Re: [XEN PATCH v3] xen: introduce function type bug_fn_t.

[Julien Grall <julien@xxxxxxx>]

Hi Federico,

On 17/11/2023 08:28, Federico Serafini wrote:
> Introduce function type bug_fn_t. This improves readability and helps
> to validate that the function passed to run_in_exception_handle() has
> the expected prototype.
Hmmm... I read the second part as you will validate the type in 
run_in_exception_handle(). But I can't find such change. How about:
"and could be used to help validating that ..."

No need to send a new revision for that. I can do it on commit.

> Use the newly-intoduced type to address a violation of MISRA
> C:2012 Rule 8.2.
>
> Suggested-by: Julien Grall <julien@xxxxxxx>
> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

> ---
>   xen/arch/arm/traps.c  | 2 +-
>   xen/include/xen/bug.h | 5 +++--
>   2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index ce89f16404..8492e2b7bb 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1236,7 +1236,7 @@ int do_bug_frame(const struct cpu_user_regs *regs, 
> vaddr_t pc)
>   
>       if ( id == BUGFRAME_run_fn )
>       {
> -        void (*fn)(const struct cpu_user_regs *) = (void *)regs->BUG_FN_REG;
> +        bug_fn_t *fn = (void *)regs->BUG_FN_REG;
>   
>           fn(regs);
>           return 0;
> diff --git a/xen/include/xen/bug.h b/xen/include/xen/bug.h
> index e8a4eea71a..cb5138410e 100644
> --- a/xen/include/xen/bug.h
> +++ b/xen/include/xen/bug.h
> @@ -99,6 +99,9 @@ struct bug_frame {
>   
>   #endif
>   
> +struct cpu_user_regs;
> +typedef void bug_fn_t(const struct cpu_user_regs *regs);
> +
If your aim is to validate the type in run_in_exception_handler(), then 
this is defined too late. You will need to define it before "asm/bug.h" 
is included so arch-specific implementations of run_in_exception_handler 
can use it.
Note that for Arm we are using a macro, but others may use a static inline.

Cheers,

--
Julien Grall