linux-kernel - Re: [PATCH]kconfig/menu.c: fix uninitialized variable warning

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Date:	Thu, 19 Sep 2013 15:13:15 -0400
From:	Benjamin Poirier <bpoirier@...e.de>
To:	"Yann E. MORIN" <yann.morin.1998@...e.fr>
Cc:	Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>, mmarek@...e.cz,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH]kconfig/menu.c: fix uninitialized variable warning

On 2013/09/19 19:27, Yann E. MORIN wrote:
> Benjamin, Madhavan, All,
> 
> On 2013-09-19 11:22 -0400, Benjamin Poirier spake thusly:
> > On 2013/09/19 12:58, Madhavan Srinivasan wrote:
> > > In file included from scripts/kconfig/zconf.tab.c:2537:0:
> > > scripts/kconfig/menu.c: In function ‘get_symbol_str’:
> > > scripts/kconfig/menu.c:586:18: warning: ‘jump’ may be used uninitialized in
> > > this function [-Wmaybe-uninitialized]
> >                    ^^^^^
> > 
> > from gcc(1):
> > 	"These warnings are made optional because GCC is not smart
> > 	enough to see all the reasons why the code might be correct
> > 	despite appearing to have an error."
> > 
> > I do not see this warning with gcc 4.7.2 or 4.8.1. Which version are you
> > using?
> > 
> > The code does:
> > 
> > static void get_prompt_str(struct gstr *r, struct property *prop,
> > [...]
> > 	if (head && location) {
> > 		jump = xmalloc(sizeof(struct jump_key));
> > [... different basic block ...]
> > 			if (head && location && menu == location)
> > 				jump->offset = r->len - 1;
> > 
> > If the second "if" is true, then the first one was true as well, and
> > "jump" is initilized.
> 
> Exactly what I was going to say.
> 
> However:
>   - I believe we should strive for a warning-free code whenever possible
>   - while still getting help from gcc to pinpoint potential issues.
> 
> Clearly, gcc is wrong here. Setting jump to NULL will cause fault if we
> try to dereference it. Since this should never happen given the code as
> it currently is, I'm slightly in favour of acking this patch.
> 
> Any other reason not to apply it?

Did you manage to get that warning as well? I didn't. If it's only from
old versions of gcc I'd feel better leaving the warning there than
masking it, in case a future code change does really introduce a use
before initialize.

> 
> > >      jump->offset = r->len - 1;
> > >                   ^
> > > scripts/kconfig/menu.c:547:19: note: ‘jump’ was declared here
> > >   struct jump_key *jump;
> > >                    ^
> > > Signed-off-by: Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
> > > ---
> > >  scripts/kconfig/menu.c |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
> > > index c1d5320..23b1827 100644
> > > --- a/scripts/kconfig/menu.c
> > > +++ b/scripts/kconfig/menu.c
> > > @@ -544,7 +544,7 @@ static void get_prompt_str(struct gstr *r, struct property *prop,
> > >  {
> > >  	int i, j;
> > >  	struct menu *submenu[8], *menu, *location = NULL;
> > > -	struct jump_key *jump;
> > > +	struct jump_key *jump = NULL;
> > > 
> > >  	str_printf(r, _("Prompt: %s\n"), _(prop->text));
> > >  	menu = prop->menu->parent;
> > > --
> > > 1.7.10.4
> > > 
> 
> Regards,
> Yann E. MORIN.
> 
> -- 
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