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While working with pending fork events, I wondered what would happen if
the user detached an inferior while a thread of that inferior had a
pending fork event. What happens with the fork child, which is
ptrace-attached by the GDB process (or by GDBserver), but not known to
the core? Sure enough, neither the core of GDB or the target detach the
child process, so GDB (or GDBserver) just stays ptrace-attached to the
process. The result is that the fork child process is stuck, while you
would expect it to be detached and run.
Make GDBserver detach of fork children it knows about. That is done in
the generic handle_detach function. Since a process_info already exists
for the child, we can simply call detach_inferior on it.
GDB-side, make the linux-nat and remote targets detach of fork children
known because of pending fork events. These pending fork events can be
stored in:
- thread_info::pending_waitstatus, if the core has consumed the event
but then saved it for later (for example, because it got the event
while stopping all threads, to present an all-stop stop on top of a
non-stop target)
- thread_info::pending_follow: if we ran to a "catch fork" and we
detach at that moment
Additionally, pending fork events can be in target-specific fields:
- For linux-nat, they can be in lwp_info::status and
lwp_info::waitstatus.
- For the remote target, they could be stored as pending stop replies,
saved in `remote_state::notif_state::pending_event`, if not
acknowledged yet, or in `remote_state::stop_reply_queue`, if
acknowledged. I followed the model of remove_new_fork_children for
this: call remote_notif_get_pending_events to process /
acknowledge any unacknowledged notification, then look through
stop_reply_queue.
Update the gdb.threads/pending-fork-event.exp test (and rename it to
gdb.threads/pending-fork-event-detach.exp) to try to detach the process
while it is stopped with a pending fork event. In order to verify that
the fork child process is correctly detached and resumes execution
outside of GDB's control, make that process create a file in the test
output directory, and make the test wait $timeout seconds for that file
to appear (it happens instantly if everything goes well).
This test catches a bug in linux-nat.c, also reported as PR 28512
("waitstatus.h:300: internal-error: gdb_signal target_waitstatus::sig()
const: Assertion `m_kind == TARGET_WAITKIND_STOPPED || m_kind ==
TARGET_WAITKIND_SIGNALLED' failed.). When detaching a thread with a
pending event, get_detach_signal unconditionally fetches the signal
stored in the waitstatus (`tp->pending_waitstatus ().sig ()`). However,
that is only valid if the pending event is of type
TARGET_WAITKIND_STOPPED, and this is now enforced using assertions (iit
would also be valid for TARGET_WAITKIND_SIGNALLED, but that would mean
the thread does not exist anymore, so we wouldn't be detaching it). Add
a condition in get_detach_signal to access the signal number only if the
wait status is of kind TARGET_WAITKIND_STOPPED, and use GDB_SIGNAL_0
instead (since the thread was not stopped with a signal to begin with).
Add another test, gdb.threads/pending-fork-event-ns.exp, specifically to
verify that we consider events in pending stop replies in the remote
target. This test has many threads constantly forking, and we detach
from the program while the program is executing. That gives us some
chance that we detach while a fork stop reply is stored in the remote
target. To verify that we correctly detach all fork children, we ask
the parent to exit by sending it a SIGUSR1 signal and have it write a
file to the filesystem before exiting. Because the parent's main thread
joins the forking threads, and the forking threads wait for their fork
children to exit, if some fork child is not detach by GDB, the parent
will not write the file, and the test will time out. If I remove the
new remote_detach_pid calls in remote.c, the test fails eventually if I
run it in a loop.
There is a known limitation: we don't remove breakpoints from the
children before detaching it. So the children, could hit a trap
instruction after being detached and crash. I know this is wrong, and
it should be fixed, but I would like to handle that later. The current
patch doesn't fix everything, but it's a step in the right direction.
Change-Id: I6d811a56f520e3cb92d5ea563ad38976f92e93dd
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28512
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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.