Bootstrapping the LLVM C/C++ Front-End

-

This document is intended to explain the process of building the -LLVM C/C++ front-end from its source code. You have to do this, for example, if -you are porting LLVM to a new architecture or operating system, if you are -working from Top-Of-Tree CVS/SVN, or if there is no precompiled snapshot -available.

- -

NOTE: This is currently a somewhat fragile, error-prone -process, and you should only try to do it if:

- -

you really, really, really can't use the binaries we distribute
you are an elite GCC hacker.
you want to use the latest bits from CVS.

- -

We welcome patches to help make this process simpler.

-

If you are building LLVM and the GCC front-end under Cygwin, please note that -the LLVM and GCC makefiles do not correctly handle spaces in paths. To deal -with this issue, make sure that your LLVM and GCC source and build trees are -located in a top-level directory (like /cygdrive/c/llvm and -/cygdrive/c/llvm-cfrontend), not in a directory that contains a space -(which includes your "home directory", because it lives under the "Documents -and Settings" directory). We welcome patches to fix this issue. -

-

It has been found that the GCC 3.3.3 compiler provided with recent Cygwin -versions is incapable of compiling the LLVM GCC front-end correctly. If your -Cygwin -installation includes GCC 3.3.3, we strongly recommend that you download -GCC 3.4.3, build it separately, and use it for compiling the LLVM GCC front-end. - This has been -shown to work correctly.

-

Some versions of Cygwin utilize an experimental version of GNU binutils that -will cause the GNU ld linker to fail an assertion when linking -components of the libstdc++. It is recommended that you replace the entire -binutils package with version 2.15 such that "ld --version" responds -with

-

GNU ld version 2.15

-not with:
-

GNU ld version 2.15.91 20040725

-

If you are building LLVM and the GCC front-end under AIX, do NOT use GNU -Binutils. They are not stable under AIX and may produce incorrect and/or -invalid code. Instead, use the system assembler and linker. -

-

- -

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 than those for building llvm-gcc3. -

- -

-
Retrieve the appropriate llvm-gcc4-x.y.source.tar.gz archive from the llvm -web site.
-
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: -
- -svn co svn://anonsvn.opensource.apple.com/svn/llvm dst-directory - -
After that, the code can be be updated in the destination directory using; -
- -svn update - -
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.

-

Aquire llvm-gcc3 from LLVM CVS or -from a release tarball.
Configure and build the LLVM libraries and tools. There are two ways to -do this: either with objdir == srcdir or -objdir != srcdir. It is recommended -that srcdir be the same as objdir for your LLVM tree (but note -that you should always use srcdir != objdir for llvm-gcc):
-
- With objdir != srcdir:
```
- % cd objdir
- % srcdir/configure --prefix=/some/path/you/can/install/to [options...]
- % gmake tools-only
-  
```
- With objdir == srcdir:
```
- % cd llvm
- % ./configure --prefix=/some/path/you/can/install/to [options...]
- % gmake tools-only
-  
```
-
This will build all of the LLVM tools and libraries. The --prefix -option defaults to /usr/local (per configure standards) but unless you are a -system administrator, you probably won't be able to install LLVM there because -of permissions. Specify a path into which LLVM can be installed (e.g. ---prefix=/home/user/llvm).
-

Add the directory containing the tools to your PATH.

-

- % set path = ( `cd llvm/Debug/bin && pwd` $path )
-

Unpack the C/C++ front-end source into cfrontend/src, either by - untar'ing a cfrontend.source.tar.gz file or checking out CVS into this - directory.

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 GCC front-end:
- -
-Linux/x86:
-Linux/IA-64:
-MacOS X/PowerPC (requires dlcompat library):
-AIX/PowerPC: -
- -
```
- % cd build
- % ../src/configure --prefix=$CFEINSTALL --disable-threads --disable-nls \
-   --disable-shared --enable-languages=c,c++ --program-prefix=llvm-
- % gmake all; gmake install
-
```
- -
Cygwin/x86:
- -
```
- % cd build
- % ../src/configure --prefix=$CFEINSTALL --disable-threads --disable-nls \
-   --disable-shared --enable-languages=c,c++ --disable-c-mbchar \
-   --program-prefix=llvm-
- % gmake all; gmake install
-
```
- -
Solaris/SPARC:
- -
-The GCC front-end can be configured for either SPARC V8 (32 bit) or SPARC V9 (64 -bit). This changes, among other things, the sizes of integer types and the -macros defined for conditional compilation. -
- -
-The SPARC V8 ABI support is more robust than the V9 ABI support and can generate -SPARC V9 code. It is highly recommended that you use the V8 ABI with LLVM, as -shown below. Also, -note that Solaris has trouble with various wide (multibyte) character -functions from C as referenced from C++, so we typically configure with ---disable-c-mbchar (cf. Bug 206). -
- -
```
- % cd build
- % ../src/configure --prefix=$CFEINSTALL --disable-threads --disable-nls \
-   --disable-shared --enable-languages=c,c++ --host=sparc-sun-solaris2.8 \
-   --disable-c-mbchar --program-prefix=llvm-
- % 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/lib/gcc/target-triplet/3.4-llvm/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 front-end - to a new architecture or compiling in a configuration that we have - not tried 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 assembler or 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.
-
Put $CFEINSTALL/bin into your PATH environment -variable.
-
- sh: export PATH=$CFEINSTALL/bin:$PATH
- csh: setenv PATH $CFEINSTALL/bin:$PATH
-
Go back into the LLVM source tree proper. Rerun configure, using -the same options as the last time. This will cause the configuration to now find -the newly built llvm-gcc and llvm-g++ executables.
Rebuild your CVS tree. This shouldn't cause the whole thing to be - rebuilt, but it should build the runtime libraries. After the tree is - built, install the runtime libraries into your GCC front-end build tree. - These are the commands you need:
-
```
- % gmake
- % gmake -C runtime install-bytecode
-
```
Optionally, build a symbol table for the newly installed runtime -libraries. Although this step is optional, you are strongly encouraged to -do this as the symbol tables will make a significant difference in your -link times. Use the llvm-ranlib tool to do this, as follows:
-
```
- % cd $CFEINSTALL/lib
- % llvm-ranlib libiberty.a
- % llvm-ranlib libstdc++.a
- % llvm-ranlib libsupc++.a
- % cd $CFEINSTALL/lib/gcc/target-triplet/3.4-llvm
- % llvm-ranlib libgcc.a
- % llvm-ranlib libgcov.a
-
```
- -
Test the newly-installed C frontend by one or more of the -following means:
-
- running the feature & regression tests via make check
- compiling and running a "hello, LLVM" program in C and C++.
- running the tests found in the llvm-test CVS module

-

-The LLVM GCC frontend is licensed to you under the GNU General Public License -and the GNU Lesser General Public License. Please see the files COPYING and -COPYING.LIB for more details. -

- -

-More information is available in the FAQ. -

- +This page has moved here.