Re: [PATCH] scripts/kconfig/menu.c warning for uninitialized "jump"

From: Joe Perches
Date: Fri Nov 28 2014 - 13:50:22 EST


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 âget_symbol_strâ:
> > scripts/kconfig/menu.c:590:18: warning: âjumpâ may be used
> > uninitialized in this function [-Wmaybe-uninitialized]
> > jump->offset = strlen(r->s);
> > ^
> > scripts/kconfig/menu.c:551:19: note: âjumpâ 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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