On 11/5/24 15:50, Ilya Leoshkevich wrote:
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.
That can't be right -- SIGRTMAX+1 is not a valid signal.
r~
