I've investigated the functions we call in the child side of a vfork()
for implementations that do more than simply place the system
call. Where wrappers exist, they are usually related to handling of Unix
signals or PThread cancellation. The implementations investigated are:
- Bionic (Android)
- FreeBSD
- glibc (Linux)
- MUSL (Linux)
- NetBSD
- OpenBSD
Relating to thread cancellation, NetBSD implements it with an internal
API that does not include Unix signals and Bionic doesn't implement
thread cancellation at all. Their wrapper functions are harmless.
The rest do use Unix signals to implement thread cancellations (called
SIGCANCEL everywhere except OpenBSD, where it's SIGTHR). Therefore, they
all block the application attempts to mask this signal or change its
handler (if they're not buggy). FreeBSD's and MUSL's do some locking in
their implementations[1][2] we really want to bypass, therefore we must
bypass their sigaction() wrappers.
The investigation also showed that the glibc[3] and NetBSD[4] abort()
implementations to be slightly unsafe, but we don't use them
ourselves. We're also adding QProcess::failChildProcessModifier() so
users won't have to resort to abort().
[1] https://github.com/bminor/musl/blob/master/src/signal/sigaction.c
[2] https://github.com/freebsd/freebsd-src/blob/main/lib/libthr/thread/thr_sig.c
[3] https://codebrowser.dev/glibc/glibc/stdlib/abort.c.html
[4] https://github.com/NetBSD/src/blob/trunk/lib/libc/stdlib/abort.c
Task-number: QTBUG-113822
Change-Id: I9201d9ecf52f4146bb04fffd17651123800e15a4
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit e71c226d6f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
0dc6ccbc5c