diff options
| author | Thiago Macieira <thiago.macieira@intel.com> | 2020-09-10 13:30:59 -0700 |
|---|---|---|
| committer | Thiago Macieira <thiago.macieira@intel.com> | 2020-09-17 00:43:47 +0000 |
| commit | d1fc991c6e3c45a5f93c925d49e3fe77ce6ce455 (patch) | |
| tree | 53247bb739a409612cbfbf0f6c7497930031a312 | |
| parent | 2ed99ff5ca338ac02f71c347b1449d4662e6c221 (diff) | |
forkfd/Linux: ask clone() to use the SIGCHLD as the termination signal
Because of these lines in the Linux kernel (kernel/fork.c, see [1][3]):
if (clone_flags & CLONE_VFORK)
trace = PTRACE_EVENT_VFORK;
else if (args->exit_signal != SIGCHLD)
trace = PTRACE_EVENT_CLONE;
else
trace = PTRACE_EVENT_FORK;
Without CLONE_VFORK (which we can't use), if the exit signal isn't
SIGCHLD, the debugger will get a PTRACE_EVENT_CLONE, which makes it
think the process we're starting is a thread, not a new process. Both
gdb and lldb remain attached to the child and when it later performs an
execve(), they get mightily confused. See gdb bug report[5].
The idea of not having an exit_signal was so that no SIGCHLD would be
delivered to the parent process in the first place. That way, some
misguided SIGCHLD handler (*cough* GLib *cough*) wouldn't reap our
processes. Unfortunately, what I didn't realize was that the kernel
sends SIGCHLD anyway (see [2][4]), so this defensive measure didn't
actually work. Consequently, we can pass SIGCHLD to clone() and get the
debuggers working again.
[ChangeLog][Linux] Fixed an issue that would cause debugging a Qt
application that uses QProcess to confuse both gdb and lldb if
the Linux kernel was version 5.4 or higher. Behavior outside of
a debugging session was not affected.
[1] https://code.woboq.org/linux/linux/kernel/fork.c.html#_do_fork
[2] https://code.woboq.org/linux/linux/kernel/signal.c.html#do_notify_parent
[3] https://elixir.bootlin.com/linux/v5.8/source/kernel/fork.c#L2432
[4] https://elixir.bootlin.com/linux/v5.8/source/kernel/signal.c#L1925
[5] https://sourceware.org/bugzilla/show_bug.cgi?id=26562
Fixes: QTBUG-86319
Pick-to: 5.15
Change-Id: I2fc68c725ba649218bd9fffd1633863613537d42
Reviewed-by: Dimitrios Apostolou <jimis@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Reviewed-by: hjk <hjk@qt.io>
| -rw-r--r-- | src/3rdparty/forkfd/forkfd_linux.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/src/3rdparty/forkfd/forkfd_linux.c b/src/3rdparty/forkfd/forkfd_linux.c index 923ced128d..c86e138b63 100644 --- a/src/3rdparty/forkfd/forkfd_linux.c +++ b/src/3rdparty/forkfd/forkfd_linux.c @@ -147,7 +147,7 @@ int system_forkfd(int flags, pid_t *ppid, int *system) } *system = 1; - unsigned long cloneflags = CLONE_PIDFD; + unsigned long cloneflags = CLONE_PIDFD | SIGCHLD; pid = sys_clone(cloneflags, &pidfd); if (pid < 0) return pid; @@ -173,7 +173,7 @@ int system_forkfd_wait(int ffd, struct forkfd_info *info, int ffdoptions, struct { siginfo_t si; int ret; - int options = __WALL | convertForkfdWaitFlagsToWaitFlags(ffdoptions); + int options = convertForkfdWaitFlagsToWaitFlags(ffdoptions); if ((options & WNOHANG) == 0) { /* check if the file descriptor is non-blocking */ |