[cfe-users] Need a GCC-free LLVM/Clang on Linux.

[Chris Green via cfe-users]

Hi,

Many thanks for this advice. I'm just now getting back to this. If I 
solve the libgcc_s problem, I'll let you know.

Thanks again,

Chris.

On 2/19/20 4:02 PM, Richard Smith wrote:
> On Thu, 23 Jan 2020 at 07:24, Christopher H Green via cfe-users 
> <cfe-users at lists.llvm.org <mailto:cfe-users at lists.llvm.org>> wrote:
>
>     Hi,
>
>     I've spent the last several days trying to build a fast,
>     full-featured relocatable distribution of LLVM/Clang 9.0.1 on
>     Linux RHEL7, which has an older native GCC (4.8.5)—I can't require
>     the RH toolset. I have access to a modern version of GCC in order
>     to make the stage-1 build, but I need the final product not only
>     to be relocatable, but also to be free of any dependence on that
>     GCC or its libraries. In other words, I want to be able to
>     distribute an LLVM/CLang which defaults to compiling using libc++,
>     libcxxabi, compiler-rt, libunwind, and ldd, and which itself
>     depends neither on libstdc++ or  libgcc_s. I'd also like to be
>     able to to provide LTO, but whether the compiler is itself the
>     beneficiary of LTO is optional. As a final wish, I'd like the
>     distribution as installed to serve as an SDK against which to
>     build other components such as separately packaged lldb and f18.
>     Oh, and I want a pony.
>
>     Here's what I have so far (CMake cache files attached for stages 1
>     and 2). Invoked  in a separate build directory with:
>
>     env CC=gcc-9 CXX=g++-9 \
>     'CXXFLAGS=-Wno-cast-function-type -Wno-deprecated-copy -Wno-init-list-lifetime -Wno-pessimizing-move -Wno-redundant-move -Wno-uninitialized -Wno-unused-function -Wno-unused-variable' \
>     cmake -GNinja -C FNAL.cmake -DCMAKE_INSTALL_PREFIX=<install-path> \
>     -DBOOTSTRAP_LLVM_CXX_STD=c++17 <src-path>
>     ninja
>     ninja install
>
>     (The CXXFLAGS are just to keep the noise down during the stage-1
>     build).
>
>     I appear (finally) to have a mostly functioning build /in situ/,
>     but the installed compiler depends upon libstdc++ to be able to
>     run, and I should have put --rtlib=compiler-rt in LINKER_FLAGS
>     rather than CXX_FLAGS. Additionally, I haven't been able to come
>     up with a good set of targets for LLVM_DISTRIBUTION_COMPONENTS,
>     but when I do I think I need to exclude static libraries if I'm
>     doing LTO, no?
>
>     I suspect I need a three stage build—well, two stage 2s, at
>     least—but any advice would be appreciated as I'm wandering around
>     in the dark at this point.
>
> I have a two-stage setup that builds a GCC-free Clang except for 
> libgcc_s (I've not looked at what's pulling that in yet, but I expect 
> that's resolvable).
>
> My stage1 cmake setup has: -DCLANG_DEFAULT_CXX_STDLIB=libc++ 
> -DCLANG_DEFAULT_RTLIB=compiler-rt
> My stage2 cmake setup additionally 
> has: -DLIBCXXABI_USE_LLVM_UNWINDER=ON -DLIBCXXABI_USE_COMPILER_RT=ON 
> -DLIBCXX_USE_COMPILER_RT=ON
> (and points CMAKE_C_COMPILER and CMAKE_CXX_COMPILER at the stage1 clang).
>
> There might be some other things you need, I'm not sure. But it should 
> be doable in two stages.
>
>     Many thanks for any help,
>
>     Chris.
>
>
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