linux-kernel - Re: [PATCH v2] compat: fixes to allow working with tile arch

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Date:	Wed, 11 May 2011 23:08:15 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Jeff Moyer <jmoyer@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>
Subject: Re: [PATCH v2] compat: fixes to allow working with tile arch

On Monday 09 May 2011, Chris Metcalf wrote:
> The existing <asm-generic/unistd.h> mechanism doesn't really provide
> enough to create the 64-bit "compat" ABI properly in a generic way,
> since the compat ABI is a mix of things were you can re-use the 64-bit
> versions of syscalls and things where you need a compat wrapper.
> 
> To provide this in the most direct way possible, I added two new macros
> to go along with the existing __SYSCALL and __SC_3264 macros: __SC_COMP
> and SC_COMP_3264.  These macros take an additional argument, typically a
> "compat_sys_xxx" function, which is passed to __SYSCALL if you define
> __SYSCALL_COMPAT when including the header, resulting in a pointer to
> the compat function being placed in the generated syscall table.
> 
> The change also adds some missing definitions to <linux/compat.h> so that
> it actually has declarations for all the compat syscalls, since the
> "[nr] = ##call" approach requires proper C declarations for all the
> functions included in the syscall table.
> 
> Finally, compat.c defines compat_sys_sigpending() and
> compat_sys_sigprocmask() even if the underlying architecture doesn't
> request it, which tries to pull in undefined compat_old_sigset_t defines.
> We need to guard those compat syscall definitions with appropriate
> __ARCH_WANT_SYS_xxx ifdefs.
> 
> Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
> ---
> Arnd - let me know if this matches what you had in mind.  Thanks!

Looks good to me, yes. It's not exactly what I would have done, but
it absolutely makes sense and I can't see any specific disadvantage
over the other slightly different approaches.

Acked-by: Arnd Bergmann <arnd@...db.de>
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