From a64afc225240b2b27129ccfb0516d7c958b98040 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Wed, 21 Apr 2021 11:50:43 +0200
Subject: [PATCH] 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 1daccf403b1bd86370eb94edca794dc106d02039 ("nptl: Move
stack list variables into _rtld_global").
Tested-by: Emil Velikov <emil.velikov@collabora.com>
---
nptl/Makefile | 19 +++-
nptl/pthread_create.c | 8 ++
nptl/tst-pthread-gdb-attach-static.c | 1 +
nptl/tst-pthread-gdb-attach.c | 143 +++++++++++++++++++++++++++
nptl_db/structs.def | 3 +-
nptl_db/td_init.c | 15 +--
nptl_db/thread_dbP.h | 2 +
7 files changed, 180 insertions(+), 11 deletions(-)
create mode 100644 nptl/tst-pthread-gdb-attach-static.c
create mode 100644 nptl/tst-pthread-gdb-attach.c
Index: glibc-2.33/nptl/Makefile
===================================================================
--- glibc-2.33.orig/nptl/Makefile
+++ glibc-2.33/nptl/Makefile
@@ -294,7 +294,8 @@ tests = tst-attr2 tst-attr3 tst-default-
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
@@ -344,6 +345,22 @@ CPPFLAGS-test-cond-printers.c := $(CFLAG
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 := \
+ $(CFLAGS-printers-tests) -DDO_ADD_SYMBOL_FILE=0
+# As of version 9.2, GDB cannot attach properly to PIE programs that
+# were launched with an explicit ld.so invocation.
+tst-pthread-gdb-attach-no-pie = yes
+
ifeq ($(build-shared),yes)
tests-printers-libs := $(shared-thread-library)
else
@@ -415,7 +432,8 @@ link-libc-static := $(common-objpfx)libc
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
Index: glibc-2.33/nptl/pthread_create.c
===================================================================
--- glibc-2.33.orig/nptl/pthread_create.c
+++ glibc-2.33/nptl/pthread_create.c
@@ -51,6 +51,14 @@ static td_thr_events_t __nptl_threads_ev
/* 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;
Index: glibc-2.33/nptl/tst-pthread-gdb-attach-static.c
===================================================================
--- /dev/null
+++ glibc-2.33/nptl/tst-pthread-gdb-attach-static.c
@@ -0,0 +1 @@
+#include "tst-pthread-gdb-attach.c"
Index: glibc-2.33/nptl/tst-pthread-gdb-attach.c
===================================================================
--- /dev/null
+++ glibc-2.33/nptl/tst-pthread-gdb-attach.c
@@ -0,0 +1,217 @@
+/* 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 <elf.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.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;
+
+/* Common prefix between 32-bit and 64-bit ELF. */
+struct elf_prefix
+{
+ unsigned char e_ident[EI_NIDENT];
+ uint16_t e_type;
+ uint16_t e_machine;
+ uint32_t e_version;
+};
+_Static_assert (sizeof (struct elf_prefix) == EI_NIDENT + 8,
+ "padding in struct elf_prefix");
+
+/* Reads the ELF header from PATH. Returns true if the header can be
+ read, false if the file is too short. */
+static bool
+read_elf_header (const char *path, struct elf_prefix *elf)
+{
+ int fd = xopen (path, O_RDONLY, 0);
+ bool result = read (fd, elf, sizeof (*elf)) == sizeof (*elf);
+ xclose (fd);
+ return result;
+}
+
+/* Searches for "gdb" alongside the path variable. See execvpe. */
+static char *
+find_gdb (void)
+{
+ const char *path = getenv ("PATH");
+ if (path == NULL)
+ return NULL;
+ while (true)
+ {
+ const char *colon = strchrnul (path, ':');
+ char *candidate = xasprintf ("%.*s/gdb", (int) (colon - path), path);
+ if (access (candidate, X_OK) == 0)
+ return candidate;
+ free (candidate);
+ if (*colon == '\0')
+ break;
+ path = colon + 1;
+ }
+ return NULL;
+}
+
+/* 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)
+{
+ char *gdb_path = find_gdb ();
+ if (gdb_path == NULL)
+ FAIL_UNSUPPORTED ("gdb command not found in PATH: %s", getenv ("PATH"));
+
+ /* Check that libthread_db is compatible with the gdb architecture
+ because gdb loads it via dlopen. */
+ {
+ char *threaddb_path = xasprintf ("%s/nptl_db/libthread_db.so",
+ support_objdir_root);
+ struct elf_prefix elf_threaddb;
+ TEST_VERIFY_EXIT (read_elf_header (threaddb_path, &elf_threaddb));
+ struct elf_prefix elf_gdb;
+ /* If the ELF header cannot be read or "gdb" is not an ELF file,
+ assume this is a wrapper script that can run. */
+ if (read_elf_header (gdb_path, &elf_gdb)
+ && memcmp (&elf_gdb, ELFMAG, SELFMAG) == 0)
+ {
+ if (elf_gdb.e_ident[EI_CLASS] != elf_threaddb.e_ident[EI_CLASS])
+ FAIL_UNSUPPORTED ("GDB at %s has wrong class", gdb_path);
+ if (elf_gdb.e_ident[EI_DATA] != elf_threaddb.e_ident[EI_DATA])
+ FAIL_UNSUPPORTED ("GDB at %s has wrong data", gdb_path);
+ if (elf_gdb.e_machine != elf_threaddb.e_machine)
+ FAIL_UNSUPPORTED ("GDB at %s has wrong machine", gdb_path);
+ }
+ free (threaddb_path);
+ }
+
+ 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)
+ {
+ xdup2 (STDOUT_FILENO, STDERR_FILENO);
+ execl (gdb_path, "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);
+ free (gdb_path);
+ return 0;
+}
+
+#include <support/test-driver.c>
Index: glibc-2.33/nptl_db/structs.def
===================================================================
--- glibc-2.33.orig/nptl_db/structs.def
+++ glibc-2.33/nptl_db/structs.def
@@ -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)
Index: glibc-2.33/nptl_db/td_init.c
===================================================================
--- glibc-2.33.orig/nptl_db/td_init.c
+++ glibc-2.33/nptl_db/td_init.c
@@ -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;
}
Index: glibc-2.33/nptl_db/thread_dbP.h
===================================================================
--- glibc-2.33.orig/nptl_db/thread_dbP.h
+++ glibc-2.33/nptl_db/thread_dbP.h
@@ -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
{