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71 lines
2.1 KiB
C
71 lines
2.1 KiB
C
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/* Auxiliary definitions for 64-bit time_t support.
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Copyright (C) 2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <stdbool.h>
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#include <atomic.h>
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/* These helper functions are used to optimize the 64-bit time_t support on
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configurations that requires support for 32-bit time_t fallback
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(!__ASSUME_TIME64_SYSCALLS). The idea is once the kernel advertises that
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it does not have 64-bit time_t support, glibc will stop to try issue the
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64-bit time_t syscall altogether.
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For instance:
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#ifndef __NR_symbol_time64
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# define __NR_symbol_time64 __NR_symbol
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#endif
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int r;
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if (supports_time64 ())
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{
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r = INLINE_SYSCALL_CALL (symbol, ...);
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if (r == 0 || errno != ENOSYS)
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return r;
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mark_time64_unsupported ();
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}
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#ifndef __ASSUME_TIME64_SYSCALLS
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<32-bit fallback syscall>
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#endif
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return r;
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On configuration with default 64-bit time_t this optimization should be
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optimized away by the compiler resulting in no overhead. */
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#ifndef __ASSUME_TIME64_SYSCALLS
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extern int __time64_support attribute_hidden;
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#endif
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static inline bool
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supports_time64 (void)
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{
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#ifdef __ASSUME_TIME64_SYSCALLS
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return true;
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#else
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return atomic_load_relaxed (&__time64_support) != 0;
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#endif
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}
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static inline void
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mark_time64_unsupported (void)
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{
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#ifndef __ASSUME_TIME64_SYSCALLS
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atomic_store_relaxed (&__time64_support, 0);
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#endif
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}
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