Re: [libvirt] [PATCH 4/4] Add ATTRIBUTE_FALLTHROUGH for switch cases without break

Daniel P. Berrange wrote: > On Wed, Feb 22, 2017 at 05:52:05PM +0000, Daniel P. Berrange wrote: > > In GCC 7 there is a new warning triggered when a switch > > case has a conditional statement (eg if ... else...) and > > some of the code paths fallthrough to the next switch > > statement. e.g. > > > > conf/domain_conf.c: In function 'virDomainChrEquals': > > conf/domain_conf.c:14926:12: error: this statement may fall through [-Werror=implicit-fallthrough=] > > if (src->targetTypeAttr != tgt->targetTypeAttr) > > ^ > > conf/domain_conf.c:14928:5: note: here > > case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: > > ^~~~ > > conf/domain_conf.c: In function 'virDomainChrDefFormat': > > conf/domain_conf.c:22143:12: error: this statement may fall through [-Werror=implicit-fallthrough=] > > if (def->targetTypeAttr) { > > ^ > > conf/domain_conf.c:22151:5: note: here > > default: > > ^~~~~~~ > > > > GCC introduced a __attribute__((fallthrough)) to let you > > indicate that this is intentionale behaviour rather than > > a bug. > > > BTW, CLang has apparently had an -Wimplicit-fallthrough > warning flag for a while, and also seems to have the same > __attribute__((fallthrough)), but I've been unable to get > CLang to trigger such warnings, and hence did not enable > __attribute__((fallthrough)) on CLang. If someone can > figure out how to reproduce the warnings on clang we > could extend internal.h to surpress them for whichever > clang version introduced the warnings. As is, the > ATTRIBUTE_FALLTHROUGH turns into a no-op for CLang unless > it claims GCC 7.0 compatibility. It *looks* like -Wimplicit-fallthrough in clang is only effective for C++11: http://clang-developers.42468.n3.nabble.com/should-Wimplicit-fallthrough-... It mentions this commit: http://llvm.org/viewvc/llvm-project?revision=167655&view=revision And it seems it wasn't changed since than.