Userspace interception of locally valid memory location

[Valdis.Kletnieks at vt.edu]

On Sun, 10 Mar 2013 19:27:52 +0530, harish badrinath said:
> Hello,
> Is it possible to intercept (both read and write) a locally valid
> address of a process and replace it with our own values (it is for a
> transparent distributed shared memory project).

(Damn, hit send too soon)

Go look at how gdb traces variables.  Note that method pretty much only
works for writes to a variable, and has some performance implications.

Tracing reads is more difficult, and will probably end up being dependent
on exactly how good the hardware debugging support is - the S/390 architecture
has had the Program Event Recording feature since the 70s, and recent x86
chipsets have had similar features - details such as how many tracepoints
you can have active, how much memory each one can cover, and whether you can
intercept an event before it completes will be dependent on the arch and CPU -
what's true for a old Pentium4 won't be true for an i7, and ARM is a whole
different beast.
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