem12-static tst-cond11-static
tst-sem12-static tst-cond11-static \
tst-pthread-gdb-attach-static
tests += tst-cancel24-static

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@ -51,6 +51,14 @@ static td_thr_events_t __nptl_threads_events __attribute_used__;
/* Pointer to descriptor with the last event. */
static struct pthread *__nptl_last_event __attribute_used__;
#ifdef SHARED
/* This variable is used to access _rtld_global from libthread_db. If
GDB loads libpthread before ld.so, it is not possible to resolve
_rtld_global directly during libpthread initialization. */
static struct rtld_global *__nptl_rtld_global __attribute_used__
= &_rtld_global;
#endif
/* Number of threads running. */
unsigned int __nptl_nthreads = 1;

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@ -0,0 +1 @@
#include "tst-pthread-gdb-attach.c"

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@ -0,0 +1,143 @@
/* Smoke testing GDB process attach with thread-local variable access.
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
<https://www.gnu.org/licenses/>. */
/* This test runs GDB against a forked copy of itself, to check
whether libthread_db can be loaded, and that access to thread-local
variables works. */
#include <errno.h>
#include <stdlib.h>
#include <support/check.h>
#include <support/support.h>
#include <support/temp_file.h>
#include <support/test-driver.h>
#include <support/xstdio.h>
#include <support/xthread.h>
#include <support/xunistd.h>
#include <unistd.h>
/* Starts out as zero, changed to 1 or 2 by the debugger, depending on
the thread. */
__thread volatile int altered_by_debugger;
/* Writes the GDB script to run the test to PATH. */
static void
write_gdbscript (const char *path, int tested_pid)
{
FILE *fp = xfopen (path, "w");
fprintf (fp,
"set trace-commands on\n"
"set debug libthread-db 1\n"
#if DO_ADD_SYMBOL_FILE
/* Do not do this unconditionally to work around a GDB
assertion failure: ../../gdb/symtab.c:6404:
internal-error: CORE_ADDR get_msymbol_address(objfile*,
const minimal_symbol*): Assertion `(objf->flags &
OBJF_MAINLINE) == 0' failed. */
"add-symbol-file %1$s/nptl/tst-pthread-gdb-attach\n"
#endif
"set auto-load safe-path %1$s/nptl_db\n"
"set libthread-db-search-path %1$s/nptl_db\n"
"attach %2$d\n",
support_objdir_root, tested_pid);
fputs ("break debugger_inspection_point\n"
"continue\n"
"thread 1\n"
"print altered_by_debugger\n"
"print altered_by_debugger = 1\n"
"thread 2\n"
"print altered_by_debugger\n"
"print altered_by_debugger = 2\n"
"continue\n",
fp);
xfclose (fp);
}
/* The test sets a breakpoint on this function and alters the
altered_by_debugger thread-local variable. */
void __attribute__ ((weak))
debugger_inspection_point (void)
{
}
/* Thread function for the test thread in the subprocess. */
static void *
subprocess_thread (void *closure)
{
/* Wait until altered_by_debugger changes the value away from 0. */
while (altered_by_debugger == 0)
{
usleep (100 * 1000);
debugger_inspection_point ();
}
TEST_COMPARE (altered_by_debugger, 2);
return NULL;
}
/* This function implements the subprocess under test. It creates a
second thread, waiting for its value to change to 2, and checks
that the main thread also changed its value to 1. */
static void
in_subprocess (void)
{
pthread_t thr = xpthread_create (NULL, subprocess_thread, NULL);
TEST_VERIFY (xpthread_join (thr) == NULL);
TEST_COMPARE (altered_by_debugger, 1);
_exit (0);
}
static int
do_test (void)
{
pid_t tested_pid = xfork ();
if (tested_pid == 0)
in_subprocess ();
char *tested_pid_string = xasprintf ("%d", tested_pid);
char *gdbscript;
xclose (create_temp_file ("tst-pthread-gdb-attach-", &gdbscript));
write_gdbscript (gdbscript, tested_pid);
pid_t gdb_pid = xfork ();
if (gdb_pid == 0)
{
clearenv ();
xdup2 (STDOUT_FILENO, STDERR_FILENO);
execlp ("gdb", "gdb", "-nx", "-batch", "-x", gdbscript, NULL);
if (errno == ENOENT)
_exit (EXIT_UNSUPPORTED);
else
_exit (1);
}
int status;
TEST_COMPARE (xwaitpid (gdb_pid, &status, 0), gdb_pid);
if (WIFEXITED (status) && WEXITSTATUS (status) == EXIT_UNSUPPORTED)
/* gdb is not installed. */
return EXIT_UNSUPPORTED;
TEST_COMPARE (status, 0);
TEST_COMPARE (xwaitpid (tested_pid, &status, 0), tested_pid);
TEST_COMPARE (status, 0);
free (tested_pid_string);
free (gdbscript);
return 0;
}
#include <support/test-driver.c>

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@ -100,8 +100,7 @@ DB_STRUCT_FIELD (pthread, dtvp)
#endif
#if !(IS_IN (libpthread) && !defined SHARED)
DB_STRUCT (rtld_global)
DB_RTLD_VARIABLE (_rtld_global)
DB_VARIABLE (__nptl_rtld_global)
#endif
DB_RTLD_GLOBAL_FIELD (dl_tls_dtv_slotinfo_list)
DB_RTLD_GLOBAL_FIELD (dl_stack_user)

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@ -33,13 +33,14 @@ td_init (void)
bool
__td_ta_rtld_global (td_thragent_t *ta)
{
if (ta->ta_addr__rtld_global == 0
&& td_mod_lookup (ta->ph, LD_SO, SYM__rtld_global,
&ta->ta_addr__rtld_global) != PS_OK)
if (ta->ta_addr__rtld_global == 0)
{
ta->ta_addr__rtld_global = (void*)-1;
return false;
psaddr_t rtldglobalp;
if (DB_GET_VALUE (rtldglobalp, ta, __nptl_rtld_global, 0) == TD_OK)
ta->ta_addr__rtld_global = rtldglobalp;
else
ta->ta_addr__rtld_global = (void *) -1;
}
else
return ta->ta_addr__rtld_global != (void*)-1;
return ta->ta_addr__rtld_global != (void *)-1;
}

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@ -108,6 +108,8 @@ struct td_thragent
# undef DB_SYMBOL
# undef DB_VARIABLE
psaddr_t ta_addr__rtld_global;
/* The method of locating a thread's th_unique value. */
enum
{