linux-kernel - Re: [PATCH 3/5] arm64: Handle TRAP

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Date:   Tue, 6 Sep 2016 17:36:18 -0400
From:   David Long <dave.long@...aro.org>
To:     Catalin Marinas <catalin.marinas@....com>,
        Pratyush Anand <panand@...hat.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux@....linux.org.uk,
        will.deacon@....com, Yang Shi <yang.shi@...aro.org>,
        steve.capper@...aro.org, srikar@...ux.vnet.ibm.com,
        Suzuki K Poulose <suzuki.poulose@....com>,
        vijaya.kumar@...iumnetworks.com, linux-kernel@...r.kernel.org,
        oleg@...hat.com, Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
        wcohen@...hat.com, Anna-Maria Gleixner <anna-maria@...utronix.de>
Subject: Re: [PATCH 3/5] arm64: Handle TRAP_HWBRKPT for user mode as well

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