On Friday 04 December 2009, Nicolas Pitre wrote:
> On Fri, 4 Dec 2009, David Brownell wrote:
>
> > Clean up arm_semihosting() entry a bit, comment some issues and just
> > which SVC opcodes are getting intercepted. Microcontroller profile
> > cores will need a new entry, since they don't use SVC there (or even
> > have an SVC mode).
>
> In that case they use BKPT 0xAB instead of SVC 0xAB. And the
> microcontroller profile has only thumb2 mode so no need to bother with
> (the non existing) spsr.
Exactly: a new entry is the simplest way.
> > - struct arm *armv4_5 = target_to_armv4_5(target);
> > + struct arm *arm = target_to_armv4_5(target);
>
> Wouldn't it be time to s/target_to_armv4_5/target_to_arm/ everywhere?
Soonish, yes. Also splitting some of the common code out to "arm.[hc]".
> > + /* Check for PC == 8: Supervisor Call vector
> > + * REVISIT: assumes low exception vectors, not hivecs...
> > + * safer to test "was this entry from a vector catch".
> > + */
>
> There is no universal "vector catch" facility. Some targets might have
> to use a breakpoint instead. And hardware breakpoints are precious
> resources i.e. Feroceon/Dragonite have only one of those already
> involved in single-step support for example. So software breakpoints
> are preferable when there is no vector catch.
>
> But yet some targets have the vectors in ROM (or flash) pointing to a
> jump table located in RAM. In that case the breakpoint has to be placed
> in the jump table instead. So there is more to it than just 0x08 or
> 0xffff0008. This is why the enabling of semihosting is really
> architecture dependent.
Right, and that's why it's just flagged as REVISIT. There are surely
a few other issues too! :)
Most of the ARM cores *do* have some flavor of vector catch, so for
those cores that will be the most straightforward solution. Tracking
that kind of debug entry will at least address the hivec issue.
> > + /* Core-specific code should make sure SPSR is retrieved
> > + * when the above checks pass...
> > + */
> > + if (!arm->spsr->valid)
> > + LOG_WARNING("SPSR not valid!");
>
> Better return an error and stop rather than continuing with wrong
> information in that case.
Good point.
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