Bootstrapping the C/C++ Front-End

This document is intended to explain the process of building the LLVM C/C++ front-end, based on GCC 3.4, from source.

NOTE: This is currently a somewhat fragile, error-prone process, and you should only try to do it if (A) you really, really, really can't use the binaries we distribute, and (B) you are a wicked good GCC hacker.

We welcome patches to help make this process simpler.


  1. Configure and build the LLVM libraries and tools using:

     % cd llvm
     % ./configure [options...]
     % gmake tools-only

    The use of the non-default target "tools-only" means that the LLVM tools and libraries will build, and the binaries will be deposited in llvm/tools/Debug, but the runtime (bytecode) libraries will not build.

  2. Add the directory containing the tools to your PATH.

     % set path = ( `cd llvm/tools/Debug && pwd` $path )
  3. Unpack the C/C++ front-end source into cfrontend/src.

  4. Edit src/configure. Change the first line (starting w/ #!) to contain the correct full pathname of sh.

  5. Make "build" and "install" directories as siblings of the "src" tree.

     % pwd
     % cd ..
     % mkdir build install
     % set CFEINSTALL = `pwd`/install
  6. Configure, build and install the C front-end:

     % cd build
     % ../src/configure --prefix=$CFEINSTALL --disable-nls --disable-shared \
     % gmake all-gcc
     % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc 
     % gmake all; gmake install

    Common Problem 1: You may get error messages regarding the fact that LLVM does not support inline assembly. Here are two common fixes:

    • Fix 1: If you have system header files that include inline assembly, you may have to modify them to remove the inline assembly, and install the modified versions in $CFEINSTALL/target-triplet/sys-include.

    • Fix 2: If you are building the C++ front-end on a CPU we haven't tried yet, you will probably have to edit the appropriate version of atomicity.h under src/libstdc++-v3/config/cpu/name-of-cpu/atomicity.h and apply a patch so that it does not use inline assembly.

    Common Problem 2: FIXME: Chris should add a section about common problems porting to a new architecture, including changes you might have to make to the gcc/gcc/config/name-of-cpu directory. For example (expand these):

    • Munge linker flags so they are compatible with gccld.
    • Change the target so it doesn't have long double; just use double instead.
    • No inline assembly for position independent code.
    • We handle init and fini differently.
    • Do not include inline assembly map things for SPARC, or profile things.
  7. Go back into the LLVM source tree proper. Edit Makefile.config to redefine LLVMGCCDIR to the full pathname of the $CFEINSTALL directory, which is the directory you just installed the C front-end into. (The ./configure script is likely to have set this to a directory which does not exist on your system.)

  8. If you edited header files during the C/C++ front-end build as described in "Fix 1" above, you must now copy those header files from $CFEINSTALL/target-triplet/sys-include to $CFEINSTALL/lib/gcc/target-triplet/3.4-llvm/include. (This should be the "include" directory in the same directory as the libgcc.a library, which you can find by running $CFEINSTALL/bin/gcc --print-libgcc-file-name.)

  9. Build and install the runtime (bytecode) libraries by running:

     % gmake -C runtime
     % mkdir $CFEINSTALL/bytecode-libs
     % gmake -C runtime install
     % setenv LLVM_LIB_SEARCH_PATH $CFEINSTALL/bytecode-libs
  10. Test the newly-installed C frontend by one or more of the following means:

    • compiling and running a "hello, world" program in C or C++.
    • running the tests under test/Programs using gmake -C test/Programs

Brian Gaeke
Last modified: $Date$