(disclaimer: I don't know about PalmOS 5.0, but I do know about ARM)
The ARM has a number of vectors in low memory (which might be ROM or
RAM, but should probably be RAM in any sane implementation). Among them
IRQ (interrupt request), SWI (software interrupt) and FIQ (fast
interrupt request). ARM based operating systems typically use SWI as a
trap instruction. The SWI instruction is an 8 bit opcode (actually 4 bit
condition code and 4 bit opcode) and a 24 bit 'comment' field that
typically tells the OS which function is desired.
Assuming any future ARM based PalmOS works this way it will be possible
to intercept all SWIs by replacing the contents of the SWI vector. A
HackMaster application would be able to claim the SWI vector to provide
the same sort of services it currently does.
YAMADA Tatsushi wrote:
>
> Hello
>
> At 00:00 01/01/23 -0800, Palm Developer Forum digest wrote:
> > >BTW, I really believe that Palm should provide such a trap manager in the
> > >OS.
> >
> >We talk about this periodically. The problem is that it's hard to QA and
> >support something that by its definition is designed to let people do
> >unsupported things. There are good arguments on both sides.
>
> Is it possible to patch traps in Arm device by arm code?
>
> YAMADA Tatsushi Hacker Dude-san
> http://simple-palm.com
> mailto:[EMAIL PROTECTED]
--
Andy Armstrong, Tagish
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