Building the LLVM GCC Front-End

- -

This section describes how to acquire and build llvm-gcc 4.2, which is based -on the GCC 4.2.1 front-end. Supported languages are Ada, C, C++, Fortran, -Objective-C and Objective-C++. Note that the instructions for building these -front-ends are completely different (and much easier!) than those for building -llvm-gcc3 in the past.

- -

Retrieve the appropriate llvm-gcc-4.2-version.source.tar.gz - archive from the LLVM web - site.
- -
It is also possible to download the sources of the llvm-gcc front end - from a read-only mirror using subversion. To check out the 4.2 code - for first time use:
- -
-
```
-svn co http://llvm.org/svn/llvm-project/llvm-gcc-4.2/trunk 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-gcc. See below for building - with support for Ada or Fortran. -

- -

Building with support for Ada amounts to following the directions in the -top-level README.LLVM file, adding ",ada" to EXTRALANGS, for example: -EXTRALANGS=,ada

- -

There are some complications however:

- -

The only platform for which the Ada front-end is known to build is - 32 bit intel x86 running linux. It is unlikely to build for other - systems without some work.
The build requires having a compiler that supports Ada, C and C++. - The Ada front-end is written in Ada so an Ada compiler is needed to - build it. Compilers known to work with the - LLVM 2.7 release - are gcc-4.2 and the - 2005, 2006 and 2007 versions of the - GNAT GPL Edition. - GNAT GPL 2008, gcc-4.3 and later will not work. - The LLVM parts of llvm-gcc are written in C++ so a C++ compiler is - needed to build them. The rest of gcc is written in C. - Some linux distributions provide a version of gcc that supports all - three languages (the Ada part often comes as an add-on package to - the rest of gcc). Otherwise it is possible to combine two versions - of gcc, one that supports Ada and C (such as the - 2007 GNAT GPL Edition) - and another which supports C++, see below.
Because the Ada front-end is experimental, it is wise to build the - compiler with checking enabled. This causes it to run much slower, but - helps catch mistakes in the compiler (please report any problems using - LLVM bugzilla).
The Ada front-end fails to - bootstrap, due to lack of LLVM support for - setjmp/longjmp style exception handling (used - internally by the compiler), so you must specify - --disable-bootstrap.

- -

Supposing appropriate compilers are available, llvm-gcc with Ada support can - be built on an x86-32 linux box using the following recipe:

- -

Download the LLVM source - and unpack it:

- -

-wget http://llvm.org/releases/2.7/llvm-2.7.tgz
-tar xzf llvm-2.7.tgz
-mv llvm-2.7 llvm
-

- -

or check out the - latest version from subversion:

- -

svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm

- -

Download the - llvm-gcc-4.2 source - and unpack it:

- -

-wget http://llvm.org/releases/2.7/llvm-gcc-4.2-2.7.source.tgz
-tar xzf llvm-gcc-4.2-2.7.source.tgz
-mv llvm-gcc-4.2-2.7.source llvm-gcc-4.2
-

- -

or check out the - latest version from subversion:

- -

-svn co http://llvm.org/svn/llvm-project/llvm-gcc-4.2/trunk llvm-gcc-4.2
-

Make a build directory llvm-objects for llvm and make it the - current directory:
- -
```
-mkdir llvm-objects
-cd llvm-objects
-
```
-
Configure LLVM (here it is configured to install into /usr/local):
- -
```
-../llvm/configure --prefix=/usr/local --enable-optimized --enable-assertions
-
```
- -
If you have a multi-compiler setup and the C++ compiler is not the - default, then you can configure like this:
- -
```
-CXX=PATH_TO_C++_COMPILER ../llvm/configure --prefix=/usr/local --enable-optimized --enable-assertions
-
```
- -
To compile without checking (not recommended), replace - --enable-assertions with --disable-assertions.
- -
Build LLVM:
- -
```
-make
-
```
-
Install LLVM (optional):
- -
```
-make install
-
```
-
Make a build directory llvm-gcc-4.2-objects for llvm-gcc and make it the - current directory:
- -
```
-cd ..
-mkdir llvm-gcc-4.2-objects
-cd llvm-gcc-4.2-objects
-
```
-

Configure llvm-gcc (here it is configured to install into /usr/local). - The --enable-checking flag turns on sanity checks inside the compiler. - To turn off these checks (not recommended), replace --enable-checking - with --disable-checking. - Additional languages can be appended to the --enable-languages switch, - for example --enable-languages=ada,c,c++.

- -

-../llvm-gcc-4.2/configure --prefix=/usr/local --enable-languages=ada,c \
-                          --enable-checking --enable-llvm=$PWD/../llvm-objects \
-			  --disable-bootstrap --disable-multilib
-

- -

If you have a multi-compiler setup, then you can configure like this:

- -

-export CC=PATH_TO_C_AND_ADA_COMPILER
-export CXX=PATH_TO_C++_COMPILER
-../llvm-gcc-4.2/configure --prefix=/usr/local --enable-languages=ada,c \
-                          --enable-checking --enable-llvm=$PWD/../llvm-objects \
-			  --disable-bootstrap --disable-multilib
-

Build and install the compiler:
- -
```
-make
-make install
-
```
-

- -

- Building the LLVM GCC Front-End -

Building llvm-gcc from Source

Building the Ada front-end

Building the Fortran front-end

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