[Openmcl-devel] Trying to build a single stepper

[73budden .]

Hi!

Thanks, Bill, I was thinking about coverage tool, and it was my
previous plan. Coverage inserts movs, so if I watch the destination of
this mov, this is a breakpoint. I made a prototype and was able to
break and see variables. Next step would be to coalesce all code-notes
and thus I would obtain a "step on/off" flag.

But it is less convenient because one has to recompile a function to
make it steppable. Recompilation is context dependent in CL, hence
recompiled function can yield e.g. different macroexpansion. So if
there is a way to instrument/uninstrument a function w/o
recompilation, it is preferrable. Also this watch based approach hurts
performance more than my current idea.

Actually what I do now is not perfect. Calls to CONS, LIST and some
other things are inlined, so they won't be steppable. But I guess
anyway it would be good as a starting point and I have rather limited
time period for that work.

Maybe coverage tool would be useful for setting breakpoint with a
mouse, because I would need to find a place in a code which
corresponds to current place in a source file. Code coverage tool
contains this data.

Ron, thanks, I know about advice, but it is global. Making a wrapper
only hurts a performance where it is used, and does not touch other
uses of PRINT. Not only wrapper function is faster, it is more
reliable too. Advising print and other system things is always
dangerous. But maybe I'll find useful code snippets to borrow from the
advice, thanks.

Meanwhile you can take a look at the similar proof-of-concept I made
for Lispworks some time ago. Lispworks rebuild a function to be
stepped in an interpreter, so it is not quite reliable approach. I did
something, but it is extremely hard to change anything in a closed
source program.

https://bitbucket.org/budden/budden-tools/src/default/experiments/hack-debugger/native-code-stepper.lisp?at=default&fileviewer=file-view-default



2018-01-18 19:29 GMT+03:00, Bill St. Clair <wws at clozure.com>:
> The thought has occurred to me that the coverage tool that Gail Zacharias
> wrote a number of years back could be extended to a single stepper. It
> would be a fair amount of work, and would require pretty deep understanding
> of CCL internals, but it would enable single-stepping of compiled code.
>
> On Thu, Jan 18, 2018 at 11:17 AM, Ron Garret <ron at flownet.com> wrote:
>
>> Rather than write your own wrapper you should consider using the advice
>> facility built in to CCL:
>>
>> https://ccl.clozure.com/manual/chapter4.3.html#Advising
>>
>> On Jan 18, 2018, at 7:41 AM, 73budden . <budden73 at gmail.com> wrote:
>>
>> > Hi!
>> >
>> > I'm trying to build a single stepper for compiled functions in CCL
>> > (vanilla "Visual Basic" like "debugger").
>> >
>> > My current idea is to find all function references (subset of
>> > ccl::lfunloop scope) and
>> > replace all of them with function wrappers. E.g. I have a function
>> > which I want to make steppable:
>> >
>> > (defun f () (print 'list))
>> >
>> > It references PRINT as a symbol.
>> > (lfunloop for v in #'f do (print v)) returns:
>> >
>> > LIST
>> > PRINT
>> > F
>> >
>> > Then I do:
>> > CCL>(compile (defun my-wrapped-print (&rest args) (break "About to
>> > call print with ~S" args) (apply #'print args)))
>> > MY-WRAPPED-PRINT
>> >
>> > And
>> > CCL>(%set-nth-immediate #'f 1 'MY-WRAPPED-PRINT)
>> >
>> > Then, when I run (f), debugger is invoked while trying to call
>> > "print". In current example #'f is too trivial and it isn't shown on
>> > the backtrace, but if we make more complex f and put it into the
>> > source file, I can see its source with SWANK debugger.
>> >
>> > So the question is: how do I say 'print (which is used as a function)
>> > from 'list (which is used as mere data). If I treat any symbol
>> > reference as a function, this would be obviously wrong.
>> >
>> > As far as I can get it, I have to track how symbols are referenced. I
>> > found already that #<acode immediate (PRINT)> is created in the
>> > nx1-call-form, so I think I can extend acode to include the type of
>> > reference. Also I found how info is extracted. So I can add a
>> > bit-vector to a functions data which stores "1" if nth-immediate is a
>> > function and 0 otherwise. But still I'm unable to find where this
>> > immediate is recorded into the generated code, so I don't know how to
>> > extend the set. Can anyone please give a hint?
>> >
>> > Also, if my approach is definitely wrong somehow, please let me know.
>> > _______________________________________________
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