linux-kernel - Re: [PATCH] vsprintf: avoid misleading "(null)" for %px

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Message-ID: <20180205094438.pfd7ffymlvklpxe7@pathway.suse.cz>
Date:   Mon, 5 Feb 2018 10:44:38 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Adam Borowski <kilobyte@...band.pl>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, "Tobin C. Harding" <me@...in.cc>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>,
        Kees Cook <keescook@...omium.org>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Laight <David.Laight@...LAB.COM>,
        Randy Dunlap <rdunlap@...radead.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH] vsprintf: avoid misleading "(null)" for %px

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 <kilobyte@...band.pl>
> ---
>  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') {
>  		/*
>  		 * Print (null) with the same width as a pointer so it makes
>  		 * tabular output look nice.
> -- 
> 2.15.1
>