From: Adam Borowski <kilobyte@angband.pl>
To: "Tobin C. Harding" <me@tobin.cc>
Cc: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Joe Perches <joe@perches.com>, Kees Cook <keescook@chromium.org>,
"Roberts, William C" <william.c.roberts@intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
David Laight <David.Laight@ACULAB.COM>,
Randy Dunlap <rdunlap@infradead.org>,
Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: [PATCH] vsprintf: avoid misleading "(null)" for %px
Date: Mon, 5 Feb 2018 16:22:19 +0100 [thread overview]
Message-ID: <20180205152218.hxgozi67zka4hgkf@angband.pl> (raw)
In-Reply-To: <20180205100305.GO29988@eros>
On Mon, Feb 05, 2018 at 09:03:05PM +1100, Tobin C. Harding wrote:
> On Mon, Feb 05, 2018 at 10:44:38AM +0100, Petr Mladek wrote:
> > On Sun 2018-02-04 18:45:21, Adam Borowski wrote:
> > > Like %pK already does, print "00000000" instead.
> > >
> > > This confused people -- the convention is that "(null)" means you tried to
> > > dereference a null pointer as opposed to printing the address.
> >
> > By other words, this avoids regressions when people convert
> > %x to %px. Do I get it right, please?
It's a regression in the sense that it confuses people. %px never could
dereference a pointer so the information provided doesn't change, merely its
presentation.
> > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > > index 77ee6ced11b1..d7a708f82559 100644
> > > --- a/lib/vsprintf.c
> > > +++ b/lib/vsprintf.c
> > > @@ -1849,7 +1849,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> > > {
> > > const int default_width = 2 * sizeof(void *);
> > >
> > > - if (!ptr && *fmt != 'K') {
> > > + if (!ptr && *fmt != 'K' && *fmt != 'x') {
>
> I don't know if it matters but with this it won't be immediately
> apparent that a null pointer was printed (since zero could hash to
> anything).
My change touches %px only, where your concern doesn't apply.
You're right, though, when it comes to %pK:
printk("%%pK: %pK, %%px: %px\n", 0, 0);
says
%pK: 00000000ba8bdc0a, %px: 0000000000000000
So what should we do? Avoid hashing 0? Print a special value?
Meow!
--
⢀⣴⠾⠻⢶⣦⠀ The bill with 3 years prison for mentioning Polish concentration
⣾⠁⢰⠒⠀⣿⡁ camps is back. What about KL Warschau (operating until 1956)?
⢿⡄⠘⠷⠚⠋⠀ Zgoda? Łambinowice? Most ex-German KLs? If those were "soviet
⠈⠳⣄⠀⠀⠀⠀ puppets", Bereza Kartuska? Sikorski's camps in UK (thanks Brits!)?
next prev parent reply other threads:[~2018-02-05 15:22 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-04 17:45 [PATCH] vsprintf: avoid misleading "(null)" for %px Adam Borowski
2018-02-05 9:44 ` Petr Mladek
2018-02-05 10:03 ` Tobin C. Harding
2018-02-05 15:22 ` Adam Borowski [this message]
2018-02-05 16:49 ` Steven Rostedt
2018-02-05 17:36 ` Randy Dunlap
2018-02-05 20:19 ` Tobin C. Harding
2018-02-05 18:57 ` Kees Cook
2018-02-05 20:15 ` Tobin C. Harding
2018-02-05 20:32 ` Kees Cook
2018-02-05 20:58 ` Adam Borowski
2018-02-05 22:22 ` Tobin C. Harding
2018-02-06 18:43 ` Andy Shevchenko
2018-02-07 15:03 ` Petr Mladek
2018-02-07 15:11 ` Geert Uytterhoeven
2018-02-07 15:41 ` Petr Mladek
2018-02-07 15:48 ` Geert Uytterhoeven
2018-02-08 15:29 ` Andy Shevchenko
2018-02-09 12:03 ` Petr Mladek
2018-02-14 14:35 ` Andy Shevchenko
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