On Thu, Feb 23, 2017 at 09:07:59PM +0400, Roman Bogorodskiy wrote:
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-req...
It mentions this commit:
http://llvm.org/viewvc/llvm-project?revision=167655&view=revision
And it seems it wasn't changed since than.
Ah I see. So they disabled it for C, because their [[clang::fallthrough]] magic annotation would not work under C. Hopefully they'll enable it one day with the more normal __attribute__((fallthrough)) syntax for C. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|