[PATCH v2 3/6] armv8: Force SP_ELx stack pointer usage

Tom Rini trini at konsulko.com
Wed Mar 2 23:41:20 CET 2022

On Fri, Feb 11, 2022 at 11:29:36AM +0000, Andre Przywara wrote:

> In ARMv8 we have the choice between two stack pointers to use: SP_EL0 or
> SP_ELx, which is banked per exception level. This choice is stored in
> the SP field of PState, and can be read and set via the SPSel special
> register. When the CPU takes an exception, it automatically switches to
> the SP_ELx stack pointer.
> Trusted Firmware enters U-Boot typically with SPSel set to 1, so we use
> SP_ELx all along as our sole stack pointer, both for normal operation and
> for exceptions.
> But if we now for some reason enter U-Boot with SPSel cleared, we will
> setup and use SP_EL0, which is fine, but leaves SP_ELx uninitialised.
> When we now take an exception, we try to save the GPRs to some undefined
> location, which will usually end badly.
> To make sure we always have SP_ELx pointing to some memory, set SPSel
> to 1 in the early boot code, to ensure safe operation at all times.
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>

Applied to u-boot/next, thanks!

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