Auto-enabling V unit and/or use of elf attributes (was Re: Adding V-ext regs to signal context w/o expanding kernel struct sigcontext to avoid glibc ABI break)

[Andy Chiu]

Hey Conor,

On Mon, Jan 23, 2023 at 8:18 PM Conor Dooley <conor.dooley at microchip.com> wrote:
> Meh, all of these discussions seem worthwhile to me!
>
> Now that things have died down though, I'm curious - what are your
> plans? Still going to submit another version of this series?
>
Yes, we have implemented most of it and are planning to send the
series in recent days. Thanks to Vineet, he is helping me to sort out
some last bits before the submission. Here are some points related to
this thread that will be in v13:

1. allocate V context in the first-use trap
2. drop prctl V-controlling because it conflicts with the idea of the
first-use trap.
2. sigframe/ptrace will not have V context if a process's VS is off
3. If the kernel is compiled with CONFIG_RISCV_ISA_V enabled, then the
auxv always reports size of the sigframe as if there is a V context.
This is because user space may need information from auxv to set up an
alternative signal stack, and it may not know if it would use V. ARM64
also reports the size assuming all extensions are used.

Thanks,
Andy