From 1ab69fc5321336938e7cb0d960a13ab26395d8d5 Mon Sep 17 00:00:00 2001
From: Eric Fiselier <eric@efcs.ca>
Date: Thu, 15 Oct 2015 22:41:51 +0000
Subject: [PATCH] [libcxx] Make libc++.so a linker script by default on most
 platforms.

Summary:
This patch turns on `LIBCXX_ENABLE_ABI_LINKER_SCRIPT` by default whenever `LLVM_HAVE_LINK_VERSION_SCRIPT` is ON. This turns out to be whenever:

1. WIN32 is not defined.
2 UNIX is defined.
3. APPLE is not defined.

While `LLVM_HAVE_LINK_VERSION_SCRIPT` is meant to reflect exactly what we are asking I think it's close enough.

After committing this patch Linux users will no longer have to use "-lc++abi" explicitly!




Reviewers: mclow.lists, danalbert, compnerd, jroelofs

Subscribers: emaste, rengolin, cbergstrom, cfe-commits

Differential Revision: http://reviews.llvm.org/D13739

llvm-svn: 250469
---
 libcxx/CMakeLists.txt                         | 14 +++++++++--
 .../cmake/Modules/HandleOutOfTreeLLVM.cmake   | 24 +++++++++++++++++++
 libcxx/docs/BuildingLibcxx.rst                |  8 +++++++
 libcxx/docs/UsingLibcxx.rst                   |  8 +++----
 4 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 7017ce4079ac..11958d9baba1 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -67,12 +67,22 @@ set(LIBCXX_CXX_ABI "${LIBCXX_CXX_ABI}" CACHE STRING
 set(CXXABIS none libcxxabi libcxxrt libstdc++ libsupc++)
 set_property(CACHE LIBCXX_CXX_ABI PROPERTY STRINGS ;${CXXABIS})
 
+# Use a static copy of the ABI library when linking libc++. This option
+# cannot be used with LIBCXX_ENABLE_ABI_LINKER_SCRIPT.
 option(LIBCXX_ENABLE_STATIC_ABI_LIBRARY "Statically link the ABI library" OFF)
 
 # Generate and install a linker script inplace of libc++.so. The linker script
-# will link libc++ to the correct ABI library.
+# will link libc++ to the correct ABI library. This option is on by default
+# On UNIX platforms other than Apple unless 'LIBCXX_ENABLE_STATIC_ABI_LIBRARY'
+# is on.
+set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE OFF)
+if (LLVM_HAVE_LINK_VERSION_SCRIPT AND NOT LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
+    set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE ON)
+endif()
+
 option(LIBCXX_ENABLE_ABI_LINKER_SCRIPT
-      "Use and install a linker script for the given ABI library" OFF)
+      "Use and install a linker script for the given ABI library"
+      ${ENABLE_LINKER_SCRIPT_DEFAULT_VALUE})
 
 # Build libc++abi with libunwind. We need this option to determine whether to
 # link with libunwind or libgcc_s while running the test cases.
diff --git a/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake b/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake
index 0e12c884ebf4..6215be7f586a 100644
--- a/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake
+++ b/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake
@@ -109,6 +109,30 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
     message(STATUS "Sphinx disabled.")
   endif()
 
+  # FIXME - This is cribbed from HandleLLVMOptions.cmake.
+  if(WIN32)
+    set(LLVM_HAVE_LINK_VERSION_SCRIPT 0)
+    if(CYGWIN)
+      set(LLVM_ON_WIN32 0)
+      set(LLVM_ON_UNIX 1)
+    else(CYGWIN)
+      set(LLVM_ON_WIN32 1)
+      set(LLVM_ON_UNIX 0)
+    endif(CYGWIN)
+  else(WIN32)
+    if(UNIX)
+      set(LLVM_ON_WIN32 0)
+      set(LLVM_ON_UNIX 1)
+      if(APPLE)
+        set(LLVM_HAVE_LINK_VERSION_SCRIPT 0)
+      else(APPLE)
+        set(LLVM_HAVE_LINK_VERSION_SCRIPT 1)
+      endif(APPLE)
+    else(UNIX)
+      MESSAGE(SEND_ERROR "Unable to determine platform")
+    endif(UNIX)
+  endif(WIN32)
+
   # Add LLVM Functions --------------------------------------------------------
   include(AddLLVM OPTIONAL)
 endif()
diff --git a/libcxx/docs/BuildingLibcxx.rst b/libcxx/docs/BuildingLibcxx.rst
index 6e45578dbb93..a7366c53e6cd 100644
--- a/libcxx/docs/BuildingLibcxx.rst
+++ b/libcxx/docs/BuildingLibcxx.rst
@@ -170,6 +170,14 @@ ABI Library Specific Options
   If this option is enabled, libc++ will try and link the selected ABI library
   statically.
 
+.. option:: LIBCXX_ENABLE_ABI_LINKER_SCRIPT:BOOL
+
+  **Default**: ``ON`` by default on UNIX platforms other than Apple unless
+  'LIBCXX_ENABLE_STATIC_ABI_LIBRARY' is ON. Otherwise the default value is ``OFF``.
+
+  This option generate and installs a linker script as ``libc++.so`` which
+  links the correct ABI library.
+
 .. option:: LIBCXXABI_USE_LLVM_UNWINDER:BOOL
 
   **Default**: ``OFF``
diff --git a/libcxx/docs/UsingLibcxx.rst b/libcxx/docs/UsingLibcxx.rst
index 8de58d8659ed..2a117917638c 100644
--- a/libcxx/docs/UsingLibcxx.rst
+++ b/libcxx/docs/UsingLibcxx.rst
@@ -54,10 +54,10 @@ An example of using ``LD_LIBRARY_PATH``:
 Using libc++ on Linux
 =====================
 
-On Linux libc++ typically links to a shared version of libc++abi. Unfortunately
-you can't simply run clang with "-stdlib=libc++" as clang is not set up to
-link for this configuration. To get around this you'll have to manually
-link libc++abi yourself. For example:
+On Linux libc++ can typically be used with only '-stdlib=libc++'. However
+some libc++ installations require the user manually link libc++abi themselves.
+If you are running into linker errors when using libc++ try adding '-lc++abi'
+to the link line.  For example:
 
 .. code-block:: bash