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Message-ID: <1509005139.10651.39.camel@perches.com>
Subject: Re: [PATCH V8 1/2] printk: remove tabular output for NULL pointer
From: Joe Perches <joe@perches.com>
To: "Tobin C. Harding" <me@tobin.cc>
Cc: kernel-hardening@lists.openwall.com,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        "Theodore Ts'o" <tytso@mit.edu>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>, Paolo Bonzini <pbonzini@redhat.com>,
        Tycho Andersen <tycho@docker.com>,
        "Roberts, William C" <william.c.roberts@intel.com>,
        Tejun Heo <tj@kernel.org>,
        Jordan Glover <Golden_Miller83@protonmail.ch>,
        Greg KH <gregkh@linuxfoundation.org>, Petr Mladek <pmladek@suse.com>,
        Ian Campbell <ijc@hellion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <wilal.deacon@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>, Chris Fries <cfries@google.com>,
        Dave Weinstein <olorin@google.com>,
        Daniel Micay <danielmicay@gmail.com>,
        Djalal Harouni <tixxdz@gmail.com>, linux-kernel@vger.kernel.org
Date: Thu, 26 Oct 2017 01:05:39 -0700
In-Reply-To: <20171026062734.GH12341@eros>
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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?