[parisc-linux] how to handle ERESTART_RESTARTBLOCK ?

[Randolph Chung <randolph@tausq.org>]

I commited some broken code into 2.6 cvs just now, so now i need some
help to fix it ;-) sorry for the verbose explanation below, but i need
to write this down to make sure i understand it myself :-)

Our signal handling code was not handling ERESTART_RESTARTBLOCK
correctly. as far as I can tell, the semantics of this is that if a
syscall function returns with that error code, we are supposed to
restart the syscall, but with a new syscall number
(__NR_restart_syscall -- which we don't define at the moment)

The problem is that our syscall mechanism doesn't really allow this
(afaict). Our syscall sequence looks like this:

    ble <address of gateway page>
    ldi <syscall number>, %r20
    [ we enter the kernel at this point ]

and the way we handle restarting other syscalls is to set the iaoq back
by two insns, so we do the ble again. there's a comment about this in
the code (signal.c)

                        /* Hooray for delayed branching.  We don't
                           have to restore %r20 (the system call
                           number) because it gets loaded in the delay
                           slot of the branch external instruction. */
                        regs->gr[31] -= 8;

which is all well and good, except i don't see how we can change the
syscall number to restart it for the ERESTART_RESTARTBLOCK case.

why is it bad to just call sys_restart_syscall directly from
do_signal()?

any suggestions on how to handle this properly?

thanks
randolph
-- 
Randolph Chung
Debian GNU/Linux Developer, hppa/ia64 ports
http://www.tausq.org/