Experimental newlib support

Arm Toolchain for Embedded uses picolibc as the standard C library. For compatibility with existing projects using newlib, a separate package of newlib-based library variants is provided.

Using pre-built newlib library package

1. Install Arm Toolchain for Embedded

2. Download corresponding ATfE-newlib-overlay package and extract it on top of the main toolchain folder.

   • Note: The overlay package copies all the newlib library variants into the lib/clang-runtimes/newlib subdirectory, so that they do not collide with the picolibc variants in lib/clang-runtimes. It also adds the newlib.cfg into the bin directory, which switches the --sysroot to the newlib subdirectory above.

3. Add the newlib.cfg config file to the command line to use newlib library variants instead of picolibc.

4. Add -lrdimon and -lcrt0-rdimon to the command line to use semihosting or -lnosys and -lcrt0-nosys otherwise.

5. You may use the provided default linker script by adding -T redboot.ld to the command line.

Example:

$ clang --config=newlib.cfg --target=arm-none-eabi -march=armv7m -T redboot.ld -lrdimon -lcrt0-rdimon -o hello hello.c

Building newlib library package

Configure the toolchain with the CMake setting -DLLVM_TOOLCHAIN_C_LIBRARY=newlib to build a newlib-based version of the toolchain.

If you also add -DLLVM_TOOLCHAIN_LIBRARY_OVERLAY_INSTALL=on then the package-llvm-toolchain CMake target will generate the newlib overlay package.

Note that the -DLLVM_TOOLCHAIN_LIBRARY_OVERLAY_INSTALL=on option only generates the newlib package, but does not install it as part of the install CMake target.

About newlib-nano

newlib-nano is provided as a separate package, and is meant to be equal to using GCC with --specs=nano.specs. In order to use the nano version of newlib, where the documentation in this file refers to newlib, replace it with newlib-nano.