Re: [RFC PATCH] target/arm: allow gdb to read ARM_CP_NORAW regs

[Peter Maydell <peter.maydell@linaro.org>]

On Wed, 7 May 2025 at 17:58, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> Before this we suppress all ARM_CP_NORAW registers being listed under
> GDB. This includes useful registers like CurrentEL which gets tagged
> as ARM_CP_NO_RAW because it is one of the ARM_CP_SPECIAL_MASK
> registers. These are registers TCG can directly compute because we
> have the information at compile time but until now with no readfn.
>
> Add a .readfn to return the CurrentEL and then loosen the restrictions
> in arm_register_sysreg_for_feature to allow ARM_CP_NORAW registers to
> be read if there is a readfn available.

The primary use case for NO_RAW is "system instructions" like
the TLB maintenance insns. These don't make sense to expose
to a debugger.

If we want the gdbstub access to system registers to be
more than our current "we provide the ones that are easy",
then I think I'd like to see a bit more up-front analysis of
what the gdbstub needs and whether we've got into a bit of
a mess with our ARM_CP_* flags that we could straighten out.

thanks
-- PMM