lld stand-alone build not working due to libunwind header dependency

[tstellar]

Bugzilla Link	49228
Version	unspecified
OS	Linux
Blocks	#48661
CC	@aabacchus,@foutrelis,@gkmhub,@MaskRay,@int3,@SeanBuller,@serge-sans-paille,@smeenai

Extended Description

2124ca1 adds a dependency on a libunwind header and the CMake changes in this commit cause the stand-alone builds of lld to stop working.

[tstellar]

In addition to the standalone build not working, lld now depends on libunwind, is there going to be tighter coupling between these two projects going forward?

[MaskRay]

lld/MachO/UnwindInfoSection.h just uses C enum and struct definitions in
libunwind/include/mach-o/compact_unwind_encoding.h . There is no undesired link-time dependency. Any tighter coupling should be a concern.

As-is, include_directories(${LLVM_MAIN_SRC_DIR}/../libunwind/include) in lld/MachO/CMakeLists.txt looks fine to me:

With llvm-config in PATH,
mkdir out
cd out
cmake -GNinja -B. -H/path/to/llvm-project/lld
ninja # lld is built

[tstellar]

lld/MachO/UnwindInfoSection.h just uses C enum and struct definitions in
libunwind/include/mach-o/compact_unwind_encoding.h . There is no undesired
link-time dependency. Any tighter coupling should be a concern.

As-is, include_directories(${LLVM_MAIN_SRC_DIR}/../libunwind/include) in
lld/MachO/CMakeLists.txt looks fine to me:

With llvm-config in PATH,
mkdir out
cd out
cmake -GNinja -B. -H/path/to/llvm-project/lld
ninja # lld is built

What I mean by a stand-alone build is that you can build lld without having any of the other source code from the monorepo. This example only works if you still have the full monorepo source.

[smeenai]

Would moving that libunwind header into LLVM (and then referencing the LLVM header from both libunwind and LLD) fix the issue? To be clear, I'm not familiar enough with libunwind to know if that's an acceptable solution; I was just curious. I know that for a while, we wanted at least libc++ and libc++abi to build without needing any LLVM bits whatsoever, and I think we still have the demangler duplicated between LLVM and libc++abi, so maybe we'd just need to duplicate the header in this case as well :(

[tstellar]

This probably deserves a project wide discussion about what is and isn't supported with regards to stand-alone builds.

I'm not really a fan of duplicating files, even if it does make lld easier to build for my (Linux distribution) use case. Moving the header into LLVM would help if that makes sense to do. If not, the other option would be to teach lld to find the necessary header in the system include directory.

[tstellar]

This bug was not resolved in time for the 12.0.0 release, so it will have to wait for 12.0.1.

If you feel this is a high-priority bug that should be fixed for 12.0.0, please re-add release-12.0.0 to the Blocks field and add a comment explaining why this is high-priority.

[SeanBuller]

I was just wondering if there has been any action on this ticket? I am still observing this issue in release 12.0.1.

[tstellar]

mentioned in issue #48661

[andrewrk]

Copy pasting the issue #53553 here as requested:

---

Steps to reproduce:

cd ~/Downloads
git clone https://github.com/llvm/llvm-project llvm-project-14
cd llvm-project-14
git checkout release/14.x

# LLVM
cd llvm
mkdir build-release
cd build-release
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/local/llvm14-release -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-release -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_LIBXML2=OFF -G Ninja -DLLVM_PARALLEL_LINK_JOBS=1
ninja install
cd ../..

# LLD
cd lld
mkdir build-release
cd build-release
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/local/llvm14-release -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-release -DCMAKE_BUILD_TYPE=Release  -G Ninja -DLLVM_PARALLEL_LINK_JOBS=1 -DCMAKE_CXX_STANDARD=17
ninja install

Output:

[2/58] Building CXX object ELF/CMakeFiles/lldELF.dir/OutputSections.cpp.o
FAILED: ELF/CMakeFiles/lldELF.dir/OutputSections.cpp.o 
/nix/store/apfyw9rd0280rpj2x685s6anyjjnz04l-gcc-wrapper-10.3.0/bin/g++ -DGTEST_HAS_RTTI=0 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/andy/Downloads/llvm-project-14/lld/build-release/ELF -I/home/andy/Downloads/llvm-project-14/lld/ELF -I/home/andy/Downloads/llvm-project-14/lld/include -I/home/andy/Downloads/llvm-project-14/lld/build-release/include -I/include -I/home/andy/local/llvm14-release/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wimplicit-fallthrough -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wmisleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -fno-rtti -MD -MT ELF/CMakeFiles/lldELF.dir/OutputSections.cpp.o -MF ELF/CMakeFiles/lldELF.dir/OutputSections.cpp.o.d -o ELF/CMakeFiles/lldELF.dir/OutputSections.cpp.o -c /home/andy/Downloads/llvm-project-14/lld/ELF/OutputSections.cpp
/home/andy/Downloads/llvm-project-14/lld/ELF/OutputSections.cpp:19:10: fatal error: llvm/Config/config.h: No such file or directory
   19 | #include "llvm/Config/config.h" // LLVM_ENABLE_ZLIB
      |          ^~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
[3/58] Building CXX object MachO/CMakeFiles/lldMachO.dir/Driver.cpp.o
FAILED: MachO/CMakeFiles/lldMachO.dir/Driver.cpp.o 
/nix/store/apfyw9rd0280rpj2x685s6anyjjnz04l-gcc-wrapper-10.3.0/bin/g++ -DGTEST_HAS_RTTI=0 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/andy/Downloads/llvm-project-14/lld/build-release/MachO -I/home/andy/Downloads/llvm-project-14/lld/MachO -I/home/andy/Downloads/llvm-project-14/lld/include -I/home/andy/Downloads/llvm-project-14/lld/build-release/include -I/include -I/home/andy/local/llvm14-release/include -I/../libunwind/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wimplicit-fallthrough -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wmisleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -fno-rtti -MD -MT MachO/CMakeFiles/lldMachO.dir/Driver.cpp.o -MF MachO/CMakeFiles/lldMachO.dir/Driver.cpp.o.d -o MachO/CMakeFiles/lldMachO.dir/Driver.cpp.o -c /home/andy/Downloads/llvm-project-14/lld/MachO/Driver.cpp
In file included from /home/andy/Downloads/llvm-project-14/lld/MachO/Driver.cpp:23:
/home/andy/Downloads/llvm-project-14/lld/MachO/UnwindInfoSection.h:16:10: fatal error: mach-o/compact_unwind_encoding.h: No such file or directory
   16 | #include "mach-o/compact_unwind_encoding.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
[19/58] Building CXX object ELF/CMakeFiles/lldELF.dir/SyntheticSections.cpp.o
ninja: build stopped: subcommand failed.

[andrewrk]

As a release tester I would please request this to be solved before a release candidate is cut. So far I have not been able to test the release/14.x branch.

[jameshilliard]

Yeah, last version I'm seeing without this bug is 11.1.0, and since we use stand-alone builds it seems to be a blocker for us.