b3e3a4c114
When interrupting a program in non-stop, the program gets interrupted
correctly, but GDB busy loops (the event loop is always woken up).
Here is how to reproduce it:
1. Start GDB: ./gdb -nx --data-directory=data-directory -ex "set non-stop 1" --args /bin/sleep 60
2. Run the program with "run"
3. Interrupt with ^C.
4. Look into htop, see GDB taking 100% CPU
Debugging `handle_file_event`, we see that the event source that wakes
up the event loop is the linux-nat one:
(top-gdb) p file_ptr.proc
$5 = (handler_func *) 0xb9cccd <handle_target_event(int, gdb_client_data)>
^^^^^^^^^^^^^^^^^^^
|
\-- the linux-nat callback
Debugging fetch_inferior_event and do_target_wait, we see that we
don't actually call `wait` on the linux-nat target, because
inferior_matches returns false:
auto inferior_matches = [&wait_ptid] (inferior *inf)
{
return (inf->process_target () != NULL
&& (threads_are_executing (inf->process_target ())
|| threads_are_resumed_pending_p (inf))
&& ptid_t (inf->pid).matches (wait_ptid));
};
because `threads_are_executing` is false.
What happens is:
1. User types ctrl-c, that writes in the linux-nat pipe, waking up
the event source.
2. linux-nat's wait gets called, the SIGINT event is returned, but
before returning, it marks the pipe again, in order for wait to
get called again:
/* If we requested any event, and something came out, assume there
may be more. If we requested a specific lwp or process, also
assume there may be more. */
if (target_is_async_p ()
&& ((ourstatus->kind != TARGET_WAITKIND_IGNORE
&& ourstatus->kind != TARGET_WAITKIND_NO_RESUMED)
|| ptid != minus_one_ptid))
async_file_mark ();
3. The SIGINT event is handled, the program is stopped, the stop
notification is printed.
4. The event loop is woken up again because of the `async_file_mark`
of step 2.
5. Because `inferior_matches` returns false, we never call
linux-nat's wait, so the pipe stays readable.
6. Goto 4.
Pedro says:
This commit fixes it by letting do_target_wait call target_wait even
if threads_are_executing is false. This will normally result in the
target returning TARGET_WAITKIND_NO_RESUMED, and _not_ marking its
event source again. This results in infrun only calling into the
target only once (i.e., breaking the busy loop).
Note that the busy loop bug didn't trigger in all-stop mode because
all-stop handles this by unregistering the target from the event loop
as soon as it was all stopped -- see
inf-loop.c:inferior_event_handler's INF_EXEC_COMPLETE handling. If we
remove that non-stop check from inferior_event_handler, and replace
the target_has_execution check for threads_are_executing instead, it
also fixes the issue for non-stop. I considered that as the final
solution, but decided that the solution proposed here instead is just
simpler and more future-proof design. With the
TARGET_WAITKIND_NO_RESUMED handling fixes done in the previous
patches, I think it should be possible to always keep the target
registered in the event loop, meaning we could eliminate the
target_async(0) call from inferior_event_handler as well as most of
the target_async(1) calls in the target backends. That would allow in
the future e.g., the remote target reporting asynchronous
notifications even if all threads are stopped. I haven't attempted
that, though.
gdb/ChangeLog:
yyyy-mm-dd Simon Marchi <simon.marchi@polymtl.ca>
Pedro Alves <pedro@palves.net>
PR gdb/26199
* infrun.c (threads_are_resumed_pending_p): Delete.
(do_target_wait): Remove threads_are_executing and
threads_are_resumed_pending_p checks from the inferior_matches
lambda. Update comments.
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README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.