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