[Buildroot] Upgrading LLVM and Clang to version 11.0.0... issue with libclc

[Romain Naour <romain.naour@gmail.com>]

Hello Michael, All,

Le 07/01/2021 ? 17:59, Michael Opdenacker a ?crit?:
> Hi,
> 
> I'm trying to bump up the versions of LLVM, Clang and lld to 11.0.0
> instead of 9.x currently. The end goal is to test and share a new
> iteration of Matthew Weber's patches for compiler-rt support.

Thanks for this work!

> 
> Though the upgrades were effortless, this broke support for libclc which
> source code has been included in the llvm-project git repository. The
> libclc sources are still available as a separate archive (for projects
> such as Buildroot that want to build each component separately), but
> configure.py script has been replaced by CMake used by LLVM.
> 
> Here's what libclc.mk looks like so far:
> 
> ################################################################################
> #
> # libclc
> #
> ################################################################################
> 
> # LLVM, Clang, lld and libclc should be version bumped together
> LIBCLC_VERSION = 11.0.0
> LIBCLC_SITE =
> https://github.com/llvm/llvm-project/releases/download/llvmorg-$(LIBCLC_VERSION)
> LIBCLC_SOURCE = libclc-$(LIBCLC_VERSION).src.tar.xz
> LIBCLC_LICENSE = BSD-like or MIT
> LIBCLC_LICENSE_FILES = LICENSE.TXT
> 
> LIBCLC_DEPENDENCIES = host-clang host-llvm
> LIBCLC_INSTALL_STAGING = YES
> 
> $(eval $(cmake-package))
> 
> Unfortunately, I haven't managed to build libclc yet. Its configuration
> step fails as follows (see the full log at the end of this e-mail):
> 
> -- Check for working CLC compiler:
> /home/mike/buildroot/output/host/bin/clang -- broken
> CMake Error at cmake/CMakeTestCLCCompiler.cmake:40 (message):
> ? The CLC compiler "/home/mike/buildroot/output/host/bin/clang" is not able
> ? to compile a simple test program.

I believe CMake try to check clang as cross-compiler before using it.
Can you share the CMake error log file ?

For now, host/bin/clang can't be used as cross-compiler to build application
(the simple test program) because we need to add a wrapper like for gcc.

configure.py was kind enough to accept host/bin/clang as is to build libclc library.

If we can skip the cmake test, the library should build as before.

> 
> How would I be supposed to add CLC support to Clang when the Clang and
> LLVM source archives that we build don't contain libclc code?
> 
> This sounds like a chicken and egg issue. It would be so much easier to
> grab the whole llvm-project sources and compile LLVM and Clang with all
> the features that we want. But hey, there must be good reasons for
> building components separately.

I don't think we have to build libclc before clang, as you can see in the
current packaging only mesa3d depends on libclc. Clang itself doesn't depend on
libclc.

You can find some details about the initial work in this blog:
https://www.linuxembedded.fr/2018/07/llvmclang-integration-into-buildroot/

> 
> Thanks in advance for any light shed on this topic...

Best regards,
Romain

> 
> Cheers,
> 
> Michael.
>