Re: [Pharo-project] squeak VM 5.0

Um, I'm _quite_ serious on insisting that Smalltalk wordSize be implemented in some way that caches the value in e.g. a class variable (or class inst var for max speed) that is reevaluated on startup.  initialPC is evaluated a lot, e.g. once for every method in a "browse inst var refs".  This is performance-critical, and going to a slow primitive to access something that can only change at startup is not a good idea.  Please arrange that e.g. SystemDictionary gains a class var that caches the word size.

On Wed, Dec 16, 2009 at 12:48 AM, John M McIntosh <[hidden email]> wrote:

RIght and it's 12:30 am again,

So the MAGIC fixes for the tracer to let you build a 64bit Pharo image are below.
No doubt they apply to closure based squeak trunk images.

Could someone can be kind enough to integrate them into the current System-Tracing.2forPharo.cs ?
Then some people in Europe? can grab the current Pharo/Trunk image and convert it, and run some smoke tests.
BTW you need to use the Squeak.5.0.0.b9.64*64.app.zip to run a 64bit image

Don't forget to convert you have to use a powerpc, or a  squeak VM that is running as powerpc (via get info settings) on your macintel machine.
Still need someone to *fix* the systemtracer so it will run on intel machines.  (Hint watch how it writes out integer data). ...

Changes below:

"This is the magic change, it's not the conversion of the image that is bad. It's the Smalltalk code assumption of is that 4 or 8 bytes? "
"There likely should be a Pharo/Squeak bug for this since it should be using wordSize not a magic number of 4"

Eliot notes  "Bravo!  But Smalltalk wordSize has to be implemented in some way that caches the value in e.g. a class variable (or class inst var for max speed) that is reevaluated on startup."

So I'll let someone propose/write a clever solution since the Smalltalk wordSize is computational heavy.

CompiledMethod>>initialPC
       "Answer the program counter for the receiver's first bytecode."

       ^ (self numLiterals + 1) * (Smalltalk wordSize) + 1


"This next method  isn't used much, should be. But the System-Tracing.2forPharo.cs trashes it with a ancient version.
This is the correct version"

SystemDictionary>>wordSize
 "Answer the size (in bytes) of an object pointer."
 "Smalltalk wordSize"
 ^[SmalltalkImage current vmParameterAt: 40] on: Error do: [4]

"Changes to properly fix up BlockClosure in the SystemTracer2"

SystemTracer2>>object: object allFieldsWithIndex: block collect: sequenceableCollectionClass
       "Evaluate block against each of the pointer fields with index, and collect the results in an instance of sequenceableCollectionClass"

       | fixedSize results varSize nilResults blockvalue |
       object isCompiledMethod ifTrue:
               [results := sequenceableCollectionClass new: 1 + object numLiterals.
               1 to: 1 + object numLiterals do:
                       [:j | results at: j put: (block value: (object objectAt: j) value: j)].
               ^ results].

       fixedSize := object class instSize.
       varSize := object basicSize.
       results := sequenceableCollectionClass new: fixedSize + varSize.
       1 to: fixedSize do:
               [:j | results at: j put: (block value: (object instVarAt: j) value: j)].
       1 to: varSize do:
               [:j |
               results at: fixedSize + j put: (block value: (object basicAt: j) value: fixedSize + j)].

       object isContextPart ifTrue:

               [(object instVarAt: 2) ifNotNil:
                       ["May need to adjust PC and startPC if changing wordSize..."

                       blockvalue := (object instVarAt: 2)+(self pcDeltaForMethod: object method).
               results at: 2 put: (block value: blockvalue value: 2)].
               ((object isMemberOf: BlockContext) and: [object home notNil]) ifTrue:
                               [results at: 5 put: (block value: (object instVarAt: 5)+(self pcDeltaForMethod: object method) value: 5)].
               "Need to fill out the nils beyond the knowable end of stack"
               nilResults := sequenceableCollectionClass new: object frameSize - object basicSize.
               1 to: nilResults size do:
                       [:j | nilResults at: j put: (block value: nil value: j)].
               ^ results , nilResults].

       object class = BlockClosure ifTrue:
               ["May need to adjust PC and startPC if changing wordSize..."

               blockvalue := (object instVarAt: 2)+(self pcDeltaForMethod: object method).
               results at: 2 put: (block value: blockvalue value: 2)].
               ^ results


>> Eliot and I spent 30 minutes chatting about what is wrong. The conclusion is we *think* we are doing the right thing,
>> yet the Virtual Machine says the image is busted.   So a quick fix is not apparent, and we'll dig more.

--
===========================================================================
John M. McIntosh <[hidden email]>   Twitter:  squeaker68882
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
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Ok, well I created Mantis 

http://bugs.squeak.org/view.php?id=7430

to document. 

Personally I would do 

Smalltalk wordSize

versus 

SystemDictionary wordSize

Also the issue is when to change the WordSize variable. 

I think in 

SmalltalkImage>>snapshot: andQuit: embedded:  

right at the 

ifTrue: [self quitPrimitive].

Cursor normal show.

you want to set things so that wordSize is reset. 

At quit time you could do the reset before the 

"self quitPrimitive"

then you know the value is reset and needs to be recalculated at startup time. 

or you can reset it before the

Cursor normal show.

which runs after startup time

Somehow I think there is more risk resetting it after startup since I'm not sure 

when something could leap in wanting a valid value. 

On 2009-12-16, at 2:44 PM, Laval Jannik wrote:

Hi Eliot, hi John,

This is what I do:

- create a class var in SystemDictionary

- accessors (wordSize and wordSize:), the first one can initialize the variable if nil, the second is to modify the value in case of 64bits image.

Maybe the second one could be integrated in System-Tracing file.

- in CompiledMethod, initialPC use it.

Maybe we could integrate it in pharoCore.

--

===========================================================================

John M. McIntosh <[hidden email]>   Twitter:  squeaker68882

Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com

===========================================================================