linux-kernel - Re: [PATCH] vsprintf: Do not break early boot with probing addresses

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Date:   Tue, 14 May 2019 14:37:51 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     David Laight <David.Laight@...lab.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        christophe leroy <christophe.leroy@....fr>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Russell Currey <ruscur@...sell.cc>,
        Stephen Rothwell <sfr@...abs.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing
 addresses


[ Purple is a nice shade on the bike shed. ;-) ]

On Tue, 14 May 2019 11:02:17 +0200
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> On Tue, May 14, 2019 at 10:29 AM David Laight <David.Laight@...lab.com> wrote:
> > > And I like Steven's "(fault)" idea.
> > > How about this:
> > >
> > >       if ptr < PAGE_SIZE              -> "(null)"
> > >       if IS_ERR_VALUE(ptr)            -> "(fault)"
> > >
> > >       -ss  
> >
> > Or:
> >         if (ptr < PAGE_SIZE)
> >                 return ptr ? "(null+)" : "(null)";

Hmm, that is useful.

> >         if IS_ERR_VALUE(ptr)
> >                 return "(errno)"  

I still prefer "(fault)" as is pretty much all I would expect from a
pointer dereference, even if it is just bad parsing of, say, a parsing
an MAC address. "fault" is generic enough. "errno" will be confusing,
because that's normally a variable not a output.

> 
> Do we care about the value? "(-E%u)"?

That too could be confusing. What would (-E22) be considered by a user
doing an sprintf() on some string. I know that would confuse me, or I
would think that it was what the %pX displayed, and wonder why it
displayed it that way. Whereas "(fault)" is quite obvious for any %p
use case.

-- Steve