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[lldb] Change most tests to build with system libc++ on Darwin (#190034)

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Today, on Darwin platforms, almost every test binary in our test suite
loads two copies of libc++, libc++abi, and libunwind. This is because
each of the test binaries explicitly link against a just-built libc++
(which is explicitly required on Darwin right now) but we don't take the
correct steps to replace the system libc++. Doing so is unnecessary and
potentially error-prone, so most tests should link against the system
libc++ where possible.

Background:
The lldb test suite has a collection of tests that rely on libc++
explicitly. The two biggest categories are data formatter tests (which
make sure that we can correctly display values for std types) and
import-std-module tests (which test that we can import the libc++ std
module). To make sure these tests are run, we require a just-built
libc++ to be used.

All of the test binaries link against the just-built libc++, so it gets
loaded. However, when any system library tries to load libc++, it
attempts to load the system one. dyld checks loaded libraries against
the request to load a new one using the full path, meaning anyone
linking against `/usr/lib/libc++.1.dylib` will get it no matter what
other libc++ dylib is already loaded.

The proper way to handle this is using `DYLD_LIBRARY_PATH`, which
switches dyld to checking the leaf name of a dylib instead of the full
path. In theory this works, but we run into an issue where the system
libc++ has additional symbols and many system libraries fail to load.
Louis Dionne added stubs in libc++abi for these missing symbols, meaning
it would be possible to make this scenario work. This may be useful for
the existing libc++ tests.
This commit is contained in:
Alex Langford 2026-04-06 15:42:22 -07:00 committed by GitHub
parent 8e1ea8af38
commit 014d5d51e1
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1 changed files with 18 additions and 11 deletions
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7
lldb/packages/Python/lldbsuite/test/make/Makefile.rules
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@ -441,6 +441,12 @@ ifeq (1, $(USE_SYSTEM_STDLIB))
endif
ifeq (,$(filter 1, $(USE_LIBSTDCPP) $(USE_LIBCPP) $(USE_SYSTEM_STDLIB)))
ifeq "$(OS)" "Darwin"
# If no explicit C++ library request was made, default to the system
# libc++. Testing a custom libc++ correctly on apple platforms is difficult
# and the apppropriate use cases are limited.
USE_SYSTEM_STDLIB := 1
else
# If no explicit C++ library request was made, but we have paths to a custom libcxx, use
# them. Otherwise, use the system library by default.
ifneq ($(and $(LIBCPP_INCLUDE_DIR), $(LIBCPP_LIBRARY_DIR)),)
@ -455,6 +461,7 @@ ifeq (,$(filter 1, $(USE_LIBSTDCPP) $(USE_LIBCPP) $(USE_SYSTEM_STDLIB)))
USE_SYSTEM_STDLIB := 1
endif
endif
endif
ifeq (1,$(USE_LIBSTDCPP))
# Clang requires an extra flag: -stdlib=libstdc++