Re: [RFC] [PATCH 1/2 v2] x86: introduce int3-based instruction patching

[H. Peter Anvin]

On 07/10/2013 02:31 PM, Jiri Kosina wrote:
> 
> If any CPU instruction execution would collide with the patching,
> it'd be trapped by the int3 breakpoint and redirected to the provided
> "handler" (which would typically mean just skipping over the patched
> region, acting as "nop" has been there, in case we are doing nop -> jump
> and jump -> nop transitions).
> 

I'm wondering if it would be easier/more general to just return to the
instruction.  The "more general" bit would allow this to be used for
other things, like alternatives, and perhaps eventually dynamic call
patching.

Returning to the instruction will, in effect, be a busy-wait for the
faulted CPU until the patch is complete; more or less what stop_machine
would do, but only for a CPU which actually strays into the affected region.

	-hpa


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