Re: Terminate and Stay Resident Software (TSR) in Linux

"karthikbg" <karthik.balaguru@xxxxxxxxxxxxxxx> wrote in message
news:1164216538.921641.77030@xxxxxxxxxxxxxxxxxxxxxxxxxxx

Your description of a TSRs leaves out one important aspect.

Before exiting, the TSR links itself into some part of the OS usually by
"hooking" itself into one or more of the OS interrupt handlers. It does
this by replacing the original interrupt vector with an address in the
TSR. If the TSR doesn't "hook" itself in then it would just be a waste
of memory since there would be no effective way for it to ever be
executed to do something useful (or malicous). If it is appropriate for
the original interrupt handler to execute, the TSR "remembers" the
original vector so it can just jump to it after doing whatever
processing it intends to do. Otherwise, the TSR does a return from
interrupt like the original interrupt handler would have done.

A user application trying to do the same thing under Linux will generate
a protection fault when it attempts to overwrite an interrupt vector.

There are ways to augment the Linux operating system after it running.
Do a Google search for "Linux loadable driver" and "Linux streams".

--
James T. White


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