Re: [blktap2] fix two 'maybe uninitialized' variables

From: Ian Campbell <Ian.Campbell@eu.citrix.com>
To: Dario Faggioli <dario.faggioli@citrix.com>
Cc: xen-devel@lists.xenproject.org, Keir Fraser <keir@xen.org>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>
Subject: Re: [blktap2] fix two 'maybe uninitialized' variables
Date: Thu, 12 Jun 2014 10:18:32 +0100	[thread overview]
Message-ID: <1402564712.8162.5.camel@kazak.uk.xensource.com> (raw)
In-Reply-To: <1402488062.16827.90.camel@Solace>

On Wed, 2014-06-11 at 14:01 +0200, Dario Faggioli wrote:
> for which gcc 4.9.0 complains about, like this:
> 
> block-qcow.c: In function ‘get_cluster_offset’:
> block-qcow.c:431:3: error: ‘tmp_ptr’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    memcpy(tmp_ptr, l1_ptr, 4096);
>    ^
> block-qcow.c:606:7: error: ‘tmp_ptr2’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    if (write(s->fd, tmp_ptr2, 4096) != 4096) {

You initialise both of these to NULL as they are defined, but the
compiler has apparently found a path where these values can be used
without subsequently being initialised, so you are passing NULL to
memcpy/write, which can't be good.

If you've proved that the compiler is wrong/confused and this cannot
happen please explain the how/why it is wrong here.

For the preferred $subject I always just look in the git log for the
appropriate file/directory.

Ian.

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel