Re: [RFA] New GDB target iq2000

[Mark Kettenis <mark dot kettenis at xs4all dot nl>]

   Date: Sat, 5 Mar 2005 14:37:39 -0500
   From: Daniel Jacobowitz <drow@false.org>

   > That suggestion has been made more than once in the past; I don't
   > really consider this viable for architectures where instructions
   > aren't fixed length.

   Could you explain why that particular property makes a difference?

Makes it difficult to ignore instructions; GDB has to know the length
of them in order to skip them.

   Here's one I've been thinking about in particular: some instructions
   are "safe" to simulate on a running process, though not all.  When a
   breakpoint covers an instruction which is "safe", we can simulate the
   instruction instead of having to remove the breakpoint and single-step. 
   Huge win with threads.

Yikes!  Well if it helps...

   > Anyway, I think most problems are caused because we are trying to use
   > the same code for two distinct cases: (a) getting an upper limit for
   > the prologue end and (b) getting a lower limit for the prologue end.
   > Combining (a) and (b) results in having to determine the end of the
   > prologue exactly, which is much harder.

   Just checking, but first-line breakpoints should go at the lower limit
   and scanning until the upper limit - is that right?

Yup.  Although the lower-limit for first-line breakpoints may cause
bogus parameter values to be printed.  I consider that less a problem
than my program unexpectedly running to completion though.  The
problem is that some people tend to think differently and we never
reached consensus about it.

Mark