linux-kernel - Re: [RFC 1/3] abi_spec: basic definitions of constraints, args and syscalls

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Date:   Wed, 23 Nov 2016 10:31:14 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     alexander.levin@...izon.com
Cc:     "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "scientist@...com" <scientist@...com>,
        "glider@...gle.com" <glider@...gle.com>,
        "andreyknvl@...gle.com" <andreyknvl@...gle.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "mathieu.desnoyers@...icios.com" <mathieu.desnoyers@...icios.com>,
        "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 1/3] abi_spec: basic definitions of constraints, args and
 syscalls

On Wed, 23 Nov 2016 15:03:23 +0000
alexander.levin@...izon.com wrote:

> It's really just made up, but I wanted it to be higher than 6 because:
> 
>  - The "6" limit is only per-arch, so there might be something that wants
> more than 6 args?
>  - This should also work for ioctls in the future.

The generic code all has a max of 6. Look at the macros for the system
calls. All they define up to is SYSCALL_DEFINE6().

If any arch creates a syscall with 7 or more args, that will be a world
of pain. I say we simply don't support it. Also, that arch would
require keeping that system call totally within the arch itself, and
wont be able to call into generic code.

I'm working to clean up the system call tracepoints, and they currently
(and will continue to) have a hard max upper limit of 6 arguments.

-- Steve