X11 CURRENT and non-altivec based macs

[Nathan Whitehorn]

Nathan Whitehorn wrote:
> Andreas Tobler wrote:
>> Hi all,
>>
>> I discovered a nasty issue which hits all non-altivec based ppc 
>> systems, mostly G3, there are some 7400 w/o altivec, which want to 
>> use X11.
>>
>> When you upgraded to -CURRENT and latest Xorg stuff including 
>> pixman-0.15.2 you'll hit a coredump when starting X with a 
>> recent/decent wm.
>>
>> Analyzing the coredump of Xorg led me to this:
>>
>> #0  0x21b9e494 in pixman_have_vmx () from 
>> /usr/local/lib/libpixman-1.so.9 Cannot find new threads: generic error
>>
>> A closer look into the build of pixman showed me that it was built 
>> with altivec support. No go on my G3.
>>
>> I helped myself with the below patch in the ports Makefile. But I do 
>> not know if the other ppc users 'have' real working Altivec support. 
>> We have Altivec support since a few moons in the kernel. Thanks Nathan!
>> I know we build the kernel w/o Altivec. How do we want to build user 
>> applications/packages? Also w/o altivec or with?
>>
>> We can either adjust the ports Makefile or try to fixup the pixman 
>> sources. They are currently 'fixed' for apple and linux only. Fixed 
>> in terms of runtime detection of Altivec capability. (see 
>> pixman/pixman-pict.c)
>>
>> Do we have already a sysctl telling us we have altivec, I do not see 
>> such a sysctl?
>>
>> Suggestions?
>> In case of disabling vmx on all ppc based systems, who do I need to 
>> ping, x11 at freebsd.org?
> Could you provide some more information than this (versions of X11, 
> pixman and name/version of the window manager)? I just tested the 
> non-Apple/non-Linux VMX detection code in pixman and it appears to 
> work properly.
>
> Providing a sysctl turned out to be problematic since PowerPC CPUs, 
> unlike x86, do not provide a features mask. You either have to have a 
> table of CPUs and capabilities, or try the instructions you want to 
> know about and see if you get SIGILL. We could do this in the kernel 
> and provide a sysctl, but you can do the more-portable SIGILL just as 
> easily from userspace, and this is what pixman currently does.
I managed to reproduce this. There's something weird going on that I'll 
look into. Thanks for investigating!
-Nathan