[Vm-dev] [OpenSmalltalk/opensmalltalk-vm] Reproduceable Segmentation fault while saving images (#444)

[Alistair Grant]

Hi Eliot and Nicolas,

Nicolas, thanks for checking on Squeak, that is useful to know.

Juraj and I have both built assert VMs and been trying to reproduce Eliot's findings.

If I add a couple of print statements to the code and run with a normal VM, I get a number of:

```
evicted zombie process from run queue
```

messages.

If I run gccrash.st with the assert VM I get:

```
((classIndex >= 1) && (classIndex <= (classTablePageSize()))) 50170

((classIndex >= 1) && (classIndex <= (classTablePageSize()))) 50170
```

before the process seg faults.

Do these provide any additional information to help track down the issue?  (I'll include more complete information below)


I tried running a headless VM and printing instance counts about FreeType external objects in a clean image:

```
$ vmh/pharo Pharo.image eval "'ftcount.st' asFileReference fileIn"
FTBBox -> 0
FTBitmap -> 0
FTBitmapSize -> 0
FTCharMapRec -> 0
FTFaceRec -> 0
FTGeneric -> 0
FTGlyphMetrics -> 0
FTGlyphSlotRec -> 0
FTListRec -> 0
FTMatrix -> 0
FTOutline -> 0
FTSizeMetrics -> 0
FTSizeRec -> 0
FTVector -> 0
FT2Handle -> 0
FT2Face -> 0
FT2Library -> 1
a FT2Library(@ 16r00000000)<0x0>
File @ ftcount.st
```

Once the image has been started normally, the pointer in FT2Library becomes non-zero.

Which to me seems to suggest that rather than the image being delivered in a corrupt state, it's something that happens early in session resumption.


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