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Subject: Re: [PATCH 3/5] arm64: Handle TRAP_HWBRKPT for user mode as well
To: Catalin Marinas <catalin.marinas@arm.com>,
        Pratyush Anand <panand@redhat.com>
References: <cover.1470114993.git.panand@redhat.com>
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 <20160906161139.GG19605@e104818-lin.cambridge.arm.com>
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        will.deacon@arm.com, Yang Shi <yang.shi@linaro.org>,
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        Suzuki K Poulose <suzuki.poulose@arm.com>,
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From: David Long <dave.long@linaro.org>
Message-ID: <57CF36D2.4010404@linaro.org>
Date: Tue, 6 Sep 2016 17:36:18 -0400
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On 09/06/2016 12:11 PM, Catalin Marinas wrote:
> On Tue, Aug 02, 2016 at 11:00:07AM +0530, Pratyush Anand wrote:
>> --- a/arch/arm64/kernel/debug-monitors.c
>> +++ b/arch/arm64/kernel/debug-monitors.c
>> @@ -246,6 +246,8 @@ static void send_user_sigtrap(int si_code)
>>   static int single_step_handler(unsigned long addr, unsigned int esr,
>>   			       struct pt_regs *regs)
>>   {
>> +	bool handler_found = false;
>> +
>>   	/*
>>   	 * If we are stepping a pending breakpoint, call the hw_breakpoint
>>   	 * handler first.
>> @@ -253,7 +255,14 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>>   	if (!reinstall_suspended_bps(regs))
>>   		return 0;
>>
>> -	if (user_mode(regs)) {
>> +#ifdef	CONFIG_KPROBES
>> +	if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
>> +		handler_found = true;
>> +#endif
>> +	if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
>> +		handler_found = true;
>> +
>> +	if (!handler_found && user_mode(regs)) {
>>   		send_user_sigtrap(TRAP_HWBKPT);
>
> Could we register kprobe_single_step_handler() via register_set_hook()
> and only invoke call_step_hook() above?
>

I seem to recall a criticism of doing that in a much earlier kprobes64 
patch of mine.  The concern was that it would cause unnecessarily more 
kernel functions to be kprobes-blacklisted.  Hence the hardcoded check 
and call.

-dl