[libvirt PATCH] All pointers to virXMLPropString() use g_autofree.

[Nicolás Brignone]

On Thu, Jul 9, 2020 at 5:15 AM Daniel P. Berrangé <berrange at redhat.com> wrote:
>
> On Wed, Jul 08, 2020 at 11:15:27PM -0400, Laine Stump wrote:
> > On 7/8/20 4:19 PM, Nicolas Brignone wrote:
> > >   All pointers to virXMLPropString() use g_autofree.
> >
> >
> > I changed the summary line like this, to be more precise:
> >
> >
> > conf: use g_autofree for all pointers to virXMLPropString() in device_conf.c
> >
> >
> > > All modified functions are similar, in all cases "cleanup" label is removed,
> > > along with all the "goto" calls.
> >
> >
> > I've been advised in the recent past to put the g_autofree additions and
> > corresponding removals of free functions into one patch, then do the removal
> > of the extra labels (in favor of directly returning) in a separate patch to
> > make it easier to hand-verify / review. Here's a couple recent examples:
> >
> >
> > https://www.redhat.com/archives/libvir-list/2020-July/msg00317.html
> >
> >
> > In your case the changes are few enough that I'm okay with it a single
> > patch, except...
> >
> >
> > >
> > > Signed-off-by: Nicolas Brignone <nmbrignone at gmail.com>
> > > ---
> > >   src/conf/device_conf.c | 183 +++++++++++++----------------------------
> > >   1 file changed, 56 insertions(+), 127 deletions(-)
> > >
> > > diff --git a/src/conf/device_conf.c b/src/conf/device_conf.c
> > > index 7d48a3f..9fa6141 100644
> > > --- a/src/conf/device_conf.c
> > > +++ b/src/conf/device_conf.c
> > > @@ -208,45 +208,43 @@ int
> > >   virPCIDeviceAddressParseXML(xmlNodePtr node,
> > >                               virPCIDeviceAddressPtr addr)
> > >   {
> > > -    char *domain, *slot, *bus, *function, *multi;
> > >       xmlNodePtr cur;
> > >       xmlNodePtr zpci = NULL;
> > > -    int ret = -1;
> > >       memset(addr, 0, sizeof(*addr));
> > > -    domain   = virXMLPropString(node, "domain");
> > > -    bus      = virXMLPropString(node, "bus");
> > > -    slot     = virXMLPropString(node, "slot");
> > > -    function = virXMLPropString(node, "function");
> > > -    multi    = virXMLPropString(node, "multifunction");
> > > +    g_autofree char *domain   = virXMLPropString(node, "domain");
> > > +    g_autofree char *bus      = virXMLPropString(node, "bus");
> > > +    g_autofree char *slot     = virXMLPropString(node, "slot");
> > > +    g_autofree char *function = virXMLPropString(node, "function");
> > > +    g_autofree char *multi    = virXMLPropString(node, "multifunction");
> >
> >
> > ... you've modified it so that local variables are being declared *below* a
> > line of executable code rather than at the top of the block. Although I
> > don't see anything in the coding style document
> > (https://libvirt.org/coding-style.html) about it, and it may just be
> > leftover from a time when we supported a compiler that required all
> > declarations to be at top of scope, I think pretty much all of libvirts code
> > declares all local variables at the top of the scope.
>
> We should really document it, and even enforce it at compile time.

I think you are asking for enabling:

-Wdeclaration-after-statement (C and Objective-C only)
           Warn when a declaration is found after a statement in a
block.  This construct, known from C++, was introduced
           with ISO C99 and is by default allowed in GCC.  It is not
supported by ISO C90.

Will take a look.

> When you have variables in the middle of a function, and do a goto
> jump over them, they are in scope at the goto label target, but
> you may have jumped over their initialization. This makes it hard
> to rationalize about correctness of the code and has led to bugs
> involving uninitialized data before.
>
> Regards,
> Daniel
> --
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