Adding a new option to CMake to disable C++ atexit on llvm-shlib.

[beanz]

Summary

This is desirable for WebKit and other clients of the llvm-shlib because C++ exit time destructors have a tendency to crash when invoked from multi-threaded applications.

Ideally this option will be temporary, because the ideal fix is to just not have exit time destructors.

[ributzka]

LGTM

Closed by commit rL223805 (authored by cbieneman).

[rnk]

How many atexit dtors do we have still? How long do you think this will stay?

Given that we had such a struggle with the other symbol override in Signals.inc, I'm surprised you went this route. :)

llvm/trunk/CMakeLists.txt

 option (LLVM_INCLUDE_DOCS "Generate build targets for llvm documentation." ON)
 option (LLVM_ENABLE_DOXYGEN "Use doxygen to generate llvm API documentation." OFF)
 option (LLVM_ENABLE_SPHINX "Use Sphinx to generate llvm documentation." OFF)
 
 option (LLVM_BUILD_EXTERNAL_COMPILER_RT
   "Build compiler-rt as an external project." OFF)
 
 option(LLVM_BUILD_LLVM_DYLIB "Build libllvm dynamic library" OFF)
+option(LLVM_DISABLE_LLVM_DYLIB_ATEXIT "Disable llvm-shlib's atexit destructors." ON)
+if(LLVM_DISABLE_LLVM_DYLIB_ATEXIT)
+  set(DISABLE_LLVM_DYLIB_ATEXIT 1)
+endif()
 
 # All options referred to from HandleLLVMOptions have to be specified
 # BEFORE this include, otherwise options will not be correctly set on
 # first cmake run
 include(config-ix)
 
 # By default, we target the host, but this can be overridden at CMake
 # invocation time.

llvm/trunk/include/llvm/Config/config.h.cmake

 #define BUG_REPORT_URL "${BUG_REPORT_URL}"
 
 /* Define if you want backtraces on crash */
 #cmakedefine ENABLE_BACKTRACES
 
 /* Define to enable crash overrides */
 #cmakedefine ENABLE_CRASH_OVERRIDES
 
+/* Define to disable C++ atexit */
+#cmakedefine DISABLE_LLVM_DYLIB_ATEXIT
+
 /* Define if position independent code is enabled */
 #cmakedefine ENABLE_PIC
 
 /* Define if timestamp information (e.g., __DATE__) is allowed */
 #cmakedefine ENABLE_TIMESTAMPS ${ENABLE_TIMESTAMPS}
 
 /* Define to 1 if you have the `arc4random' function. */
 #cmakedefine HAVE_DECL_ARC4RANDOM ${HAVE_DECL_ARC4RANDOM}

llvm/trunk/tools/llvm-shlib/libllvm.cpp

 //===-libllvm.cpp - LLVM Shared Library -----------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file is empty and serves only the purpose of making CMake happy because
 // you can't define a target with no sources.
 //
 //===----------------------------------------------------------------------===//
+
+#include "llvm/Config/config.h"
+
+#if defined(DISABLE_LLVM_DYLIB_ATEXIT)
+extern "C" int __cxa_atexit();
+extern "C" int __cxa_atexit() { return 0; }
+#endif