[libvirt] [PATCH 3/4] qemu: add missing break in qemuDomainDeviceCalculatePCIConnectFlags

[Daniel P. Berrange]

On Wed, Feb 22, 2017 at 09:19:15PM +0100, Martin Kletzander wrote:
> On Wed, Feb 22, 2017 at 02:44:01PM -0500, Laine Stump wrote:
> > On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
> > > One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags
> > > was missing a break that could result it in falling through to
> > > an incorrect codepath.
> > 
> > Actually that's not true. Every codepath of the preceding case ends with
> > a "return blah".  This is true for the entire function - every case of
> > every switch in the function ends with "return blah". The entire purpose
> > of the function is to determine the flags value, and there are no
> > resources that need cleaning up before returning, so as soon as the
> > value is determined, it immediately returns.
> > 
> > I suppose it could be rewritten to change all of those into "ret = blah;
> > break;", then "return ret;" at the end, but it seemed safer to return
> > immediately than to trust that no new code would be added later in the
> > function (and also it's more compact)
> > 
> > I wonder if this is just a more extreme case of the logic in whatever
> > check necessitated that I add an extra "return 0" at the very end of the
> > function. (that happens even in gcc 6.x; at an earlier point when the
> > function was simpler, that wasn't needed, but after some additions it
> > started producing the "control reaches end of function that requires a
> > return value" or whatever that warning is, and the only way to eliminate
> > it was with the extra return 0.)
> > 
> > If adding the break shuts up the warning, then I guess ACK, but it would
> > probably be better if 1) gcc fixed their incorrect warning, or 2) we
> > switched the entire function to use the less-compact "ret = blah;
> > break;" style instead of returning directly, so there wasn't a single
> > stray break sitting in the middle.
> > 
> 
> I would say NACK since 1) is the correct option (at least for now),
> there is no reason for adding more lines of code that don't make sense
> just because of a compiler version that was not released yet, or does
> not even have a release plan yet.

GCC 7 *is* released - and has even had a bug fix release too, so ignoring
this is not an option. In any case, as Eric mentions this is a genuine
bug in our code since we can fall out of the inner switch if the input
variable contains a value that doesn't map to an named enum value.

Regards,
Daniel
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