wiki:Projects/CLANG

CLANG

This page is intended to capture notes and information about using Clang to compile RTEMS.

All supporting files, patches, replacement files, etc. needed should be in http://www.rtems.org/ftp/pub/rtems/people/joel/clang/. If something is missing, let Joel know.

Development Log

Open Issues

These are issues in clang for them to address:

These are issues in clang for us to address:

  • clang does not know the RTEMS include paths. No immediate solution.
  • clang when targeting i386-rtems needs to define USER_LABEL_PREFIX. Other ports probably have something similar and something like a register prefix macro.
  • clang has problem to handle the "-B" option which does not search the header files under the directory include specified by option "-B".

These are issues in newlib:

  • newlib has warnings for PTHREAD_MUTEX_xxx being redefined - need to submit patch.
  • newlib has warnings in rtems specific crt0.c - need to submit patch.

There are the issues identified so far in RTEMS:

  • Remove dependency on -specs or change the format of -specs option from "-specs specs_file" by default to "-specs=specs_file".

Commit History

2011-07-07: Small patch to make sure rtems was defined was committed.

2011-07-01: The initial patches which add RTEMS support to clang and llvm (clang-rtems-20110629.diff and llvm-rtems-20110629.diff) were merged. This was reported in http://lists.cs.uiuc.edu/pipermail/cfe-dev/2011-July/015913.html

Base Tools

For now, you need the regular RTEMS toolchain installed. We are using the normal RTEMS binutils and gdb. In addition, the way I have been building requires using the CPU-rtems4.11-gcc as a helper wrapper.

Building Clang

Check out LLVM and Clang using the instructions at http://clang.llvm.org/get_started.html#build. In my case, I started in a working directory (/users/joel/llvm) and checked out into /users/joel/llvm/llvm. After the checkout completed, I performed the following commands:

cd /users/joel/llvm
mkdir b-llvm
cd b-llvm
../llvm/configure --prefix=/users/joel/llvm/install
make
make install

After this completed, I ensured that my PATH included /opt/rtems-4.11/bin and /users/joel/llvm/install/bin for subsequent builds.

Building Newlib With Clang

I created a script file named /users/joel/llvm/j-newlib with the following contents.

CPU=i386
../newlib-1.19.0/configure --host=${CPU}-rtems4.11 \
  --prefix=/users/joel/llvm/install \
  --with-newlib \
  CC="clang -ccc-host-triple ${CPU}-rtems4.11 -ccc-gcc-name ${CPU}-rtems4.11-gcc" \
  CC_FOR_TARGET="clang -ccc-host-triple ${CPU}-rtems4.11 -ccc-gcc-name ${CPU}-rtems4.11-gcc" \
  CC_FOR_BUILD="clang " \
  PONIES=true \
  AR=${CPU}-rtems4.11-ar \
  AS=${CPU}-rtems4.11-as >c.log 2>&1 && \
make -j4 >b.log 2>&1 && \
make install >i.log 2>&1 

echo $?

newlib must be patched as appropriate for the version of RTEMS being built.

I used the j-newlib script to build newlib as follows:

cd /users/joel/llvm
mkdir b-newlib
cd b-newlib
sh -x ../j-newlib

clang cannot build the file newlib/libc/sys/rtems/crt0.c. There is a replacement of that file on the ftp site. I am not sure if this is a clang bug, questionable code in crt0.c or a combination of the two.

Building RTEMS

I have successfully built RTEMS follow the command below.

CPU=i386
../rtems/configure --target=${CPU}-rtems4.11 \
  --prefix=/users/joel/llvm/install \
  AR=${CPU}-rtems4.11-ar \
  AS=${CPU}-rtems4.11-as \
  CC_FOR_BUILD="clang " \
  CC_FOR_TARGET="clang -ccc-host-triple ${CPU}-rtems4.11 -ccc-gcc-name ${CPU}-rtems4.11-gcc " \
  CC_FOR_HOST="clang -ccc-host-triple ${CPU}-rtems4.11 -ccc-gcc-name ${CPU}-rtems4.11-gcc " >c.log 2>&1 

make RTEMS_BSP="pc386" >b.log 2>&1

There are maybe some bugs in the rtems configure system. when attach the CC_FOR_TARGET,CC_FOR_BUILD flags to the cofigure command, it will generate some config.status inside which will add CC="cross compiler" to every subdir,but some subdir do not expect this CC, like in dir i386-rtems4.11/c/pc386/lib/libbsp/i386/pc386/tools. It contains some host code compiled by host compiler which should be auto detected, if you add CC="cross compiler" it will failed, So if you encounter this error you need delete the CC="cross compiler" command in the file i386-rtems4.11/c/pc386/lib/libbsp/i386/pc386/config.status for tools.

References

Last modified on Feb 27, 2012 at 6:39:42 PM Last modified on Feb 27, 2012, 6:39:42 PM