linux-kernel - Re: [RFC PATCH v1 1/4] arm64: Implement infrastructure for stack trace reliability checks

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Message-ID: <ecdca67a-223f-40de-ebfa-89183e15a2a8@linux.microsoft.com>
Date:   Thu, 1 Apr 2021 12:44:53 -0500
From:   "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     mark.rutland@....com, jpoimboe@...hat.com, jthierry@...hat.com,
        catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 1/4] arm64: Implement infrastructure for stack
 trace reliability checks



On 4/1/21 10:27 AM, Mark Brown wrote:
> On Tue, Mar 30, 2021 at 02:09:52PM -0500, madvenka@...ux.microsoft.com wrote:
>> From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
>>
>> Implement a check_reliability() function that will contain checks for the
>> presence of various features and conditions that can render the stack trace
>> unreliable.
> 
> This looks good to me with one minor stylistic thing:
> 
>> +/*
>> + * Special functions where the stack trace is unreliable.
>> + */
>> +static struct function_range	special_functions[] = {
>> +	{ 0, 0 }
>> +};
> 
> Might be good to put a comment here saying that this is terminating the
> list rather than detecting a NULL function pointer:
> 
> 	{ /* sentinel */ }
> 
> is a common idiom for that.
> 
> Given that it's a fixed array we could also...
> 
>> +	for (func = special_functions; func->start; func++) {
>> +		if (pc >= func->start && pc < func->end)
> 
> ...do these as
> 
> 	for (i = 0; i < ARRAY_SIZE(special_functions); i++) 
> 
> so you don't need something like that, though that gets awkward when you
> have to write out special_functions[i].field a lot.
> 
> So many different potential colours for the bikeshed!
I will make the above changes.

Thanks!

Madhavan