[libcxxabi] Introduce a -fno-exceptions libc++abi libary variant

Currently there is only support for a -fno-exceptions libc++ build. This is
problematic for functions such as std::terminate() which are defined in
libc++abi and using any of those functions throws away most of the benefits
of using -fno-exceptions (code-size). This patch introduces a -fno-exceptions
libc++abi build to address this issue.

This new variant of libc++abi cannot be linked against any with-exceptions
code as some symbols necessary for handling exceptions are missing in this
library.

Differential revision: http://reviews.llvm.org/D20677

Reviewers: EricWF, mclow.lists, bcraig
llvm-svn: 271267

Author: Asiri Rathnayake

libcxxabi/CMakeLists.txt

@@ -108,6 +108,7 @@ endif()
 #===============================================================================
 
 # Define options.
+option(LIBCXXABI_ENABLE_EXCEPTIONS "Use exceptions." ON)
 option(LIBCXXABI_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
 option(LIBCXXABI_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
 option(LIBCXXABI_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
@@ -242,13 +243,20 @@ if (LIBCXXABI_ENABLE_PEDANTIC)
 endif()
 
 # Get feature flags.
-# Exceptions
-# Catches C++ exceptions only and tells the compiler to assume that extern C
-# functions never throw a C++ exception.
 append_if(LIBCXXABI_CXX_FLAGS LIBCXXABI_HAS_FSTRICT_ALIASING_FLAG -fstrict-aliasing)
-append_if(LIBCXXABI_CXX_FLAGS LIBCXXABI_HAS_EHSC_FLAG -EHsc)
 
-append_if(LIBCXXABI_C_FLAGS LIBCXXABI_HAS_FUNWIND_TABLES -funwind-tables)
+# Exceptions
+if (LIBCXXABI_ENABLE_EXCEPTIONS)
+  # Catches C++ exceptions only and tells the compiler to assume that extern C
+  # functions never throw a C++ exception.
+  append_if(LIBCXXABI_CXX_FLAGS LIBCXXABI_HAS_EHSC_FLAG -EHsc)
+  append_if(LIBCXXABI_C_FLAGS LIBCXXABI_HAS_FUNWIND_TABLES -funwind-tables)
+else()
+  add_definitions(-D_LIBCXXABI_NO_EXCEPTIONS)
+  append_if(LIBCXXABI_CXX_FLAGS LIBCXXABI_HAS_NO_EXCEPTIONS_FLAG -fno-exceptions)
+  append_if(LIBCXXABI_CXX_FLAGS LIBCXXABI_HAS_NO_EHS_FLAG -EHs-)
+  append_if(LIBCXXABI_CXX_FLAGS LIBCXXABI_HAS_NO_EHA_FLAG -EHa-)
+endif()
 
 append_if(LIBCXXABI_COMPILE_FLAGS LIBCXXABI_HAS_FVISIBILITY_HIDDEN_FLAG -fvisibility=hidden)
 

libcxxabi/src/CMakeLists.txt

@@ -4,12 +4,10 @@ set(LIBCXXABI_SOURCES
   cxa_aux_runtime.cpp
   cxa_default_handlers.cpp
   cxa_demangle.cpp
-  cxa_exception.cpp
   cxa_exception_storage.cpp
   cxa_guard.cpp
   cxa_handlers.cpp
   cxa_new_delete.cpp
-  cxa_personality.cpp
   cxa_unexpected.cpp
   cxa_vector.cpp
   cxa_virtual.cpp
@@ -19,6 +17,13 @@ set(LIBCXXABI_SOURCES
   typeinfo.cpp
 )
 
+if (LIBCXXABI_ENABLE_EXCEPTIONS)
+  list(APPEND LIBCXXABI_SOURCES cxa_exception.cpp)
+  list(APPEND LIBCXXABI_SOURCES cxa_personality.cpp)
+else()
+  list(APPEND LIBCXXABI_SOURCES cxa_noexception.cpp)
+endif()
+
 if (UNIX AND NOT (APPLE OR CYGWIN))
   list(APPEND LIBCXXABI_SOURCES cxa_thread_atexit.cpp)
 endif()

libcxxabi/src/cxa_aux_runtime.cpp

@@ -17,16 +17,28 @@
 namespace __cxxabiv1 {
 extern "C" {
 _LIBCXXABI_FUNC_VIS LIBCXXABI_NORETURN void __cxa_bad_cast(void) {
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
   throw std::bad_cast();
+#else
+  std::terminate();
+#endif
 }
 
 _LIBCXXABI_FUNC_VIS LIBCXXABI_NORETURN void __cxa_bad_typeid(void) {
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
   throw std::bad_typeid();
+#else
+  std::terminate();
+#endif
 }
 
