linux-kernel - Re: [PATCH] Function stack size and its name mismatch in arm64

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Date:   Wed, 31 Jul 2019 14:56:36 +0100
From:   James Morse <james.morse@....com>
To:     Jiping Ma <jiping.ma2@...driver.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
        linux-kernel@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] Function stack size and its name mismatch in arm64

Hi Jiping,

(CC: +linux-arm-kernel)

On 31/07/2019 11:57, Steven Rostedt wrote:
> On Wed, 31 Jul 2019 17:04:37 +0800
> Jiping Ma <jiping.ma2@...driver.com> wrote:

> Note, the subject is not properly written, as it is missing the
> subsystem. In this case, it should start with "tracing: "
> 
> 
>> The PC of one the frame is matched to the next frame function, rather
>> than the function of his frame.
> 
> The above change log doesn't make sense. I have no idea what the actual
> problem is here. Why is this different for arm64 and no one else? Seems
> the bug is with the stack logic code in arm64 not here.

Please copy the mailing list for the arm64 arch code too.

Is this thing a recent change? arm64's stacktrace code gained some better protection for
loops at -rc2.


Thanks,

James


>> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
>> index 5d16f73898db..ed80b95abf06 100644
>> --- a/kernel/trace/trace_stack.c
>> +++ b/kernel/trace/trace_stack.c
>> @@ -40,16 +40,28 @@ static void print_max_stack(void)
>>  
>>  	pr_emerg("        Depth    Size   Location    (%d entries)\n"
>>  			   "        -----    ----   --------\n",
>> +#ifdef CONFIG_ARM64
> 
> We do not allow arch specific defines in generic code. Otherwise this
> would blow up and become unmaintainable. Not to mention it makes the
> code ugly and hard to follow.
> 
> Please explain the problem better. I'm sure there's much better ways to
> solve this than this patch.
> 
> Thanks,
> 
> -- Steve
> 
> 
> 
>> +			   stack_trace_nr_entries - 1);
>> +#else
>>  			   stack_trace_nr_entries);
>> -
>> +#endif
>> +#ifdef CONFIG_ARM64
>> +	for (i = 1; i < stack_trace_nr_entries; i++) {
>> +#else
>>  	for (i = 0; i < stack_trace_nr_entries; i++) {
>> +#endif
>>  		if (i + 1 == stack_trace_nr_entries)
>>  			size = stack_trace_index[i];
>>  		else
>>  			size = stack_trace_index[i] - stack_trace_index[i+1];
>>  
>> +#ifdef CONFIG_ARM64
>> +		pr_emerg("%3ld) %8d   %5d   %pS\n", i-1, stack_trace_index[i],
>> +				size, (void *)stack_dump_trace[i-1]);
>> +#else
>>  		pr_emerg("%3ld) %8d   %5d   %pS\n", i, stack_trace_index[i],
>>  				size, (void *)stack_dump_trace[i]);
>> +#endif
>>  	}
>>  }
>>  
>> @@ -324,8 +336,11 @@ static int t_show(struct seq_file *m, void *v)
>>  		seq_printf(m, "        Depth    Size   Location"
>>  			   "    (%d entries)\n"
>>  			   "        -----    ----   --------\n",
>> +#ifdef CONFIG_ARM64
>> +			   stack_trace_nr_entries - 1);
>> +#else
>>  			   stack_trace_nr_entries);
>> -
>> +#endif
>>  		if (!stack_tracer_enabled && !stack_trace_max_size)
>>  			print_disabled(m);
>>  
>> @@ -334,6 +349,10 @@ static int t_show(struct seq_file *m, void *v)
>>  
>>  	i = *(long *)v;
>>  
>> +#ifdef CONFIG_ARM64
>> +	if (i == 0)
>> +		return 0;
>> +#endif
>>  	if (i >= stack_trace_nr_entries)
>>  		return 0;
>>  
>> @@ -342,9 +361,14 @@ static int t_show(struct seq_file *m, void *v)
>>  	else
>>  		size = stack_trace_index[i] - stack_trace_index[i+1];
>>  
>> +#ifdef CONFIG_ARM64
>> +	seq_printf(m, "%3ld) %8d   %5d   ", i-1, stack_trace_index[i], size);
>> +	trace_lookup_stack(m, i-1);
>> +#else
>>  	seq_printf(m, "%3ld) %8d   %5d   ", i, stack_trace_index[i], size);
>>  
>>  	trace_lookup_stack(m, i);
>> +#endif
>>  
>>  	return 0;
>>  }
>