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.

This section describes how to aquire and build llvm-gcc4, which is based on +the GCC 4.0.1 front-end. This front-end supports C, C++, Objective-C, and +Objective-C++. Note that the instructions for building this front-end are +completely different (and much easier!) than those for building llvm-gcc3 in +the past.

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.
+
Retrieve the appropriate llvm-gcc4-x.y.source.tar.gz archive from the + llvm web site.
-
Add the directory containing the tools to your PATH.
-
```
- % set path = ( `cd llvm/tools/Debug && pwd` $path )
-
```
- -
Unpack the C/C++ front-end source into cfrontend/src.
+
It is also possible to download the sources of the llvm-gcc4 front end + from a read-only mirror using subversion. To check out the code the + first time use:
-
Edit src/configure. Change the first line (starting w/ #!) to - contain the correct full pathname of sh.
- -

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

- % pwd
- /usr/local/example/cfrontend/src
- % cd ..
- % mkdir build install
- % set CFEINSTALL = `pwd`/install
+svn co svn://anonsvn.opensource.apple.com/svn/llvm/trunk dst-directory

Configure, build and install the C front-end:
-
```
- % cd build
- % ../src/configure --prefix=$CFEINSTALL --disable-nls --disable-shared \
-   --enable-languages=c,c++
- % gmake all-gcc
- % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc 
- % gmake all; gmake install
-
```
+
After that, the code can be be updated in the destination directory + using:
-
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 - $CFEINSTALL/target-triplet/sys-include.
  - -
- Fix 2: If you are building the C++ front-end on a CPU we - haven't tried yet, you will probably have to edit the appropriate - version of atomicity.h under - src/libstdc++-v3/config/cpu/name-of-cpu/atomicity.h - and apply a patch so that it does not use inline assembly.
  -
- -
Common Problem 2: FIXME: Chris should add a section about - common problems porting to a new architecture, including changes you - might have to make to the gcc/gcc/config/name-of-cpu - directory. For example (expand these):
- -
- Munge linker flags so they are compatible with gccld. -
- Change the target so it doesn't have long double; just use double - instead. -
- No inline assembly for position independent code. -
- We handle init and fini differently. -
- Do not include inline assembly map things for SPARC, or profile things. -
- -
Go back into the LLVM source tree proper. Edit Makefile.config -to redefine LLVMGCCDIR to the full pathname of the -$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.)
- -
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.)
- -

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
-

svn update

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; -
+
The mirror is brought up to date every evening.

Follow the directions in the top-level README.LLVM file for + up-to-date instructions on how to build llvm-gcc4.