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A candidate for the "weirdest bug ever" award

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Stéphane Rollandin

A candidate for the "weirdest bug ever" award

I have a nice one:

In (seemingly) any 5.0 image, with the latest Spur, type the following
in a workspace and printIt a couple of time:

(1 to: 3) collect: [:i |
m := ''.
2 timesRepeat: [m := m, ('1234' perform: #copyFrom:to: with: 2 with: 4)].
m]

I get kind of randomly either #('234' '' '') or the correct #('234234'
'234234' '234234'), or at times #('234234' '' '').

Attached is the same code, this time in a method. It is even funkier,
since a common answer is then 'copyFrom:to:234', although I sometimes
get '234234' ...

Stef

Try.st (674 bytes) Download Attachment

Levente Uzonyi

Re: A candidate for the "weirdest bug ever" award

I found that
- it requires the use of primitive 83 with 3 arguments (aka
#perform:with:with:. 2 and 4 argument variants don't trigger the bug)
- its result must be passed immediately as an argument to another method
(using a temporary to store the intermediate value won't trigger the error)
- all this has to be evaluated in a block at least twice (the first
evaluation won't trigger the bug).

Here's a smaller example:

[ '' copyReplaceFrom: 1 to: 0 with: ('' perform: #copyFrom:to: with: 1 with: 0) ] value; value

I decided to use #copyReplaceFrom:to:with: instead of #,, because the
former will raise a debugger due to the invalid arguments.

Here's a different one:

[ self haltIf: ({ true } perform: #at:put: with: 1 with: false) ] value; value

This clearly shows, that first argument of #perform:with:with: stays on
the stack somehow.

Going through the code in the debugger doesn't trigger the bug, which
makes me think that the jitted version of #perform:with:with: doesn't pop
its first argument from the stack.

Levente

On Tue, 23 Feb 2016, Stéphane Rollandin wrote:

> I have a nice one:
>
> In (seemingly) any 5.0 image, with the latest Spur, type the following in a
> workspace and printIt a couple of time:
>
>
> (1 to: 3) collect: [:i |
> m := ''.
> 2 timesRepeat: [m := m, ('1234' perform: #copyFrom:to: with: 2 with:
> 4)].
> m]
>
>
> I get kind of randomly either #('234' '' '') or the correct #('234234'
> '234234' '234234'), or at times #('234234' '' '').
>
>
> Attached is the same code, this time in a method. It is even funkier, since a
> common answer is then 'copyFrom:to:234', although I sometimes get '234234'
> ...
>
>
>
> Stef
>
>

Eliot Miranda-2

Re: A candidate for the "weirdest bug ever" award

Hi Levente,

On Tue, Feb 23, 2016 at 3:09 PM, Levente Uzonyi <[hidden email]> wrote:

I found that
- it requires the use of primitive 83 with 3 arguments (aka #perform:with:with:. 2 and 4 argument variants don't trigger the bug)
- its result must be passed immediately as an argument to another method (using a temporary to store the intermediate value won't trigger the error)
- all this has to be evaluated in a block at least twice (the first evaluation won't trigger the bug).

Here's a smaller example:

[ '' copyReplaceFrom: 1 to: 0 with: ('' perform: #copyFrom:to: with: 1 with: 0) ] value; value

I decided to use #copyReplaceFrom:to:with: instead of #,, because the former will raise a debugger due to the invalid arguments.

Here's a different one:

[ self haltIf: ({ true } perform: #at:put: with: 1 with: false) ] value; value

This clearly shows, that first argument of #perform:with:with: stays on the stack somehow.

Going through the code in the debugger doesn't trigger the bug, which makes me think that the jitted version of #perform:with:with: doesn't pop its first argument from the stack.

Bingo! Thanks. In fact the primitive fails to pop all but the last argument. I'll have a fix ready soon.

Levente

On Tue, 23 Feb 2016, Stéphane Rollandin wrote:

I have a nice one:

In (seemingly) any 5.0 image, with the latest Spur, type the following in a workspace and printIt a couple of time:

(1 to: 3) collect: [:i |
m := ''.
2 timesRepeat: [m := m, ('1234' perform: #copyFrom:to: with: 2 with: 4)].
m]

I get kind of randomly either #('234' '' '') or the correct #('234234' '234234' '234234'), or at times #('234234' '' '').

