Initial run-time detection of C++ EH ABI variant.

On Itanium C++ ABI platforms, there are a lot of different variations
that have subtly different structure layouts.  This commit adds a
run-time test that throws a C++ exception through a function that has
its personality function replaced with a wrapper so that we can inspect
a C++ exception in controlled conditions.

Initially, this just detects the exception type value used for C++
exceptions.

CMakeLists.txt

@@ -264,7 +264,6 @@ if (MSVC)
 endif()
 
 
-add_library(objc SHARED ${libobjc_C_SRCS} ${libobjc_ASM_SRCS} ${libobjc_OBJC_SRCS} ${libobjc_OBJCXX_SRCS} ${libobjc_ASM_OBJS})
 
 if (ENABLE_OBJCXX)
 	if (WIN32)
@@ -302,9 +301,15 @@ if (ENABLE_OBJCXX)
 				set(ENABLE_OBJCXX false)
 			endif()
 		endif ()
+		add_custom_command(OUTPUT eh_trampoline.S
+			COMMAND ${CMAKE_CXX_COMPILER} -fPIC -S "${CMAKE_SOURCE_DIR}/eh_trampoline.cc" -o - -fexceptions -fno-inline | sed "s/__gxx_personality_v0/test_eh_personality/g" > "${CMAKE_BINARY_DIR}/eh_trampoline.S"
+			MAIN_DEPENDENCY eh_trampoline.cc)
+		list(APPEND libobjc_ASM_SRCS eh_trampoline.S)
+		list(APPEND libobjc_CXX_SRCS cxx_eh_setup.cc)
 	endif ()
 endif (ENABLE_OBJCXX)
 
+add_library(objc SHARED ${libobjc_C_SRCS} ${libobjc_ASM_SRCS} ${libobjc_OBJC_SRCS} ${libobjc_OBJCXX_SRCS} ${libobjc_ASM_OBJS})
 
 if (ENABLE_OBJCXX)
 	if (NOT CXXRT_IS_STDLIB)

cxx_eh_setup.cc

@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "objc/runtime.h"
+#include "dwarf_eh.h"
+#include "objcxx_eh.h"
+
+void cxx_throw()
+{
+	throw 1;
+}
+
+int eh_trampoline();
+uint64_t cxx_exception_class;
+
+namespace
+{
+inline _Unwind_Reason_Code continueUnwinding(struct _Unwind_Exception *ex,
+                                                    struct _Unwind_Context *context)
+{
+#if defined(__arm__) && !defined(__ARM_DWARF_EH__)
+	if (__gnu_unwind_frame(ex, context) != _URC_OK) { return _URC_FAILURE; }
+#endif
+	return _URC_CONTINUE_UNWIND;
+}
+
+bool done_setup;
+}
+
+extern "C"
+BEGIN_PERSONALITY_FUNCTION(test_eh_personality)
+	fprintf(stderr, "Fake EH personality called\n");
+	if (!done_setup)
+	{
+		done_setup = true;
+		cxx_exception_class = exceptionClass;
+	}
+	return CALL_PERSONALITY_FUNCTION(__gxx_personality_v0);
+}
+
+extern "C" void test_cxx_eh_implementation()
+{
+	bool caught = false;
+	try
+	{
+		eh_trampoline();
+	}
+	catch(int)
+	{
+		caught = true;
+	}
+	assert(caught);
+}
+

eh_personality.c

@@ -20,6 +20,8 @@
 #define __builtin_unreachable abort
 #endif
 
+void test_cxx_eh_implementation();
+
 
 /**
  * Class of exceptions to distinguish between this and other exception types.
@@ -326,6 +328,11 @@ static inline _Unwind_Reason_Code internal_objc_personality(int version,
 	void *object = NULL;
 
 #ifndef NO_OBJCXX
+	if (cxx_exception_class == 0)
+	{
+		test_cxx_eh_implementation();
+	}
+
 	if (exceptionClass == cxx_exception_class)
 	{
 		int objcxx;
@@ -486,6 +493,10 @@ BEGIN_PERSONALITY_FUNCTION(__gnustep_objc_personality_v0)
 }
 
 BEGIN_PERSONALITY_FUNCTION(__gnustep_objcxx_personality_v0)
+	if (cxx_exception_class == 0)
+	{
+		test_cxx_eh_implementation();
+	}
 	if (exceptionClass == objc_exception_class)
 	{
 		struct objc_exception *ex = objc_exception_from_header(exceptionObject);

eh_trampoline.cc

@@ -0,0 +1,8 @@
+void cxx_throw();
+
+int eh_trampoline()
+{
+	struct X { ~X() {} } x;
+	cxx_throw();
+	return 0;
+}

objcxx_eh.h

@@ -51,7 +51,20 @@ void *objc_object_for_cxx_exception(void *thrown_exception, int *isValid);
 __attribute__((weak))
 void print_type_info(void *thrown_exception);
 
-static const uint64_t cxx_exception_class = EXCEPTION_CLASS('G','N','U','C','C','+','+','\0');
+/**
+ * The exception class that we've detected that C++ runtime library uses.
+ */
+extern uint64_t cxx_exception_class;
+
+/**
+ * The exception class that libsupc++ and libcxxrt use.
+ */
+const uint64_t gnu_cxx_exception_class = EXCEPTION_CLASS('G','N','U','C','C','+','+','\0');
+
+/**
+ * The exception class that libc++abi uses.
+ */
+const uint64_t llvm_cxx_exception_class = EXCEPTION_CLASS('C','L','N','G','C','+','+','\0');
 
 #ifdef __cplusplus
 }