= CLANG =



[[TOC(Projects/CLANG, depth=2)]]


This page is intended to capture notes and information about using [http://clang.llvm.org/ 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:
 *  newlib uses pragma warning which clang does not know
  *  [http://llvm.org/bugs/show_bug.cgi?id=10300 PR10300].
  *  Reported 2011-07-07 to http://lists.cs.uiuc.edu/pipermail/cfe-dev/2011-July/date.html

 *  clang does not know registers used in RTEMS i386 FP context macros
  *  [http://llvm.org/bugs/show_bug.cgi?id=10299 PR10299].
  *  Reported 2011-07-07 to http://lists.cs.uiuc.edu/pipermail/cfe-dev/2011-July/016022.html

 *  clang does not preprocess score/cpu/i386/cpu_asm.S the same as gcc.  Generates incorrect code. 
  *  [http://llvm.org/bugs/show_bug.cgi?id=10298 PR10298].
  *  Initially reported 2011-07-07 to http://lists.cs.uiuc.edu/pipermail/cfe-dev/2011-July/016019.html

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 not successfully built RTEMS yet.  I assume the problem is that I must pass in some combination of CC, CC_FOR_TARGET, and CC_FOR_BUILD in a way that makes the RTEMS build happy.
= References =

 *  [http://clang.llvm.org/ Clang Page]
 *  [https://www.studentrobotics.org/trac/wiki/Beagleboard_DSP/Building TIC6x+Newlib Toolchain Build Instructions]