[cfarm-users] cfarm95: RISC-V host with RVV 1.0 vector extension

[Andy Polyakov]

>>> We are happy to announce the addition of cfarm95, a BPI-F3 machine
>>> from BananaPi. This RISC-V machine is based on a SpacemiT K1 SoC
>>> with 8 SpacemiT X60 cores. The most interesting feature of this
>>> hardware is its implementation of the RVV 1.0 vector extension;
>>
>> Cool! There is a problem though. If an asynchronous signal, e.g. SIGALRM, is
>> delivered to a thread that is executing vector instruction the application
>> crashes with SIGILL. I assume that return-from-signal code path doesn't
>> restore some processor state bit. Just in case anybody runs into it...
> 
> Interesting!  Do you think the issue comes from the compiler, from the
> libc, or from the kernel?  Which compiler are you using?

As implied I blame the kernel. I naturally might be wrong, but I base 
the conclusion on the assumption that relevant processor state bits 
ought to be privileged(*) and ultimately it's the kernel that reigns 
over that. It can't be a compiler issue, because I write in assembly. 
Just in case for reference, on a practical note. If I execute under 
debugger, the crashing instruction is always different. Well, it has to 
be a vector one, but other than that it's just random.

Cheers.

(*) If they're not, then applications would be able to spy on each 
other's vector register contents, which may not be the case.