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 > > > > > >
