sdk-ng icon indicating copy to clipboard operation
sdk-ng copied to clipboard

Published 20 hours ago • verified publisher icon zephyrproject-rtos

Clang/LLVM Toolchain Support

Open stephanosio opened this issue 1 year ago • 10 comments
trafficstars

This enhancement issue describes the Clang/LLVM toolchain support plan in the Zephyr SDK.

Goals

  • Provide LLVM Binary Utilities as part of the SDK
  • Provide Clang C/C++ Compiler as part of the SDK
  • Support SDK Clang/LLVM toolchain in Zephyr

Specifications

  • LLVM Binary Utilities

    • LLVM Binary Utilities shall be an optional component of the SDK that is available separately from the SDK GNU Binutils.
    • The following LLVM Binary Utilities binaries shall be provided [1]:
      • dsymutil
      • lld
      • llvm-ar
      • llvm-cov
      • llvm-cxxfilt
      • llvm-dwarfdump
      • llvm-nm
      • llvm-objcopy
      • llvm-objdump
      • llvm-profdata
      • llvm-ranlib (-> llvm-ar)
      • llvm-readelf (-> llvm-readobj)
      • llvm-readobj
      • llvm-size
      • llvm-strip (-> llvm-objcopy)
      • llvm-symbolizer
      • wasm-ld (-> lld)

  • Clang Compiler

    • Clang Compiler shall be an optional component of the SDK that is available separately from the SDK GCC.
    • Clang Compiler shall be configured to C and C++ languages.
    • The following Clang compiler binaries shall be provided:
      • clang
      • clang++ (-> clang)
      • clang-cpp (->clang)

  • Pre-built Libraries

    • The following pre-built libraries shall be provided:
      • compiler-rt
      • picolibc
      • libunwind
      • libc++abi
      • libc++
    • The pre-built libraries shall be provided for the following Arm targets [2]:
      • armv6m_soft_nofp
      • armv7em_hard_fpv4_sp_d16
      • armv7em_hard_fpv5_d16
      • armv7em_soft_nofp
      • armv7m_soft_fpv4_sp_d16
      • armv7m_soft_nofp
      • armv8.1m.main_hard_fp_nomve
      • armv8.1m.main_hard_fpdp_nomve
      • armv8.1m.main_hard_nofp_mve
      • armv8.1m.main_hard_nofp_nomve
      • armv8.1m.main_hard_fp
      • armv8.1m.main_soft_nofp
    • The pre-built libraries shall be provided for the following RISC-V targets [3]:
      • rv32e_zicsr_zifencei/ilp32e
      • rv32em_zicsr_zifencei/ilp32e
      • rv32emc_zicsr/ilp32e
      • rv32emc_zicsr_zba_zbb_zbc_zbs/ilp32e
      • rv32emc_zicsr_zifencei/ilp32e
      • rv32emc_zicsr_zifencei_zba_zbb_zbc_zbs/ilp32e
      • rv32i_zicsr_zifencei/ilp32
      • rv32if_zicsr_zifencei/ilp32
      • rv32im_zicsr_zifencei/ilp32
      • rv32im_zicsr_zifencei_zba_zbb_zbc_zbs/ilp32
      • rv32imac_zicsr_zifencei/ilp32
      • rv32imafc_zicsr_zifencei/ilp32
      • rv32imafd_zicsr_zifencei/ilp32
      • rv32imfc_zicsr_zifencei/ilp32

  • Zephyr Build System Integration

    • The SDK Clang/LLVM toolchain shall be selectable by setting ZEPHYR_TOOLCHAIN_VARIANT=zephyr-llvm.
      • The existing ZEPHYR_TOOLCHAIN_VARIANT=zephyr (aka. GCC) shall be renamed to ZEPHYR_TOOLCHAIN_VARIANT=zephyr-gnu.
      • ZEPHYR_TOOLCHAIN_VARIANT=zephyr shall map to ZEPHYR_TOOLCHAIN_VARIANT=zephyr-gnu for the foreseeable in order to ensure compatibility.
    • The zephyr-llvm toolchain shall invoke Clang compiler with LLVM Linker [4]:
      • Build system configuration: COMPILER=clang, BINTOOLS=llvm, LINKER=lld