 _LIBCXXABI_FUNC_VIS LIBCXXABI_NORETURN void
 __cxa_throw_bad_array_new_length(void) {
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
   throw std::bad_array_new_length();
+#else
+  std::terminate();
+#endif
 }
 } // extern "C"
 } // abi

libcxxabi/src/cxa_handlers.cpp

@@ -61,21 +61,21 @@ __attribute__((visibility("hidden"), noreturn))
 void
 __terminate(terminate_handler func) _NOEXCEPT
 {
-#if __has_feature(cxx_exceptions)
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
     try
     {
-#endif  // __has_feature(cxx_exceptions)
+#endif  // _LIBCXXABI_NO_EXCEPTIONS
         func();
         // handler should not return
         abort_message("terminate_handler unexpectedly returned");
-#if __has_feature(cxx_exceptions)
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
     }
     catch (...)
     {
         // handler should not throw exception
         abort_message("terminate_handler unexpectedly threw an exception");
     }
-#endif  // #if __has_feature(cxx_exceptions)
+#endif  // _LIBCXXABI_NO_EXCEPTIONS
 }
 
 __attribute__((noreturn))

libcxxabi/src/cxa_new_delete.cpp

@@ -47,7 +47,11 @@ operator new(std::size_t size)
         if (nh)
             nh();
         else
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
             throw std::bad_alloc();
+#else
+            break;
+#endif
     }
     return p;
 }
@@ -74,13 +78,17 @@ operator new(size_t size, const std::nothrow_t&)
 #endif
 {
     void* p = 0;
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
     try
     {
+#endif
         p = ::operator new(size);
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
     }
     catch (...)
     {
     }
+#endif
     return p;
 }
 
@@ -115,13 +123,17 @@ operator new[](size_t size, const std::nothrow_t&)
 #endif
 {
     void* p = 0;
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
     try
     {
+#endif
         p = ::operator new[](size);
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
     }
     catch (...)
     {
     }
+#endif
     return p;
 }
 

libcxxabi/src/cxa_noexception.cpp

@@ -0,0 +1,60 @@
+//===------------------------- cxa_exception.cpp --------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//  
+//  This file implements the "Exception Handling APIs"
+//  http://mentorembedded.github.io/cxx-abi/abi-eh.html
+//  
+//===----------------------------------------------------------------------===//
+
+// Support functions for the no-exceptions libc++ library
+
+#include "config.h"
+#include "cxxabi.h"
+
+#include <exception>        // for std::terminate
+#include "cxa_exception.hpp"
+#include "cxa_handlers.hpp"
+
+namespace __cxxabiv1 {
+
+#pragma GCC visibility push(default)
+
+extern "C" {
+
+void
+__cxa_increment_exception_refcount(void *thrown_object) throw() {
+    if (thrown_object != nullptr)
+        std::terminate();
+}
+
+void
+__cxa_decrement_exception_refcount(void *thrown_object) throw() {
+    if (thrown_object != nullptr)
+      std::terminate();
+}
+
+
+void *__cxa_current_primary_exception() throw() { return nullptr; }
+
+void
+__cxa_rethrow_primary_exception(void* thrown_object) {
+    if (thrown_object != nullptr)
+      std::terminate();
+}
+
+bool
+__cxa_uncaught_exception() throw() { return false; }
+
+unsigned int
+__cxa_uncaught_exceptions() throw() { return 0; }
+
+}  // extern "C"
+
+#pragma GCC visibility pop
+
+}  // abi

libcxxabi/test/CMakeLists.txt

@@ -14,6 +14,7 @@ pythonize_bool(LLVM_BUILD_32_BITS)
 pythonize_bool(LIBCXX_ENABLE_SHARED)
 pythonize_bool(LIBCXXABI_ENABLE_SHARED)
 pythonize_bool(LIBCXXABI_ENABLE_THREADS)
+pythonize_bool(LIBCXXABI_ENABLE_EXCEPTIONS)
 pythonize_bool(LIBCXXABI_USE_LLVM_UNWINDER)
 pythonize_bool(LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL)
 set(LIBCXXABI_TARGET_INFO "libcxx.test.target_info.LocalTI" CACHE STRING

libcxxabi/test/backtrace_test.pass.cpp

@@ -6,6 +6,9 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: libcxxabi-no-exceptions
+
 #include <assert.h>
 #include <stddef.h>
 #include <unwind.h>

libcxxabi/test/catch_array_01.pass.cpp

@@ -9,10 +9,10 @@
 
 // Can you have a catch clause of array type that catches anything?
 
-
 // GCC incorrectly allows array types to be caught by reference.
 // See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69372
 // XFAIL: gcc
+// UNSUPPORTED: libcxxabi-no-exceptions
 
 #include <cassert>
 

libcxxabi/test/catch_array_02.pass.cpp

@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 // Can you have a catch clause of array type that catches anything?
+// UNSUPPORTED: libcxxabi-no-exceptions
 
 #include <cassert>