RISC-V compiler-rt with no dependency on GCC ?

[ihiasi]

Hi - I am trying to build compiler-rt for RISC-V with no dependency on the GCC toolchain. Ideally, for bare metal development, but I'll take Linux as well if bare metal is not possible yet :).
I am on an Apple Silicon M1 MacMini, latest LLVM checkout (as of sometimes around May10th 2024) and my cmake config is :

export CMAKE_APPLE_SILICON_PROCESSOR=arm64 && cmake -GXcode -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
-DCMAKE_INSTALL_PREFIX=~/install \
-DCMAKE_BUILD_TYPE=Debug \
-DCMAKE_CXX_STANDARD=17 \
-DCMAKE_OSX_ARCHITECTURES=arm64 \
-DLLVM_ENABLE_PROJECTS="clang;lld;lldb;lldb;pstl;libc" \
-DLLVM_ENABLE_RUNTIMES="libcxx;libc;libunwind;compiler-rt" \
-DLLVM_BUILD_EXTERNAL_COMPILER_RT=ON \
-DCOMPILER_RT_DEFAULT_TARGET_TRIPLE="riscv64-unknown-elf" \
-DLLVM_DEFAULT_TARGET_TRIPLE="riscv64-unknown-elf" \
-DLLVM_TARGETS_TO_BUILD="RISCV" \
-DCOMPILER_RT_BAREMETAL_BUILD=ON \
-DLLVM_LINK_LLVM_DYLIB=ON \
-DBUILTINS_CMAKE_ARGS=-DLLVM_CMAKE_DIR=~/work/llvm-project/build/ \
-DLLVM_ENABLE_ASSERTIONS=ON \
-DLLVM_ENABLE_RTTI=OFF  \
-DLLVM_ENABLE_EH=OFF  \
-DLLVM_LIT_ARGS=-v \
-DLLDB_USE_SYSTEM_DEBUGSERVER=ON \
-DLLVM_PARALLEL_LINK_JOBS=1 \
../llvm

I used BUILTINS_CMAKE_ARGS to point to the newly built clang (after I read various LLVM Discord articles and StackOverflow and Github issues here) but it seems like Xcode still tries to use the system toolchain (in /Applications/Xcode) instead :

...
Showing All Messages
-- The C compiler identification is AppleClang 15.0.0.15000309
-- The CXX compiler identification is AppleClang 15.0.0.15000309
-- The ASM compiler identification is Clang with GNU-like command-line
...

I am using musl instead of libc :

./Debug/bin/clang --target=riscv64 -march=rv64g -I~/work/musl/build/include -L~/work/musl/build/lib -o ../test ../test.c
ld.lld: error: cannot open ~/work/llvm-project/build/Debug/bin/../lib/clang-runtimes/riscv64/lib/libclang_rt.builtins.a: No such file or directory
clang: error: ld.lld command failed with exit code 1 (use -v to see invocation)

Two questions :

1. is it possible to build compiler-rt with no dependency on the GCC toolchain ?
2. if the answer to 1 is YES, what is the cmake configuration I should use ?

Thank you.

[llvmbot]

@llvm/issue-subscribers-backend-risc-v

Author: Ionut Hristodorescu (ihiasi)

Hi - I am trying to build compiler-rt for RISC-V with no dependency on the GCC toolchain. Ideally, for bare metal development, but I'll take Linux as well if bare metal is not possible yet :). I am on an Apple Silicon M1 MacMini, latest LLVM checkout (as of sometimes around May10th 2024) and my cmake config is : ``` export CMAKE_APPLE_SILICON_PROCESSOR=arm64 && cmake -GXcode -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \ -DCMAKE_INSTALL_PREFIX=~/install \ -DCMAKE_BUILD_TYPE=Debug \ -DCMAKE_CXX_STANDARD=17 \ -DCMAKE_OSX_ARCHITECTURES=arm64 \ -DLLVM_ENABLE_PROJECTS="clang;lld;lldb;lldb;pstl;libc" \ -DLLVM_ENABLE_RUNTIMES="libcxx;libc;libunwind;compiler-rt" \ -DLLVM_BUILD_EXTERNAL_COMPILER_RT=ON \ -DCOMPILER_RT_DEFAULT_TARGET_TRIPLE="riscv64-unknown-elf" \ -DLLVM_DEFAULT_TARGET_TRIPLE="riscv64-unknown-elf" \ -DLLVM_TARGETS_TO_BUILD="RISCV" \ -DCOMPILER_RT_BAREMETAL_BUILD=ON \ -DLLVM_LINK_LLVM_DYLIB=ON \ -DBUILTINS_CMAKE_ARGS=-DLLVM_CMAKE_DIR=~/work/llvm-project/build/ \ -DLLVM_ENABLE_ASSERTIONS=ON \ -DLLVM_ENABLE_RTTI=OFF \ -DLLVM_ENABLE_EH=OFF \ -DLLVM_LIT_ARGS=-v \ -DLLDB_USE_SYSTEM_DEBUGSERVER=ON \ -DLLVM_PARALLEL_LINK_JOBS=1 \ ../llvm ``` I used BUILTINS_CMAKE_ARGS to point to the newly built clang (after I read various LLVM Discord articles and StackOverflow and Github issues here) but it seems like Xcode still tries to use the system toolchain (in /Applications/Xcode) instead : ``` ... Showing All Messages -- The C compiler identification is AppleClang 15.0.0.15000309 -- The CXX compiler identification is AppleClang 15.0.0.15000309 -- The ASM compiler identification is Clang with GNU-like command-line ... ``` I am using `musl` instead of `libc` : ``` ./Debug/bin/clang --target=riscv64 -march=rv64g -I~/work/musl/build/include -L~/work/musl/build/lib -o ../test ../test.c ld.lld: error: cannot open ~/work/llvm-project/build/Debug/bin/../lib/clang-runtimes/riscv64/lib/libclang_rt.builtins.a: No such file or directory clang: error: ld.lld command failed with exit code 1 (use -v to see invocation) ``` Two questions : 1. is it possible to build compiler-rt with no dependency on the GCC toolchain ? 2. if the answer to 1 is YES, what is the cmake configuration I should use ?

Thank you.