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Re: [PATCH v2] ipc: provide generic compat versions of IPC syscalls

To: Chris Metcalf <>
Subject: Re: [PATCH v2] ipc: provide generic compat versions of IPC syscalls
From: Andrew Morton <>
Date: Fri, 9 Dec 2011 13:48:52 -0800
Cc: Arnd Bergmann <>, Ralf Baechle <>, Benjamin Herrenschmidt <>, Paul Mackerras <>, Martin Schwidefsky <>, Heiko Carstens <>,, "David S. Miller" <>, Thomas Gleixner <>, Ingo Molnar <>, "H. Peter Anvin" <>,, "Eric W. Biederman" <>, Christoph Hellwig <>, Lucas De Marchi <>, Dmitry Torokhov <>, "J. Bruce Fields" <>, NeilBrown <>,,,,,
In-reply-to: <>
References: <> <> <>
On Fri, 9 Dec 2011 10:29:07 -0500
Chris Metcalf <> wrote:

> 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 define that can be
> set in <asm/compat.h> 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 supply this define, and thus can
> avoid having any IPC-specific code at all in their architecture-specific
> compat layer.  In the same vein, if this define is omitted, 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.

What would we need to do to get all architectures using the new
interfaces, and remove __ARCH_WANT_OLD_COMPAT_IPC?

Regarding the implementation: rather than patching the header
files, it would be more conventional (and arguably better) to add


to arch/*/Kconfig, then use CONFIG_ARCH_WANT_OLD_COMPAT_IPC.

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