trouble building clang with libc++ on linux

Clang Frontend
1

Does someone have a working shell script that builds and installs clang and libc++ on linux using gcc?

I’ve been trying to follow the instructions at http://libcxx.llvm.org to build on linux, where it says

The following instructions are for building libc++ on FreeBSD, Linux, or Mac using libc++abi as the C++ ABI library. On Linux, it is also possible to use libsupc++ or libcxxrt.

In-tree build:

  • Check out libcxx and libcxxabi into llvm/projects
  • cd llvm
  • mkdir build && cd build
  • cmake .. # Linux may require -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
  • make cxx
    I can’t tell what libsupc++ or libcxxrt are for from these pages, so I’m ignoring that.

I take it that the above instructions assume that I have already built clang. Right? It doesn’t say so.

Here’s an example of an attempt:

0 Tue 0:56:53 yost s6 /usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src
568 Z% ls -l projects
total 12
-rw-r–r–. 1 yost mill 999 Feb 27 2014 CMakeLists.txt
lrwxrwxrwx. 1 yost mill 27 Nov 24 15:10 compiler-rt → …/…/compiler-rt-3.5.0.src
lrwxrwxrwx. 1 yost mill 22 Nov 24 15:10 libcxx → …/…/libcxx-3.5.0.src
lrwxrwxrwx. 1 yost mill 25 Nov 24 15:10 libcxxabi → …/…/libcxxabi-3.5.0.src
-rw-r–r–. 1 yost mill 664 Dec 12 2011 LLVMBuild.txt
-rw-r–r–. 1 yost mill 1013 Mar 12 2014 Makefile
0 Tue 0:56:54 yost s6 /usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src
569 Z% mkdir build ; cd build
0 Tue 0:56:59 yost s6 /usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build
570 Z% cmake …
– The C compiler identification is GNU 4.4.7
– The CXX compiler identification is GNU 4.4.7
– Check for working C compiler: /usr/bin/cc
– Check for working C compiler: /usr/bin/cc – works
– Detecting C compiler ABI info
– Detecting C compiler ABI info - done
– Check for working CXX compiler: /usr/bin/c++
– Check for working CXX compiler: /usr/bin/c++ – works
…
CMake Error at cmake/modules/HandleLLVMOptions.cmake:13 (message):
Host GCC version must be at least 4.7!
Call Stack (most recent call first):
CMakeLists.txt:315 (include)

– Configuring incomplete, errors occurred!
See also “/usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build/CMakeFiles/CMakeOutput.log”.
See also “/usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build/CMakeFiles/CMakeError.log”.
1 Tue 0:57:10 yost s6 /usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build
571 Z% which g++
/usr/local/gcc/4.8.2/bin/g++
0 Tue 0:57:26 yost s6 /usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build
572 Z%

It seems that cmake doesn’t bother to look in my PATH, so I try saying exactly where to find clang.

0 Tue 1:00:18 yost s6 /usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build
815 Z% cmake -DCMAKE_C_COMPILER=/usr/local/llvm/3.5.0/bin/clang -DCMAKE_CXX_COMPILER=/usr/local/llvm/3.5.0/bin/clang++ …
– Target triple: x86_64-unknown-linux-gnu
– Native target architecture is X86
– Threads enabled.
– Doxygen disabled.
– Sphinx disabled.
CMake Error at cmake/modules/HandleLLVMOptions.cmake:13 (message):
Host GCC version must be at least 4.7!
Call Stack (most recent call first):
CMakeLists.txt:315 (include)

– Configuring incomplete, errors occurred!
See also “/usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build/CMakeFiles/CMakeOutput.log”.
See also “/usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build/CMakeFiles/CMakeError.log”.
You have changed variables that require your cache to be deleted.
Configure will be re-run and you may have to reset some variables.
The following variables have changed:
CMAKE_C_COMPILER= /usr/local/llvm/3.5.0/bin/clang
CMAKE_CXX_COMPILER= /usr/local/llvm/3.5.0/bin/clang++

– Generating done
– Build files have been written to: /usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build
1 Tue 1:00:49 yost s6 /usr/local/modulebuild/llvm/3.5.0…libc++/build/llvm-3.5.0.src/build
816 Z%

Still it seems to be looking for gcc in /usr/bin/. Why?

