Bug 3380

Created attachment 3995 [details]
early version of the generating script

I had a minute right now so i did the generating script. I'll try to integrate
it, add ppc64 support and in general just clean it up some time this week when
I'll have a little bit more time. I'm attaching in case someone has more spare
time than I do. Ah, and the offset computation in BRANCH_OFFSET is more
pseudo-code than assembly right now ;)

Created attachment 4014 [details]
script generating dispatch code for ppc32 

k, as far as ppc32 generation, this should be it.

I managed to build libGL with this, but when running glxinfo, it dies with
SIGILL in glGetString (the first gl[^X] function called).

Created attachment 4026 [details] [review]
Mesa patch to use generated PPC assembly

Testing instructions:

* Save the current version of the generator script as
Mesa/src/mesa/glapi/gl_ppc_asm.py
* Apply the Mesa patch
* make -C Mesa/src/mesa/glapi
* Rebuild libGL (you may have to manually remove at least
Mesa/src/mesa/main/dispatch.o) and watch glxinfo die with SIGILL ;)

Ok, I suppose I can fix that :) But first I need to understand how the whole 
thing is supposed to work... It's not very clear between python stuff 
generating asm stubs, magic macros, etc etc... (btw. I think there are bugs 
there but I'll have to dbl check when I understand what the stuff is actually 
supposed to do in the first place). 
 
Can somebody explain me how it works without the asm stuff (the pure C stuff) 
and what the "optimized" version is supposed to do ? I have enabled 
-DGLX_USE_TLS and the resulting stubs look not too bad, but I could probably 
make them a bit better with asm (like doing a proper tail call). 
 
However, I suppose that if I could acutally generate code at runtime, I could 
do even better and generating a branch island that loads the absolute address 
of the target and branch to it (basically about 4 or 5 insns in 32 bits, maybe 
a bit more in 64 bits). But first I need to get a bit more familiar with how 
this all fits together in the mesa source, so far I'm just confused :) 
 

Added myself to cc as this one looks promising.

Sorry, I didn't go back on that yet... I read the code for about 2 hours and
just got more confused about what is it supposed to do. Some comments would have
been useful. I might get back to it at one point, I'm a bit too busy at the moment

Ian Romanick 
Do you still experience this issue with newer soft ?
Please check the status of your issue.

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