> > Since Xiang already added support for NuttX on libcxx mainstream: > https://reviews.llvm.org/D88718?id=303700 > > I think it is time to phase out my libcxx repository and we will stick > to libcxx mainline. > > Do you agree on that?
In general, yes. However, with your modified version, I was able to build and use libcxx without libsupc++ at all. With the upstream version, libsupc++ is required. I'm still not sure how I was able to get away without this before. It seems building libsupc++.a is not the easiest. The gcc build system is a complicated beast. Instead, I have added support for building the libcxxabi library alongside libcxx. I have now successfully gotten it to build and run, but exception unwinding does not work. Xiang, are you actually using exceptions? Can you confirm whether exception unwinding is actually working for you with gcc and libsupc++.a? Best, Anthony On Sat, Jan 9, 2021 at 11:57 AM Xiang Xiao <xiaoxiang781...@gmail.com> wrote: > On Sat, Jan 9, 2021 at 8:11 AM Anthony Merlino <anth...@vergeaero.com> > wrote: > > > Thanks for the info Xiang! I was on the right track but it is good to > have > > some affirmation that I'm not missing something. > > > > The issue with the Arm maintained toolchain, as Greg has warned many > times, > > is its use of newlib. Are you doing anything to ensure the wrong math > > library is not used? > > > > > Yes, from the theory, the potential conflict may happen since NuttX has its > own libc/libm implementation which is totally different from newlib, but at > least the follow combination is good from the practice: > > 1. libc and libm come from NuttX, libsupc++ come from newlib > 2. libc come from NuttX, libm and libsupc++ come from newlib > > We use item 2 for all arm based products and sim develop environment. > > I will work on improving buildroot to also build and include libsupcxx.a. > > > > With Alan's modified version of libcxx, he disabled some exception logic > > and maybe some other logic that was allowing me to build without > libsupxx.a > > entirely. > > > > > libcxx will turn on/off exception and rtti automatically, you just need > specify the right compiler flag(e.g. -fno-exceptions and -fno-rtti): > > https://github.com/llvm/llvm-project/blob/main/libcxx/include/__config#L433-L435 > > https://github.com/llvm/llvm-project/blob/main/libcxx/include/__config#L1092-L1098 > > > > Also, may I ask why we are building libcxx by manually grabbing the > source > > files and building it? Are we against just driving the build from their > > existing build system? > > > libcxx uses CMake, it's hard to integrate their build system. But, it will > be great if we can find a clean solution to reuse their build script. > > > > I ask because there are options in the way libcxx is > > built that might be useful to us and we have to replicate all of that if > we > > just grab the source. > > > > > Except the build system integration, all NuttX specific changes are > upstream to the llvm project. We have to apply the following patches: > > https://github.com/apache/incubator-nuttx/blob/master/libs/libxx/0001-libc-Fix-a-few-warnings.patch > > https://github.com/apache/incubator-nuttx/blob/master/libs/libxx/0001-libc-Fix-tests-failing-with-Clang-after-removing-GCC.patch > > https://github.com/apache/incubator-nuttx/blob/master/libs/libxx/0001-libc-NFC-Fix-several-GCC-warnings-in-the-test-suite.patch > > https://github.com/apache/incubator-nuttx/blob/master/libs/libxx/0001-libcxx-Check-_LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE-fir.patch > > https://github.com/apache/incubator-nuttx/blob/master/libs/libxx/0001-libcxx-Port-to-NuttX-https-nuttx.apache.org-RTOS.patch > just because the new libcxx contains our change doesn't release yet. Once > the new release is out, I will remove all patches from the NuttX repo. > > > > > > Best, > > Anthony > > > > > > On Sat, Jan 9, 2021, 7:32 AM Xiang Xiao <xiaoxiang781...@gmail.com> > wrote: > > > > > On Fri, Jan 8, 2021 at 9:57 AM Anthony Merlino <anth...@vergeaero.com> > > > wrote: > > > > > > > Hey all, > > > > > > > > Would someone be willing to share their experience with libcxx and > > their > > > > toolchain? > > > > > > > > > This toolchain should work: > > > > > > > > > https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm > > > > > > > > > > I've now caught up to the tip of master, which now downloads > > > > and builds libcxx for me instead of using Alan's modified version. I > am > > > > facing an issue I've faced before, and would really love to properly > > > > understand how this is supposed to work. > > > > > > > > My issues mostly center around libsupc++.a > > > > > > > > Currently, my build fails because it can't find libsupc++. From my > > > > understanding, this should be provided by my toolchain. But I am > using > > a > > > > toolchain built by the NuttX buildroot and it does not build the C++ > > > > libraries. I am not using RTTI or exceptions, so I don't need what > > > > > > > > > > libsupc++.a doesn't only provide RTTI and exectpions, but also provide > > some > > > basic functions called by compiler: > > > > > > > > > https://github.com/gcc-mirror/gcc/tree/master/libstdc%2B%2B-v3/libsupc%2B%2B > > > > > > libsupc++ provides, however the Kconfig option > > > > `[ ] Have libsupc++ (required)` > > > > says, it's required. > > > > > > > > What's the right answer here? What are others doing about this? > > > > > > > > > > > Three methods you can try: > > > > > > 1. Switch to the ARM maintained toolchain > > > 2. Build libsupc++.a for NuttX toolchain > > > 3. Enhance NuttX's libc++ runtime support > > > > > > > > > https://github.com/apache/incubator-nuttx/tree/master/libs/libxx > > > > > > > > > > Is getting NuttX buildroot to build and provide libsupc++.a the > *right* > > > > solution? > > > > > > > > > > > Yes, a complete toolchain should provide libsupc++.a. libsupc++.a just > > like > > > libgcc.a should part of toolchain, not part of c/c++ library > > > implemetnation, because libsupc++.a tightly couple with the > implementaion > > > detail of compiler. > > > > > > > > > > Do we need to change how libcxx is built in this case? > > > > > > > > > > > > > > https://libcxx.llvm.org/docs/BuildingLibcxx.html#using-alternate-abi-libraries > > > > > > > > > > > Then you need port the libcxxrt: > > > https://github.com/libcxxrt/libcxxrt > > > > > > > > > > Thank you! > > > > > > > > Anthony > > > > > > > > > >