I am on a CentOS system, with old versions of tools in /usr and /usr/bin. Everything I build with has to come from PATH, etc.

Thanks

2

Does someone have a working shell script that builds and installs clang
and libc++ on linux using gcc?

No.

I’ve been trying to follow the instructions at http://libcxx.llvm.org to
build on linux, where it says

These should be fine.

    The following instructions are for building libc++ on FreeBSD,
    Linux, or Mac using libc++abi <http://libcxxabi.llvm.org/&gt; as the
    C++ ABI library. On Linux, it is also possible to use libsupc++
    <“libc++” C++ Standard Library — libc++ documentation; or libcxxrt
    <“libc++” C++ Standard Library — libc++ documentation.

    In-tree build:

      o Check out libcxx and libcxxabi <http://libcxxabi.llvm.org/&gt; into
        llvm/projects
      o |cd llvm|
      o |mkdir build && cd build|
      o |cmake .. # Linux may require -DCMAKE_C_COMPILER=clang
        -DCMAKE_CXX_COMPILER=clang++|
      o |make cxx|

I can’t tell what libsupc++ or libcxxrt are for from these pages, so I’m
ignoring that.

I take it that the above instructions assume that I have already built
clang. Right? It doesn’t say so.

No, clang or llvm does not need to be built first.

Here’s an example of an attempt:
...
CMake Error at cmake/modules/HandleLLVMOptions.cmake:13 (message):
   Host GCC version must be at least 4.7!
Call Stack (most recent call first):
   CMakeLists.txt:315 (include)

Right, so it's trying to compile with your system compiler, which is gcc 4.4.7, and it needs gcc of at least 4.7.

It seems that cmake doesn’t bother to look in my PATH, so I try saying
exactly where to find clang.

Are you trying to use gcc to build or clang to build?

0 Tue 1:00:18 yost s6
/usr/local/modulebuild/llvm/3.5.0..libc++/build/llvm-3.5.0.src/build
815 Z% cmake -DCMAKE_C_COMPILER=/usr/local/llvm/3.5.0/bin/clang
-DCMAKE_CXX_COMPILER=/usr/local/llvm/3.5.0/bin/clang++ ..
-- Target triple: x86_64-unknown-linux-gnu
-- Native target architecture is X86
-- Threads enabled.
-- Doxygen disabled.
-- Sphinx disabled.
CMake Error at cmake/modules/HandleLLVMOptions.cmake:13 (message):
   Host GCC version must be at least 4.7!
Call Stack (most recent call first):
   CMakeLists.txt:315 (include)

-- Configuring incomplete, errors occurred!
See also
"/usr/local/modulebuild/llvm/3.5.0..libc++/build/llvm-3.5.0.src/build/CMakeFiles/CMakeOutput.log".
See also
"/usr/local/modulebuild/llvm/3.5.0..libc++/build/llvm-3.5.0.src/build/CMakeFiles/CMakeError.log".
You have changed variables that require your cache to be deleted.
Configure will be re-run and you may have to reset some variables.

It's telling you that YOU need to delete CMakeCache...

The following variables have changed:
CMAKE_C_COMPILER= /usr/local/llvm/3.5.0/bin/clang
CMAKE_CXX_COMPILER= /usr/local/llvm/3.5.0/bin/clang++

Because these variables have changed.

-- Generating done
-- Build files have been written to:
/usr/local/modulebuild/llvm/3.5.0..libc++/build/llvm-3.5.0.src/build
1 Tue 1:00:49 yost s6
/usr/local/modulebuild/llvm/3.5.0..libc++/build/llvm-3.5.0.src/build
816 Z%

Still it seems to be looking for gcc in /usr/bin/. Why?

I am on a CentOS system, with old versions of tools in /usr and
/usr/bin. Everything I build with has to come from PATH, etc.

Delete CMakeCache, and point cmake to a version of GCC of at least 4.7.

Ben