Re: Dynamically altering code segments

Andreas Dilger (
Tue, 27 Feb 2001 10:05:37 -0700 (MST)

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?"               -- Dogbert
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