linux-kernel - Re: RFC: script to convert vsprintf uses of %pf to %ps and %pF to %pS

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Message-ID: <20181130165823.pmqw6l4fldfmwd2a@pathway.suse.cz>
Date:   Fri, 30 Nov 2018 17:58:23 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Joe Perches <coupons@...ches.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: RFC: script to convert vsprintf uses of %pf to %ps and %pF to %pS

On Sun 2018-11-25 01:13:51, Joe Perches wrote:
> commit 04b8eb7a4ccd ("symbol lookup: introduce dereference_symbol_descriptor()}"
> 
> deprecated vsprintf extension %pf and %pF.
> 
> so a script to convert all the %pf uses to %ps and %pF uses to %pS
> could be useful.
> 
> There are a few files that appear should not be converted.
> 
> $ git grep -w --name-only -i '%pf'| \
>   grep -vP '^(?:Documentation|tools|include/linux/freezer.h)'| \
>   xargs sed -i -e 's/%pf/%ps/g' -e 's/%pF/%pS/g'
> 
> If that script above is run, it leaves the following patch
> to be applied:

> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 37a54a6dd594..393002bf5298 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1872,8 +1870,6 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  	}
>  
>  	switch (*fmt) {
> -	case 'F':
> -	case 'f':

Please, keep handling these modifiers so that they do not get reused
anytime soon.

The pointer modifiers are evil. Any misuse can easily lead to a crash.
Any mistakes with upstreaming 3rd party patches or backporting stable
fixes would be hard to notice.

Well, it is perfectly fine to just explicitly fallback to
the default %p behavior. I mean something like:

	case 'F':
	case 'f':
		/* Replaced by %ps and %pS and removed in 4.21 */
		break;

Best Regards,
Petr