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author | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2020-08-20 09:18:15 -0300 |
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committer | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2020-08-24 14:27:15 -0300 |
commit | 02c91eb6115872219a85bb93724affd7fcdedf7a (patch) | |
tree | 70eba2b827fa99ebca9202b9915894694e2a03af /sysdeps/unix/sysv/linux/time64-support.h | |
parent | 756c306502498f999fdd494477b9cea1b45e4faf (diff) | |
download | glibc-02c91eb6115872219a85bb93724affd7fcdedf7a.tar.gz glibc-02c91eb6115872219a85bb93724affd7fcdedf7a.tar.xz glibc-02c91eb6115872219a85bb93724affd7fcdedf7a.zip |
linux: Add helper function to optimize 64-bit time_t fallback support
These helper functions are used to optimize the 64-bit time_t support on configurations that requires support for 32-bit time_t fallback (!__ASSUME_TIME64_SYSCALLS). The idea is once the kernel advertises that it does not have 64-bit time_t support, glibc will stop to try issue the 64-bit time_t syscall altogether. For instance: #ifndef __NR_symbol_time64 # define __NR_symbol_time64 __NR_symbol #endif int r; if (supports_time64 ()) { r = INLINE_SYSCALL_CALL (symbol, ...); if (r == 0 || errno != ENOSYS) return r; mark_time64_unsupported (); } #ifndef __ASSUME_TIME64_SYSCALLS <32-bit fallback syscall> #endif return r; On configuration with default 64-bit time_t this optimization should be optimized away by the compiler resulting in no overhead.
Diffstat (limited to 'sysdeps/unix/sysv/linux/time64-support.h')
-rw-r--r-- | sysdeps/unix/sysv/linux/time64-support.h | 70 |
1 files changed, 70 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/time64-support.h b/sysdeps/unix/sysv/linux/time64-support.h new file mode 100644 index 0000000000..ebba155f98 --- /dev/null +++ b/sysdeps/unix/sysv/linux/time64-support.h @@ -0,0 +1,70 @@ +/* Auxiliary definitions for 64-bit time_t support. + Copyright (C) 2020 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#include <stdbool.h> +#include <atomic.h> + +/* These helper functions are used to optimize the 64-bit time_t support on + configurations that requires support for 32-bit time_t fallback + (!__ASSUME_TIME64_SYSCALLS). The idea is once the kernel advertises that + it does not have 64-bit time_t support, glibc will stop to try issue the + 64-bit time_t syscall altogether. + + For instance: + + #ifndef __NR_symbol_time64 + # define __NR_symbol_time64 __NR_symbol + #endif + int r; + if (supports_time64 ()) + { + r = INLINE_SYSCALL_CALL (symbol, ...); + if (r == 0 || errno != ENOSYS) + return r; + + mark_time64_unsupported (); + } + #ifndef __ASSUME_TIME64_SYSCALLS + <32-bit fallback syscall> + #endif + return r; + + On configuration with default 64-bit time_t this optimization should be + optimized away by the compiler resulting in no overhead. */ + +#ifndef __ASSUME_TIME64_SYSCALLS +extern int __time64_support attribute_hidden; +#endif + +static inline bool +supports_time64 (void) +{ +#ifdef __ASSUME_TIME64_SYSCALLS + return true; +#else + return atomic_load_relaxed (&__time64_support) != 0; +#endif +} + +static inline void +mark_time64_unsupported (void) +{ +#ifndef __ASSUME_TIME64_SYSCALLS + atomic_store_relaxed (&__time64_support, 0); +#endif +} |