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[libc++][release] Do not force building the runtimes with -fPIC

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There's a lot of history behind this, so here's a summary:

1. I stopped forcing -fPIC when building the runtimes in 30f305efe2,
   before the LLVM 9 release back in 2019.

2. Someone complained that libc++.a couldn't be used in shared libraries
   built without -fPIC (http://llvm.org/PR43604) since the LLVM 9 release.
   This had been caused by my removal of -fPIC when building libc++.a in (1).

3. I suggested two ways of fixing the issue, the first being to force
   -fPIC back unconditionally (http://llvm.org/D104328), and the second
   being to specify that option explicitly when building the LLVM release
   (http://llvm.org/D104327). We converged on the first solution.

4. I landed D104328, which forced building the runtimes with -fPIC.
   This was included in the LLVM 13.0 release.

5. People complained about that and requested that we be able to
   customize this setting (basically we should have done the second
   solution).

This patch makes it such that the LLVM release script will specifically
ask for building with -fPIC using CMAKE_POSITION_INDEPENDENT_CODE,
however by default the runtimes will not force that option onto users.

This patch has the unintended effect that Clang and the LLVM libraries
(not only the runtime ones like libc++) will also be built with -fPIC
in the release. It would be better if we could specify that -fPIC is to
be used only when building the runtimes, however this is left as a
future improvement. The release should probably be using a bootstrapping
build and passing those options to the stage that builds the runtimes
only, see https://reviews.llvm.org/D112748 for that change.

Differential Revision: https://reviews.llvm.org/D110261
This commit is contained in:
Louis Dionne 2021-09-22 12:09:07 -04:00
parent de467afe18
commit a6e5563dfa
8 changed files with 28 additions and 11 deletions
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6
libcxx/docs/ReleaseNotes.rst
View file

@ -157,3 +157,9 @@ Build System Changes
.. code-block:: bash
-DLLVM_RUNTIME_TARGETS=i386-unknown-linux
- Libc++, libc++abi and libunwind will not be built with ``-fPIC`` by default anymore.
If you want to build those runtimes with position independent code, please specify
``-DCMAKE_POSITION_INDEPENDENT_CODE=ON`` explicitly when configuring the build, or
``-DRUNTIMES_<target-name>_CMAKE_POSITION_INDEPENDENT_CODE=ON`` if using the
bootstrapping build.

2
libcxx/src/CMakeLists.txt
View file

@ -208,7 +208,6 @@ if (LIBCXX_ENABLE_SHARED)
VERSION "${LIBCXX_ABI_VERSION}.0"
SOVERSION "${LIBCXX_ABI_VERSION}"
DEFINE_SYMBOL ""
POSITION_INDEPENDENT_CODE ON
)
cxx_add_common_build_flags(cxx_shared)
cxx_set_common_defines(cxx_shared)
@ -284,7 +283,6 @@ if (LIBCXX_ENABLE_STATIC)
COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
LINK_FLAGS "${LIBCXX_LINK_FLAGS}"
OUTPUT_NAME "c++"
POSITION_INDEPENDENT_CODE ON
)
cxx_add_common_build_flags(cxx_static)
cxx_set_common_defines(cxx_static)

3
libcxx/test/libcxx/debug/extern-templates.sh.cpp
View file

@ -14,6 +14,7 @@
// UNSUPPORTED: libcxx-no-debug-mode
// UNSUPPORTED: libcpp-has-no-localization
// UNSUPPORTED: cant-build-shared-library
// This test relies on linking a shared library and then passing that shared
// library as input when linking an executable; this is generally not supported
@ -23,7 +24,7 @@
// UNSUPPORTED: windows
// RUN: %{cxx} %{flags} %{compile_flags} %s %{link_flags} -fPIC -DTU1 -D_LIBCPP_DEBUG=1 -fvisibility=hidden -shared -o %t.lib
// RUN: cd %T && %{cxx} %{flags} %{compile_flags} %s ./%basename_t.tmp.lib %{link_flags} -fPIC -DTU2 -D_LIBCPP_DEBUG=1 -fvisibility=hidden -o %t.exe
// RUN: cd %T && %{cxx} %{flags} %{compile_flags} %s ./%basename_t.tmp.lib %{link_flags} -DTU2 -D_LIBCPP_DEBUG=1 -fvisibility=hidden -o %t.exe
// RUN: %{exec} %t.exe
#include <cassert>

