[squeak-dev] [Vm-dev] Sign-bit bug in character literals > 16r7FFF ... related to SistaV1?

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Wed Mar 9 09:25:27 UTC 2022


IOW, the Character value being unsigned, it would be preferable to use
extend A rather than extend B in #genPushCharacter:
My understanding is that this would require a VM change too...

Le mer. 9 mars 2022 à 10:08, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> a écrit :

> Oups forgot to respond to squeak-dev too...
>
> in #interpretNextSistaV1InstructionFor: we se that extB is interpreted as
> signed char
>
> extB := (extB = 0 and: [extByte > 127])
> ifTrue: [extByte - 256]
> ifFalse: [(extB bitShift: 8) + extByte]
>
> Then in interpretNext2ByteSistaV1Instruction: bytecode for: client extA:
> extA extB: extB startPC: startPC
>
> ^client pushSpecialConstant: (Character value: (extB bitShift: 8) + byte)
>
> In our case, extA=0, extB=-128, bytecode=233
>
> Le mer. 9 mars 2022 à 10:02, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> a écrit :
>
>> Hi Marcel,
>> yes, I agree, the bug is in bytecode encoding/decoding of immediate
>> Character value,
>> I stepped into (Compiler evaluate: (String with: $$ with: (Character
>> value: 16r8000))), and if we step into executeMethod, we can inspect what
>> is going on.
>>
>>
>> Le mer. 9 mars 2022 à 08:39, Marcel Taeumel <marcel.taeumel at hpi.de> a
>> écrit :
>>
>>>
>>> Hi Nicolas --
>>>
>>> There is a bug in the EncoderForSistaV1. The behavior is okay for
>>> EncoderForV3PlusClosures. We can discuss this on squeak-dev now, I suppose.
>>>
>>> CompiledCode preferredBytecodeSetEncoderClass: EncoderForSistaV1.
>>> CompiledCode preferredBytecodeSetEncoderClass: EncoderForV3PlusClosures.
>>>
>>> If you do send #halt instead of #asInteger, you get another interesting
>>> debugger when trying to start debugging:
>>>
>>>
>>>
>>> Best,
>>> Marcel
>>>
>>> Am 09.03.2022 08:34:11 schrieb Nicolas Cellier <
>>> nicolas.cellier.aka.nice at gmail.com>:
>>> Ah OK, I see it on macos too
>>> It remains to determine which operation exactly is involved...
>>> The TextMorph holding the printed result is correct - a WideString,
>>> whose
>>> last Character is (Character value: 32768).
>>>
>>> Le mer. 9 mars 2022 à 08:08, Marcel Taeumel a
>>> écrit :
>>>
>>> >
>>> > Hi Dave, hi Nicolas --
>>> >
>>> > I am working in Windows 10.
>>> >
>>> > > I cannot reproduce on Linux 64 bit either:
>>> > > (Character value: 16r8000) asInteger hex ==> '16r8000'
>>> >
>>> > That's not how you would reproduce it. The bug affects character
>>> literals,
>>> > not character objects/instances. You have to evaluate code on that
>>> > character literal.
>>> >
>>> > Maybe this picture helps:
>>> >
>>> >
>>> >
>>> > Best,
>>> > Marcel
>>> >
>>> > Am 08.03.2022 18:56:09 schrieb David T. Lewis :
>>> >
>>> > I cannot reproduce on Linux 64 bit either:
>>> >
>>> > (Character value: 16r8000) asInteger hex ==> '16r8000'
>>> >
>>> > Dave
>>> >
>>> >
>>> > On Tue, Mar 08, 2022 at 06:45:23PM +0100, Nicolas Cellier wrote:
>>> > >
>>> > > Hi Marcel,
>>> > > which OS ?
>>> > > I cannot reproduce on macos 64,
>>> > >
>>> > > Cog[Spur] VM [CoInterpreterPrimitives VMMaker.oscog-eem.3172]
>>> > > 5.20211023.2003
>>> > > Mac OS X built on Mar 6 2022 15:31:16 CET Compiler: 4.2.1 Compatible
>>> > Apple
>>> > > LLVM 10.0.1 (clang-1001.0.46.4)
>>> > > platform sources revision VM: 202110232003
>>> > >
>>> > > Le mar. 8 mars 2022 ?? 17:57, Marcel Taeumel a
>>> > > ??crit :
>>> > >
>>> > > >
>>> > > > Hi Eliot, hi all --
>>> > > >
>>> > > > I think we have an sign-bit bug for character literals with code
>>> > points >
>>> > > > 16r7FFF.
>>> > > >
>>> > > > Steps to reproduce:
>>> > > >
>>> > > > 1. Print it: "Character value: 16r8000"
>>> > > > 2. Inspect the result by evaluating the character literal or send
>>> > > > #asInteger to it. It will most likely not render in a standard
>>> Squeak
>>> > and
>>> > > > show up like "$? asInteger".
>>> > > >
