commit 1ec6a1148ad3ca06f48be269e1b61cb9c61a0938
Author: Pedro Alves <palves@redhat.com>
Date: Fri Jan 5 18:30:49 2018 +0000
Fix regression: cannot start with LD_PRELOAD=libSegFault.so (PR gdb/18653#c7)
At https://sourceware.org/bugzilla/show_bug.cgi?id=18653#c7, Andrew
reports that the fix for PR gdb/18653 made GDB useless if you preload
libSegFault.so, because GDB internal-errors on startup:
$ LD_PRELOAD=libSegFault.so gdb
src/gdb/common/signals-state-save-restore.c:64: internal-error: unexpected signal handler
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Aborted (core dumped)
$
The internal error comes from the code saving the signal dispositions
inherited from gdb's parent:
(top-gdb) bt
#0 0x000000000056b001 in internal_error(char const*, int, char const*, ...) (file=0xaf5f38 "src/gdb/common/signals-state-save-restore.c", line=64, fmt=0xaf5f18 "unexpected signal handler") at src/gdb/common/errors.c:54
#1 0x00000000005752c9 in save_original_signals_state() () at src/gdb/common/signals-state-save-restore.c:64
#2 0x00000000007425de in captured_main_1(captured_main_args*) (context=0x7fffffffd860)
at src/gdb/main.c:509
#3 0x0000000000743622 in captured_main(void*) (data=0x7fffffffd860) at src/gdb/main.c:1145
During symbol reading, cannot get low and high bounds for subprogram DIE at 24065.
#4 0x00000000007436f9 in gdb_main(captured_main_args*) (args=0x7fffffffd860) at src/gdb/main.c:1171
#5 0x0000000000413acd in main(int, char**) (argc=1, argv=0x7fffffffd968) at src/gdb/gdb.c:32
This commit downgrades the internal error to a warning. You'll get
instead:
~~~
$ LD_PRELOAD=libSegFault.so gdb
warning: Found custom handler for signal 11 (Segmentation fault) preinstalled.
Some signal dispositions inherited from the environment (SIG_DFL/SIG_IGN)
won't be propagated to spawned programs.
GNU gdb (GDB) 8.0.50.20171213-git
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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and "show warranty" for details.
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Type "show configuration" for configuration details.
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(gdb)
~~~
This also moves the location where save_original_signals_state is
called a bit further below (to after option processing), so that "-q"
disables the warning:
~~~
$ LD_PRELOAD=libSegFault.so gdb -q
(gdb)
~~~
New testcase included.
gdb/ChangeLog:
2018-01-05 Pedro Alves <palves@redhat.com>
PR gdb/18653
* common/signals-state-save-restore.c
(save_original_signals_state): New parameter 'quiet'. Warn if we
find a custom handler preinstalled, instead of internal erroring.
But only warn if !quiet.
* common/signals-state-save-restore.h
(save_original_signals_state): New parameter 'quiet'.
* main.c (captured_main_1): Move save_original_signals_state call
after option handling, and pass QUIET.
gdb/gdbserver/ChangeLog:
2018-01-05 Pedro Alves <palves@redhat.com>
PR gdb/18653
* server.c (captured_main): Pass quiet=false to
save_original_signals_state.
gdb/testsuite/ChangeLog:
2018-01-05 Pedro Alves <palves@redhat.com>
PR gdb/18653
* gdb.base/libsegfault.exp: New.
### a/gdb/ChangeLog
### b/gdb/ChangeLog
## -1,3 +1,15 @@
+2018-01-05 Pedro Alves <palves@redhat.com>
+
+ PR gdb/18653
+ * common/signals-state-save-restore.c
+ (save_original_signals_state): New parameter 'quiet'. Warn if we
+ find a custom handler preinstalled, instead of internal erroring.
+ But only warn if !quiet.
+ * common/signals-state-save-restore.h
+ (save_original_signals_state): New parameter 'quiet'.
+ * main.c (captured_main_1): Move save_original_signals_state call
+ after option handling, and pass QUIET.
