Question about linux non-standard powerpc SPE FPU

Hi all,




I have one question about kernel / debian operation.

I have computer A1222+ with CPU P1022 ( two e500v2 cores ). It is NG Amiga 
with AmigaOS4, but linux runs here nice too.

P1022 CPU is 32-bit powerpc processor, it has no powerpc FPU but have 
embedded SPE FPU instead.  Also it has SPE SIMD unit. It has no FP or vector
registers, instead it has GPRs extended for 64bit for FPU and SIMD 
operations. So it has different ABI than standard powerpc for floating-point
parameter calls.




There was in past powerpcspe port of Debian. It was dropped somewhere in 
2016, due to excluding of SPE extension from gcc.

Debian 8+ powerpcspe snapshot from these times runs very well, with full 3D 
desktop support. There is customized kernel for A1222+, which was maintained
by xeno74. Last version I found is 5.4. All this is normal and expected.

There are no other native powerpcspe distro ( or at least I am not hear 
about it).




But now I tried standart powerpc Ubuntu 16.04 and also last version of 
powerpc 32-bit Void linux.

If I used custom kernel from xeno74 and standart powerpc distro, it works on
my powerpcspe machine with different ABI.

( So now I have in plan to install more modern Debian from snapshots, or 
Fienix distro, which is based on modern Debian )




Please, how does it works? How is possible that powerpc code with fpu not 
crashes?

I can imagine, that in custom kernel there are soft-float calls. But there 
shoud be some powerpc FPU emulator or what...

Please, do you have any idea?




thans




Martina




-- 
Martina Hřebcová