[Vm-dev] Re: I need help building Cog on 64bit Linux (new Squeak server)

[Frank Shearar]

On 4 February 2013 08:41, Jeremy Kajikawa <jeremy.kajikawa at gmail.com> wrote:
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> The behaviour in SmallTalk relies on the underlying framework which you state is C language and full of undefined behaviour...

That's not quite true. Smalltalk's behaviour is perfectly well
defined, in terms of a stack machine. This PARTICULAR VM is built
using Slang, a stripped down dialect of Smalltalk that can be mapped
quite easily to C.

There is nothing in Smalltalk's definition about how you implement a
virtual machine and, in fact, people have implemented a VM in PyPy,
while others have run Smalltalk _directly_on_hardware_.

frank

> Doesn't that make the SmallTalk environment Undefined Behavior as well by inheriting the UB from the C layer it builds on?

No.

> Or is that just irrational F.U.D. in promotion of SmallTalk by detraction against C?

Yes.

frank

> *both* languages are capable and leave defining behavior to the authoring programmer/coder/software-developer/...
>
> Or at least that is my own understanding...
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> Belxjander
>
> On Feb 4, 2013 5:32 PM, "Camillo Bruni" <camillobruni at gmail.com> wrote:
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>>
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>> On 2013-02-04, at 08:49, Igor Stasenko <siguctua at gmail.com> wrote:
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>> >
>> > On 28 January 2013 23:07, Nicolas Cellier
>> > <nicolas.cellier.aka.nice at gmail.com> wrote:
>> >>
>> >> 2013/1/28 Ken Causey <ken at kencausey.com>:
>> >>>
>> >>> Eliot said:
>> >>>>
>> >>>> Hmmm.  Sorry to put you to this but what happens when you run the r2669,
>> >>>> r2672 and r2673 VMs from http://www.mirandabanda.org/files/Cog/VM/? If
>> >>>> these don't crash then it might be something to do with gcc 4.4.x.  But
>> >>>> I'd
>> >>>> have to take a look, and time is tight right now...  But if any of them do
>> >>>> work could you use them for the interim?
>> >>>
>> >>>
>> >>> Not a problem and thanks for the reply.
>> >>>
>> >>> Well I started with 2673 and the tests are still running but it would have
>> >>> crashed by now if the same problem exists so it's looking like the gcc
>> >>> version is the issue.  I will try earlier gcc versions and report back.
>> >>>
>> >>> It's a little disheartening that in this day and age we are tickling gcc
>> >>> issues when the same version of gcc is used to build the kernel and
>> >>> thousands upon thousands of Debian binaries which (by and large anyway) seem
>> >>> to be fine.
>> >>>
>> >>> Ken
>> >>
>> >> And the answer would be: don't rely on UB (Undefined Behavior)
>> >> Modern interpretation of the standards is that a compiler has a
>> >> license to ignore UB in order to perform optimizations... This is
>> >> because no one should rely on UB.
>> >> Unfortunately, the underlying C language is full of UB, and the signed
>> >> arithmetic model is particularly broken...
>> >>
>> >> I doubt the thousands of packages have been working unchanged...
>> >> They work with army of programmers maintaining the code and chasing
>> >> the compiler warnings.
>> >> As long as we ignore the warnings, we are in danger.
>> >> As long as we have several hundreds warnings, there is no easy way to
>> >> analyze their dangerosity...
>> >>
>> >
>> > I cannot agree more.
>>
>> well you mute them, right?
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