Re: [PATCH v4 13/13] arm64: debug: remove debug exception registration infrastructure

[Will Deacon <will@kernel.org>]

On Fri, Jun 20, 2025 at 10:12:07PM +0100, Ada Couprie Diaz wrote:
> Now that debug exceptions are handled individually and without the need
> for dynamic registration, remove the unused registration infrastructure.
> 
> This removes the external caller for `debug_exception_enter()` and
> `debug_exception_exit()`.
> Make them static again and remove them from the header.
> 
> Remove `early_brk64()` as it has been made redundant by
> (arm64: debug: split brk64 exception entry) and is not used anymore.
> Note : in `early_brk64()` `bug_brk_handler()` is called unconditionally
> as a fall-through, but now `call_break_hook()` only calls it if the
> immediate matches.
> This does not change the behaviour in early boot, as if
> `bug_brk_handler()` was called on a non-BUG immediate it would return
> DBG_HOOK_ERROR anyway, which `call_break_hook()` will do if no immediate
> matches.
> 
> Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> Tested-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
> ---
>  arch/arm64/include/asm/debug-monitors.h |  2 -
>  arch/arm64/include/asm/exception.h      |  6 ---
>  arch/arm64/include/asm/system_misc.h    |  4 --
>  arch/arm64/kernel/debug-monitors.c      |  3 --
>  arch/arm64/kernel/entry-common.c        |  4 +-
>  arch/arm64/kernel/traps.c               | 26 +-----------
>  arch/arm64/mm/fault.c                   | 53 -------------------------
>  7 files changed, 3 insertions(+), 95 deletions(-)

[...]

> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index 654c8ea46ec6..d6c5268e6947 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -1101,29 +1101,5 @@ int ubsan_brk_handler(struct pt_regs *regs, unsigned long esr)
>  }
>  #endif
>  
> -/*
> - * Initial handler for AArch64 BRK exceptions
> - * This handler only used until debug_traps_init().
> - */
> -int __init early_brk64(unsigned long addr, unsigned long esr,
> -		struct pt_regs *regs)
> -{
> -#ifdef CONFIG_CFI_CLANG
> -	if (esr_is_cfi_brk(esr))
> -		return cfi_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
> -#endif
> -#ifdef CONFIG_KASAN_SW_TAGS
> -	if ((esr_brk_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
> -		return kasan_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
> -#endif
> -#ifdef CONFIG_UBSAN_TRAP
> -	if (esr_is_ubsan_brk(esr))
> -		return ubsan_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
> -#endif
> -	return bug_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
> -}
> -
>  void __init trap_init(void)
> -{
> -	debug_traps_init();
> -}
> +{}

nit: I think you can actually just remove trap_init() entirely as there's
a weak definition in init/main.c

With that:

Reviewed-by: Will Deacon <will@kernel.org>

Will