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Harding" To: Petr Mladek Cc: Adam Borowski , Sergey Senozhatsky , Steven Rostedt , linux-kernel@vger.kernel.org, Andrew Morton , Joe Perches , Kees Cook , "Roberts, William C" , Linus Torvalds , David Laight , Randy Dunlap , Geert Uytterhoeven Subject: Re: [PATCH] vsprintf: avoid misleading "(null)" for %px Message-ID: <20180205100305.GO29988@eros> References: <20180204174521.21383-1-kilobyte@angband.pl> <20180205094438.pfd7ffymlvklpxe7@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180205094438.pfd7ffymlvklpxe7@pathway.suse.cz> X-Mailer: Mutt 1.5.24 (2015-08-30) User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 05, 2018 at 10:44:38AM +0100, Petr Mladek wrote: > Hi, > > I add people who actively commented on adding %px modifier, > see the thread starting at > https://lkml.kernel.org/r/1511921105-3647-5-git-send-email-me@tobin.cc > > Just for reference. It seems to be related to the commit 9f36e2c448007b54 > ("printk: use %pK for /proc/kallsyms and /proc/modules"). > > > 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? > > > Signed-off-by: Adam Borowski > > --- > > lib/vsprintf.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > 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). thanks, Tobin.