>>> > > > In a 32-bit VM, I will get the (positive) integer value
>>> 16r3FFF8000.
>>> > > > In a 64-bit VM, I will get the (negative) integer value
>>> '-16r8000'.
>>> > > >
>>> > > > Somehow, starting at bit 0, the bits 16 to 29 flip from 0 to 1. In
>>> > 64-bit,
>>> > > > this means a negative number. Not sure about bits 30 and 31 here.
>>> > > >
>>> > > > Is there a bug in the upper tag bits of immediate characters?
>>> > > > Is this related to the 2-byte or 3-byte byte codes in SistaV1?
>>> > > >
>>> > > > Works fine up to 16r7FFF. (This is unrelated to #leadingChar. Mine
>>> was
>>> > 0
>>> > > > in this experiment.)
>>> > > >
>>> > > > VM: 202112201228 (VMMaker.oscog-eem.3116)
>>> > > >
>>> > > > Best,
>>> > > > Marcel
>>> > > >
>>> >
>>> >
>>> Ah OK, I see it on macos too
>>> It remains to determine which operation exactly is involved...
>>> The TextMorph holding the printed result is correct - a WideString,
>>> whose last Character is (Character value: 32768).
>>>
>>> Le mer. 9 mars 2022 à 08:08, Marcel Taeumel <marcel.taeumel at hpi.de> a
>>> écrit :
>>>
>>>>
>>>>
>>>> Hi Dave, hi Nicolas --
>>>>
>>>> I am working in Windows 10.
>>>>
>>>> > I cannot reproduce on Linux 64 bit either:
>>>> > (Character value: 16r8000) asInteger hex ==> '16r8000'
>>>>
>>>> That's not how you would reproduce it. The bug affects character
>>>> literals, not character objects/instances. You have to evaluate code on
>>>> that character literal.
>>>>
>>>> Maybe this picture helps:
>>>>
>>>>
>>>>
>>>> Best,
>>>> Marcel
>>>>
>>>>
>>>> Am 08.03.2022 18:56:09 schrieb David T. Lewis <lewis at mail.msen.com>:
>>>>
>>>> I cannot reproduce on Linux 64 bit either:
>>>>
>>>> (Character value: 16r8000) asInteger hex ==> '16r8000'
>>>>
>>>> Dave
>>>>
>>>>
>>>> On Tue, Mar 08, 2022 at 06:45:23PM +0100, Nicolas Cellier wrote:
>>>> >
>>>> > Hi Marcel,
>>>> > which OS ?
>>>> > I cannot reproduce on macos 64,
>>>> >
>>>> > Cog[Spur] VM [CoInterpreterPrimitives VMMaker.oscog-eem.3172]
>>>> > 5.20211023.2003
>>>> > Mac OS X built on Mar 6 2022 15:31:16 CET Compiler: 4.2.1 Compatible
>>>> Apple
>>>> > LLVM 10.0.1 (clang-1001.0.46.4)
>>>> > platform sources revision VM: 202110232003
>>>> >
>>>> > Le mar. 8 mars 2022 ?? 17:57, Marcel Taeumel a
>>>> > ??crit :
>>>> >
>>>> > >
>>>> > > Hi Eliot, hi all --
>>>> > >
>>>> > > I think we have an sign-bit bug for character literals with code
>>>> points >
>>>> > > 16r7FFF.
>>>> > >
>>>> > > Steps to reproduce:
>>>> > >
>>>> > > 1. Print it: "Character value: 16r8000"
>>>> > > 2. Inspect the result by evaluating the character literal or send
>>>> > > #asInteger to it. It will most likely not render in a standard
>>>> Squeak and
>>>> > > show up like "$? asInteger".
>>>> > >
>>>> > > In a 32-bit VM, I will get the (positive) integer value 16r3FFF8000.
>>>> > > In a 64-bit VM, I will get the (negative) integer value '-16r8000'.
>>>> > >
>>>> > > Somehow, starting at bit 0, the bits 16 to 29 flip from 0 to 1. In
>>>> 64-bit,
>>>> > > this means a negative number. Not sure about bits 30 and 31 here.
>>>> > >
>>>> > > Is there a bug in the upper tag bits of immediate characters?
>>>> > > Is this related to the 2-byte or 3-byte byte codes in SistaV1?
>>>> > >
>>>> > > Works fine up to 16r7FFF. (This is unrelated to #leadingChar. Mine
>>>> was 0
>>>> > > in this experiment.)
>>>> > >
>>>> > > VM: 202112201228 (VMMaker.oscog-eem.3116)
>>>> > >
>>>> > > Best,
>>>> > > Marcel
>>>> > >
>>>>
>>>>
>>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.squeakfoundation.org/pipermail/squeak-dev/attachments/20220309/b63d324a/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 14513 bytes
Desc: not available
URL: <http://lists.squeakfoundation.org/pipermail/squeak-dev/attachments/20220309/b63d324a/attachment-0002.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 90427 bytes
Desc: not available
URL: <http://lists.squeakfoundation.org/pipermail/squeak-dev/attachments/20220309/b63d324a/attachment-0003.png>


More information about the Squeak-dev mailing list