y2038: linux: Provide __time64 implementation

In the glibc the time function can use vDSO (on power and x86 the
USE_IFUNC_TIME is defined), time syscall or 'default' time() from
./time/time.c (as a fallback).

In this patch the last function (time) has been refactored and moved
to ./sysdeps/unix/sysv/linux/time.c to be Linux specific.

The new __time64 explicit 64 bit function for providing 64 bit value of
seconds after epoch (by internally calling __clock_gettime64) has been
introduced.

Moreover, a 32 bit version - __time has been refactored to internally
use __time64.

The __time is now supposed to be used on systems still supporting 32 bit
time (__TIMESIZE != 64) - hence the necessary check for time_t potential
overflow.

The iFUNC vDSO direct call optimization has been removed from both i686 and
powerpc32 (USE_IFUNC_TIME is not defined for those architectures
anymore). The Linux kernel does not provide a y2038 safe implementation of
time neither it plans to provide it in the future, __clock_gettime64
should be used instead. Keeping support for this optimization would require
to handle another build permutation (!__ASSUME_TIME64_SYSCALLS &&
USE_IFUNC_TIME which adds more complexity and has limited use (since the
idea is to eventually have a y2038 safe glibc build).

Build tests:
./src/scripts/build-many-glibcs.py glibcs

Run-time tests:
- Run specific tests on ARM/x86 32bit systems (qemu):
https://github.com/lmajewski/meta-y2038 and run tests:
https://github.com/lmajewski/y2038-tests/commits/master

Above tests were performed with Y2038 redirection applied as well as
without to test proper usage of both __time64 and __time.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/time.h b/include/time.h
index edf6cdf..caf2af5 100644
--- a/include/time.h
+++ b/include/time.h
@@ -317,6 +317,13 @@ extern int __timespec_get64 (struct __timespec64 *ts, int base);
 libc_hidden_proto (__timespec_get64)
 #endif
 
+#if __TIMESIZE == 64
+# define __time64 __time
+#else
+extern __time64_t __time64 (__time64_t *timer);
+libc_hidden_proto (__time64)
+#endif
+
 /* Use in the clock_* functions.  Size of the field representing the
    actual clock ID.  */
 #define CLOCK_IDFIELD_SIZE	3