1 | /* |
2 | * Copyright (c) 2021 Apple Inc. All rights reserved. |
3 | * |
4 | * @APPLE_LICENSE_HEADER_START@ |
5 | * |
6 | * This file contains Original Code and/or Modifications of Original Code |
7 | * as defined in and that are subject to the Apple Public Source License |
8 | * Version 2.0 (the 'License'). You may not use this file except in |
9 | * compliance with the License. Please obtain a copy of the License at |
10 | * http://www.opensource.apple.com/apsl/ and read it before using this |
11 | * file. |
12 | * |
13 | * The Original Code and all software distributed under the License are |
14 | * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER |
15 | * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, |
16 | * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, |
17 | * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. |
18 | * Please see the License for the specific language governing rights and |
19 | * limitations under the License. |
20 | * |
21 | * @APPLE_LICENSE_HEADER_END@ |
22 | */ |
23 | |
24 | #ifndef _OS_ALLOC_UTIL_H |
25 | #define _OS_ALLOC_UTIL_H |
26 | |
27 | #include <sys/cdefs.h> |
28 | #if defined(__cplusplus) && __cplusplus >= 201103L |
29 | extern "C++" { |
30 | #include <os/cpp_util.h> |
31 | } |
32 | #endif |
33 | |
34 | /*! |
35 | * @macro os_is_ptr_like |
36 | * |
37 | * @abstract |
38 | * Tell whether the given expression resembles a pointer. |
39 | * |
40 | * @discussion |
41 | * When pointer bounds are enabled, only types that are actually classified |
42 | * as pointers will be considered pointer-like. Otherwise, any pointer-sized |
43 | * type will be considered pointer-like. |
44 | * |
45 | * @param P the expression to be checked |
46 | */ |
47 | #if __has_ptrcheck |
48 | #define os_is_ptr_like(P) (__builtin_classify_type(P) == 5) |
49 | #else /* __has_ptrcheck */ |
50 | #define os_is_ptr_like(P) (sizeof(P) == sizeof(void *)) |
51 | #endif /* __has_ptrcheck */ |
52 | |
53 | /*! |
54 | * @macro os_ptr_load_and_erase |
55 | * |
56 | * @abstract |
57 | * Load the value of @c elem into a temporary, set @c elem to NULL, and |
58 | * return the value. |
59 | * |
60 | * @param elem the pointer whose value will be taken, and which will |
61 | * be set to NULL. |
62 | */ |
63 | #define os_ptr_load_and_erase(elem) ({ \ |
64 | _Static_assert(os_is_ptr_like(elem), \ |
65 | "elem isn't pointer sized"); \ |
66 | __auto_type *__single __eptr = &(elem); \ |
67 | __auto_type __elem = *__eptr; \ |
68 | _Pragma("clang diagnostic push") \ |
69 | _Pragma("clang diagnostic ignored \"-Wold-style-cast\"") \ |
70 | *__eptr = (__typeof__(__elem))NULL; \ |
71 | _Pragma("clang diagnostic pop") \ |
72 | __elem; \ |
73 | }) |
74 | |
75 | /*! |
76 | * @macro os_get_pointee_type |
77 | * |
78 | * @abstract |
79 | * Get the type pointed to by @c ptr. |
80 | * |
81 | * @discussion |
82 | * C++ forbids dereferencing a void pointer. |
83 | * This macro provides an abstraction that is safe to use with any pointer, |
84 | * both from C, and from C++. |
85 | * |
86 | * @param ptr the pointer we want to get the pointee's type for |
87 | */ |
88 | |
89 | #if defined(__cplusplus) && __has_builtin(__remove_pointer) && \ |
90 | __has_builtin(__remove_reference_t) |
91 | /* |
92 | * The reason we're using the compiler builtins is that those are able to |
93 | * properly deal with __ptrauth-qualified pointers, unlike template |
94 | * specializations. Moreover, template specializations would require forwarding |
95 | * type definitions, and currently __attribute__((xnu_usage_semantics(...))) |
96 | * annotations are not carried over across typedefs. |
97 | * |
98 | * It is safe to assume that if the compiler does not support such builtins, |
99 | * it also does not implement D150875, and we can therefore safely dereference |
100 | * void pointers. |
101 | */ |
102 | #define os_get_pointee_type(ptr) \ |
103 | __remove_pointer(__remove_reference_t(__typeof__(ptr))) |
104 | #else |
105 | #define os_get_pointee_type(ptr) \ |
106 | _Pragma("clang diagnostic push") \ |
107 | _Pragma("clang diagnostic ignored \"-Wvoid-ptr-dereference\"") \ |
108 | __typeof__(*(ptr)) \ |
109 | _Pragma("clang diagnostic pop") |
110 | #endif |
111 | |
112 | #endif /* _OS_ALLOC_UTIL_H */ |
113 | |