Re: RIP-relative addressing bug

[Ulrich Drepper <drepper at redhat dot com>]

Vara Prasad wrote:
> I don't like the approach of kernel communicating with a user level
> program to get the correct
> address to put the probes,

I doubt this is what Roland meant by disassembling.  This certainly
should be done in the kernel.

And it really is not that hard, even in the general way.  To recognize
RIP instruction it is only necessary to skip over prefixes and the
actual instruction bits.  These are simple tables which can be
automatically generated.  Then determine whether the instruction uses a
modr/m byte and if yes, whether this together with the REX prefix
indicate that the addressing mode is RIP based.

It's not necessary to know what the instruction actually does.  The
transformation can be done without this information.

--
â Ulrich Drepper â Red Hat, Inc. â 444 Castro St â Mountain View, CA â

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