Adding V-ext regs to signal context w/o expanding kernel struct sigcontext to avoid glibc ABI break

[Vineet Gupta]

Hi Andy,

On 12/28/22 02:53, Andy Chiu wrote:
> On Fri, Dec 23, 2022 at 4:28 AM Vineet Gupta <vineetg at rivosinc.com> wrote:
>> This approach looks perfect. Lets productize it to fold this patch into
>> the respective patch(es).
>> We would then need fixups to not unconditionally enable V on fork/execve
>> and hook that up to a prctl.
>> Let me work on that and provide something on top of your series.
> Hi Vineet, I have included the approach into the Vector series
> according to suggestions, which makes it formaler than the PoC one.
> Additionally, I picked up your prctl patch and added a kconfig to
> compile a kernel that won't unconditionally enable V. Please tell me
> if this does not seem right to you.

The prctl support in there is really rudimentary and incomplete. There's 
more work needed to use the dynamic state of enablement - for say signal 
frame etc. The new Kconfig CONFIG_RISCV_VSTATE_INIT_ALL seems like a 
hack bolted on top.
It would be best to drop it in the current state and rework properly 
based on your patches.

> I will submit the series if this
> seems well to you and let's discuss some more details further in that
> thread. Here is the tree, thanks:
>
> https://github.com/sifive/riscv-linux/tree/dev/andyc/for-next-v13.1-newapi-prctl

I would also suggesting dropping the 2 patches for in-kernel enablement 
for your submission as it might require some more thinking/design and 
builds naturally on top of the baseline patches.

Thx,
-Vineet