  • SDK Distribution

    • Distribution Archive
      • ~~The existing "GNU toolchain distribution archive" (toolchain_HOST-TARGET) shall be split into "GNU Binutils distribution archive" (toolchain_gnu-binutils_OS-TARGET) and "GCC distribution archive" (toolchain_gcc_HOST-TARGET) [5].~~ Binutils and GCC will be kept in the same "GNU" archive since Zephyr SDK LLVM support will default to using LLVM lld, not GNU ld.
      • A new distribution archive for LLVM Binary Utilities (toolchain_llvm-binutils_HOST) shall be added.
      • A new distribution archive for Clang Compiler (toolchain_clang-base_HOST) shall be added.
      • A new distribution archive for Clang Pre-built Libraries (toolchain_clang-lib_HOST-TARGET) shall be added.
    • Distribution Bundle
      • The existing "GNU toolchain distribution bundle" (zephyr-sdk-VER_HOST) shall be renamed to zephyr-sdk-VER-gcc_HOST.
      • A new distribution bundle consisting of Clang/LLVM toolchain (zephyr-sdk-VER-clang_HOST) shall be added.
      • The distribution bundle installation script shall be updated to support installation of individual GNU Binutils, LLVM Binutils, GCC, Clang components for the minimal distribution bundle.

  • Clang/LLVM Toolchain Build Process

    • A custom build script shall be implemented for building Clang/LLVM toolchain [6].

[1] Based on the "LLVM Binary Utilities" included in LLVM Embedded Toolchain for Arm. [2] Based on the pre-built multi-libs included in LLVM Embedded Toolchain for Arm. [3] Based on the pre-built 32-bit RISC-V multi-libs currently included in the SDK GCC. [4] ~~LLVM Linker (lld) support is currently very limited and it is desirable to use GNU Linker (ld) for maximum compatibility. Note that GNU Linker is used by default for ZEPHYR_TOOLCHAIN_VARIANT=llvm as well.~~ lld support seems to be sufficiently mature now. [5] This ensures that GNU Linker, which is part of GNU Binutils, can be installed alongside Clang/LLVM toolchain without installing GCC. [6] Ideally, we would implement Clang/LLVM toolchain support in crosstool-ng and upstream it; but, doing so will likely delay this task too much for our liking -- we will see.

Tasks

Phase 1

Inclusion of Clang/LLVM toolchain binaries and pre-built compiler-rt library for Arm-M-profile cores and RISC-V RV32I and RV32E cores in the SDK

  • [x] Implement LLVM binary utilities build process
  • [x] Implement Clang compiler build process
  • [x] Implement compiler-rt multi-lib build process for Arm
  • [ ] Implement compiler-rt multi-lib build process for RISC-V
  • [x] Rework the distribution archive build process as per the "SDK Distribution" specifications above
  • [ ] Rework the distribution bundle build process as per the "SDK Distribution" specifications above

Phase 2

Addition of pre-built C/C++ libraries for Arm M-profile cores and RISC-V RV32I and RV32E cores to the SDK

  • [x] Implement Picolibc multi-lib build process
  • [x] Implement libunwind multi-lib build process
  • [x] Implement libc++abi multi-lib build process
  • [x] Implement libc++ multi-lib build process

Future

(Nothing concrete about these ...)

  • [ ] Implement Clang/LLVM toolchain support in crosstool-ng and refactor the SDK build process to use it
  • [ ] Add pre-built libraries for other architectures (i.e. other than Arm and RISC-V)

Resources

stephanosio avatar Sep 06 '24 16:09 stephanosio