[CMake] LLDB framework / shared library

Hello Alex, hello Pavel

I spent some time creating/streamlining our CMake infrastructure downstream of LLDB and learned a few things about bundles, versions, code-signing etc. (mostly on the Darwin side of things). I am currently sorting out what can be upstreamed and prepare reviews.

Some work is still todo for the LLDB shared library/framework (for simplicity I will call it LLDB.framework). It would be great to know, if you have concerns or comments on the following points:

(1) The liblldb target builds the actual LLDB.framework, while the lldb-framework target adds headers, symlinks, etc. What is the reason for this separation? Can I merge that into one target with post-build steps?

(2) In previous reviews there was an effort to centralize the code for building LLDB.framework, which makes sense to me. With the current LLDBFramework.cmake approach, however, it’s spread over at least 3 different files (lldb/CMakeLists.txt for init and lldb/source/API/CMakeLists.txt for actual definition). In a similar case downstream, I did all that in a single CMakeLists.txt in the source folder. While I see that LLDBFramework affects the whole project, I don’t see why we need a separate LLDBFramework.cmake (BTW upstream it’s included only once). Do you think I can move things to lldb/source/API/CMakeLists.txt where possible?

(3) Currently the build directory for LLDB.framework is determined from LLDB_FRAMEWORK_INSTALL_DIR, which I think is a little confusing. Can I clean this up? (e.g. having a LLDB_FRAMEWORK_BUILD_DIR)

(4) With Xcode, executables are emitted in bin and copied to LLDB.framework where necessary. CMake emits them into LLDB.framework directly and creates symlinks to bin. With LLVM_EXTERNALIZE_DEBUGINFO on Darwin, this has the effect, that by default their dSYMs will end up in LLDB.framework. Thus, I would prefer the Xcode behaviour here.

(5) Couldn’t (4) also simplify the INCLUDE_IN_SUITE logic? I would consider it to be LLDB.framework’s responsibility to set dependencies and adjust RPATHs for all required artefacts. The tools wouldn’t need to care about that (though, they could still check LLDB_BUILD_FRAMEWORK). The RPATH-login for case ARG_INCLUDE_IN_SUITE && LLDB_BUILD_FRAMEWORK is quite complicated though and I wonder if there are strong reasons not to do that. What do you think?

(6) Just out of interest: why is LLDB_BUILD_FRAMEWORK is not supported on CMake < 3.7?

Best
Stefan

cc lldb-dev since the original message cc'd it.

Hello Stefan,

first off, I want to point out that although I spent a lot of time
digging through our cmake files, I am not using the framework build, nor
am familiar with it's details.

I also don't know why the framework was split into multiple targets.
What I do know is that we then ended up adding extra indirections so
that we can make setting up dependencies easier (lldb can just depend on
${LLDB_SUITE_TARGET} without knowing whether framework was enabled or
not). If you can merge everything into a single target, then this
indirection could also go away.

Your ideas sound reasonable to me. As Alex points out, centralizing
everything to API/CMakeLists.txt may be tricky, although I agree that is
the natural place to do this sort of thing. The trickyness comes from
the fact that our cmake files are not processed in dependency order.
Although this would be somewhat unconventional, I wouldn't be opposed to
changing the cmake processing order so that it more closely matches the
dependencies. If that makes things easier for you, that is.

One way to achieve this would be to take out source/API and
tools/debugserver invocations out of source and tools CMakeLists.txt
files, respectively. and put them into the top level file. So then the
top level file would do something like:

add_subdirectory(source) # Build all consituent libraries

# Tools going into the lldb framework
add_subdirectory(tools/debugserver)
add_subdirectory(tools/argdumper)
...

add_subdirectory(source/API) # Build LLDB.framework (or liblldb) itself
add_subdirectory(tools) # Build tools that depend on the framework

This could be cleaned up if we moved the source code around, but I'm not
sure we want to take that hit (I don't think it's worth it). Also, it's
just an idea, I don't know whether that will make your job easier or not.

Good luck,
pavel

Hi Alex, hi Pavel

Thanks for your feedback and sorry for the late reply, I was a little busy on the other sites.

Ok, so making the LLDB_FRAMEWORK_INSTALL_DIR vs. LLDB_FRAMEWORK_BUILD_DIR distinction and changing the approach for tools from symlink to copy sound like good tasks to start with.

I will see how far I get without changing the processing order. I am a little afraid about Pandora's box here. Anyway, thanks for the explanation and proposal!

Had a look at the history and it turned out the reason for the 3.7 requirement was a bug in CMake (https://gitlab.kitware.com/cmake/cmake/issues/16363). There was a workaround, but it was dropped (https://reviews.llvm.org/rLLDB289841). Policy-wise CMake always acts as if it was cmake_minimum_required, so I am always sceptic about version checks, but for a bug like this it seems fine. Let’s keep it as long as cmake_minimum_required is below.

Best
Stefan