[libcxx-commits] [PATCH] D110261: [libc++][release] Do not force building the runtimes with -fPIC

[Louis Dionne via Phabricator via libcxx-commits]

ldionne created this revision.
ldionne added reviewers: miyuki, chandlerc, MaskRay, JamesNagurne, sylvestre.ledru.
Herald added subscribers: libcxx-commits, mgorny.
Herald added a project: libunwind.
Herald added a reviewer: libunwind.
ldionne requested review of this revision.
Herald added projects: libc++, libc++abi, LLVM.
Herald added a reviewer: libc++.
Herald added a reviewer: libc++abi.
Herald added a subscriber: llvm-commits.

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

1. I stopped forcing -fPIC when building the runtimes in 30f305efe279, 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 <https://reviews.llvm.org/D104328>, which forced building the runtimes with -fPIC.

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.

As-is, this patch will have 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 (hint: the release should probably be
using a bootstrapping build and passing those options to the stage that
builds the runtimes only).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110261

Files:
  libcxx/docs/ReleaseNotes.rst
  libcxx/src/CMakeLists.txt
  libcxxabi/src/CMakeLists.txt
  libunwind/src/CMakeLists.txt
  llvm/utils/release/test-release.sh


Index: llvm/utils/release/test-release.sh
===================================================================
--- llvm/utils/release/test-release.sh
+++ llvm/utils/release/test-release.sh
@@ -386,12 +386,14 @@
     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-$Flavor.log
Index: libunwind/src/CMakeLists.txt
===================================================================
--- libunwind/src/CMakeLists.txt
+++ libunwind/src/CMakeLists.txt
@@ -144,7 +144,6 @@
       OUTPUT_NAME "unwind"
       VERSION "1.0"
       SOVERSION "1"
-      POSITION_INDEPENDENT_CODE ON
   )
   list(APPEND LIBUNWIND_BUILD_TARGETS "unwind_shared")
   if (LIBUNWIND_INSTALL_SHARED_LIBRARY)
@@ -170,7 +169,6 @@
       LINK_FLAGS "${LIBUNWIND_LINK_FLAGS}"
       LINKER_LANGUAGE C
       OUTPUT_NAME "unwind"
-      POSITION_INDEPENDENT_CODE ON
   )
 
   if(LIBUNWIND_HIDE_SYMBOLS)
Index: libcxxabi/src/CMakeLists.txt
===================================================================
--- libcxxabi/src/CMakeLists.txt
+++ libcxxabi/src/CMakeLists.txt
@@ -191,7 +191,6 @@
       SOVERSION "1"
       VERSION "${LIBCXXABI_LIBRARY_VERSION}"
       DEFINE_SYMBOL ""
-      POSITION_INDEPENDENT_CODE ON
   )
 
   list(APPEND LIBCXXABI_BUILD_TARGETS "cxxabi_shared")
@@ -244,7 +243,6 @@
       COMPILE_FLAGS "${LIBCXXABI_COMPILE_FLAGS}"
       LINK_FLAGS "${LIBCXXABI_LINK_FLAGS}"
       OUTPUT_NAME "c++abi"
-      POSITION_INDEPENDENT_CODE ON
     )
 
   if(LIBCXXABI_HERMETIC_STATIC_LIBRARY)
Index: libcxx/src/CMakeLists.txt
===================================================================
--- libcxx/src/CMakeLists.txt
+++ libcxx/src/CMakeLists.txt
@@ -205,7 +205,6 @@
       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)
@@ -280,7 +279,6 @@
       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)
Index: libcxx/docs/ReleaseNotes.rst
===================================================================
--- libcxx/docs/ReleaseNotes.rst
+++ libcxx/docs/ReleaseNotes.rst
@@ -49,4 +49,6 @@
 API Changes
 -----------
 
-- ...
+- 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.


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