On Fri, Oct 08, 2021 at 04:45:44PM +0000, Alan Hayward wrote: > > On 8 Oct 2021, at 16:28, Mark Brown <broonie@xxxxxxxxxx> wrote: > > On Fri, Oct 08, 2021 at 02:11:46PM +0000, Alan Hayward wrote: > >> Can NT_ARM_SSVE return a fpsimd? > > It's documented that way for simplicity but in the current > > implementation it won't ever actually do so in practice. The > > only case where I could see that it might happen would be if we > > change the syscalls to stay in streaming mode over syscall, in > > that case we could do as we do for SVE and preserve FPSIMD > > registers only. At present we drop out of streaming mode if we > > get a syscall with it enabled so it's a non-issue, if people > > agree that that's the right thing for the syscalls then we should > > update the documentation to specify this since otherwise we'll > > doubtless catch someone by surprise if we ever manage to start > > doing it in the future. > ….or it’ll end up executing some code that was written to cope with fpsimd, but has never been > run. Might be worth making it explicit in the documentation. I will if/when it gets fixed that way. Actually, while looking at that code I was tempted to remove the support for returning FPSIMD only registers via NT_ARM_SVE entirely and just always convert to SVE format - I'm not sure what the use case was there? It's not a pressing thing but it seemed like it was a bit of an implementation detail that we were revealing.
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