Debian #943425: [s390x] setjmp/longjmp do not save/restore all registers in use (was Use of $v10 register (was Re: klibc: [s390x] SIGSEGV in mksh testcase funsub-2))

Dixi quod…

>So, setjmp/longjmp in klibc save f1/f3/f5/f7 (as shown on Wikipedia
>https://en.wikipedia.org/wiki/Calling_convention#IBM_System/360_and_successors
>“the z/Architecture ABI,[11] used in Linux” a page down), while
>glibc’s save f8–f15 instead.

Jessica Clarke brought out docs saying f8‥f15 must be saved, the
other FPU registers not:
https://refspecs.linuxfoundation.org/ELF/zSeries/lzsabi0_zSeries.html#AEN413

This matches what glibc does. Maybe an s390x porter wishes to fix
Wikipedia?

>https://share.confex.com/share/124/webprogram/Handout/Session16897/SHARE_Seattle_2015_SIMD.pdf
>shows that the vector registers overlap and extend the FPU registers.

>• is register v10 (vector extension) even supposed to be used?

This needs to be answered, I guess, because…

>• klibc does not really support the FPU anyway

… GCC chooses to allocate an FPU register for a pointer value.

>• the half of v10 that equals f10 just HAPPENS to be saved by
>  glibc, but what if the upper half, that is outside of the FPU,
>  is used?

The question here is, does GCC only use the halves of the half
of the vector registers that match the FPU registers?

@klibc list: as indicated earlier, I can provide a patch if needed
(though it should be obvious).

bye,
//mirabilos
-- 
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22:21⎜<asarch> And the distance between the craziness and geniality is
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inconsistent. The essence of sanity is to be inconsistently inconsistent