9
libcxx/utils/libcxx/test/dsl.py
View file

@ -112,18 +112,19 @@ def _makeConfigTest(config):
os.remove(tmp.name)
return TestWrapper(suite, pathInSuite, config)
@_memoizeExpensiveOperation(lambda c, s: (c.substitutions, c.environment, s))
def sourceBuilds(config, source):
@_memoizeExpensiveOperation(lambda c, s, f=[]: (c.substitutions, c.environment, s, f))
def sourceBuilds(config, source, additionalFlags=[]):
"""
Return whether the program in the given string builds successfully.
This is done by compiling and linking a program that consists of the given
source with the %{cxx} substitution, and seeing whether that succeeds.
source with the %{cxx} substitution, and seeing whether that succeeds. If
any additional flags are passed, they are appended to the compiler invocation.
"""
with _makeConfigTest(config) as test:
with open(test.getSourcePath(), 'w') as sourceFile:
sourceFile.write(source)
_, _, exitCode, _ = _executeScriptInternal(test, ['%{build}'])
_, _, exitCode, _ = _executeScriptInternal(test, ['%{{build}} {}'.format(' '.join(additionalFlags))])
return exitCode == 0
@_memoizeExpensiveOperation(lambda c, p, args=None: (c.substitutions, c.environment, p, args))

13
libcxx/utils/libcxx/test/features.py
View file

@ -59,6 +59,19 @@ DEFAULT_FEATURES = [
int main(int, char**) { return x.is_lock_free(); }
""")),
# Some tests rely on creating shared libraries which link in the C++ Standard Library. In some
# cases, this doesn't work (e.g. if the library was built as a static archive and wasn't compiled
# as position independent). This feature informs the test suite of whether it's possible to create
# a shared library in a shell test by using the '-shared' compiler flag.
#
# Note: To implement this check properly, we need to make sure that we use something inside the
# compiled library, not only in the headers. It should be safe to assume that all implementations
# define `operator new` in the compiled library.
Feature(name='cant-build-shared-library',
when=lambda cfg: not sourceBuilds(cfg, """
void f() { new int(3); }
""", ['-shared'])),
Feature(name='apple-clang', when=_isAppleClang),
Feature(name=lambda cfg: 'apple-clang-{__clang_major__}'.format(**compilerMacros(cfg)), when=_isAppleClang),
Feature(name=lambda cfg: 'apple-clang-{__clang_major__}.{__clang_minor__}'.format(**compilerMacros(cfg)), when=_isAppleClang),

2
libcxxabi/src/CMakeLists.txt
View file

@ -192,7 +192,6 @@ if (LIBCXXABI_ENABLE_SHARED)
SOVERSION "1"
VERSION "${LIBCXXABI_LIBRARY_VERSION}"
DEFINE_SYMBOL ""
POSITION_INDEPENDENT_CODE ON
)
list(APPEND LIBCXXABI_BUILD_TARGETS "cxxabi_shared")
@ -245,7 +244,6 @@ if (LIBCXXABI_ENABLE_STATIC)
COMPILE_FLAGS "${LIBCXXABI_COMPILE_FLAGS}"
LINK_FLAGS "${LIBCXXABI_LINK_FLAGS}"
OUTPUT_NAME "c++abi"
POSITION_INDEPENDENT_CODE ON
)
if(LIBCXXABI_HERMETIC_STATIC_LIBRARY)

2
libunwind/src/CMakeLists.txt
View file

@ -145,7 +145,6 @@ if (LIBUNWIND_ENABLE_SHARED)
OUTPUT_NAME "unwind"
VERSION "1.0"
SOVERSION "1"
POSITION_INDEPENDENT_CODE ON
)
list(APPEND LIBUNWIND_BUILD_TARGETS "unwind_shared")
if (LIBUNWIND_INSTALL_SHARED_LIBRARY)
@ -171,7 +170,6 @@ if (LIBUNWIND_ENABLE_STATIC)
LINK_FLAGS "${LIBUNWIND_LINK_FLAGS}"
LINKER_LANGUAGE C
OUTPUT_NAME "unwind"
POSITION_INDEPENDENT_CODE ON
)
if(LIBUNWIND_HIDE_SYMBOLS)

2
llvm/utils/release/test-release.sh
View file

@ -386,12 +386,14 @@ function configure_llvmCore() {
echo "#" env CC="$c_compiler" CXX="$cxx_compiler" \
cmake -G "$generator" \
-DCMAKE_BUILD_TYPE=$BuildType -DLLVM_ENABLE_ASSERTIONS=$Assertions \
-DCMAKE_POSITION_INDEPENDENT_CODE=ON \
-DLLVM_ENABLE_PROJECTS="$project_list" \
$ExtraConfigureFlags $BuildDir/llvm-project/llvm \
2>&1 | tee $LogDir/llvm.configure-Phase$Phase-$Flavor.log
env CC="$c_compiler" CXX="$cxx_compiler" \
cmake -G "$generator" \
-DCMAKE_BUILD_TYPE=$BuildType -DLLVM_ENABLE_ASSERTIONS=$Assertions \
-DCMAKE_POSITION_INDEPENDENT_CODE=ON \
-DLLVM_ENABLE_PROJECTS="$project_list" \
$ExtraConfigureFlags $BuildDir/llvm-project/llvm \
2>&1 | tee $LogDir/llvm.configure-Phase$Phase-$Flavor.log