[lldb-dev] Some API test failures are really opaque/could be improved

Mon Oct 25 21:42:56 PDT 2021

On Mon, Oct 25, 2021 at 1:28 PM Louis Dionne <ldionne at apple.com> wrote:

> I believe the issue is probably not related so much to
> LLVM_ENABLE_PROJECTS vs LLVM_ENABLE_RUNTIMES, but rather to the fact that
> LLVM_ENABLE_RUNTIMES uses per-target runtime directories now (hasn't always
> been the case), which basically means that libc++ ends up in
> `<prefix>/lib/<target-triple>/libc++.so` instead of
> `<prefix>/lib/libc++.so`.
>

Ish, yes. It's a bug in LLVM_ENABLE_RUNTIMES that isn't present in
LLVM_ENABLE_PROJECTS, so for now if I want to run the lldb pretty printer
tests for libc++ on Linux it seems the only way I can is by using the
deprecated functionality of libc++ in LLVM_ENABLE_PROJECTS.

Consider this a bug report (looks like a bug in the lldb CMake
configuration, not in libc++'s build itself, but something to figure out if
Linux lldb devs are going to use libc++ +.ENABLE_RUNTIMES path) on that
deprecation?

> I think you either want to specify the per-target library dir when running
> against libc++, or you want to disable that and use
> `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=OFF` when configuring the runtimes. In
> all cases, you want to be using `LLVM_ENABLE_RUNTIMES` and not
> `LLVM_ENABLE_PROJECTS`, since the latter is deprecated now.
>

I didn't enable LLVM_ENABLE_PER_TARGET_RUNTIME_DIR myself/in the root cmake
config. It looks like it's hardcoded(?) into the ENABLE_RUNTIMES sub-build?
https://github.com/llvm/llvm-project/blob/e5fb79b31424267704e9d2d9674089fd7316453e/llvm/runtimes/CMakeLists.txt#L76
I'm not sure there's any way to override that from the root? And in any
case I'd have thought the defaults would need to/be intended to work
correctly on supported platforms?

So something in lldb's dir handling (maybe some general infrastructure in
LLVM could use some improvement to provide an LLVM_RUNTIME_LIBS_DIR, or
similar? that could then be used from other places - rather than libc++,
for instance, creating that directory for itself based on LLVM_LIBS_DIR and
LLVM_ENABLE_PER_TARGET_RUNTIME_DIR, etc) needs some fixes to support the
current defaults/hardcoded modes on Linux?

