On Tue, 2024-11-05 at 08:39 -0700, Warner Losh wrote: > On Thu, Oct 24, 2024 at 2:00 PM Ilya Leoshkevich <i...@linux.ibm.com> > wrote: > > Attaching to the gdbstub of a running process requires stopping its > > threads. For threads that run on a CPU, cpu_exit() is enough, but > > the > > only way to grab attention of a thread that is stuck in a long- > > running > > syscall is to interrupt it with a signal. > > > > Reserve a host realtime signal for this, just like it's already > > done > > for TARGET_SIGABRT on Linux. This may reduce the number of > > available > > guest realtime signals by one, but this is acceptable, since there > > are > > quite a lot of them, and it's unlikely that there are apps that > > need > > them all. > > > > Set signal_pending for the safe_sycall machinery to prevent > > invoking > > the syscall. This is a lie, since we don't queue a guest signal, > > but > > process_pending_signals() can handle the absence of pending > > signals. > > The syscall returns with QEMU_ERESTARTSYS errno, which arranges for > > the automatic restart. This is important, because it helps avoiding > > disturbing poorly written guests. > > > > Signed-off-by: Ilya Leoshkevich <i...@linux.ibm.com> > > --- > > bsd-user/signal.c | 12 ++++++++++++ > > include/user/signal.h | 2 ++ > > linux-user/signal.c | 11 +++++++++++ > > 3 files changed, 25 insertions(+) > > > > diff --git a/bsd-user/signal.c b/bsd-user/signal.c > > index a2b11a97131..992736df5c5 100644 > > --- a/bsd-user/signal.c > > +++ b/bsd-user/signal.c > > @@ -49,6 +49,8 @@ static inline int sas_ss_flags(TaskState *ts, > > unsigned long sp) > > on_sig_stack(ts, sp) ? SS_ONSTACK : 0; > > } > > > > +int host_interrupt_signal = SIGRTMAX; > > + > > > > > I'd be tempted to use SIGRTMAX + 1 or even TARGET_NSIG. 127 or 128 > would > work and not overflow any arrays (or hit any bounds tests) I'd likely > use SIGRTMAX + 1, > though, since it avoids any edge-cases from sig == NSIG that might be > in the code > unnoticed. > > Now, having said that, I don't think that there's too many (any?) > programs we need > to run as bsd-user that have real-time signals, much less one that > uses SIGRTMAX, > but stranger things have happened. But it is a little wiggle room > just in case. > > Other than that: > > Reviewed-by: Warner Losh <i...@bsdimp.com>
Thanks for the suggestion, I'll use SIGRTMAX + 1 in v2.
