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Message-ID: <1417200612.4305.7.camel@perches.com>
Subject: Re: [PATCH] scripts/kconfig/menu.c warning for uninitialized "jump"
From: Joe Perches <joe@perches.com>
To: Michal Marek <mmarek@suse.cz>
Cc: Peter Teoh <htmldeveloper@gmail.com>, LKML <linux-kernel@vger.kernel.org>
Date: Fri, 28 Nov 2014 10:50:12 -0800
In-Reply-To: <547879BE.4050502@suse.cz>
References: <CAHnt0GXeTAmAaa3queHDP2kssYESgHLmohXj41F04gQvcB__ug@mail.gmail.com>
	 <547879BE.4050502@suse.cz>
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On Fri, 2014-11-28 at 14:33 +0100, Michal Marek wrote:
> On 2014-11-21 05:22, Peter Teoh wrote:
> > This warning was found in v3.18-rc3-68-g20f3963 of Linus git-tree.
> > 
> >   SHIPPED scripts/kconfig/zconf.hash.c
> >   HOSTCC  scripts/kconfig/zconf.tab.o
> > In file included from scripts/kconfig/zconf.tab.c:2537:0:
> > scripts/kconfig/menu.c: In function ‘get_symbol_str’:
> > scripts/kconfig/menu.c:590:18: warning: ‘jump’ may be used
> > uninitialized in this function [-Wmaybe-uninitialized]
> >      jump->offset = strlen(r->s);
> >                   ^
> > scripts/kconfig/menu.c:551:19: note: ‘jump’ was declared here
> >   struct jump_key *jump;
> >                    ^
> 
> First of all, the warning is bogus (the condition under which 'jump' is
> used is stronger than that under which 'jump' is initialized). But since
> people have been reporting the warning on and off for some time, we have
> to shut it up somehow, as the affected gcc versions are not dying out,
> apparently.
> 
> 
> > -                       if (head && location && menu == location)
> > +                       if (head && location && (menu == location) && (jump))
> >                                 jump->offset = strlen(r->s);
> 
> Let's assume, for the sake of argument, that gcc is right and jump may
> be uninitialized here. Then the added check for jump being non-null just
> tests an uninitialized variable and thus behaves randomly. It prevents
> the code from writing to NULL->offset, but does not prevent it from
> writing to <random address>->offset.

Maybe the 'right' thing to do is to mark the xmalloc
prototype as "__attribute__((returns_nonnull))"


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