support for ARM GNU/Linux

[Philip Blundell]

>I'm slightly curious about what is going on with all these different
>breakpoints (I should hasten to point out that I'm _not_ the ARM
>expert/maintainer :-).  Stan Shebs recently commited the change:

Under Linux/ARM (and I think RISC iX, which is probably where the original 
breakpoint definitions came from) the traditional way to perform a breakpoint 
is to execute a particular SWI.  The kernel will then stop the inferior 
process with SIGTRAP and wake the debugger.  For systems where there is no 
explicit OS support for breakpoints, the set of opcodes that Stan put in 
will provoke a CPU "undefined instruction" exception which again stops the 
process.  Plus of course there's an equivalent set for Thumb.

I think all of these are needed for their respective target systems.  The RISC 
iX support probably wants splitting out into its own file anyway; at the 
moment it's hiding away in various files that are named as if they contain 
only ARM generic code.

>Could I suggest including a comment explaining where your breakpoint
>instructions come from.  If it is part of the LINUX/ARM environment then
>make a reference to that.

OK.

p.