linux-kernel - Re: [PATCH] Add a text

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Message-ID: <20131121130715.GC8044@home.goodmis.org>
Date:	Thu, 21 Nov 2013 08:07:15 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Add a text_poke syscall

On Tue, Nov 19, 2013 at 08:10:34PM +0100, Andi Kleen wrote:
> 
> Self modifying code is by definition x86 specific.

How so? Ftrace works on several archs, and does so with self modifying code.

> 
> Very likely any other method to do this would be Linux specific
> in some form or another, as there doesn't seem to be any
> existing art.

Seems you need to solve a catch-22 on this. You need to show that there's a
need (application), that requires this new feature and also show that all the
existing kernel features are inefficient for what is needed.

The catch-22 may be that a application wont be created without the feature,
but that's the problem you need to solve.

Personally, I rather see the userspace patching be completele separate from
the kernel space patching, as the kernel space patching must not be
complicated by any requirement of userspace patching.

I don't see how userspace doesn't need anything but a CPU sync call to do
the required sync. Add a breakpoint, sync, change the code, sync, remove
breakpoint, done!

And as a bonus, doing this in userspace could easily extend it. Say you want
to do special things with that breakpoint handler.

-- Steve
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