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

[Vineet Gupta]

On 12/21/22 11:45, Vineet Gupta wrote:
>
> 4. Kernel with RVV support + user program using original Glibc sigcontext
> In this case, the kernel needs to save vector registers context to
> memory. The user program may encounter memory issues if the user space
> does not reserve enough memory size for the kernel to create the
> sigcontext. However, we can't seem to avoid this case since there is
> no flexible memory area in struct sigcontext for future expansion.

This is not an issue, if we don't change sigcontext (in kernel and 
glibc) - it is essentially the case of existing binaries.
kernel still saves regs on user stack, in rt_sigframe, its just that  
userspace is not able to access them in SA_SIGINFO signal handers.
aarch64 have this implemented this approach and it is likely they can't 
do that either for SVE regs.