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
66namespace LIBC_NAMESPACE_DECL {
67namespace internal {
68LIBC_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