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Date: Thu, 26 Oct 2017 01:05:39 -0700
From: Joe Perches <joe@...ches.com>
To: "Tobin C. Harding" <me@...in.cc>
Cc: kernel-hardening@...ts.openwall.com, "Jason A. Donenfeld"
 <Jason@...c4.com>,  Theodore Ts'o <tytso@....edu>, Linus Torvalds
 <torvalds@...ux-foundation.org>, Kees Cook <keescook@...omium.org>, Paolo
 Bonzini <pbonzini@...hat.com>, Tycho Andersen <tycho@...ker.com>, "Roberts,
 William C" <william.c.roberts@...el.com>,  Tejun Heo <tj@...nel.org>,
 Jordan Glover <Golden_Miller83@...tonmail.ch>, Greg KH
 <gregkh@...uxfoundation.org>, Petr Mladek <pmladek@...e.com>, Ian Campbell
 <ijc@...lion.org.uk>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, 
 Catalin Marinas <catalin.marinas@....com>, Will Deacon
 <wilal.deacon@....com>, Steven Rostedt <rostedt@...dmis.org>,  Chris Fries
 <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com>, Daniel Micay
 <danielmicay@...il.com>,  Djalal Harouni <tixxdz@...il.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH V8 1/2] printk: remove tabular output for NULL pointer

On Thu, 2017-10-26 at 17:27 +1100, Tobin C. Harding wrote:
> Hi Joe,
> 
> thanks for your review.
> 
> On Wed, Oct 25, 2017 at 09:57:23PM -0700, Joe Perches wrote:
> > On Thu, 2017-10-26 at 13:53 +1100, Tobin C. Harding wrote:
> > > Currently pointer() checks for a NULL pointer argument and then if so
> > > attempts to print "(null)" with _some_ standard width. This width cannot
> > > correctly be ascertained here because many of the printk specifiers
> > > print pointers of varying widths.
> > 
> > I believe this is not a good change.
> > Only pointers without a <foo> extension call pointer()
>
> Sorry, I don't understand what you mean here. All the %p<foo> specifier code is
> handled by pointer()?

Sorry, I was imprecise/wrong.

None of the %p<foo> extensions except %pK and %p<invalid_foo>
actually use this bit of the pointer() call.

All of the other valid %p<foo> extension uses do not end up
at this block being executed so it's effectively only regular
pointers being output by number()

> > > Remove the attempt to print NULL pointers with a correct width.
> > 
> > the correct width for a %p is the default width.
> 
> It is the default width if we are printing addresses. Once we hash 64
> bit address to a 32 bit identifier then we don't have a default width.

Perhaps that 32 bit identifier should use leading 0's for
the default width.

aside:

Why hash 64 bits to 32?
Why shouldn't the hash width be 64 bits on 64 bit systems?


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