y2038: IPC system call conversion

This is a follow-up to Deepa's work on the timekeeping system calls,
providing a y2038-safe syscall API for SYSVIPC. It uses a combination
of two strategies:

For sys_msgctl, sys_semctl and sys_shmctl, I do not introduce a completely
new set of replacement system calls, but instead extend the existing
ones to return data in the reserved fields of the normal data structure.

This should be completely transparent to any existing user space, and
only after the 32-bit time_t wraps, it will make a difference in the
returned data.

libc implementations will consequently have to provide their own data
structures when they move to 64-bit time_t, and convert the structures
in user space from the ones returned by the kernel.

In contrast, mq_timedsend, mq_timedreceive and and semtimedop all do
need to change because having a libc redefine the timespec type
breaks the ABI, so with this series there will be two separate entry
points for 32-bit architectures.

There are three cases here:

- little-endian architectures (except powerpc and mips) can use
  the normal layout and just cast the data structure to the user space
  type that contains 64-bit numbers.

- parisc and sparc can do the same thing with big-endian user space

- little-endian powerpc and most big-endian architectures have
  to flip the upper and lower 32-bit halves of the time_t value in memory,
  but can otherwise keep using the normal layout

- mips and big-endian xtensa need to be more careful because
  they are not consistent in their definitions, and they have to provide
  custom libc implementations for the system calls to use 64-bit time_t.
Version: GnuPG v1

y2038: ipc: Redirect ipc(SEMTIMEDOP, ...) to compat_ksys_semtimedop

32-bit architectures implementing 64BIT_TIME and COMPAT_32BIT_TIME
need to have the traditional semtimedop() behavior with 32-bit timestamps
for sys_ipc() by calling compat_ksys_semtimedop(), while those that
are not yet converted need to keep using ksys_semtimedop() like
64-bit architectures do.

Note that I chose to not implement a new SEMTIMEDOP64 function that
corresponds to the new sys_semtimedop() with 64-bit timeouts. The reason
here is that sys_ipc() should no longer be used for new system calls,
and libc should just call the semtimedop syscall directly.

One open question remain to whether we want to completely avoid the
sys_ipc() system call for architectures that do not yet have all the
individual calls as they get converted to 64-bit time_t. Doing that
would require adding several extra system calls on m68k, mips, powerpc,
s390, sh, sparc, and x86-32.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
1 file changed