linux-kernel - Re: [patch 0/2] Immediate Values

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Message-ID: <20080428224438.GA6974@elte.hu>
Date:	Tue, 29 Apr 2008 00:44:38 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [patch 0/2] Immediate Values - jump patching update


* H. Peter Anvin <hpa@...or.com> wrote:

> What I'm proposing is:
>
> >   [ .... fastpath head ......     ]
> >   [ ....   5-byte CALL .......... ]  ---> NOP-ed out
> >   [ .... fastpath tail .......... ]
> >   [ ............................. ]
>
> The call site is created with an asm() statement as opposed to a gcc 
> function call; it is up to the logging function to take the state and 
> mangle it into whatever format it wants to; the debugging information 
> (e.g. DWARF) should tell it all it needs to know about how the 
> register/memory state maps onto the C state.  This mapping can either 
> be done online, with a small piece of dynamic code, or offline 
> (although offline makes it tricky to know what memory tems to gather.)

that would be rather impractical as we'd force DEBUG_INFO builds on 
anyone (it's HUGE) just to do some trivial tracing. Look at the ftrace 
plugin usage model - it wants to be widely available and easy to use.

	Ingo
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