[Vm-dev] [COG] primitiveClosureValue assert is failing with StackVM (possible BUG in bytecodes!!)

Mariano Martinez Peck marianopeck at gmail.com
Wed Dec 22 20:03:25 UTC 2010

Hi Eliot. If I compile a StackVM, and I just press the left arrow in a code
pane of a OB windows, in a pharo image, I get an asser that fails:
(oop & 1) 19202

Sorry I bother with these asserts, but I am trying to solve the crashes I
have and I think starting for the asserts is a good idea.

The assert that fails is in primitiveClosureValue()  the part:

blockClosure = longAt(GIV(stackPointer) + (GIV(argumentCount) *
    /* begin quickFetchInteger:ofObject: */
    oop = longAt((blockClosure + BaseHeaderSize) + (ClosureNumArgsIndex <<
    assert((oop & 1));
    numArgs = (oop >> 1);
    if (!(GIV(argumentCount) == numArgs)) {
        /* begin primitiveFail */
        if (GIV(primFailCode) == 0) {
            GIV(primFailCode) = 1;

numArgs results to be a large number (using #printNum:   was 718613205), and
if I try to do a #printOop:  I got a " 0x55aa55aa0x55aa55aa is not on the

Now, of course, the "if (!(GIV(argumentCount) == numArgs)) " fails.

What it is funny is that I did a #printOop: of blockClosure instVar, and
this is what I get:  0x1f59b578: a(n) Association

Association? WTF ?   so...I guess something weird is happening. I continue
debugging it..and I noticed that:

- Several classes were called in addition to Association,like Character.
These seems to be compact classes and implement #value and #value:   ;)
- Both, #bytecodePrimValue and #bytecodePrimValueWithArg  were not calling
#primitiveClosureValue. So, "isBlock" was false...

I tried modifying #bytecodePrimValueWithArg and #bytecodePrimValue  this

isBlock := objectMemory is: rcvr instanceOf:
ClassBlockClosurecompactClassIndex: ClassBlockClosureCompactIndex.

to this one:

isBlock := objectMemory is: rcvr instanceOf: (self splObj:
ClassBlockClosure) compactClassIndex: ClassBlockClosureCompactIndex.

WIth this change, at least, the assert doesn't fail anymore. I made progress
(maybe). But still, for normal closures, "isBlock" seems to be false.
So.....all block values are being managed as a normal send ????

Now, I don't understand why ClassBlockClosureCompactIndex  is 0. I think
this may be the problem. Why it is not 12? (in Pharo  Smalltalk
compactClassesArray at: 12 ->>> BlockClosure.)
I notice that ObjectMemory >> initializeCompactClassIndices  does:

    ClassBlockClosureCompactIndex := 0 "12". "Prospective.  Currently
TranslatedMethod class"

Notice that this ZERO changes the sematic of #is: oop instanceOf: classOop
compactClassIndex: compactClassIndex
called from the #bytecodePrimValue and bytecodePrimValueWithArg

Finally, I changed the mentioned line to this:

isBlock := objectMemory is: rcvr instanceOf: (self splObj:
ClassBlockClosure) compactClassIndex: 12.

and finally, with block closures, it is calling the primitive, and for
Association it doesn't fail the assert.  ahh and the image doesn't crash ;)

I don't know if this is a bug, if my solution was ok, nor it impact. Please
let me know.


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