/*
* Copyright (c) 2021 Apple Inc. All rights reserved.
*
* @APPLE_LICENSE_HEADER_START@
*
* This file contains Original Code and/or Modifications of Original Code
* as defined in and that are subject to the Apple Public Source License
* Version 2.0 (the 'License'). You may not use this file except in
* compliance with the License. Please obtain a copy of the License at
* http://www.opensource.apple.com/apsl/ and read it before using this
* file.
*
* The Original Code and all software distributed under the License are
* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
* Please see the License for the specific language governing rights and
* limitations under the License.
*
* @APPLE_LICENSE_HEADER_END@
*/
#ifndef _OS_ALLOC_UTIL_H
#define _OS_ALLOC_UTIL_H
#include <sys/cdefs.h>
#if defined(__cplusplus) && __cplusplus >= 201103L
extern "C++" {
#include <os/cpp_util.h>
}
#endif
/*!
* @macro os_is_ptr_like
*
* @abstract
* Tell whether the given expression resembles a pointer.
*
* @discussion
* When pointer bounds are enabled, only types that are actually classified
* as pointers will be considered pointer-like. Otherwise, any pointer-sized
* type will be considered pointer-like.
*
* @param P the expression to be checked
*/
#if __has_ptrcheck
#define os_is_ptr_like(P) (__builtin_classify_type(P) == 5)
#else /* __has_ptrcheck */
#define os_is_ptr_like(P) (sizeof(P) == sizeof(void *))
#endif /* __has_ptrcheck */
/*!
* @macro os_ptr_load_and_erase
*
* @abstract
* Load the value of @c elem into a temporary, set @c elem to NULL, and
* return the value.
*
* @param elem the pointer whose value will be taken, and which will
* be set to NULL.
*/
#define os_ptr_load_and_erase(elem) ({ \
_Static_assert(os_is_ptr_like(elem), \
"elem isn't pointer sized"); \
__auto_type *__single __eptr = &(elem); \
__auto_type __elem = *__eptr; \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Wold-style-cast\"") \
*__eptr = (__typeof__(__elem))NULL; \
_Pragma("clang diagnostic pop") \
__elem; \
})
/*!
* @macro os_get_pointee_type
*
* @abstract
* Get the type pointed to by @c ptr.
*
* @discussion
* C++ forbids dereferencing a void pointer.
* This macro provides an abstraction that is safe to use with any pointer,
* both from C, and from C++.
*
* @param ptr the pointer we want to get the pointee's type for
*/
#if defined(__cplusplus) && __has_builtin(__remove_pointer) && \
__has_builtin(__remove_reference_t)
/*
* The reason we're using the compiler builtins is that those are able to
* properly deal with __ptrauth-qualified pointers, unlike template
* specializations. Moreover, template specializations would require forwarding
* type definitions, and currently __attribute__((xnu_usage_semantics(...)))
* annotations are not carried over across typedefs.
*
* It is safe to assume that if the compiler does not support such builtins,
* it also does not implement D150875, and we can therefore safely dereference
* void pointers.
*/
#define os_get_pointee_type(ptr) \
__remove_pointer(__remove_reference_t(__typeof__(ptr)))
#else
#define os_get_pointee_type(ptr) \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Wvoid-ptr-dereference\"") \
__typeof__(*(ptr)) \
_Pragma("clang diagnostic pop")
#endif
#endif /* _OS_ALLOC_UTIL_H */