Re: [patch 0/2] Immediate Values - jump patching update

From: Ingo Molnar
Date: Mon Apr 28 2008 - 19:07:47 EST



* H. Peter Anvin <hpa@xxxxxxxxx> 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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