Building LDC runtime libraries

Starting with version 1.4, LDC ships with a small build tool to allow you to recompile the D runtime and standard library (and optionally the accompanying testrunners) the way you want, ldc-build-runtime.

Use cases

• Link-Time Optimization (LTO) for the runtime libraries by recompiling with -flto, which produces smaller binaries and may show significant performance gains
• Adding sanitizer checks via -fsanitize
• Cross-compilation for other platforms, as the D runtime and standard library must be generated for your target platform before you can cross-compile and link D executables and shared libraries

Prerequisites

• CMake
• Either Make, the default, or Ninja (recommended, enable with --ninja)
• C toolchain (compiler, linker and libraries): gcc, clang, Microsoft Visual C++, …

How it works

If run without special command-line options, ldc-build-runtime automates:

• Creating a build directory
• Downloading & extracting the LDC source archive matching the LDC version
• Invoking CMake to generate the Make or Ninja build script for the runtime libraries
• Calling Make or Ninja to build the runtime libraries

The runtime libraries end up in the lib subdirectory of the build directory, i.e. ./ldc-build-runtime.tmp/lib by default. You can replace your existing LDC runtime libraries or link against the new libraries by specifying their directory in the LDC command line: ldc2 … -L-L/path/to/ldc-build-runtime.tmp/lib.

Basic usage

The primary aim is to allow specifying additional compiler/linker command-line options and customizing CMake variables.
Run ldc-build-runtime -h for the full list of command-line options.

ldc-build-runtime [--ninja] [-j4] [--testrunners] [--targetPreset=…] [--dFlags=…] [--cFlags=…] [--linkerFlags=…] [CMAKE_VAR1=value1] [CMAKE_VAR2=value2 …]

For example, to prepare for link-time optimization between your user code and the static runtime libraries, you can recompile the runtime libraries with:

ldc-build-runtime --ninja --dFlags="-flto=full" BUILD_SHARED_LIBS=OFF

OSX only: a ThinLTO version of the standard library will result in linker errors due to this issue: https://github.com/ldc-developers/ldc/issues/2312 (not an issue if gold or lld is used)

Usage for cross-compilation

CC=cross-gcc ldc-build-runtime [--ninja] [-j4] [--testrunners] --dFlags="-mtriple=…;…" [--cFlags=…] [--linkerFlags=…] --targetSystem=… …

For example, to cross-compile from linux/x64 with glibc to an Alpine linux/x64 container just requires specifying a C cross-compiler and a different cross-compilation triple (install the clang and musl packages in Arch linux to try this out):

CC=musl-clang ldc-build-runtime --dFlags="-w;-mtriple=x86_64-alpine-linux-musl"

From Linux/x86_64 to Linux/ARM:

CC=arm-linux-gnueabihf-gcc ldc-build-runtime --ninja --dFlags="-w;-mtriple=arm-linux-gnueabihf" --targetSystem="Linux;UNIX" 

From Windows to Linux/ARM, e.g., by using an official Raspberry PI toolchain:

set CC=arm-linux-gnueabihf-gcc
ldc-build-runtime --ninja --dFlags=-w;-mtriple=arm-linux-gnueabihf --targetSystem=Linux;UNIX CMAKE_SYSTEM_NAME=Linux CMAKE_C_COMPILER_WORKS=True BUILD_SHARED_LIBS=OFF

Cross-compiling to Android/ARM using the Android NDK is more involved, so LDC features a target configuration preset for Android. On Linux/x86_64, set the path to your NDK's C cross-compiler and simply specify the Android target configuration which has been preset for you, while still being able to override the C and linker flags or append your own D flags, by passing those flags in yourself:

export CC=/path/to/your/android-ndk-r15c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang
ldc-build-runtime [--ninja] [--testrunners] --targetPreset=Android-arm

For full instructions on Android cross-compilation, including using ldc-build-runtime from Windows, see the Android page. It also shows examples of using ldc with the newly generated runtime libraries to compile your own code.