> Cheers,
> Louis
>
> On Oct 25, 2021, at 13:57, David Blaikie <dblaikie at gmail.com> wrote:
>
> +Louis Dionne <ldionne at apple.com> - perhaps the libcxx and lldb folks
> would be interesting in finding a suitable way to address this issue, since
> currently either option (using libcxx in ENABLE_PROJECTS or using it in
> ENABLE_RUNTIMES) is incomplete - if I use ENABLE_RUNTIMES I get the libcxx
> testing run against the just-built clang and generally this is the
> "supported" configuration, but then some lldb tests fail because they can't
> find libcxx.so.1 (on Linux) - and using ENABLE_PROJECTS means not using the
> just-built clang for libcxx tests (so missing the libcxx breakages caused
> by my array name change) but do use the just-built libcxx in lldb tests and
> find failures there...
>
> On Wed, Oct 20, 2021 at 1:57 PM David Blaikie <dblaikie at gmail.com> wrote:
>
>> On Tue, Oct 19, 2021 at 4:55 PM David Blaikie <dblaikie at gmail.com> wrote:
>>
>>> On Tue, Oct 19, 2021 at 9:08 AM Raphael Isemann <teemperor at gmail.com>
>>> wrote:
>>>
>>>> Actually the RPATH theory is wrong, but the LLVM_ENABLE_PROJECT
>>>> workaround *should* still work.
>>>>
>>>
>>> I'll give that a go (it's running at the moment) though I guess this is
>>> inconsistent with the direction libcxx is moving in for building, re:
>>> https://groups.google.com/g/llvm-dev/c/tpuLxk_ipLw
>>>
>>
>> Yep, it does work with LLVM_ENABLE_PROJECT rather than
>> LLVM_ENABLE_RUNTIME.
>>
>> Specifically the test binary is linked with an rpath to the just-built
>> lib directory that ensures the just-built libc++.so is found:
>>
>> /usr/local/google/home/blaikie/dev/llvm/build/release/bin/clang main.o -g
>> -O0 -fno-builtin -m64  -I/usr/local/google/home/blaikie/dev/llvm/src/lldb/packages/Python/lldbsuite/test/make/../../../../../include
>> -I/usr/local/google/home/blaikie/dev/llvm/src/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/list
>> -I/usr/local/google/home/blaikie/dev/llvm/src/lldb/packages/Python/lldbsuite/test/make
>> -include
>> /usr/local/google/home/blaikie/dev/llvm/src/lldb/packages/Python/lldbsuite/test/make/test_common.h
>> -fno-limit-debug-info  -gsplit-dwarf    -stdlib=libc++
>> -Wl,-rpath,/usr/local/google/home/blaikie/dev/llvm/build/release/./lib
>> --driver-mode=g++ -o "a.out"
>>
>> Oh, actually it passes the same rpath when using LLVM_ENABLE_RUNTIME, but
>> the libc++.so.1 is in a different place:
>> ./lib/x86_64-unknown-linux-gnu/libc++.so.1
>>
>> Looks like this rpath setting happens here: (changing this to a junk
>> argument causes the test to fail to build as expected)
>>
>> https://github.com/llvm/llvm-project/blob/618583565687f5a494066fc902a977f6057fc93e/lldb/packages/Python/lldbsuite/test/make/Makefile.rules#L400
>>
>> And it gets the LLVM_LIBS_DIR from here:
>> https://github.com/llvm/llvm-project/blob/207998c242c8c8a270ff22a5136da87338546725/lldb/test/API/lit.cfg.py#L163
>>
>> So maybe we need to pass down the default target triple too, since that
>> seems to be how libc++ is deciding where to put the library? (
>> https://github.com/llvm/llvm-project/blob/207998c242c8c8a270ff22a5136da87338546725/libcxx/CMakeLists.txt#L424
>> ) at least on non-apple :/ (or maybe there's some way to make the
>> connection between the two less brittle - for libc++'s build to export some
>> variable that lldb can use, or for LLVM to provide something for both to
>> use?)
>>
>> Yeah, applying this change does work for me, but wouldn't work on Apple
>> for instance (where libcxx doesn't add the default target triple to the
>> path):
>> $ git diff
>> *diff --git lldb/test/API/lit.site.cfg.py.in <http://lit.site.cfg.py.in/>
>> lldb/test/API/lit.site.cfg.py.in <http://lit.site.cfg.py.in/>*
>> *index 987078a53edb..e327429b7ff9 100644*
>> *--- lldb/test/API/lit.site.cfg.py.in <http://lit.site.cfg.py.in/>*
>> *+++ lldb/test/API/lit.site.cfg.py.in <http://lit.site.cfg.py.in/>*
>> @@ -3,7 +3,7 @@
>>  config.llvm_src_root = "@LLVM_SOURCE_DIR@"
>>  config.llvm_obj_root = "@LLVM_BINARY_DIR@"
>>  config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
>> -config.llvm_libs_dir = "@LLVM_LIBS_DIR@"
>> +config.llvm_libs_dir = "@LLVM_LIBS_DIR@/@LLVM_DEFAULT_TARGET_TRIPLE@"
>>  config.llvm_shlib_dir = "@SHLIBDIR@"
>>  config.llvm_build_mode = "@LLVM_BUILD_MODE@"
>>  config.lit_tools_dir = "@LLVM_LIT_TOOLS_DIR@"
>>
>> Thoughts?
>>
>
>
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