klibc - May 2021 - 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
only measured by the success 18:35?<asarch> "Psychotics are
consistently
inconsistent. The essence of sanity is to be inconsistently inconsistent

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Dixi quod?
>Jessica Clarke brought out docs saying f8?f15 must be saved, the
>other FPU registers not:
This needs to be fixed in klibc.
>>? klibc does not really support the FPU anyway
>
>? GCC chooses to allocate an FPU register for a pointer value.
This is a curiosity.
>>? 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?
04:41??jrtc27:#debian-x32? hephaistor: re s390x vector registers, reading the
gcc and llvm sources they're
     ?    all call-clobbered by default, only the float parts are call-saved
04:41??jrtc27:#debian-x32? so that's why setjmp/longjmp don't need to
save/restore them
04:42??jrtc27:#debian-x32? there *is* a vector calling convention, but it's
not the default for the ABI,
     ?    it's opt-in, and setjmp/longjmp won't be annotated as such

So we indeed need to only save the registers glibc does.
>@klibc list: as indicated earlier, I can provide a patch if needed
>(though it should be obvious).
bye,
//mirabilos
-- 
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