Re: [PATCH v2 01/20] target/arm: Add commentary for CPUARMState.exclusive_high

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi,

On 26/5/23 01:25, Richard Henderson wrote:
> Document the meaning of exclusive_high in a big-endian context,
> and why we can't change it now.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   target/arm/cpu.h | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> index d469a2637b..4e16eab82e 100644
> --- a/target/arm/cpu.h
> +++ b/target/arm/cpu.h
> @@ -677,8 +677,15 @@ typedef struct CPUArchState {
>           uint64_t zcr_el[4];   /* ZCR_EL[1-3] */
>           uint64_t smcr_el[4];  /* SMCR_EL[1-3] */
>       } vfp;
> +
>       uint64_t exclusive_addr;
>       uint64_t exclusive_val;
> +    /*
> +     * Contains the 'val' for the second 64-bit register of LDXP, which comes
> +     * from the higher address, not the high part of a complete 128-bit value.
> +     * This is perhaps confusingly named, but the name is now baked into the
> +     * migration format.
> +     */
>       uint64_t exclusive_high;

Can't we rename the field if we add the old name to check_fields_match()
in scripts/vmstate-static-checker.py?

Juan, could we store this renamed information directly in the code in
VMState? Maybe adding some VMSTATE_KEY_ALIAS(_old_key, _new_key) macro
and have the migration/ code magically deal with that :)

I.e. here:

   VMSTATE_KEY_ALIAS("exclusive_val", high_addr),