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1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #ifndef CONTENT_BROWSER_MAC_CLOSURE_BLOCKS_LEOPARD_COMPAT_H_ | |
6 #define CONTENT_BROWSER_MAC_CLOSURE_BLOCKS_LEOPARD_COMPAT_H_ | |
7 #pragma once | |
8 | |
9 // libclosure (blocks) compatibility for Mac OS X 10.5 (Leopard) | |
10 // | |
11 // Background material: | |
12 // http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Blocks | |
13 // http://opensource.apple.com/source/libclosure/libclosure-38/ | |
14 // | |
15 // Leopard doesn't support blocks. Chrome supports Leopard. Chrome needs to use | |
16 // blocks. | |
17 // | |
18 // In any file where you use blocks (any time you type ^{...}), you must | |
19 // #include this file to ensure that the runtime symbols referenced by code | |
20 // emitted by the compiler are marked for weak-import. This means that if | |
21 // these symbols are not present at runtime, the program will still load, but | |
22 // their values will be NULL. | |
23 // | |
24 // In any target (in the GYP sense) where you use blocks, you must also depend | |
25 // on the closure_blocks_leopard_compat target to ensure that these symbols | |
26 // will be available at link time, even when the 10.5 SDK is in use. This | |
27 // allows the continued use of the 10.5 SDK, which does not contain these | |
28 // symbols. | |
29 // | |
30 // This does not relieve you of the responsibility to not use blocks on | |
31 // Leopard. Because runtime support for Blocks still isn't present on that | |
32 // operating system, the weak-imported symbols will have value 0 and attempts | |
33 // to do anything meaningful with them will fail or crash. You must take care | |
34 // not to enter any codepath that uses blocks on Leopard. The base::mac::IsOS* | |
35 // family may be helpful. | |
36 // | |
37 // Although this scheme allows the use of the 10.5 SDK and 10.5 runtime in an | |
38 // application that uses blocks, it is still necessary to use a compiler that | |
39 // supports blocks. GCC 4.2 as shipped with Xcode 3.2 for Mac OS X 10.6 | |
40 // qualifies, as do sufficiently recent versions of clang. GCC 4.2 as shipped | |
41 // with Xcode 3.1 for Mac OS X 10.5 does not qualify. | |
42 | |
43 // _NSConcreteGlobalBlock and _NSConcreteStackBlock are private implementation | |
44 // details of libclosure defined in libclosure/libclosure-38/Block_private.h, | |
45 // but they're exposed from libSystem as public symbols, and the block-enabled | |
46 // compiler will emit code that references these symbols. Because the symbols | |
47 // aren't present in 10.5's libSystem, they must be declared as weak imports | |
48 // in any file that uses blocks. Any block-using file must #include this | |
49 // header to guarantee that the symbols will show up in linked output as weak | |
50 // imports when compiling for a 10.5 deployment target. Because the symbols | |
51 // are always present in 10.6 and higher, they do not need to be a weak | |
52 // imports when the deployment target is at least 10.6. | |
53 // | |
54 // Both GCC and clang emit references to these symbols, providing implicit | |
55 // declarations as needed, but respecting any user declaration when present. | |
56 // See gcc-5666.3/gcc/c-parser.c build_block_struct_initlist, | |
57 // gcc-5666.3/gcc/cp/parser.c build_block_struct_initlist, and | |
58 // clang-2.9/lib/CodeGen/CodeGenModule.cpp | |
59 // CodeGenModule::getNSConcreteGlobalBlock() and | |
60 // CodeGenModule::getNSConcreteStackBlock(). | |
61 | |
62 #include <AvailabilityMacros.h> | |
63 | |
64 #if defined(MAC_OS_X_VERSION_10_6) && \ | |
65 MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_6 // SDK >= 10.6 | |
66 // Get the system's own declarations of these things if using an SDK where | |
67 // they are present. | |
68 #include <Block.h> | |
69 #endif // SDK >= 10.6 | |
70 | |
71 extern "C" { | |
72 | |
73 #if MAC_OS_X_VERSION_MIN_REQUIRED <= MAC_OS_X_VERSION_10_5 // DT <= 10.5 | |
74 #define MAYBE_WEAK_IMPORT __attribute__((weak_import)) | |
75 #else // DT > 10.5 | |
76 #define MAYBE_WEAK_IMPORT | |
77 #endif // DT <= 10.5 | |
78 | |
79 MAYBE_WEAK_IMPORT extern void* _Block_copy(const void*); | |
80 MAYBE_WEAK_IMPORT extern void _Block_release(const void*); | |
81 MAYBE_WEAK_IMPORT extern void _Block_object_assign(void*, | |
82 const void*, | |
83 const int); | |
84 MAYBE_WEAK_IMPORT extern void _Block_object_dispose(const void*, const int); | |
85 | |
86 MAYBE_WEAK_IMPORT extern void* _NSConcreteGlobalBlock[32]; | |
87 MAYBE_WEAK_IMPORT extern void* _NSConcreteStackBlock[32]; | |
88 | |
89 #undef MAYBE_WEAK_IMPORT | |
90 | |
91 } // extern "C" | |
92 | |
93 // Macros from <Block.h>, in case <Block.h> is not present. | |
94 | |
95 #ifndef Block_copy | |
96 #define Block_copy(...) \ | |
97 ((__typeof(__VA_ARGS__))_Block_copy((const void *)(__VA_ARGS__))) | |
98 #endif | |
99 | |
100 #ifndef Block_release | |
101 #define Block_release(...) _Block_release((const void *)(__VA_ARGS__)) | |
102 #endif | |
103 | |
104 #endif // CONTENT_BROWSER_MAC_CLOSURE_BLOCKS_LEOPARD_COMPAT_H_ | |
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