[Simh] Simh for testsuite usage

[Jan-Benedict Glaw]

Hi!

I just attended the GNU Tools Cauldron 2014 meeting, where we
discussed to use Simh for testing produced code for VAX and PDP
processors. While Simh isn't The Real Thing, it would probably work
quite well.

  On a first glance, there are some issues that I'd like to discuss.
First of all, a given testcase needs to be loaded. (Usually, this
would be a small binary calling abort() or returning with zero from
main(). We would just supply a fake libc that sets r0 to zero /
nonzero and calls HLT.)

  Here's the first problem: The PDP11 simulator seems to LOAD a file
with kind of a load address -- content --- load address -- content ...
scheme, while the VAX simulator loads a raw byte. Instead of these
ad-hoc formats, our impression is that it would be nice to have an ELF
and/or a.out loader for a static binary. Either a minimal one, or one
using libelf. Would a patch for this be accepted?  An alternate route
could be to put some helper scripts and converter programs together
that build up the proper LOADable files.

  A second issue I found is that the remote telnet port isn't serviced
unless the simulator is actually running. It would be quite cool to
expose it's capabilities even earlier: The final intention is to
interface it with GDB as a debugger. In this setup, GDB would see Simh
as something like a "probe" or "accessor" to a (real) VAX system, like
remote debugging for some other development boards is done today.

Thanks, JBG

-- 
      Jan-Benedict Glaw      jbglaw at lug-owl.de              +49-172-7608481
Signature of:          GDB has a 'break' feature; why doesn't it have 'fix' too?
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