Attached is the same code, this time in a method. It is even funkier, since a common answer is then 'copyFrom:to:234', although I sometimes get '234234' ...

Stef

_,,,^..^,,,_

best, Eliot

Benoit St-Jean

Re: A candidate for the "weirdest bug ever" award

In reply to this post by Stéphane Rollandin

If that's of any hint/help, I get the exact same thing on latest Pharo/Spur on Windows.

-----------------
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"A standpoint is an intellectual horizon of radius zero". (A. Einstein)

From: Stéphane Rollandin <[hidden email]>
To: liste <liste@>
Sent: Tuesday, February 23, 2016 5:21 PM
Subject: [squeak-dev] A candidate for the "weirdest bug ever" award

I have a nice one:

In (seemingly) any 5.0 image, with the latest Spur, type the following
in a workspace and printIt a couple of time:

(1 to: 3) collect: [:i |
    m := ''.
    2 timesRepeat: [m := m, ('1234' perform: #copyFrom:to: with: 2 with: 4)].
    m]

I get kind of randomly either #('234' '' '') or the correct #('234234'
'234234' '234234'), or at times #('234234' '' '').

Attached is the same code, this time in a method. It is even funkier,
since a common answer is then 'copyFrom:to:234', although I sometimes
get '234234' ...

Stef

Chris Muller-3

Re: A candidate for the "weirdest bug ever" award

In reply to this post by Eliot Miranda-2

Wow, that is one nasty bug. Amazing catch you guys.

On Tue, Feb 23, 2016 at 6:04 PM, Eliot Miranda <[hidden email]> wrote:

> Hi Levente,
>
> On Tue, Feb 23, 2016 at 3:09 PM, Levente Uzonyi <[hidden email]>
> wrote:
>>
>> I found that
>> - it requires the use of primitive 83 with 3 arguments (aka
>> #perform:with:with:. 2 and 4 argument variants don't trigger the bug)
>> - its result must be passed immediately as an argument to another method
>> (using a temporary to store the intermediate value won't trigger the error)
>> - all this has to be evaluated in a block at least twice (the first
>> evaluation won't trigger the bug).
>>
>> Here's a smaller example:
>>
>> [ '' copyReplaceFrom: 1 to: 0 with: ('' perform: #copyFrom:to: with: 1
>> with: 0) ] value; value
>>
>> I decided to use #copyReplaceFrom:to:with: instead of #,, because the
>> former will raise a debugger due to the invalid arguments.
>>
>> Here's a different one:
>>
>> [ self haltIf: ({ true } perform: #at:put: with: 1 with: false) ] value;
>> value
>>
>> This clearly shows, that first argument of #perform:with:with: stays on
>> the stack somehow.
>>
>> Going through the code in the debugger doesn't trigger the bug, which
>> makes me think that the jitted version of #perform:with:with: doesn't pop
>> its first argument from the stack.
>
>
> Bingo! Thanks. In fact the primitive fails to pop all but the last
> argument. I'll have a fix ready soon.
>
>> Levente
>>
>>
>> On Tue, 23 Feb 2016, Stéphane Rollandin wrote:
>>
>>> I have a nice one:
>>>
>>> In (seemingly) any 5.0 image, with the latest Spur, type the following in
>>> a workspace and printIt a couple of time:
>>>
>>>
>>> (1 to: 3) collect: [:i |
>>> m := ''.
>>> 2 timesRepeat: [m := m, ('1234' perform: #copyFrom:to: with: 2
>>> with: 4)].
>>> m]
>>>
>>>
>>> I get kind of randomly either #('234' '' '') or the correct #('234234'
>>> '234234' '234234'), or at times #('234234' '' '').
>>>
>>>
>>> Attached is the same code, this time in a method. It is even funkier,
>>> since a common answer is then 'copyFrom:to:234', although I sometimes get
>>> '234234' ...
>>>
>>>
>>>
>>> Stef
>>>
>>
>>
>>
>
>
>
> --
> _,,,^..^,,,_
> best, Eliot
>
>
>