• BuildingFreeBSDWithClang

Building FreeBSD with clang/llvm

This is an effort to get FreeBSD to build with clang/llvm, clang is a compiler built on the Low Level Virtual Machine compiler infrastructure. Both clang and llvm are released under a BSD like license. This is work in progress, play at your own risk

Status

The amd64 and i386 kernels boot multiuser. All of userland compiles except for libc, libobjc (cc1obj: not found) and C++ code. There are some pending patches to FreeBSD.

Tracking bug is 3696.

Quickstart

CLANGBSD IS WORK-IN-PROGRESS, THINGS MIGHT NOT WORK

Checkout the ClangBSD branch:

# svn co svn://svn.freebsd.org/base/projects/clangbsd src

Setup /etc/src.conf like this:

WITH_CLANG=
WITH_CLANG_IS_CC=
NO_WERROR=
WERROR=
# Don't forget this when using Jails!
NO_FSCHG=

Building/installing world (into a chroot).

# make buildworld
# make installworld DESTDIR=/usr/obj/clang
# chroot /usr/obj/clang /bin/echo Hello clang world!
Hello clang world!
# chroot /usr/obj/clang /bin/tcsh

Building/installing kernel.

# make kernel KERNCONF=GENERIC INSTKERNNAME=clang

Boot it.

OK set module_path=/boot/clang
OK boot clang

To update the ClangBSD tree perform the following steps.

# cd src/
# svn up

Using the static analyzer

On the kernel (This requires lots of space in the output directory, 406M when using "scan-build make MODULES_OVERRIDE=").

# cd /sys/{amd64,i386}/conf/
# config GENERIC
# cd ../compile/GENERIC/
# make depend
# scan-build make MODULES_OVERRIDE=
# {firefox,epiphany,konqueror,lynx,less} /tmp/scan-build-YYYY-MM-DD-N/index.html

On a userland program.

# cd /usr/src/usr.bin/make/
# make cleandir && make obj && make depend
# scan-build make
# {firefox,epiphany,konqueror,lynx,less} /tmp/scan-build-YYYY-MM-DD-N/index.html

Using the analyzer on vanilla sources, no ClangBSD required

Scanning the FreeBSD sources using the static analyzer requires you to:

# svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm
# cd llvm/tools && svn co http://llvm.org/svn/llvm-project/cfe/trunk clang
# cd .. && ./configure --enable-optimized && gmake
# cp -p tools/clang/utils/ccc-analyzer tools/clang/utils/scan-build tools/clang/utils/scanview.css tools/clang/utils/sorttable.js Release/bin

Now you have all the necessary tools in llvm/Release/bin. They need to be next to each other, as we will be using the full-path to scan-build later and it must find clang-cc, which it searches in it's own directory and $PATH. As $PATH will be cleansed during buildworld, only the first option remains.

Running the analyzer is now as easy as

# cd /usr/src && /path/to/llvm/Release/bin/scan-build -k make buildworld

Weekly scans of buildworld and buildkernel can be studied at https://www.spoerlein.net/scan-build. The insane amount of false positives due to missing intra-procedural analysis (IPA) in ccc-analyzer makes them not very useful though. One run usually produces 3 GB of HTML output.

Link Time Optimizations

LLVM supports LTO. It can be used by these pseudo steps

0) build gold and libLLVMgold.so (see http://llvm.org/docs/LinkTimeOptimization.html)
1) CFLAGS+=-emit-llvm
2) setenv LD "/tmp/ld-new --plugin /tmp/libLLVMgold.so"
3) setenv CC clang
4) build the kernel

This currently does not work because of assertion being hit in llvm. Once this is fixed I dont know if the kernel works. There are suggestions
for using export maps. Investigate that.

This does not link because of missing symbols. Some variation of SYSTEM_LD from conf/kern.pre.mk should be used though. This is work in progress.

Automatic test generation with KLEE

KLEE is a symbolic virtual machine built on top of the LLVM compiler infrastructure. More about KLEE here and paper here.

Building KLEE

# svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm
# svn co http://llvm.org/svn/llvm-project/cfe/trunk llvm/tools/clang
# svn co http://llvm.org/svn/llvm-project/klee/trunk klee
# cd llvm/
# ./configure --prefix=/usr/local --enable-optimized --enable-targets=host-only --enable-bindings=none
# gmake
# gmake install
# cd ../klee/
# ./configure --with-llvm=$PWD/../llvm
# gmake LLVMGCC=/usr/local/bin/clang
# cp Release/bin/* /usr/local/bin/
# cp Release/lib/* /usr/local/lib/

Using KLEE

# cd /usr/src/usr.bin/touch/
# clang -c -g -emit-llvm -o touch.bc touch.c
# klee touch.bc
KLEE: output directory = "klee-out-0"
...

More to come later...

Known issues

• FreeBSD printf format-extensions need implementation

Contacts

• irc://irc.oftc.net/#freebsd-clang

• irc://irc.oftc.net/#llvm

• RomanDivacky, PawelWorach and EdSchouten

Resources

• Introduction to the LLVM Compiler System

• LLVM and Clang: Next Generation Compiler Technology

• LLVM 2.0 and Beyond!(Google Tech Talk Video)

• LLVM New C Front-end part 1234