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

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Wed Mar 9 09:08:36 UTC 2022


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
>>> > >
>>>
>>>
>>
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