On 07/03/2017, Sage Weil wrote: > We have three competing PRs to address the crashes when -O0 is used: > > lixiaoy1 https://github.com/ceph/ceph/pull/12796 > kefu https://github.com/ceph/ceph/pull/13819 > adam https://github.com/ceph/ceph/pull/12931 > > Adam's is appealing because it will ensure the bounded encodes are in fact > constant at compile time. Unfortunately, it requires you to define DENC > twice, like so: > > - DENC_FEATURED(bar_t, v, p, f) { > + DENC_FEATURED_BOUNDED(bar_t, v, p, f) { > ::denc(v.a, p, f); > ::denc(v.b, p, f); > } > + DENC_FEATURED_BOUND_ENCODE(bar_t, p, f) { > + DENC_START(1, 1, p); > + ::denc(bounded_t<decltype(bar_t::a)>{}, p, f); > + ::denc(bounded_t<decltype(bar_t::b)>{}, p, f); > + DENC_FINISH(p); > + } > > which feels like a deal-killer to me... I think I'd rather just drop the > check entirely and rely on the developer to be careful. I have an fix for that in mind (it's why I haven't been pushing that PR too hard) but it's complicated. Essentially, for bounded types, I /think/ I can hack together a way let people do something like: struct Foo { TypeA a; TypeB b; TypeC c; }; BUILD_BOUNDED_DENC(Foo, &Foo::a, &Foo::b, &Foo::c); and not have to divide things up. We could probably go things involving fancier pants to handle features and other stuff. > The other two PRs fix up the handful of type(s) that were actually > causing failures to manually define bound (again making the single > DENC macro unusable). > > What about instead changing all of the instances of > > denc(*(const T*)nullptr, elem_size); > > with a macro that will either do the above "*(const T*)nullptr" -or-, if > it looks like this is a debug build or compiler optimizations are off or > some other compiler environment indicates it won't work, replace it with > "T()"? That avoids crashes in the -O0 case, but still lets us keep some > safeguard for other builds? I would really, really rather not do this. The whole nullptr trick is definitely one of the black rituals of Nasal Goetia. Even if redefining it happens to make -O0 on gcc work now, other compilers, GCC on other architectures, or other versions of GCC are free to start crashing again. -- Senior Software Engineer Red Hat Storage, Ann Arbor, MI, US IRC: Aemerson@{RedHat, OFTC} 0x80F7544B90EDBFB9 E707 86BA 0C1B 62CC 152C 7C12 80F7 544B 90ED BFB9 -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
