Re: debug and backtrace

[Neil Jerram <neil@ossau.uklinux.net>]

Andy Wingo <wingo@pobox.com> writes:

> Hi Mike,
>
> On Sun 13 Sep 2009 16:30, ludo@gnu.org (Ludovic Courtès) writes:
>
>> Mike Gran <spk121@yahoo.com> writes:
>>
>>> With the default behavior of 1.9.x, REPL debug and backtrace are broken.
>>
>> Indeed, it looks like the VM frames are ignored.
>
> Hopefully by the next release, and certainly by the following one, this
> will be fixed: by having everything on the VM stack. So yes it sucks
> now, but it's because we have so many kinds of procedures and stacks
> that it's tough to make a nice debugging interface.

Actually I think I just found and fixed one problem.  From the time when
a #<program> was a SMOB, really_make_boot_program in vm.c was still
using SCM_SET_SMOB_FLAGS to set the SCM_F_PROGRAM_IS_BOOT flag - which
meant that it was setting flag 1<<32 :-) which obviously was then missed
by the SCM_PROGRAM_IS_BOOT calls in stacks.c.

So now, with my test script

  ((lambda _
     (car 1) 23))

I get a backtrace:

  neil@arudy:~/SW/Guile/git$ meta/guile --debug -s ../testcar.scm 
  Backtrace:
  In ice-9/boot-9.scm:
  1772: 0* [save-module-excursion #<program 9dc0630 at ice-9/boot-9.scm:1785:3 ()>]
  In unknown file:
     ?: {1}* [dynamic-wind #<program 9dc0620 at ice-9/boot-9.scm:1771:18 ()> ...]
  In ice-9/boot-9.scm:
   935: 2* [load "../testcar.scm"]
  In unknown file:
     ?: 3* [with-fluid* #<fluid 9> #f #<program 9dc0600 at ice-9/boot-9.scm:935:4 ()>]
  In ice-9/boot-9.scm:
   940: 4* [#<program 9dc0600 at ice-9/boot-9.scm:935:4 ()>]
  In unknown file:
     ?: 5* [load-compiled/vm "/home/neil/SW/Guile/git/cache/guile/ccache/1.9-0.D-LE-4/home/neil/SW/Guile/testcar.scm.go"]
  In ../testcar.scm:
     2: 6* [#<program 9e3e4e0 at ../testcar.scm:0:1 _> 23]

  ERROR: In procedure vm-debug-engine:
  ERROR: Wrong type argument in position 1 (expecting pair): 1

I'll push the fix a bit later.  (I also have fixes for the incorrect
stack count warning.)

But I notice that there is only ever one frame per VM.  E.g. with code
like

  (define (foo n)
    (let ((a 1))
      (let ((b 2))
        (string-append (* a b)))))

(which deliberately passes an invalid arg to string-append), the
interpreter backtrace would show the two `let' frames, whereas the VM
backtrace doesn't.

Is that intended, or something else to investigate?

Regards,
        Neil