[PATCH v3] ipc: provide generic compat versions of IPC syscalls

When using the "compat" APIs, architectures will generally want to
be able to make direct syscalls to msgsnd(), shmctl(), etc., and
in the kernel we would want them to be handled directly by
compat_sys_xxx() functions, as is true for other compat syscalls.

However, for historical reasons, several of the existing compat IPC
syscalls do not do this.  semctl() expects a pointer to the fourth
argument, instead of the fourth argument itself.  msgsnd(), msgrcv()
and shmat() expect arguments in different order.

This change adds an ARCH_WANT_OLD_COMPAT_IPC config option that can be
set to preserve this behavior for ports that use it (x86, sparc, powerpc,
s390, and mips).  No actual semantics are changed for those architectures,
and there is only a minimal amount of code refactoring in ipc/compat.c.

Newer architectures like tile (and perhaps future architectures such
as arm64 and unicore64) should not select this option, and thus can
avoid having any IPC-specific code at all in their architecture-specific
compat layer.  In the same vein, if this option is not selected, IPC_64
mode is assumed, since that's what the <asm-generic> headers expect.

The workaround code in "tile" for msgsnd() and msgrcv() is removed
with this change; it also fixes the bug that shmat() and semctl() were
not being properly handled.

Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 6d99a5fcc090..0ff53e350092 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -218,6 +218,7 @@ config COMPAT
         prompt "Kernel support for 31 bit emulation"
         depends on 64BIT
         select COMPAT_BINFMT_ELF
+        select ARCH_WANT_OLD_COMPAT_IPC
         help
           Select this option if you want to enable your system kernel to
           handle system-calls from ELF binaries for 31 bit ESA.  This option