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

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.