1/* Auxiliary definitions for 64-bit time_t support.
2 Copyright (C) 2020-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <stdbool.h>
20#include <atomic.h>
21
22/* These helper functions are used to optimize the 64-bit time_t support on
23 configurations that requires support for 32-bit time_t fallback
24 (!__ASSUME_TIME64_SYSCALLS). The idea is once the kernel advertises that
25 it does not have 64-bit time_t support, glibc will stop to try issue the
26 64-bit time_t syscall altogether.
27
28 For instance:
29
30 #ifndef __NR_symbol_time64
31 # define __NR_symbol_time64 __NR_symbol
32 #endif
33 int r;
34 if (supports_time64 ())
35 {
36 r = INLINE_SYSCALL_CALL (symbol, ...);
37 if (r == 0 || errno != ENOSYS)
38 return r;
39
40 mark_time64_unsupported ();
41 }
42 #ifndef __ASSUME_TIME64_SYSCALLS
43 <32-bit fallback syscall>
44 #endif
45 return r;
46
47 On configuration with default 64-bit time_t this optimization should be
48 optimized away by the compiler resulting in no overhead. */
49
50#ifndef __ASSUME_TIME64_SYSCALLS
51extern int __time64_support attribute_hidden;
52#endif
53
54static inline bool
55supports_time64 (void)
56{
57#ifdef __ASSUME_TIME64_SYSCALLS
58 return true;
59#else
60 return atomic_load_relaxed (&__time64_support) != 0;
61#endif
62}
63
64static inline void
65mark_time64_unsupported (void)
66{
67#ifndef __ASSUME_TIME64_SYSCALLS
68 atomic_store_relaxed (&__time64_support, 0);
69#endif
70}
71