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

On 02/22/2017 01:44 PM, 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". Every explicit codepath. But there are implicit codepaths - the default case. Such paths are unreachable, unless dev->type can ever hold a value that doesn't map to virDomainDeviceType (since we are relying the the compiler to fail compilation if we expand the enum but forget to expand the switch, by intentionally omitting our default case).

> 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. Gcc is correct - we can fall through to the outer case VIR_DOMAIN_DEVICE_FS: label from the outer case VIR_DOMAIN_DEVICE_CONTROLLER: label, if the inner switch ((virDomainControllerType) cont->type) lands on the (implicit) default: branch because of storing a non-enum value. Such a fallthrough is never going to happen in real life, but adding the break shuts up the compiler, for the same reason that the function ends with:

> 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 don't think the warning is incorrect.