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<p class="MsoNormal">Dear LLVM developers,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal">I’m trying to find a way of cross-compiling my c code against Baremetal Cortex-M device (so target triple will be arm-none-eabi) only using LLVM/Clang, and not using anything from GNU (ld or libc).<o:p></o:p></p>
<p class="MsoNormal">I’m doing this to know which one of LLVM/clang and GCC produces smaller flash image size because saving flash is a big deal in our projects.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">1) When I just follow this - <a href="https://clang.llvm.org/docs/CrossCompilation.html">
https://clang.llvm.org/docs/CrossCompilation.html</a> using LLVM/Clang Prebuilt binary 5.0.0, I got this error,<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><i>daniel@daniel-VirtualBox:~/clang/crosscompile$ make clean all<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>rm -f main *.o *.map *.a<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>"clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin"/clang -static --target=arm-none-eabi -mcpu=cortex-m0 -c -o main.o main.c<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>"clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin"/clang -static --target=arm-none-eabi -mcpu=cortex-m0 -c -o a.o a.c<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>"clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin"/clang -static --target=arm-none-eabi -mcpu=cortex-m0 -c -o reset.o reset.c<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>"clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin"/clang -v -static --target=armv6m-none-eabi -o main main.o a.o reset.o<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>clang version 5.0.0 (tags/RELEASE_500/final)<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>Target: armv6m-none--eabi<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>Thread model: single<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>InstalledDir: clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>"clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin/ld.lld" main.o a.o reset.o -Bstatic -Lclang+llvm-5.0.0-linux-x86_64-ubuntu16.04/lib/clang/5.0.0/lib/baremetal -lc -lm -lclang_rt.builtins-armv6m.a -o main<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin/ld.lld: error:
<b>unable to find library -lc</b><o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin/ld.lld: error:
<b>unable to find library -lm</b><o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>clang+llvm-5.0.0-linux-x86_64-ubuntu16.04/bin/ld.lld: error:
<b>unable to find library -lclang_rt.builtins-armv6m.a</b><o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>clang-5.0: error: ld.lld command failed with exit code 1 (use -v to see invocation)<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>makefile:33: recipe for target 'main' failed<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>make: *** [main] Error 1</i><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">2) To get clang_rt.builtins-armv6m.a or libc, libm, I tried to build LLVM/Clang (compiler_rt) from LLVM/Clang source following this -
<a href="http://llvm.org/docs/HowToCrossCompileLLVM.html">http://llvm.org/docs/HowToCrossCompileLLVM.html</a> but I got this error,<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><i>TARGET_TRIPLE=arm-none-eabi<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>MYHOSTBIN=${HOME}/clang/source/build_x64/bin<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>MYGNUARM_ROOT=${HOME}/opt/gcc-arm-none-eabi-6-2017-q2-update<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>MYCFLAGS="--specs=nosys.specs -mcpu=cortex-m4 -mthumb -mfloat-abi=softfp -mfpu=fpv4-sp-d16"<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>cmake -G "Ninja" \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_CROSSCOMPILING=True \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_BUILD_TYPE=Release \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_INSTALL_PREFIX=${HOME}/clang/toInstall \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DLLVM_TABLEGEN=${MYHOSTBIN}/llvm-tblgen \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCLANG_TABLEGEN=${MYHOSTBIN}/clang-tblgen \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DLLVM_DEFAULT_TARGET_TRIPLE=arm-none-eabi \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DLLVM_TARGET_ARCH=ARM \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DLLVM_TARGETS_TO_BUILD=ARM \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DLLVM_ENABLE_LTO=Full \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_C_FLAGS="${MYCFLAGS}" \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_CXX_FLAGS="${MYCFLAGS}" \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_SYSROOT=${MYGNUARM_ROOT} \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_TOOLCHAIN_FILE=../toolchain.txt \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_C_COMPILER=${MYGNUARM_ROOT}/bin/arm-none-eabi-gcc \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_CXX_COMPILER=${MYGNUARM_ROOT}/bin/arm-none-eabi-g++ \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> -DCMAKE_ASM_COMPILER=${MYGNUARM_ROOT}/bin/arm-none-eabi-as \<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> ../llvm<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>…<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>-- Looking for __atomic_load_8 in atomic<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>-- Looking for __atomic_load_8 in atomic - not found<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>CMake Error at cmake/modules/CheckAtomic.cmake:74 (message):<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> <b>Host compiler appears to require libatomic, but cannot find it</b>.<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>Call Stack (most recent call first):<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> cmake/config-ix.cmake:350 (include)<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i> CMakeLists.txt:585 (include)</i><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">arm-none-eabi toolchain doesn’t contain libatomic, but I need to build compiler_rt using this tool to get the runtime for ARM, so it’s confusing. Or building compiler_rt using arm-none-eabi toolchain is completely wrong idea in the first
place.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">3) Then I found this mail thread <a href="http://lists.llvm.org/pipermail/llvm-dev/2017-August/116134.html">http://lists.llvm.org/pipermail/llvm-dev/2017-August/116134.html</a> which seems very close to the thing I’m trying, but the mail
thread is unfinished.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So, my question is, <o:p></o:p></p>
<p class="MsoNormal">Is there a way of cross-compiling c code against Baremetal Cortex-M device only using LLVM/Clang, and not using anything from GNU (ld or libc)?<o:p></o:p></p>
<p class="MsoNormal">If so, do I have to build LLVM/Clang source code to get clang_rt.builtins-armv6m.a or libc, libm for ARM?<o:p></o:p></p>
<p class="MsoNormal">If so, the method 2) or 3) above is the right approach? Or are there any other instruction?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Any advice would be a great help for me.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thank you<o:p></o:p></p>
<p class="MsoNormal">Daniel<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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