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objcxx_eh.cc
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objcxx_eh.cc
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#include <atomic>
#include <stdlib.h>
#include <stdio.h>
#include "dwarf_eh.h"
#include "objcxx_eh_private.h"
#include "objcxx_eh.h"
#include "objc/objc-arc.h"
/**
* Helper function that has a custom personality function.
* This calls `cxx_throw` and has a destructor that must be run. We intercept
* the personality function calls and inspect the in-flight C++ exception.
*/
int eh_trampoline();
uint64_t cxx_exception_class;
using namespace __cxxabiv1;
namespace
{
/**
* Helper needed by the unwind helper headers.
*/
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;
}
/**
* Flag indicating that we've already inspected a C++ exception and found all
* of the offsets.
*/
std::atomic<bool> done_setup;
/**
* The offset of the C++ type_info object in a thrown exception from the unwind
* header in a `__cxa_exception`.
*/
std::atomic<ptrdiff_t> type_info_offset;
/**
* The size of the `_Unwind_Exception` (including padding) in a
* `__cxa_exception`.
*/
std::atomic<size_t> exception_struct_size;
/**
* Exception cleanup function for C++ exceptions that wrap Objective-C
* exceptions.
*/
void exception_cleanup(_Unwind_Reason_Code reason,
struct _Unwind_Exception *ex)
{
// __cxa_exception takes a pointer to the end of the __cxa_exception
// structure, and so we find that by adding the size of the generic
// exception structure + padding to the pointer to the generic exception
// structure field of the enclosing structure.
auto *cxxEx = pointer_add<__cxa_exception>(ex, exception_struct_size);
__cxa_free_exception(cxxEx);
}
}
using namespace std;
static BOOL isKindOfClass(Class thrown, Class type)
{
do
{
if (thrown == type)
{
return YES;
}
thrown = class_getSuperclass(thrown);
} while (Nil != thrown);
return NO;
}
namespace gnustep
{
namespace libobjc
{
__objc_type_info::__objc_type_info(const char *name) : type_info(name) {}
bool __objc_type_info::__is_pointer_p() const { return true; }
bool __objc_type_info::__is_function_p() const { return false; }
bool __objc_type_info::__do_catch(const type_info *thrown_type,
void **thrown_object,
unsigned) const
{
assert(0);
return false;
};
bool __objc_type_info::__do_upcast(
const __class_type_info *target,
void **thrown_object) const
{
return false;
};
/**
* The `id` type is mangled to `@id`, which is not a valid mangling
* of anything else.
*/
__objc_id_type_info::__objc_id_type_info() : __objc_type_info("@id") {};
}
static inline id dereference_thrown_object_pointer(void** obj) {
/* libc++-abi does not have __is_pointer_p and won't do the double dereference
* required to get the object pointer. We need to do it ourselves if we have
* caught an exception with libc++'s exception class. */
#ifndef __MINGW32__
if (cxx_exception_class == llvm_cxx_exception_class) {
return **(id**)obj;
}
return *(id*)obj;
#else
#ifdef _LIBCPP_VERSION
return **(id**)obj;
#else
return *(id*)obj;
#endif // _LIBCPP_VERSION
#endif // __MINGW32__
}
};
static bool AppleCompatibleMode = true;
extern "C" int objc_set_apple_compatible_objcxx_exceptions(int newValue)
{
bool old = AppleCompatibleMode;
AppleCompatibleMode = newValue;
return old;
}
gnustep::libobjc::__objc_class_type_info::~__objc_class_type_info() {}
gnustep::libobjc::__objc_id_type_info::~__objc_id_type_info() {}
bool gnustep::libobjc::__objc_class_type_info::__do_catch(const type_info *thrownType,
void **obj,
unsigned outer) const
{
id thrown = nullptr;
bool found = false;
// Id throw matches any ObjC catch. This may be a silly idea!
if (dynamic_cast<const __objc_id_type_info*>(thrownType)
|| (AppleCompatibleMode &&
dynamic_cast<const __objc_class_type_info*>(thrownType)))
{
thrown = dereference_thrown_object_pointer(obj);
// nil only matches id catch handlers in Apple-compatible mode, or when thrown as an id
if (0 == thrown)
{
return false;
}
// Check whether the real thrown object matches the catch type.
