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
Copyright (C) 2017 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
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For help, type "help".
Type "apropos word" to search for commands related to "word"...
(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.
This applies the second part of GDB's End of Year Procedure, which
updates the copyright year range in all of GDB's files.
gdb/ChangeLog:
Update copyright year range in all GDB files.
The ARI complains about this new file:
common/signals-state-save-restore.c:46: warning: gettext: All messages should be marked up with _.
common/signals-state-save-restore.c:59: warning: gettext: All messages should be marked up with _.
common/signals-state-save-restore.c:87: warning: gettext: All messages should be marked up with _.
common/signals-state-save-restore.c:92: warning: gettext: All messages should be marked up with _.
Since these are untranslatable strings, use () instead of _().
gdb/ChangeLog:
2016-08-10 Pedro Alves <palves@redhat.com>
* common/signals-state-save-restore.c
(save_original_signals_state, restore_original_signals_state):
Wrap perror_with_name arguments with '()'.
gdb's (or gdbserver's) own signal handling should not interfere with
the signal dispositions their spawned children inherit. However, it
currently does. For example, some paths in gdb cause SIGPIPE to be
set to SIG_IGN, and as consequence, the child starts with SIGPIPE to
set to SIG_IGN too, even though gdb was started with SIGPIPE set to
SIG_DFL.
This is because the exec family of functions does not reset the signal
disposition of signals that are set to SIG_IGN:
http://pubs.opengroup.org/onlinepubs/7908799/xsh/execve.html
Signals set to the default action (SIG_DFL) in the calling process
image are set to the default action in the new process
image. Signals set to be ignored (SIG_IGN) by the calling process
image are set to be ignored by the new process image. Signals set to
be caught by the calling process image are set to the default action
in the new process image (see <signal.h>).
And neither does it reset signal masks or flags.
In order to be transparent, when spawning new child processes to debug
(with "run", etc.), reset signal actions and mask back to what was
originally inherited from gdb/gdbserver's parent, just before execing
the target program to debug.
gdb/ChangeLog:
2016-08-09 Pedro Alves <palves@redhat.com>
PR gdb/18653
* Makefile.in (SFILES): Add
common/signals-state-save-restore.c.
(HFILES_NO_SRCDIR): Add common/signals-state-save-restore.h.
(COMMON_OBS): Add signals-state-save-restore.o.
(signals-state-save-restore.o): New rule.
* configure: Regenerate.
* fork-child.c: Include "signals-state-save-restore.h".
(fork_inferior): Call restore_original_signals_state.
* main.c: Include "signals-state-save-restore.h".
(captured_main): Call save_original_signals_state.
* common/common.m4: Add sigaction to AC_CHECK_FUNCS checks.
* common/signals-state-save-restore.c: New file.
* common/signals-state-save-restore.h: New file.
gdb/gdbserver/ChangeLog:
2016-08-09 Pedro Alves <palves@redhat.com>
PR gdb/18653
* Makefile.in (OBS): Add signals-state-save-restore.o.
(signals-state-save-restore.o): New rule.
* config.in: Regenerate.
* configure: Regenerate.
* linux-low.c: Include "signals-state-save-restore.h".
(linux_create_inferior): Call
restore_original_signals_state.
* server.c: Include "dispositions-save-restore.h".
(captured_main): Call save_original_signals_state.
gdb/testsuite/ChangeLog:
2016-08-09 Pedro Alves <palves@redhat.com>
PR gdb/18653
* gdb.base/signals-state-child.c: New file.
* gdb.base/signals-state-child.exp: New file.
* gdb.gdb/selftest.exp (do_steps_and_nexts): Add new pattern.
