[cfe-dev] Cannot CMake self-hosted clang on Windows for lack of libxml2

Mon Aug 23 12:20:05 PDT 2021

I bisected back to c4c3883b00d3a6aa657a5e3e515c90c9ea1f81c6 .  Before that,
our CMake scripts still required Python 2, which I no longer have installed
(because it confuses lldb builds to have both Python 2 and 3 on the
machine).  Thus the dependency was probably introduced some time before
April 2020.

So even if it was inadvertent, the problem has existed long enough that we
probably just have to accept that libxml2 is now a requirement for LLVM
builds on Windows.  I'll propose a documentation change.

Adrian.

On Fri, Aug 20, 2021 at 5:31 PM Shoaib Meenai <smeenai at fb.com> wrote:

> This is a workaround and not a solution, but you should be able to add
> /manifest:no to your link flags (similar to
> https://github.com/llvm/llvm-project/blob/3187a4f3f1d4d68a75a21154569db1232a62a57d/llvm/cmake/platforms/WinMsvc.cmake#L286-L287)
> to prevent CMake from trying to invoke mt.
>
>
>
> *From: *cfe-dev <cfe-dev-bounces at lists.llvm.org> on behalf of cfe-dev <
> cfe-dev at lists.llvm.org>
> *Reply-To: *Adrian McCarthy <amccarth at google.com>
> *Date: *Friday, August 20, 2021 at 4:35 PM
> *To: *cfe-dev <cfe-dev at lists.llvm.org>
> *Subject: *[cfe-dev] Cannot CMake self-hosted clang on Windows for lack
> of libxml2
>
>
>
> I recently tried to build a self-hosted clang on Windows, but it fails
> when I use CMake to generate a Ninja file.
>
>
>
> CMake finds my MSVC-built clang and tries to test it.  This invokes
> llvm-mt (the LLVM implementation of the manifest tool).  This tool depends
> on libxml2, which isn't typically installed on Windows.
>
>
>
> I'm told the Windows build shouldn't need to invoke llvm-mt, so this is
> probably due to a CMake change.  Unfortunately, I don't know how far back I
> have to go to find a working build so that I can bisect the breaking
> change.  It's been a long time since I've tried a self-hosted build.
>
>
>
> Maybe somebody changed this intentionally, and we just need to update the
> documentation to include libxml2 on the (already very long) list of things
> Windows developers have to install in order to build llvm.
>
>
>
> If you have knowledge of this, let me know.  In the meantime, I'll attempt
> to bisect.
>
>
>
> See below for the gory details.
>
>
>
> Adrian.
>
>
>
> cmake -GNinja -DPYTHON_HOME="C:\Program Files\Python38"
> -DLLDB_PYTHON_HOME="C:\Program Files\Python38"
> -DPYTHON_EXECUTABLE="C:\Program Files\Python38\bin\python.exe"
> -DPython3_ROOT_DIR="C:\Program Files\Python38" -DPython3_FIND_REGISTRY=LAST
> ..\..\llvm-project\llvm -DLLVM_ENABLE_ZLIB=OFF
> -DLLVM_ENABLE_PROJECTS="clang;lld;lldb" -DLLVM_TARGETS_TO_BUILD=X86
> -DCMAKE_BUILD_TYPE=Release
> -DCMAKE_C_COMPILER=D:/src/llvm/build/ninja/bin/clang-cl.exe
> -DCMAKE_CXX_COMPILER=D:/src/llvm/build/ninja/bin/clang-cl.exe
>
>
>
> -- The C compiler identification is Clang 14.0.0 with MSVC-like
> command-line
> -- The CXX compiler identification is Clang 14.0.0 with MSVC-like
> command-line
> -- The ASM compiler identification is Clang
> -- Found assembler: D:/src/llvm/build/ninja/bin/clang-cl.exe
> -- Detecting C compiler ABI info
> -- Detecting C compiler ABI info - failed
> -- Check for working C compiler: D:/src/llvm/build/ninja/bin/clang-cl.exe
> -- Check for working C compiler: D:/src/llvm/build/ninja/bin/clang-cl.exe
> - broken
> CMake Error at C:/Program Files (x86)/Microsoft Visual
> Studio/2019/Professional/Common7/IDE/CommonExtensions/Microsoft/CMake/CMake/share/cmake-3.20/Modules/CMakeTestCCompiler.cmake:66
> (message):
>
>   The C compiler
>
>
>     "D:/src/llvm/build/ninja/bin/clang-cl.exe"
>
>   is not able to compile a simple test program.
>
>   It fails with the following output:
>
>     Change Dir: D:/src/llvm/build/selfhost/CMakeFiles/CMakeTmp
>
>     Run Build
> Command(s):C:/PROGRA~2/MICROS~1/2019/PROFES~1/Common7/IDE/COMMON~1/MICROS~1/CMake/Ninja/ninja.exe
> cmTC_62af5 && [1/2] Building C object
> CMakeFiles\cmTC_62af5.dir\testCCompiler.c.obj
>     [2/2] Linking C executable cmTC_62af5.exe
>     FAILED: cmTC_62af5.exe
>     cmd.exe /C "cd . && "C:\Program Files (x86)\Microsoft Visual
> Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake\bin\cmake.exe"
> -E vs_link_exe --intdir=CMakeFiles\cmTC_62af5.dir
> --rc=C:\PROGRA~2\WI3CF2~1\10\bin\100183~1.0\x64\rc.exe
> --mt=D:\src\llvm\build\ninja\bin\llvm-mt.exe --manifests  --
> D:\src\llvm\build\ninja\bin\lld-link.exe /nologo
> CMakeFiles\cmTC_62af5.dir\testCCompiler.c.obj  /out:cmTC_62af5.exe
> /implib:cmTC_62af5.lib /pdb:cmTC_62af5.pdb /version:0.0 /machine:x64
>  /debug /INCREMENTAL /subsystem:console  kernel32.lib user32.lib gdi32.lib
> winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib
> advapi32.lib && cd ."
>     MT: command "D:\src\llvm\build\ninja\bin\llvm-mt.exe /nologo /manifest
> CMakeFiles\cmTC_62af5.dir/intermediate.manifest
> /out:CMakeFiles\cmTC_62af5.dir/embed.manifest /notify_update" failed (exit
> code 0x1) with the following output:
>     llvm-mt: error: no libxml2
>     llvm-mt: ignoring unsupported 'notify_update' option
>
>     ninja: build stopped: subcommand failed.
>
>
>
>
>
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