[Tarantool-patches] [PATCH luajit v1] tools: fix luajit-gdb stack dump

[Sergey Ostanevich]

Igor,

Sure you can proceed with the push.

Sergos.

> On 22 Jul 2021, at 14:48, Igor Munkin <imun at tarantool.org> wrote:
> 
> Sergos,
> 
> Thanks for your review! TL;DR: I would rather leave the patch with no
> changes, but please consider my comments regarding your alternative
> approach for iterating through the guest stack.
> 
> On 22.07.21, Sergey Ostanevich wrote:
>> Hi!
>> 
>> Thanks for the patch!
>> 
>> I would rather remove all mentions of ‘bottom loop’ as we named it at
>> Intel. I'm not a big pro in python, still the ‘for’ loop works fine 
>> for me:
>> 
>> If we can unwind to the next frame - dump it (and further)
>> 
>>>>> s=[1]
>>>>> for i in s:
>> ...   if (i==1):
>> ...     s.append(2)
>> ...     continue
>> ...   print(i)
>> ... 
>> 2
>> 
>> If it is the only one (dummy):
>> 
>>>>> s=[3]
>>>>> for i in s:
>> ...   if (i==1):
>> ...     s.append(2)
>> ...     continue
>> ...   print(i)
>> ... 
>> 3
>> 
>> Does it make sense in this case?
> 
> Let's see what would we get for our case with guest stack unwinding. The
> algorithm is described by Sergey in the comment near the loop. But
> imagine, we are iterating (backwards) through [L->stack, L-top] segment
> via for loop (as you suggest above). There is one condition to check
> whether we have reached the bottom of the frame (dump framelink slot and
> continue the same way you showed above). However, we need one more
> condition to skip the second slot for the framelink in LJ_FR2 mode.  As
> a result we have a loop that iterates through the stack with at least
> two conditions to skip some slots or dump them in other way.
> Furthermore, your proposal leads to much more complex change in the
> extension, comparing to those made by Sergey.
> 
> As I've already said, postcondition loop is the classic way for this
> case. Moreover, I googled "how to emulate a do-while loop in Python?"
> and the second option is unrolling the first iteration[1]. If one
> wonders what is the first option -- use "while-true" loop with the
> conditional break at the end. I equally hate both, so I'm OK with the
> one chosen by Sergey. If you prefer "while-true", I believe Sergey can
> rewrite this part, but considering your LGTM below, I guess you're OK
> also with the current solution. So, I'll push the patch in a jiffy.
> 
>> 
>> Anyways, it’s too much of nitpicking - LGTM in its current version.
>> 
>> Regards,
>> Sergos
>> 
>> 
> 
> <snipped>
> 
>> 
> 
> [1]: https://stackoverflow.com/a/743186 <https://stackoverflow.com/a/743186>
> 
> -- 
> Best regards,
> IM

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