libc/src/errno/libc_errno.cpp

   1 //===-- Implementation of libc_errno --------------------------------------===//
   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 #include "libc_errno.h"
  10 #include "src/__support/macros/config.h"
  11
  12 // libc uses a fallback default value, either system or thread local.
  13 #define LIBC_ERRNO_MODE_DEFAULT 0
  14 // libc never stores a value; `errno` macro uses get link-time failure.
  15 #define LIBC_ERRNO_MODE_UNDEFINED 1
  16 // libc maintains per-thread state (requires C++ `thread_local` support).
  17 #define LIBC_ERRNO_MODE_THREAD_LOCAL 2
  18 // libc maintains shared state used by all threads, contrary to standard C
  19 // semantics unless always single-threaded; nothing prevents data races.
  20 #define LIBC_ERRNO_MODE_SHARED 3
  21 // libc doesn't maintain any internal state, instead the embedder must define
  22 // `int *__llvm_libc_errno(void);` C function.
  23 #define LIBC_ERRNO_MODE_EXTERNAL 4
  24 // libc uses system `<errno.h>` `errno` macro directly in the overlay mode; in
  25 // fullbuild mode, effectively the same as `LIBC_ERRNO_MODE_EXTERNAL`.
  26 #define LIBC_ERRNO_MODE_SYSTEM 5
  27
  28 #if !defined(LIBC_ERRNO_MODE) || LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_DEFAULT
  29 #undef LIBC_ERRNO_MODE
  30 #if defined(LIBC_FULL_BUILD) || !defined(LIBC_COPT_PUBLIC_PACKAGING)
  31 #define LIBC_ERRNO_MODE LIBC_ERRNO_MODE_THREAD_LOCAL
  32 #else
  33 #define LIBC_ERRNO_MODE LIBC_ERRNO_MODE_SYSTEM
  34 #endif
  35 #endif // LIBC_ERRNO_MODE
  36
  37 #if LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_DEFAULT &&                              \
  38     LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_UNDEFINED &&                            \
  39     LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_THREAD_LOCAL &&                         \
  40     LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_SHARED &&                               \
  41     LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_EXTERNAL &&                             \
  42     LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_SYSTEM
  43 #error LIBC_ERRNO_MODE must be one of the following values: \
  44 LIBC_ERRNO_MODE_DEFAULT, \
  45 LIBC_ERRNO_MODE_UNDEFINED, \
  46 LIBC_ERRNO_MODE_THREAD_LOCAL, \
  47 LIBC_ERRNO_MODE_SHARED, \
  48 LIBC_ERRNO_MODE_EXTERNAL, \
  49 LIBC_ERRNO_MODE_SYSTEM
  50 #endif
  51
  52 namespace LIBC_NAMESPACE_DECL {
  53
  54 #if LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_UNDEFINED
  55
  56 void Errno::operator=(int) {}
  57 Errno::operator int() { return 0; }
  58
  59 #elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_THREAD_LOCAL
  60
  61 namespace {
  62 LIBC_THREAD_LOCAL int thread_errno;
  63 }
  64
  65 extern "C" int *__llvm_libc_errno() noexcept { return &thread_errno; }
  66
  67 void Errno::operator=(int a) { thread_errno = a; }
  68 Errno::operator int() { return thread_errno; }
  69
  70 #elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_SHARED
  71
  72 namespace {
  73 int shared_errno;
  74 }
  75
  76 extern "C" int *__llvm_libc_errno() noexcept { return &shared_errno; }
  77
  78 void Errno::operator=(int a) { shared_errno = a; }
  79 Errno::operator int() { return shared_errno; }
  80
  81 #elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_EXTERNAL
  82
  83 void Errno::operator=(int a) { *__llvm_libc_errno() = a; }
  84 Errno::operator int() { return *__llvm_libc_errno(); }
  85
  86 #elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_SYSTEM
  87
  88 void Errno::operator=(int a) { errno = a; }
  89 Errno::operator int() { return errno; }
  90
  91 #endif
  92
  93 // Define the global `libc_errno` instance.
  94 Errno libc_errno;
  95
  96 } // namespace LIBC_NAMESPACE_DECL