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Subject: Re: [PATCH 0/3][RESEND] add support for never printing hashed
 addresses
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Timur Tabi <timur@kernel.org>, Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        akpm@linux-foundation.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        roman.fietze@magna.com, Kees Cook <keescook@chromium.org>,
        John Ogness <john.ogness@linutronix.de>,
        akinobu.mita@gmail.com, glider@google.com,
        Andrey Konovalov <andreyknvl@google.com>,
        Marco Elver <elver@google.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
References: <20210210051814.845713-1-timur@kernel.org>
 <6da0be5a-7cb0-4943-e61f-7c3275e60cb6@i-love.sakura.ne.jp>
 <20210210111836.2468f10a@gandalf.local.home>
 <e996ff2f-d350-1399-bb6b-8373bf70e687@i-love.sakura.ne.jp>
 <20210210114633.1b755f6e@gandalf.local.home>
From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Message-ID: <cd421230-f6cd-fb79-64ad-d029bcee7b4e@i-love.sakura.ne.jp>
Date:   Thu, 11 Feb 2021 02:07:21 +0900
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On 2021/02/11 1:46, Steven Rostedt wrote:
> On Thu, 11 Feb 2021 01:39:41 +0900
> Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote:
> 
>> On 2021/02/11 1:18, Steven Rostedt wrote:
>>> The point of this exercise is to be able to debug the *same* kernel that
>>> someone is having issues with. And this is to facilitate that debugging.  
>>
>> That's too difficult to use. If a problem is not reproducible, we will have
>> no choice but always specify "never hash pointers" command line option. If a
>> problem is reproducible, we can rebuild that kernel with "never hash pointers"
>> config option turned on.
> 
> Now the question is, why do you need the unhashed pointer?

Because unhashed pointers might give some clue. We can rebuild the same kernel
using the same kernel config / compiler etc. and compare unhashed pointers with
addresses in System.map / kallsyms files without reproducing the problem.

> 
> Currently, the instruction pointer is what is fine right? You get the
> a function and its offset. If there's something that is needed, perhaps we
> should look at how to fix that, instead of just unhashing all pointers by
> default.

I'm not refusing to use kernel command line options. I'm expecting that we can
also hardcode using kernel config options. Since boot-time switching via kernel
command line options makes the kernel behave differently, less boot-time
switching is better for avoiding unexpected problems (e.g. unintended LSM was
enabled).