linux-kernel - Re: [PATCH v4 2/4] lib: vsprintf: Fix handling of number field widths in vsscanf

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHp75VcwTg1e=apHuOzCNmpK9c6LuZ_BLDZvq9BpaTC8Rcgguw@mail.gmail.com>
Date:   Fri, 5 Feb 2021 17:53:41 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Richard Fitzgerald <rf@...nsource.cirrus.com>,
        Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Shuah Khan <shuah@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        "patches@...nsource.cirrus.com" <patches@...nsource.cirrus.com>
Subject: Re: [PATCH v4 2/4] lib: vsprintf: Fix handling of number field widths
 in vsscanf

On Fri, Feb 5, 2021 at 5:23 PM David Laight <David.Laight@...lab.com> wrote:
> From: Andy Shevchenko
> > Sent: 05 February 2021 12:51
> > On Fri, Feb 5, 2021 at 1:35 PM Richard Fitzgerald
> > <rf@...nsource.cirrus.com> wrote:
> > > On 04/02/2021 16:35, Petr Mladek wrote:
> > > > On Wed 2021-02-03 21:45:55, Andy Shevchenko wrote:
> > > >> On Wed, Feb 03, 2021 at 04:50:07PM +0000, Richard Fitzgerald wrote:
> >
> > ...
> >
> > > >>> +   for (; max_chars > 0; max_chars--) {
> > > >>
> > > >> Less fragile is to write
> > > >>
> > > >>      while (max_chars--)
> > > >
> > > > Except that the original was more obvious at least for me.
> > > > I always prefer more readable code when the compiler might do
> > > > the optimization easily. But this is my personal taste.
> > > > I am fine with both variants.
> >
> > I *slightly* prefer while-loop *in this case* due to less characters
> > to parse to understand the logic.
>
> The two loops are also have different values for 'max_chars'
> inside the loop body.

off-by-one to be precise.

> If 'max_chars' is known to be non-zero the do ... while (--max_chars);
> loop will probable generate better code.

What?! while (--x)  and while(x--) are equivalent.

> But there is no accounting for just how odd some decisions gcc
> makes are.

Why should we care about the compiler bugs here?

-- 
With Best Regards,
Andy Shevchenko