On Wed, Jan 3, 2018 at 1:31 AM, Sage Weil <sweil@xxxxxxxxxx> wrote: > On Tue, 2 Jan 2018, kefu chai wrote: >> On Tue, Jan 2, 2018 at 11:28 PM, Ken Dreyer <kdreyer@xxxxxxxxxx> wrote: >> > On Tue, Dec 26, 2017 at 4:24 AM, kefu chai <tchaikov@xxxxxxxxx> wrote: >> >> right. unless we swing our own homebrew gcc-7. >> > >> > Can we ask the devtoolset maintainers to change this option? >> > >> > I imagine they would be interested in this type of feedback from the field. >> >> https://git.centos.org/blob/rpms!devtoolset-7-gcc.git/2e5ef6c7934d4417e095855478736742b35bd0af/SPECS!gcc.spec#L1026 > > For reference, > > ``` > # Force the old ABI unconditionally, the new one does not work in the > # libstdc++_nonshared.a model against RHEL 6/7 libstdc++.so.6. > sed -i -e 's/\(define[[:blank:]]*_GLIBCXX_USE_DUAL_ABI[[:blank:]]*\)1/\10/' $f > ``` > >> I think we need to think about this before sending any inquiries to them. > > The problem I see is that it is impossible to write/build many native > C++11 (or 14 or 17) apps with the toolchain since the old ABI precludes > O(1) std::list. i sort of agree with you. but i think we can still use C++11 (and probably 14 or 17) with the old ABI. see https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html <quote> the choice of ABI to use is independent of the -std option used to compile your code </quote> in other words, if we rely on the O(1) std::list and copy-on-write string, then, yes, we cannot write/build apps using this toolchain. > > If I'm following the _nonshared thing, it's a feature that lets you build > with teh new toolchain but deploy on systems with much older libstdc++ > installed (new symbols are statically instead of dynamically linked). > Is the problem with the "dual ABI" feature? i think so. also by inspecting https://git.centos.org/blob/rpms!devtoolset-7-gcc.git/c7/SOURCES!gcc7-libstdc++-compat.patch, libstdc++_nonshared.a includes lots of C++98 and C++11 symbols. in the case of list::size(), it is completely implemented in the header file. but probably there are also some pieces of libstdc++ implemented in the source files. in that case, it would be difficult to include both ABIs a class, std::basic_string<> for example, in the same .a file. because they are conditionalized by the "_GLIBCXX_USE_CXX11_ABI" macro at build time. and they are both in the namespace of std::__cxx11 namespace. will drop a mail to SCLs asking for more info on this. -- Regards Kefu Chai -- 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
