linux-kernel - Re: [PATCH 2/6] trace: add support for 32 bit compat syscalls on x86

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Date:	Mon, 26 Mar 2012 21:49:46 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	David Sharp <dhsharp@...gle.com>,
	Justin Teravest <teravest@...gle.com>,
	Laurent Chavey <chavey@...gle.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Michael Davidson <md@...gle.com>
Subject: Re: [PATCH 2/6] trace: add support for 32 bit compat syscalls on
 x86_64

On 03/26/2012 11:39 AM, Vaibhav Nagarnaik wrote:
> +/*
> + * syscall metadata for 32 bit compatible system calls
> + *
> + * The metadata entries are in the same order as the system call table
> + * but this is just to make it easier to check them for completeness
> + * and correctness.
> + */
> +
> +COMPAT_SYSCALL_METADATA0(restart_syscall)
> +COMPAT_SYSCALL_METADATA1(exit, int, error_code)
   [...]
> +COMPAT_SYSCALL_METADATA5(recvmmsg, int, fd, struct mmsghdr __user *, mmsg, unsigned int, vlen, unsigned int, flags, struct timespec __user *, timeout)

> +/*
> + * This is truly horrible.

Yes, it is.  How on Earth do you expect the above to ever be maintained?

> + *
> + * There is no header file that defines a *complete* set of 32 bit system
> + * call numbers (unistd_32.h only defines ones that are currently exported
> + * to user space and omits lots of old system calls that are still implemented
> + * by the kernel.

> + * There is also no table that can be used to map a system call number into
> + * the canonical name of that system call.

arch/x86/syscalls has all of those.  If it's not in there, it doesn't
exist, because that's where the system call table comes from.

	-hpa
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