Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT_TIME

[Paul Burton]

Hi Jason,

On Tue, Dec 31, 2019 at 08:10:56PM -0800, Paul Burton wrote:
> I'm still not quite sure *why* this happens; perhaps GCC just decides it
> doesn't need to save & restore $gp/$28 when it spots that it's being
> "used" for __current_thread_info (even though that's never actually
> referenced in the VDSO)?

Ah:

> After defining a global register variable, for the current compilation
> unit:
> 
> - If the register is a call-saved register, call ABI is affected: the
>   register will not be restored in function epilogue sequences after
>   the variable has been assigned. Therefore, functions cannot safely
>   return to callers that assume standard ABI.

https://gcc.gnu.org/onlinedocs/gcc/Global-Register-Variables.html

That makes sense then. What doesn't make sense is how this ever
worked. A question for another day...

Thanks,
    Paul