+
2018-01-05 Pedro Alves <palves@redhat.com>
* spu-tdep.c (spu_catch_start): Pass
Index: gdb-7.6.1/gdb/common/signals-state-save-restore.c
===================================================================
--- gdb-7.6.1.orig/gdb/common/signals-state-save-restore.c 2018-01-08 15:30:48.182057111 +0100
+++ gdb-7.6.1/gdb/common/signals-state-save-restore.c 2018-01-08 15:37:50.450183830 +0100
@@ -24,6 +24,7 @@
#include "signals-state-save-restore.h"
#include <signal.h>
+#include <string.h>
/* The original signal actions and mask. */
@@ -40,11 +41,12 @@
/* See signals-state-save-restore.h. */
void
-save_original_signals_state (void)
+save_original_signals_state (int quiet)
{
#ifdef HAVE_SIGACTION
int i;
int res;
+ int found_preinstalled = 0;
res = sigprocmask (0, NULL, &original_signal_mask);
if (res == -1)
@@ -64,9 +66,31 @@
perror_with_name ("sigaction");
/* If we find a custom signal handler already installed, then
- this function was called too late. */
- if (oldact->sa_handler != SIG_DFL && oldact->sa_handler != SIG_IGN)
- internal_error (__FILE__, __LINE__, _("unexpected signal handler"));
+ this function was called too late. This is a warning instead
+ of an internal error because this can also happen if you
+ LD_PRELOAD a library that installs a signal handler early via
+ __attribute__((constructor)), like libSegFault.so. */
+ if (!quiet
+ && oldact->sa_handler != SIG_DFL
+ && oldact->sa_handler != SIG_IGN)
+ {
+ found_preinstalled = 1;
+
+ /* Use raw fprintf here because we're being called in early
+ startup, because GDB's filtered streams are are
+ created. */
+ fprintf (stderr,
+ _("warning: Found custom handler for signal "
+ "%d (%s) preinstalled.\n"), i,
+ strsignal (i));
+ }
+ }
+
+ if (found_preinstalled)
+ {
+ fprintf (stderr, _("\
+Some signal dispositions inherited from the environment (SIG_DFL/SIG_IGN)\n\
+won't be propagated to spawned programs.\n"));
}
#endif
}
Index: gdb-7.6.1/gdb/common/signals-state-save-restore.h
===================================================================
--- gdb-7.6.1.orig/gdb/common/signals-state-save-restore.h 2018-01-08 15:30:48.613060301 +0100
+++ gdb-7.6.1/gdb/common/signals-state-save-restore.h 2018-01-08 15:35:15.538036768 +0100
@@ -28,9 +28,10 @@
back to what was originally inherited from gdb/gdbserver's parent,
just before execing the target program to debug. */
-/* Save the signal state of all signals. */
+/* Save the signal state of all signals. If !QUIET, warn if we detect
+ a custom signal handler preinstalled. */
-extern void save_original_signals_state (void);
+extern void save_original_signals_state (int quiet);
/* Restore the signal state of all signals. */
Index: gdb-7.6.1/gdb/gdbserver/server.c
===================================================================
--- gdb-7.6.1.orig/gdb/gdbserver/server.c 2018-01-08 15:30:48.613060301 +0100
+++ gdb-7.6.1/gdb/gdbserver/server.c 2018-01-08 15:38:02.115270202 +0100
@@ -2896,7 +2896,7 @@
exit (1);
}
- save_original_signals_state ();
+ save_original_signals_state (0);
/* We need to know whether the remote connection is stdio before
starting the inferior. Inferiors created in this scenario have
Index: gdb-7.6.1/gdb/main.c
===================================================================
--- gdb-7.6.1.orig/gdb/main.c 2018-01-08 15:30:51.951085018 +0100
+++ gdb-7.6.1/gdb/main.c 2018-01-08 15:31:46.874491703 +0100
@@ -394,7 +394,6 @@
textdomain (PACKAGE);
bfd_init ();
- save_original_signals_state ();
make_cleanup (VEC_cleanup (cmdarg_s), &cmdarg_vec);
dirsize = 1;
@@ -778,6 +777,8 @@
quiet = 1;
}
+ save_original_signals_state (quiet);
+
/* Initialize all files. Give the interpreter a chance to take
control of the console via the deprecated_init_ui_hook (). */
gdb_init (gdb_program_name);
Index: gdb-7.6.1/gdb/testsuite/gdb.base/libsegfault.exp
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ gdb-7.6.1/gdb/testsuite/gdb.base/libsegfault.exp 2018-01-08 15:30:51.951085018 +0100
@@ -0,0 +1,84 @@
+# Copyright 2017-2018 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+# This file is part of the gdb testsuite.
+
+# Test that GDB tolerates being started with libSegFault.so preloaded
+# with LD_PRELOAD, and that GDB warns about a custom SIGSEGV custom
+# handler. See PR gdb/18653
+# <https://sourceware.org/bugzilla/show_bug.cgi?id=18653#c7>.
+
+# We cannot expect remote hosts to see environment variables set on
+# the local machine.
+if { [is_remote host] } {
+ unsupported "can't set environment variables on remote host"
+ return -1
+}
+
+# Spawn GDB with LIB preloaded with LD_PRELOAD. CMDLINE_OPTS are
+# command line options passed to GDB.
+
+proc gdb_spawn_with_ld_preload {lib cmdline_opts} {
+ global env
+
+ save_vars { env(LD_PRELOAD) } {
+ if { ![info exists env(LD_PRELOAD) ]
+ || $env(LD_PRELOAD) == "" } {
+ set env(LD_PRELOAD) "$lib"
+ } else {
+ append env(LD_PRELOAD) ":$lib"
+ }
+
+ gdb_spawn_with_cmdline_opts $cmdline_opts
+ }
+}
+
+proc test_libsegfault {} {
+ global gdb_prompt
+
+ set libsegfault "libSegFault.so"
+
+ # When started normally, if libSegFault.so is preloaded, GDB
+ # should warn about not being able to propagate the signal
+ # disposition of SIGSEGV.
+ gdb_exit
+ gdb_spawn_with_ld_preload $libsegfault ""
+
+ set test "gdb emits custom handler warning"
+ gdb_test_multiple "" $test {
+ -re "cannot be preloaded.*\r\n$gdb_prompt $" {
+ # Glibc 2.22 outputs:
+ # ERROR: ld.so: object 'libSegFault.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.
+ untested "cannot preload libSegFault.so"
+ return
+ }
+ -re "Found custom handler.*won't be propagated.*\r\n$gdb_prompt $" {
+ pass $test
+ }
+ }
+
+ # "-q" should disable the warning, though.
+ gdb_exit
+ gdb_spawn_with_ld_preload $libsegfault "-q"
+
+ set test "quiet suppresses custom handler warning"
+ gdb_test_multiple "" $test {
+ -re "^$gdb_prompt $" {
+ pass $test
+ }
+ }
+}
+
+test_libsegfault