Need a GCC-free LLVM/Clang on Linux.

Clang Frontend Using Clang
1

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.

Many thanks for any help,

Chris.

FNAL-stage2.cmake (2.03 KB)

FNAL.cmake (2.43 KB)

2

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.

3

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.

4

Hi,

build-clang.log.bz2 (28 KB)

FNAL-stage2.cmake (2.38 KB)

FNAL.cmake (2.98 KB)