Use clock_settime to implement settimeofday

System Internals / glibc - Zack Weinberg [] - 30 October 2019 20:05 UTC

Unconditionally, on all ports, use clock_settime to implement settimeofday. Remove sysdeps/unix/clock_settime.c, which implemented clock_settime by calling settimeofday; new OS ports must henceforth provide a real implementation of clock_settime.

Hurd had a real implementation of settimeofday but not of clock_settime; this patch converts it into an implementation of clock_settime. It only supports CLOCK_REALTIME and microsecond resolution; Hurd/Mach does not appear to have any support for finer-resolution clocks.

The vestigial "set time zone" feature of settimeofday complicates the generic settimeofday implementation a little. The only remaining uses of this feature that aren't just bugs, are using it to inform the Linux kernel of the offset between the hardware clock and UTC, on systems where the hardware clock doesn't run in UTC (usually because of dual-booting with Windows). There currently isn't any other way to do this. However, the callers that do this call settimeofday with _only_ the timezone argument non-NULL. Therefore, glibc's new behavior is: callers of settimeofday must supply one and only one of the two arguments. If both arguments are non-NULL, or both arguments are NULL, the call fails and sets errno to EINVAL.

When only the timeval argument is supplied, settimeofday calls __clock_settime(CLOCK_REALTIME), same as stime.

When only the timezone argument is supplied, settimeofday calls a new internal function called __settimezone. On Linux, only, this function will pass the timezone structure to the settimeofday system call. On all other operating systems, and on Linux architectures that don't define __NR_settimeofday, __settimezone is a stub that always sets errno to ENOSYS and returns -1.

The settimeoday syscall is enabled on Linux by the flag COMPAT_32BIT_TIME, which is an option to either 32-bits ABIs or COMPAT builds (defined usually by 64-bit kernels that want to support 32-bit ABIs, such as x86). The idea to future 64-bit time_t only ABIs is to not provide settimeofday syscall.

The same semantics are implemented for Linux/Alpha's GLIBC_2.0 compat symbol for settimeofday.

There are no longer any internal callers of __settimeofday, so the internal prototype is removed.

Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64le-linux-gnu, powerpc64-linux-gnu, powerpc-linux-gnu, and aarch64-linux-gnu.

c3f9aef063 Use clock_settime to implement settimeofday.
NEWS | 24 ++++++++++
include/sys/time.h | 3 +-
sysdeps/{unix => mach/hurd}/clock_settime.c | 52 ++++++++++------------
sysdeps/unix/syscalls.list | 1 -
sysdeps/unix/sysv/linux/alpha/osf_settimeofday.c | 14 +++++-
sysdeps/unix/sysv/linux/alpha/settimeofday.c | 22 +++++++++
sysdeps/unix/sysv/linux/alpha/syscalls.list | 1 -
sysdeps/unix/sysv/linux/alpha/tv32-compat.h | 6 +++
sysdeps/unix/sysv/linux/settimezone.c | 36 +++++++++++++++
time/Makefile | 8 ++--
time/settimeofday.c | 24 ++++++++--
.../mach/hurd/settimeofday.c => time/settimezone.c | 34 +++-----------
12 files changed, 153 insertions(+), 72 deletions(-)


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