Re: [PATCH v5 3.1.0-rc4-tip 5/26] Uprobes: copy of the originalinstruction.

From: Oleg Nesterov
Date: Wed Oct 05 2011 - 13:58:07 EST

On 10/05, Srikar Dronamraju wrote:
> * Oleg Nesterov <oleg@xxxxxxxxxx> [2011-10-03 18:29:05]:
> > But I am starting to think I simply do not understand this change.
> > To the point, I do not underestand why do we need copy_insn() at all.
> > We are going to replace this page, can't we save/analyze ->insn later
> > when we copy the content of the old page? Most probably I missed
> > something simple...
> >
> Copying the instruction at the time we replace the original instruction
> would have been ideal. However there are a few irritants to handle.
> ...
> How do we distinguish if the
> breakpoint instruction was around in the text or somebody inserted a
> breakpoint in that address-space? Since we read from the page-cache,
> we can easily resolve this.

Ah. I see.

> - On archs like x86, with variable size instructions, the original
> instruction can be across 2 pages.

Heh. Indeed ;)

Thanks Srikar.


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