57e5cd0b06
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74 lines
3.1 KiB
Diff
74 lines
3.1 KiB
Diff
From a82032351c921c3d5d57122aca57b47f83f9b9d1 Mon Sep 17 00:00:00 2001
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From: Thiago Macieira <thiago.macieira@intel.com>
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Date: Thu, 10 Sep 2020 13:30:59 -0700
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Subject: [PATCH] forkfd/Linux: ask clone() to use the SIGCHLD as the
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termination signal
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Because of these lines in the Linux kernel (kernel/fork.c, see [1][3]):
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if (clone_flags & CLONE_VFORK)
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trace = PTRACE_EVENT_VFORK;
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else if (args->exit_signal != SIGCHLD)
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trace = PTRACE_EVENT_CLONE;
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else
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trace = PTRACE_EVENT_FORK;
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Without CLONE_VFORK (which we can't use), if the exit signal isn't
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SIGCHLD, the debugger will get a PTRACE_EVENT_CLONE, which makes it
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think the process we're starting is a thread, not a new process. Both
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gdb and lldb remain attached to the child and when it later performs an
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execve(), they get mightily confused. See gdb bug report[5].
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The idea of not having an exit_signal was so that no SIGCHLD would be
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delivered to the parent process in the first place. That way, some
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misguided SIGCHLD handler (*cough* GLib *cough*) wouldn't reap our
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processes. Unfortunately, what I didn't realize was that the kernel
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sends SIGCHLD anyway (see [2][4]), so this defensive measure didn't
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actually work. Consequently, we can pass SIGCHLD to clone() and get the
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debuggers working again.
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[ChangeLog][Linux] Fixed an issue that would cause debugging a Qt
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application that uses QProcess to confuse both gdb and lldb if
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the Linux kernel was version 5.4 or higher. Behavior outside of
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a debugging session was not affected.
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[1] https://code.woboq.org/linux/linux/kernel/fork.c.html#_do_fork
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[2] https://code.woboq.org/linux/linux/kernel/signal.c.html#do_notify_parent
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[3] https://elixir.bootlin.com/linux/v5.8/source/kernel/fork.c#L2432
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[4] https://elixir.bootlin.com/linux/v5.8/source/kernel/signal.c#L1925
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[5] https://sourceware.org/bugzilla/show_bug.cgi?id=26562
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Fixes: QTBUG-86319
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Change-Id: I2fc68c725ba649218bd9fffd1633863613537d42
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Reviewed-by: Dimitrios Apostolou <jimis@qt.io>
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Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
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Reviewed-by: hjk <hjk@qt.io>
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(cherry picked from commit d1fc991c6e3c45a5f93c925d49e3fe77ce6ce455)
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Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
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---
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src/3rdparty/forkfd/forkfd_linux.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/src/3rdparty/forkfd/forkfd_linux.c b/src/3rdparty/forkfd/forkfd_linux.c
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index 523fbca3ccc..ffe0e9a5e24 100644
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--- a/src/3rdparty/forkfd/forkfd_linux.c
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+++ b/src/3rdparty/forkfd/forkfd_linux.c
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@@ -147,7 +147,7 @@ int system_forkfd(int flags, pid_t *ppid, int *system)
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}
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*system = 1;
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- unsigned long cloneflags = CLONE_PIDFD;
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+ unsigned long cloneflags = CLONE_PIDFD | SIGCHLD;
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pid = sys_clone(cloneflags, &pidfd);
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if (ppid)
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*ppid = pid;
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@@ -171,7 +171,7 @@ int system_forkfd_wait(int ffd, struct forkfd_info *info, int ffdoptions, struct
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{
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siginfo_t si;
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int ret;
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- int options = __WALL | convertForkfdWaitFlagsToWaitFlags(ffdoptions);
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+ int options = convertForkfdWaitFlagsToWaitFlags(ffdoptions);
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if ((options & WNOHANG) == 0) {
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/* check if the file descriptor is non-blocking */
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