[PATCH] Add a dummy register to sbi_trap_regs

[Jessica Clarke]

On 9 Jan 2025, at 23:52, Chao-ying Fu <icebergfu at gmail.com> wrote:
> 
> SBI_TRAP_CONTEXT_SIZE becomes a multiple of 8 bytes for RV32
> or 16 bytes for RV64, so we have sp aligned to 8 or 16 bytes
> to have better performance on some platforms,
> ---
> include/sbi/sbi_trap.h | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/sbi/sbi_trap.h b/include/sbi/sbi_trap.h
> index d5182bf..df99d8e 100644
> --- a/include/sbi/sbi_trap.h
> +++ b/include/sbi/sbi_trap.h
> @@ -84,8 +84,10 @@
> #define SBI_TRAP_REGS_mstatus 33
> /** Index of mstatusH member in sbi_trap_regs */
> #define SBI_TRAP_REGS_mstatusH 34
> +/** Index of a dummy register */
> +#define SBI_TRAP_REGS_dummy 35
> /** Last member index in sbi_trap_regs */
> -#define SBI_TRAP_REGS_last 35
> +#define SBI_TRAP_REGS_last 36
> 
> /** Index of cause member in sbi_trap_info */
> #define SBI_TRAP_INFO_cause 0
> @@ -194,6 +196,8 @@ struct sbi_trap_regs {
> unsigned long mstatus;
> /** mstatusH register state (only for 32-bit) */
> unsigned long mstatusH;
> + /** a dummy register */
> + unsigned long dummy;

This is ugly and fragile for when changes are made to the structure.
Either make SBI_TRAP_CONTEXT_SIZE round up the size or, if for some
reason that doesn’t work, you can always make the struct type
overaligned.

Also, sp is aligned to 16 bytes anyway, that’s mandated by the ABI. So
I don’t understand your justification.

Strong NAK.

Jess