On Wed, Jan 13, 2021 at 12:44 AM Anthony Merlino <anth...@vergeaero.com> wrote:
> > > > 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? > > Yes, the exception can work as expect, I just try cxxtest with CONFIG_CXX_EXCEPTION: https://github.com/apache/incubator-nuttx-apps/tree/master/testing/cxxtest Here is the output from a board with Cortex M33: test ofstream=========================== printf: Starting test_ostream printf: Successfully opened /dev/console cout: Successfully opened /dev/console Writing this to /dev/console test iostream=========================== Hello, this is only a test Print an int: 190 Print a char: d test vector============================= v1=1 2 3 Hello World Good Luck test map================================ test rtti=============================== extend test exception========================== Catch exception: runtime error The simulator has the same output too. BTW, to make the exception work, the link script need .ARM.extab and.ARM.exidx sections: .ARM.extab : ALIGN(4) { *(.ARM.extab*) } > ROM .ARM.exidx : ALIGN(4) { __exidx_start = ABSOLUTE(.); *(.ARM.exidx*) __exidx_end = ABSOLUTE(.); } > ROM > 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 > > > > > > > > > > > > > > >
