Bootstrapping the LLVM C/C++ Front-End

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Written by Brian R. Gaeke

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This document is intended to explain the process of building the -LLVM C/C++ front-end, based on GCC 3.4, from its source code. You -would have to do this, for example, if you are porting LLVM to a new -architecture or operating system.

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

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you really, really, really can't use the binaries we distribute
you need GCC to fix some of the header files on your system
you are an elite GCC hacker.

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We welcome patches to help make this process simpler.

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Configure and build the LLVM libraries and tools using:
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```
- % cd llvm
- % ./configure [options...]
- % gmake tools-only
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```
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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.

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

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- % pwd
- /usr/local/example/cfrontend/src
- % cd ..
- % mkdir build install
- % set CFEINSTALL = `pwd`/install
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Configure, build, and install the C front-end:
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-Linux/x86: -
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```
- % cd build
- % ../src/configure --prefix=$CFEINSTALL --disable-threads --disable-nls --disable-shared \
-   --enable-languages=c,c++
- % gmake all-gcc
- % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc 
- % gmake all; gmake install
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```
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-Solaris/SPARC: -
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-For Solaris/SPARC, LLVM only supports the SPARC V9. Therefore, the -configure command line should specify sparcv9, as shown below. Also, -note that Solaris has trouble with various wide (multibyte) character -functions from C as referenced from C++, so we typically configure with ---disable-c-mbchar (cf. Bug 206). -
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```
- % cd build
- % ../src/configure --prefix=$CFEINSTALL --disable-threads --disable-nls \
-   --disable-shared --enable-languages=c,c++ --host=sparcv9-sun-solaris2.8 \
-   --disable-c-mbchar
- % gmake all-gcc
- % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc 
- % gmake all; gmake install
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```
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Common Problem: You may get error messages regarding the fact - that LLVM does not support inline assembly. Here are two common - fixes:
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- 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 - $CFEINSTALL/target-triplet/sys-include.
- Fix 2: If you are building the C++ front-end on a CPU we - haven't tried yet, you will probably have to edit the appropriate - version of atomicity.h under - src/libstdc++-v3/config/cpu/name-of-cpu/atomicity.h - and apply a patch so that it does not use inline assembly.
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Porting to a new architecture: If you are porting the new front-end - to a new architecture, or compiling in a different configuration that we have - previously, there are probably several changes you will have to make to the GCC - target to get it to work correctly. These include:
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- Often targets include special or assembler linker flags which - gccas/gccld does not understand. In general, these can - just be removed.
- LLVM currently does not support any floating point values other than - 32-bit and 64-bit IEEE floating point. The primary effect of this is - that you may have to map "long double" onto "double".
- The profiling hooks in GCC do not apply at all to the LLVM front-end. - These may need to be disabled.
- No inline assembly for position independent code. At the LLVM level, - everything is position independent.
- We handle .init and .fini differently.
- You may have to disable multilib support in your target. Using multilib - support causes the GCC compiler driver to add a lot of "-L" - options to the link line, which do not relate to LLVM and confuse - gccld. To disable multilibs, delete any - MULTILIB_OPTIONS lines from your target files.
- Did we mention that we don't support inline assembly? You'll probably - have to add some fixinclude hacks to disable it in the system - headers.
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Go back into the LLVM source tree proper. Edit Makefile.config -to redefine LLVMGCCDIR to the full pathname of the -$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:

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- % gmake -C runtime
- % mkdir $CFEINSTALL/bytecode-libs
- % gmake -C runtime install-bytecode
- % setenv LLVM_LIB_SEARCH_PATH $CFEINSTALL/bytecode-libs
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Test the newly-installed C frontend by one or more of the -following means:
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- compiling and running a "hello, LLVM" program in C and C++.
- running the tests under test/Programs using gmake -C - test/Programs
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+This page has moved here.

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-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. -

- -

-The software also has the following additional copyrights: -

- -

-Copyright (c) 1994
-Hewlett-Packard Company
-
-Permission to use, copy, modify, distribute and sell this software
-and its documentation for any purpose is hereby granted without fee,
-provided that the above copyright notice appear in all copies and
-that both that copyright notice and this permission notice appear
-in supporting documentation.  Hewlett-Packard Company makes no
-representations about the suitability of this software for any
-purpose.  It is provided "as is" without express or implied warranty.
-
-Copyright (c) 1996, 1997, 1998, 1999
-Silicon Graphics Computer Systems, Inc.
-
-Permission to use, copy, modify, distribute and sell this software
-and its documentation for any purpose is hereby granted without fee,
-provided that the above copyright notice appear in all copies and
-that both that copyright notice and this permission notice appear
-in supporting documentation.  Silicon Graphics makes no
-representations about the suitability of this software for any
-purpose.  It is provided "as is" without express or implied warranty.
-

-