I've committted the attached.

As Ulrich explains in the below, trying to use STEP_FRAME_ID was 
creating a big nasty rat hole.
The patch does preserve the old behavior when legacy_frame_p (hmm, which 
must be on its last legs :-).

> Andrew Cagney wrote:
> 
>>>> > It will run into the first if, and simply use step_frame_id,
>>>> > which is wrong in this case.  That's why my patch add another
>>>> > condition to the first if, to make it not taken and actually
>>>> > use the (correct) get_prev_frame case.
>>
>>> 
>>> Where is step_frame_id pointing?
> 
> 
> To the function that was interrupted by the signal (i.e. the
> function where I entered 'next').

Good.

>>> Anyway, I think this code:
>>>  >   if (frame_id_p (step_frame_id)
>>>  >       && !IN_SOLIB_DYNSYM_RESOLVE_CODE (sr_sal.pc))
>>>  >     /* NOTE: cagney/2004-02-27: Use the global state's idea of the
>>>  >        stepping frame ID.  I suspect this is done as it is lighter
>>>  >        weight than a call to get_prev_frame.  */
>>>  >     sr_id = step_frame_id;
>>> should simply be deleted.  I wondered about it and you've just confirmed 
>>> my suspicions.  With that code gone is half the problem solved?
> 
> 
> Yes, deleting this works just fine for me, in fact ...

Good.

>>> That leaves the other problem, which is much harder :-(
> 
> 
> ... it even solves the other problem as well!

Yow!

> The reason for this is that the whole problematic if 
> that uses frame_id_inner becomes irrelevant:
> 
>       if (pc_in_sigtramp (stop_pc)
>           && frame_id_inner (step_frame_id,
>                              frame_id_build (read_sp (), 0)))
>         /* We stepped out of a signal handler, and into its
>            calling trampoline.  This is misdetected as a
>            subroutine call, but stepping over the signal
>            trampoline isn't such a bad idea.  In order to do that,
>            we have to ignore the value in step_frame_id, since
>            that doesn't represent the frame that'll reach when we
>            return from the signal trampoline.  Otherwise we'll
>            probably continue to the end of the program.  */
>         step_frame_id = null_frame_id;
> 
>       step_over_function (ecs);
> 
> With those lines in step_over_function deleted, step_over_function
> does not care about step_frame_id at all any more, and thus there
> is no need to fiddle with step_frame_id here ...

>>>> > Finally, the patch below reintroduces a pc_in_sigtramp
>>>> > gdbarch callback to s390-tdep.c; I had thought this would
>>>> > be no longer necessary when using the new frame code, but
>>>> > apparently there's still other users ...
>>
>>> 
>>> Yes, it shouldn't be needed.  get_frame_type == SIGTRAMP_FRAME is 
>>> sufficient.  work-in-progress.
> 
> 
> Actually, when deleting the lines in step_over_function, it turns
> out that I don't need pc_in_sigtramp any more ...
> 
> Summing up: after completely reverting my patch, and simply 
> deleting those lines, I get a gdb that passes signals.exp
> (and has no test suite regressions), and also handles stepping
> out of a signal handler correctly.

ya!

thanks,
Andrew