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.

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.

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.
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
-

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
-
```
- -
Common Problem: 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 - $CFEINSTALL/target-triplet/sys-include.
- Fix 2: If you are building the C++ front-end on a CPU we - haven't tried yet, you will probably have to edit the appropriate - version of atomicity.h under - src/libstdc++-v3/config/cpu/name-of-cpu/atomicity.h - and apply a patch so that it does not use inline assembly.
- -
Porting to a new architecture: If you are porting the new front-end - to a new architecture, or compiling in a different configuration that we have - previously, there are probably several changes you will have to make to the GCC - target to get it to work correctly. These include:
- -
- Often targets include special or assembler linker flags which - gccas/gccld does not understand. In general, these can - just be removed.
- LLVM currently does not support any floating point values other than - 32-bit and 64-bit IEEE floating point. The primary effect of this is - that you may have to map "long double" onto "double".
- The profiling hooks in GCC do not apply at all to the LLVM front-end. - These may need to be disabled.
- No inline assembly for position independent code. At the LLVM level, - everything is position independent.
- We handle .init and .fini differently.
- You may have to disable multilib support in your target. Using multilib - support causes the GCC compiler driver to add a lot of "-L" - options to the link line, which do not relate to LLVM and confuse - gccld. To disable multilibs, delete any - MULTILIB_OPTIONS lines from your target files.
- Did we mention that we don't support inline assembly? You'll probably - have to add some fixinclude hacks to disable it in the system - headers.
-
Go back into the LLVM source tree proper. Edit Makefile.config -to redefine LLVMGCCDIR to the full pathname of the -$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
-

Test the newly-installed C frontend by one or more of the -following means:
-
- compiling and running a "hello, LLVM" program in C and C++.
- running the tests under test/Programs using gmake -C - test/Programs
-
-