Re: [PATCH] firmware: fw_base: make stack guard setup conditional on Zkr

[Yu-Chine Peter Lin <peter.lin@sifive.com>]

Hi Joel,

Thanks for the patch,

On 3/31/26 5:59 PM, buenocalvachejoel@gmail.com wrote:
> From: Joel Bueno <buenocalvachejoel@gmail.com>
> 
> Zkr isn't explicitly selected as a mandatory extension to run OpenSBI
> as per: docs/platform_requirements.md
> 
> Since this happens very early on the boot flow of OpenSBI where the
> dynamic extension checks haven't yet happened, we must guard the Zkr
> stack setup behind an ifdef block so that it only gets compiled for
> targets that do actually have the extension.
> 
> Signed-off-by: Joel Bueno <buenocalvachejoel@gmail.com>
> ---
>   firmware/fw_base.S | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/firmware/fw_base.S b/firmware/fw_base.S
> index 63bb4473..9ea93907 100644
> --- a/firmware/fw_base.S
> +++ b/firmware/fw_base.S
> @@ -107,6 +107,7 @@ _bss_zero:
>   	add	s4, s4, __SIZEOF_POINTER__
>   	blt	s4, s5, _bss_zero
>   
> +#if defined(__riscv_zkr)
>   	/* Trying to initialize the stack guard via the Zkr extension */
>   	lla	t0, __stack_chk_guard_done
>   	csrw	CSR_MTVEC, t0
> @@ -130,6 +131,7 @@ __stack_chk_guard_loop:
>   	j	__stack_chk_guard_done
>   	.align 3
>   __stack_chk_guard_done:
> +#endif

The current trap-based detection mechanism is intentional and works 
correctly
on systems both with and without Zkr.
Using #ifdef guards would break binary portability, e.g. using single 
binary on
heterogeneous systems (e.g., SMP with mixed Zkr/non-Zkr cores)

Regards,
Peter Lin

>   
>   	/* Setup temporary trap handler */
>   	lla	s4, _start_hang


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