1 //===-- Common internal contructs -------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #ifndef LLVM_LIBC_SRC___SUPPORT_COMMON_H
10 #define LLVM_LIBC_SRC___SUPPORT_COMMON_H
11
12 #ifndef LIBC_NAMESPACE
13 #error "LIBC_NAMESPACE macro is not defined."
14 #endif
15
16 #include "src/__support/macros/attributes.h"
17 #include "src/__support/macros/config.h"
18 #include "src/__support/macros/properties/architectures.h"
19
20 #ifndef LLVM_LIBC_FUNCTION_ATTR
21 #define LLVM_LIBC_FUNCTION_ATTR
22 #endif
23
24 // clang-format off
25 // Allow each function `func` to have extra attributes specified by defining:
26 // `LLVM_LIBC_FUNCTION_ATTR_func` macro, which should always start with
27 // "LLVM_LIBC_EMPTY, "
28 //
29 // For examples:
30 // #define LLVM_LIBC_FUNCTION_ATTR_memcpy LLVM_LIBC_EMPTY, [[gnu::weak]]
31 // #define LLVM_LIBC_FUNCTION_ATTR_memchr LLVM_LIBC_EMPTY, [[gnu::weak]] [[gnu::visibility("default")]]
32 // clang-format on
33 #define LLVM_LIBC_EMPTY
34
35 #define GET_SECOND(first, second, ...) second
36 #define EXPAND_THEN_SECOND(name) GET_SECOND(name, LLVM_LIBC_EMPTY)
37
38 #define LLVM_LIBC_ATTR(name) EXPAND_THEN_SECOND(LLVM_LIBC_FUNCTION_ATTR_##name)
39
40 // At the moment, [[gnu::alias()]] is not supported on MacOS, and it is needed
41 // to cleanly export and alias the C++ symbol `LIBC_NAMESPACE::func` with the C
42 // symbol `func`. So for public packaging on MacOS, we will only export the C
43 // symbol. Moreover, a C symbol `func` in macOS is mangled as `_func`.
44 #if defined(LIBC_COPT_PUBLIC_PACKAGING)
45 #ifndef __APPLE__
46 #define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) \
47 LLVM_LIBC_ATTR(name) \
48 LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name) \
49 __##name##_impl__ __asm__(#name); \
50 decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]]; \
51 type __##name##_impl__ arglist
52 #else // __APPLE__
53 #define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) \
54 LLVM_LIBC_ATTR(name) \
55 LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name) name asm("_" #name); \
56 type name arglist
57 #endif // __APPLE__
58 #else // LIBC_COPT_PUBLIC_PACKAGING
59 #define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) type name arglist
60 #endif // LIBC_COPT_PUBLIC_PACKAGING
61
62 // This extra layer of macro allows `name` to be a macro to rename a function.
63 #define LLVM_LIBC_FUNCTION(type, name, arglist) \
64 LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)
65
66 namespace LIBC_NAMESPACE_DECL {
67 namespace internal {
same_string(char const * lhs,char const * rhs)68 LIBC_INLINE constexpr bool same_string(char const *lhs, char const *rhs) {
69 for (; *lhs || *rhs; ++lhs, ++rhs)
70 if (*lhs != *rhs)
71 return false;
72 return true;
73 }
74 } // namespace internal
75 } // namespace LIBC_NAMESPACE_DECL
76
77 #define __LIBC_MACRO_TO_STRING(str) #str
78 #define LIBC_MACRO_TO_STRING(str) __LIBC_MACRO_TO_STRING(str)
79
80 // LLVM_LIBC_IS_DEFINED checks whether a particular macro is defined.
81 // Usage: constexpr bool kUseAvx = LLVM_LIBC_IS_DEFINED(__AVX__);
82 //
83 // This works by comparing the stringified version of the macro with and without
84 // evaluation. If FOO is not undefined both stringifications yield "FOO". If FOO
85 // is defined, one stringification yields "FOO" while the other yields its
86 // stringified value "1".
87 #define LLVM_LIBC_IS_DEFINED(macro) \
88 !LIBC_NAMESPACE::internal::same_string( \
89 LLVM_LIBC_IS_DEFINED__EVAL_AND_STRINGIZE(macro), #macro)
90 #define LLVM_LIBC_IS_DEFINED__EVAL_AND_STRINGIZE(s) #s
91
92 #endif // LLVM_LIBC_SRC___SUPPORT_COMMON_H
93