y2038: linux: Provide __utimensat64 implementation

This patch provides new __utimensat64 explicit 64 bit function for
setting access and modification time of a file. Moreover, a 32 bit version
- __utimensat has been refactored to internally use __utimensat64.

The __utimensat is now supposed to be used on systems still supporting
32 bit time (__TIMESIZE != 64) - hence the necessary conversions to 64 bit
struct __timespec64.
When pointer to struct __timespec64 is NULL - the file access and modification
time is set to the current one and no conversions from struct timespec to
__timespec64 are performed.

The new utimensat_time64 syscall available from Linux 5.1+ has been used,
when applicable.
The new helper function - __utimensat64_helper - has been introduced to
facilitate code re-usage on function providing futimens syscall handling.
The Linux kernel checks if passed tv_nsec value overflows, so there is no
need to repeat it in glibc.
When utimensat syscall on systems supporting 32 bit time ABI is used,
the check is performed if passed data (which may have 64 bit tv_sec) fits
into 32 bit range.

Build tests:
- The code has been tested on x86_64/x86 (native compilation):
make PARALLELMFLAGS="-j8" && make xcheck PARALLELMFLAGS="-j8"

- The glibc has been build tested (make PARALLELMFLAGS="-j8") for
x86 (i386), x86_64-x32, and armv7

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

- Use of cross-test-ssh.sh for ARM (armv7):
make PARALLELMFLAGS="-j8" test-wrapper='./cross-test-ssh.sh root@192.168.7.2' xcheck

Linux kernel, headers and minimal kernel version for glibc build test
matrix:
- Linux v5.1 (with utimensat_time64) and glibc build with v5.1 as
minimal kernel version (--enable-kernel="5.1.0")
The __ASSUME_TIME64_SYSCALLS flag defined.

- Linux v5.1 and default minimal kernel version
The __ASSUME_TIME64_SYSCALLS not defined, but kernel supports utimensat_time64
syscall.

- Linux v4.19 (no utimensat_time64 support) with default minimal kernel
version for contemporary glibc
This kernel doesn't support utimensat_time64 syscall, so the fallback
to utimensat is tested.

The above tests were performed with Y2038 redirection applied as well as
without (so the __TIMESIZE != 64 execution path is checked as well).

No regressions were observed.

1 files changed, 12 insertions, 0 deletions

diff --git a/include/time.h b/include/time.h
index 000672e3bc..7debf9f9cc 100644
--- a/include/time.h
+++ b/include/time.h
@@ -146,6 +146,18 @@ extern int __clock_getres64 (clockid_t clock_id,
 libc_hidden_proto (__clock_getres64);
 #endif
 
+#if __TIMESIZE == 64
+# define __utimensat64 __utimensat
+#else
+extern int __utimensat64 (int fd, const char *file,
+                          const struct __timespec64 tsp[2], int flags);
+libc_hidden_proto (__utimensat64);
+#endif
+
+extern int __utimensat64_helper (int fd, const char *file,
+                                 const struct __timespec64 tsp[2], int flags);
+libc_hidden_proto (__utimensat64_helper);
+
 /* Compute the `struct tm' representation of T,
    offset OFFSET seconds east of UTC,
    and store year, yday, mon, mday, wday, hour, min, sec into *TP.