[PATCH v2 11/11] arm64: debug: remove debug exception registration infrastructure

[Ada Couprie Diaz]

On 21/05/2025 10:38, Will Deacon wrote:

> On Mon, May 12, 2025 at 06:43:26PM +0100, Ada Couprie Diaz wrote:
>> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
>> index 50d7a6a75f45..ce20f46e08cb 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_brk_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM)
>> -		return ubsan_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
>> -#endif
>> -	return bug_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
> The early bug handler is now only called if the brk immediate matches,
> but I couldn't spot any problems with that.

Correct, as far as I can tell the behaviour is unchanged for a 
fall-through :
`bug_brk_handler()` would have called `report_bug()`, which would
not have found a non-BUG BRK and bailed early with BUG_TRAP_TYPE_NONE,
leading `bug_brk_handler()` to return `DBG_HOOK_ERROR`.

Now, we would return `DBG_HOOK_ERROR` anyway if it's not an immediate we 
know how to handle. (This also seems to match better with the 
expectations of the comment in `is_valid_bugaddr()`, in `kernel/traps.c` !)

> Will

Happy to have my logic checked or add a mention in a commit message
(either this one, or patch 02 ?)

Thanks,
Ada