On 19/12/2020 22:21, Steffen Nurpmeso wrote:
Steffen Nurpmeso wrote in
<20201219172838.1B-WB%steffen@xxxxxxxxxx>:
|Long story short, after falsely accusing BSD make of not working
After dinner i shortened it a bit more, and attach it again, ok?
It is terrible, but now less redundant than before.
Sorry for being so terse, that problem crosses my head for about
a week, and i was totally mislead and if you bang your head
against the wall so many hours bugs or misbehaviours in a handful
of other programs is not the expected outcome.
I think a minimal test case is simply
all:
$(SHELL) -c 'trap "echo TTOU" TTOU; set -m; echo all good'
unless I accidentally oversimplified.
The SIGTTOU is caused by setjobctl's xtcsetpgrp(fd, pgrp) call to make
its newly started process group the foreground process group when job
control is enabled, where xtcsetpgrp is a wrapper for tcsetpgrp. (That's
in dash, the other variants may have some small differences.) tcsetpgrp
has this little bit in its specification:
Attempts to use tcsetpgrp() from a process which is a member of
a background process group on a fildes associated with its con‐
trolling terminal shall cause the process group to be sent a
SIGTTOU signal. If the calling thread is blocking SIGTTOU sig‐
nals or the process is ignoring SIGTTOU signals, the process
shall be allowed to perform the operation, and no signal is
sent.
Ordinarily, when job control is enabled, SIGTTOU is ignored. However,
when a trap action is specified for SIGTTOU, the signal is not ignored,
and there is no blocking in place either, so the tcsetpgrp() call is not
allowed.
The lowest impact change to make here, the one that otherwise preserves
the existing shell behaviour, is to block signals before calling
tcsetpgrp and unblocking them afterwards. This ensures SIGTTOU does not
get raised here, but also ensures that if SIGTTOU is sent to the shell
for another reason, there is no window where it gets silently ignored.
Another way to fix this is by not trying to make the shell start a new
process group, or at least not make it the foreground process group.
Most other shells appear to not try to do this.
Cheers,
Harald van Dijk
