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#include "src/__support/macros/properties/compiler.h"
20
21#ifndef LLVM_LIBC_FUNCTION_ATTR
22#define LLVM_LIBC_FUNCTION_ATTR
23#endif
24
25// clang-format off
26// Allow each function `func` to have extra attributes specified by defining:
27// `LLVM_LIBC_FUNCTION_ATTR_func` macro, which should always start with
28// "LLVM_LIBC_EMPTY, "
29//
30// For examples:
31// #define LLVM_LIBC_FUNCTION_ATTR_memcpy LLVM_LIBC_EMPTY, [[gnu::weak]]
32// #define LLVM_LIBC_FUNCTION_ATTR_memchr LLVM_LIBC_EMPTY, [[gnu::weak]] [[gnu::visibility("default")]]
33// clang-format on
34#define LLVM_LIBC_EMPTY
35
36#define GET_SECOND(first, second, ...) second
37#define EXPAND_THEN_SECOND(name) GET_SECOND(name, LLVM_LIBC_EMPTY)
38
39#define LLVM_LIBC_ATTR(name) EXPAND_THEN_SECOND(LLVM_LIBC_FUNCTION_ATTR_##name)
40
41// At the moment, [[gnu::alias()]] is not supported on MacOS, and it is needed
42// to cleanly export and alias the C++ symbol `LIBC_NAMESPACE::func` with the C
43// symbol `func`. So for public packaging on MacOS, we will only export the C
44// symbol. Moreover, a C symbol `func` in macOS is mangled as `_func`.
45#if defined(LIBC_COPT_PUBLIC_PACKAGING) && !defined(LIBC_COMPILER_IS_MSVC)
46#ifndef __APPLE__
47#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) \
48 LLVM_LIBC_ATTR(name) \
49 LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name) \
50 __##name##_impl__ asm(#name); \
51 decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]]; \
52 type __##name##_impl__ arglist
53#else // __APPLE__
54#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) \
55 LLVM_LIBC_ATTR(name) \
56 LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name) name asm("_" #name); \
57 type name arglist
58#endif // __APPLE__
59#else // LIBC_COPT_PUBLIC_PACKAGING
60#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) type name arglist
61#endif // LIBC_COPT_PUBLIC_PACKAGING
62
63// This extra layer of macro allows `name` to be a macro to rename a function.
64#define LLVM_LIBC_FUNCTION(type, name, arglist) \
65 LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)
66
67namespace LIBC_NAMESPACE_DECL {
68namespace internal {
69LIBC_INLINE constexpr bool same_string(char const *lhs, char const *rhs) {
70 for (; *lhs || *rhs; ++lhs, ++rhs)
71 if (*lhs != *rhs)
72 return false;
73 return true;
74}
75} // namespace internal
76} // namespace LIBC_NAMESPACE_DECL
77
78#define __LIBC_MACRO_TO_STRING(str) #str
79#define LIBC_MACRO_TO_STRING(str) __LIBC_MACRO_TO_STRING(str)
80
81// LLVM_LIBC_IS_DEFINED checks whether a particular macro is defined.
82// Usage: constexpr bool kUseAvx = LLVM_LIBC_IS_DEFINED(__AVX__);
83//
84// This works by comparing the stringified version of the macro with and without
85// evaluation. If FOO is not undefined both stringifications yield "FOO". If FOO
86// is defined, one stringification yields "FOO" while the other yields its
87// stringified value "1".
88#define LLVM_LIBC_IS_DEFINED(macro) \
89 !LIBC_NAMESPACE::internal::same_string( \
90 LLVM_LIBC_IS_DEFINED__EVAL_AND_STRINGIZE(macro), #macro)
91#define LLVM_LIBC_IS_DEFINED__EVAL_AND_STRINGIZE(s) #s
92
93#endif // LLVM_LIBC_SRC___SUPPORT_COMMON_H
94