On 12-01-23 13:50, Jes Sorensen wrote: > On 01/22/12 01:49, Michal Soltys wrote: >> Below is approach to the "problem" from a bit different angle - >> using alias-permitting type definitions consistently where necessary >> - so assuring compiler won't (shouldn't ?) pursue any funny ideas no >> matter what. I'd guess it's the "right" thing to do - aside from >> going kernel way and using -fno-strict-aliasing everywhere (or >> #pragmas). >> >> The compilation goes cleanly at Wstrict-aliasing=1 - so most >> aggresive yet most dumb at the same time (note, not checked on 4.7, >> but obviously I included necessary equivalent changes to the Jes's >> patch). >> >> Anyway - side effects of Wstrict-aliasing=1 are false positives - >> quite a few of them actually (funcion argument casts where only >> pointers are involved, some pointers which are not dereferenced >> "nearby" and/or in the same block) - but false negatives should be >> (almost ?) nonexistent. As mdadm is rather critical, and itself >> compiled with Wall, Wextra and Werror - I assume to be extra careful >> - this should complement those settings well. >> >> On a bad side of this approach - it doesn't necessary make the code >> prettier, and might make people ask "the hell is this ...". > > Hi Michal, > > Personally I'd rather have someone who knows about the ddf on disk > format go through the code and fix properly. > IMHO adding more ugly typedefs is a situation of where the cure is > worse than the disease. Btw, the patch went through the whole mdadm, not just ddf part. And afaik, if we aim to be formally correct - there's no going around typedefs (which are required for "may_alias" on simple types). Otherwise, it just tricking gcc into not issuing warnings (even if the chance of actual problems occuring is absolutely minuscule). > We're all going through the code trying to come up with workarounds > for gcc (myself included), rather than fixing the code. Well, IMHO the [probably] best workaround for now would be -fno-strict-aliasing then - which avoids warnings, ugly attribute [over]use, and should assure expected behavior. Say, near the top of Makefile: -CFLAGS = $(CWFLAGS) $(CXFLAGS) -DSendmail=\""$(MAILCMD)"\" $(CONFFILEFLAGS) $(DIRFLAGS) +CFLAGS = $(CWFLAGS) $(CXFLAGS) -fno-strict-aliasing -DSendmail=\""$(MAILCMD)"\" $(CONFFILEFLAGS) $(DIRFLAGS) -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