found = isKindOfClass(object_getClass(thrown),
(Class)objc_getClass(name()));
}
else if (dynamic_cast<const __objc_class_type_info*>(thrownType))
{
thrown = dereference_thrown_object_pointer(obj);
found = isKindOfClass((Class)objc_getClass(thrownType->name()),
(Class)objc_getClass(name()));
}
if (found)
{
*obj = (void*)thrown;
}
return found;
};
bool gnustep::libobjc::__objc_id_type_info::__do_catch(const type_info *thrownType,
void **obj,
unsigned outer) const
{
// Id catch matches any ObjC throw
if (dynamic_cast<const __objc_class_type_info*>(thrownType))
{
*obj = dereference_thrown_object_pointer(obj);
DEBUG_LOG("gnustep::libobjc::__objc_id_type_info::__do_catch caught 0x%x\n", *obj);
return true;
}
if (dynamic_cast<const __objc_id_type_info*>(thrownType))
{
*obj = dereference_thrown_object_pointer(obj);
DEBUG_LOG("gnustep::libobjc::__objc_id_type_info::__do_catch caught 0x%x\n", *obj);
return true;
}
DEBUG_LOG("gnustep::libobjc::__objc_id_type_info::__do_catch returning false\n");
return false;
};
/**
* Public interface to the Objective-C++ exception mechanism
*/
extern "C"
{
/**
* The public symbol that the compiler uses to indicate the Objective-C id type.
*/
OBJC_PUBLIC gnustep::libobjc::__objc_id_type_info __objc_id_type_info;
struct _Unwind_Exception *objc_init_cxx_exception(id obj)
{
id *newEx = static_cast<id*>(__cxa_allocate_exception(sizeof(id)));
*newEx = obj;
_Unwind_Exception *ex = pointer_add<_Unwind_Exception>(newEx, -exception_struct_size);
*pointer_add<std::type_info*>(ex, type_info_offset) = &__objc_id_type_info;
ex->exception_class = cxx_exception_class;
ex->exception_cleanup = exception_cleanup;
__cxa_get_globals()->uncaughtExceptions++;
return ex;
}
void* objc_object_for_cxx_exception(void *thrown_exception, int *isValid)
{
ptrdiff_t type_offset = type_info_offset;
if (type_offset == 0)
{
*isValid = 0;
return nullptr;
}
const std::type_info *thrownType =
*pointer_add<const std::type_info*>(thrown_exception, type_offset);
if (!dynamic_cast<const gnustep::libobjc::__objc_id_type_info*>(thrownType) &&
!dynamic_cast<const gnustep::libobjc::__objc_class_type_info*>(thrownType))
{
*isValid = 0;
return 0;
}
*isValid = 1;
return *pointer_add<id>(thrown_exception, exception_struct_size);
}
} // extern "C"
MagicValueHolder::MagicValueHolder() { magic_value = magic; }
/**
* Function that simply throws an instance of `MagicValueHolder`.
*/
PRIVATE void cxx_throw()
{
MagicValueHolder x;
throw x;
}
/**
* Personality function that wraps the C++ personality and inspects the C++
* exception structure on the way past. This should be used only for the
* `eh_trampoline` function.
*/
extern "C"
PRIVATE
BEGIN_PERSONALITY_FUNCTION(test_eh_personality)
// Don't bother with a mutex here. It doesn't matter if two threads set
// these values at the same time.
if (!done_setup)
{
uint64_t cls = __builtin_bswap64(exceptionClass);
type_info_offset = find_backwards(exceptionObject, &typeid(MagicValueHolder));
exception_struct_size = find_forwards(exceptionObject, MagicValueHolder::magic);
cxx_exception_class = exceptionClass;
done_setup = true;
}
return CALL_PERSONALITY_FUNCTION(__gxx_personality_v0);
}
/**
* Probe the C++ exception handling implementation. This throws a C++
* exception through a function that uses `test_eh_personality` as its
* personality function, allowing us to inspect a C++ exception that is in a
* known state.
*/
#ifndef __MINGW32__
extern "C" void test_cxx_eh_implementation()
{
if (done_setup)
{
return;
}
bool caught = false;
try
{
eh_trampoline();
}
catch(MagicValueHolder)
{
caught = true;
}
assert(caught);
}
#endif