17 Sep
2015
17 Sep
'15
6:09 p.m.
On Sep 17, 2015, at 5:52 PM, Jay Jaeger <cube1 at
charter.net> wrote:
On 9/17/2015 2:27 PM, Paul Koning wrote:
Don't / didn't some machines do/did this by setting an address trap
register rather than modifying the breakpointed instruction?
Yes, that's why I said "software breakpoints", meaning breakpoints created
by replacing the instruction with a break instruction, as opposed to "hardware
breakpoints" which use address trap instructions. Perhaps that's not universal
terminology, but it's what GDB calls these things.
On Sep 17, 2015, at 2:56 PM, dwight <dkelvey
at hotmail.com> wrote:
What is the definition of self modifying?
Is it changing an instruction to execute in the thread to be run?
How about adding or subtracting something to be done in an execution
queue?
I'm not sure if there is a universally agreed to definition.
It also matters why the question is asked. I can think of a couple of answers:
1. the contents of instruction memory is subject to change.
2. the contents of instruction memory is subject to change during execution of the
program.
3. individual instructions in a program are changed by the execution of that program.
4. individual instructions in a program are changed by explicit data manipulation actions
of that program.
#1 is true for most computers past and present, because they allow a program to be loaded
into memory from external storage.
#2 is true in any program that uses overlays, or if the program is controlled by a
debugger that uses "software breakpoints".
Also, if the machine had explicit handling of overlays/segments, then
that part of this becomes identical to #1. (Burroughs?)
Or it's outside the picture entirely. I was thinking of virtual address space here.
If you have paging or the like with physically addressed caches, then those are part of
#1, yes.
paul