Re: Dynamically altering code segments

[Andreas Dilger]

Tom Collins writes:
> I am wanting to dynamically modify the kernel in specific places to
> implement a custom kernel trace mechanism.  The general idea is that,
> when the "trace" is off, there are NOP instruction sequences at various
> places in the kernel.  When the "trace" is turned on, those same NOPs
> are replaced by JMPs to code that implements the trace (such as logging
> events, using the MSR and PMC's etc..).
> 
> This was a trick that was done in my old days of OS/2 performance tools 
> developement to get trace information from the running kernel.
> 
> Is it possible to do the same thing in Linux?

See IBM "dprobes" project.  It is basically what you are describing
(AFAIK).  It makes sense, because a lot of the OS/2 folks are now working
on Linux.

Cheers, Andreas
-- 
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert