dynamic_cast.cc

/* 
 * Copyright 2010-2011 PathScale, Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "typeinfo.h"
#include <stdio.h>

using namespace ABI_NAMESPACE;

/**
 * Vtable header.
 */
struct vtable_header
{
	/** Offset of the leaf object. */
	ptrdiff_t leaf_offset;
	/** Type of the object. */
	const __class_type_info *type;
};

/**
 * Simple macro that does pointer arithmetic in bytes but returns a value of
 * the same type as the original.
 */
#define ADD_TO_PTR(x, off) reinterpret_cast<__typeof__(x)>(reinterpret_cast<char*>(x) + off)

bool std::type_info::__do_catch(std::type_info const *ex_type,
                                void **exception_object,
                                unsigned int outer) const
{
	const type_info *type = this;

	if (type == ex_type)
	{
		return true;
	}
	if (const __class_type_info *cti = dynamic_cast<const __class_type_info *>(type))
	{
		return ex_type->__do_upcast(cti, exception_object);
	}
	return false;
}

bool __pbase_type_info::__do_catch(std::type_info const *ex_type,
                                   void **exception_object,
                                   unsigned int outer) const
{
	if (ex_type == this)
	{
		return true;
	}
	if (!ex_type->__is_pointer_p())
	{
		// Can't catch a non-pointer type in a pointer catch
		return false;
	}

	if (!(outer & 1))
	{
		// If the low bit is cleared on this means that we've gone
		// through a pointer that is not const qualified.
		return false;
	}
	// Clear the low bit on outer if we're not const qualified.
	if (!(__flags & __const_mask))
	{
		outer &= ~1;
	}

	const __pbase_type_info *ptr_type =
	        static_cast<const __pbase_type_info*>(ex_type);

	if (ptr_type->__flags & ~__flags)
	{
		// Handler pointer is less qualified
		return false;
	}

	// Special case for void* handler.  
	if(*__pointee == typeid(void))
	{
		return true;
	}

	return __pointee->__do_catch(ptr_type->__pointee, exception_object, outer);
}

void *__class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
{
	if (this == other)
	{
		return obj;
	}
	return 0;
}

void *__si_class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
{
	if (this == other)
	{
		return obj;
	}
	return __base_type->cast_to(obj, other);
}
bool __si_class_type_info::__do_upcast(const __class_type_info *target,
                                     void **thrown_object) const
{
	if (this == target)
	{
		return true;
	}
	return __base_type->__do_upcast(target, thrown_object);
}

void *__vmi_class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
{
	if (__do_upcast(other, &obj))
	{
		return obj;
	}
	return 0;
}

bool __vmi_class_type_info::__do_upcast(const __class_type_info *target,
		                      void **thrown_object) const
{
	if (this == target)
	{
		return true;
	}
	for (unsigned int i=0 ; i<__base_count ; i++)
	{
		const __base_class_type_info *info = &__base_info[i];
		ptrdiff_t offset = info->offset();
		// If this is a virtual superclass, the offset is stored in the
		// object's vtable at the offset requested; 2.9.5.6.c:
		//
		// 'For a non-virtual base, this is the offset in the object of the
		// base subobject. For a virtual base, this is the offset in the
		// virtual table of the virtual base offset for the virtual base
		// referenced (negative).'

		void *obj = *thrown_object;
		if (info->isVirtual())
		{
			// Object's vtable
			ptrdiff_t *off = *static_cast<ptrdiff_t**>(obj);
			// Offset location in vtable
			off = ADD_TO_PTR(off, offset);
			offset = *off;
		}
		void *cast = ADD_TO_PTR(obj, offset);

		if (info->__base_type == target ||
		    (info->__base_type->__do_upcast(target, &cast)))
		{
			*thrown_object = cast;
			return true;
		}
	}
	return 0;
}


/**
 * ABI function used to implement the dynamic_cast<> operator.  Some cases of
 * this operator are implemented entirely in the compiler (e.g. to void*).
 * This function implements the dynamic casts of the form dynamic_cast<T>(v).
 * This will be translated to a call to this function with the value v as the
 * first argument.  The type id of the static type of v is the second argument
 * and the type id of the destination type (T) is the third argument.
 *
 * The third argument is a hint about the compiler's guess at the correct
 * pointer offset.  If this value is negative, then -1 indicates no hint, -2
 * that src is not a public base of dst, and -3 that src is a multiple public
 * base type but never a virtual base type
 */
extern "C" void* __dynamic_cast(const void *sub,
                                const __class_type_info *src,
                                const __class_type_info *dst,
                                ptrdiff_t src2dst_offset)
{
	const char *vtable_location = *static_cast<const char * const *>(sub);
	const vtable_header *header =
		reinterpret_cast<const vtable_header*>(vtable_location - sizeof(vtable_header));
	void *leaf = ADD_TO_PTR(const_cast<void *>(sub), header->leaf_offset);
	return header->type->cast_to(leaf, dst);
}