Question about mouse grabbing and X on Apple hardware.

[Nathan Whitehorn]

On 08/03/11 10:12, Super Bisquit wrote:
>
>
> On Wed, Aug 3, 2011 at 4:13 AM, Matthieu Herrb <matthieu.herrb at laas.fr 
> <mailto:matthieu.herrb at laas.fr>> wrote:
>
>     On Wed, Aug 03, 2011 at 03:18:22AM -0400, Super Bisquit wrote:
>     > On Wed, Aug 3, 2011 at 1:49 AM, Matthieu Herrb
>     <matthieu.herrb at laas.fr <mailto:matthieu.herrb at laas.fr>>wrote:
>     >
>     > > On Tue, Aug 02, 2011 at 07:00:12PM -0400, Super Bisquit wrote:
>     > > > My apologies before hand.
>     > > > I'm wondering how the OpenBSD PPC port dealt with the mouse
>     > > > grabbing.
>     > >
>     > > Sorry, I don't understand the question. What kind of grabbing
>     are you
>     > > talking about? At the X server level, there is nothing MI in this
>     > > area.
>     > >
>     >
>     > The mouse pointer will get caught on the left edge of the screen
>     and then
>     > only a restart of X allows the pointer to be free again.
>     > And thanks for the reply.
>
>     On OpenBSD/macppc, I don't remember having seen that problem, but I
>     may be wrong, and I don't use it on a daily basis anymore. We had it
>     on other architectures though.
>
>     The main reason for this bug is the SIGIO handler in the
>     Xserver. By default X processes all the data from the mouse driver in
>     the signal handler attached to SIGIO. With the new pointer
>     acceleration code this includes a good amount of floating point
>     computations, and may even trigger some MMX/SSE2 operations in
>     libpixman to repaint the pointer on the screen.
>
>     If your signal handling code doesn't preserve the FPU (and the
>     altivec) registers, this is likely to trigger the bug.
>
>     The easiest solution is to disable the code that uses SIGIO to
>     asynchronously update the pointer. pass --disable-use-sigio-by-default
>     to configure for this, or set the option in xorg.conf.
>
>     >
>     >
>     > >
>     > > > I would like- if possible and with permission- to use the
>     same method
>     > > with
>     > > > FreeBSD PowerPC to solve/prevent the grabbing.
>     > > > Again, my apologies beforehand if this post to the mailing
>     list seems or
>     > > is
>     > > > out of place.
>
>
>     --
>     Matthieu Herrb
>
>
> Thank you for the help and tell DeRaadt thanks also. I'm forwarding 
> this mail to the FreeBSD PowerPC list for the others to see it.
>

That's a really fascinating problem. Our signal handling code explicitly 
preserves FP and Altivec registers. Our setjmp()/longjmp() code does 
not, for various reasons, but that shouldn't be related to this problem. 
Are you sure this actually solves the problem permanently?
-Nathan