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.
