linux-kernel - Re: gcc fixed size char array initialization bug

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Message-ID: <9a8748490708021303h683a8be7if194a9314483c218@mail.gmail.com>
Date:	Thu, 2 Aug 2007 22:03:03 +0200
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Jan Engelhardt" <jengelh@...putergmbh.de>
Cc:	"Guennadi Liakhovetski" <g.liakhovetski@....de>,
	linux-kernel@...r.kernel.org
Subject: Re: gcc fixed size char array initialization bug - known?

On 02/08/07, Jan Engelhardt <jengelh@...putergmbh.de> wrote:
>
> On Aug 2 2007 21:55, Guennadi Liakhovetski wrote:
> >Hi
> >
> >I've run across the following gcc "feature":
> >
> >       char c[4] = "01234";
> >
> >gcc emits a nice warning
> >
> >warning: initializer-string for array of chars is too long
> >
> >But do a
> >
> >       char c[4] = "0123";
> >
> >and - a wonder - no warning. No warning with gcc 3.3.2, 3.3.5, 3.4.5,
> >4.1.2. I was told 4.2.x does produce a warning. Now do a
> >
> >       struct {
> >               char c[4];
> >               int i;
> >       } t;
> >       t.i = 0x12345678;
> >       strcpy(t.c, c);
> >
> >and t.i is silently corrupted. Just wanted to ask if this is known,
> >really...
>
> What does this have to do with the kernel? The string "0123" is
> generally _five_ characters long, so c[4] is not enough.
> Or use strncpy.
>
I believe Guennadi's point is that gcc does not warn about it in the
case of  c[4] = "0123"; but only in the case of c[4] = "01234" - so if
we do have such initializations in the kernel we may have some bugs
hiding there that gcc doesn't warn us about.

-- 
Jesper Juhl <jesper.juhl@...il.com>
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