1Examples 2======== 3This directory contains a few example programs which illustrate how one can set 4up their own projects to use LLVM's libc, either as an overlay or as the only 5libc in their projects. See the 6[the usage mode document](https://libc.llvm.org/usage_modes.html) for more 7information about the different modes in which one can build and use the libc. 8 9Building the Examples 10===================== 11Each example has its own directory which contain the source code and the CMake 12build set up. To build an example, create a directory named `build` in the 13example's directory: 14 15```bash 16cd <example directory> 17mkdir build 18cd build 19``` 20 21Each example can be built to use the libc in either 22[the overlay mode](https://libc.llvm.org/overlay_mode.html) or the 23[full build mode](https://libc.llvm.org/fullbuild_mode.html). The CMake 24configure step differs slightly depending on the mode you want to use the libc 25in. 26 27Building against an overlay libc 28-------------------------------- 29 30Before you can link an example against the overlay libc, you will have to 31install it. See [the documentation of the overlay mode](https://libc.llvm.org/overlay_mode.html) 32to learn how to install the libc's overlay static archive named `libllvmlibc.a`. 33Once installed, to build an example against it, you have specify the directory 34in which the static archive is installed with the option 35`LIBC_OVERLAY_ARCHIVE_DIR`: 36 37```bash 38cmake ../ -G <GEN> \ 39 -DLIBC_OVERLAY_ARCHIVE_DIR=<dir in which libc is installed> 40``` 41 42Next, if `Ninja` is used for `<GEN>`, you can build the example as follows: 43 44```bash 45ninja <example name> 46``` 47 48Building against a full libc 49---------------------------- 50 51Before you can link an example against the full libc, you will have to first 52install it. See [the documentation of the full build mode](https://libc.llvm.org/fullbuild_mode.html) 53to learn how to install a full libc along with the other LLVM toolchain pieces 54like `clang`, `lld` and `compiler-rt`. The CMake build for the examples will 55assume that you have all of these components installed in a special sysroot 56(see decription of the `--sysroot` option 57[here](https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html).) Once you 58have installed them, you have to inform CMake that we are linking against the 59full libc as follows: 60 61```bash 62cmake ../ -G <GEN> -DLLVM_LIBC_FULL_BUILD=ON \ 63 -DCMAKE_SYSROOT=<SYSROOT> \ 64 -DCMAKE_C_COMPILER=<SYSROOT>/bin/clang \ 65 -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY 66``` 67 68`<SYSROOT>` is the path to the sysroot directory you have set up while 69installing the full libc. The option 70`-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY` tells CMake to not attempt 71linking full executables against shared libraries. We have to use this as LLVM's 72libc does not yet have support for shared libraries and dynamic linking. After 73the above `cmake` command, assuming `Ninja` was used for `<GEN>`, you can build 74the example as follows: 75 76 77```bash 78ninja <example name> 79``` 80