[OpenSmalltalk/opensmalltalk-vm] primitiveImageFormatVersion may be not correct (Issue #638)
The return value of `primitiveImageFormatVersion` is hard-coded and does not consider the value of `multipleBytecodeSetsActive`, which is indeed important when trying to open a particular image with a particular VM.
See: - Interpreter >> #imageFormatVersion - StackInterpreter >> #imageFormatVersion - ObjectMemory >> #imageFormatVersion - Spur32BitMemoryManager >> #imageFormatVersion - Spur64BitMemoryManager >> #imageFormatVersion
Note that this can be fixed on the image-side by checking primitiveMultipleBytecodeSetsActive.
It is a VM bug, sorry for overlooking this. Proposed fix in VMMaker inbox VMMaker.oscog-dtl.3185
Fix is in VMMaker (VMMaker.oscog-dtl.3185), still need to commit generated code and build VM.
@marceltaeumel the fix inVMMaker.oscog-dtl.3185 is trivial, but I need someone else (you or Eliot) to do the code generation this time. The reason is that my generated code has differences that I cannot account for (specifically one value in the primitiveMetadataTable array is generated as 0x100 but should be 0x200, and in several places there are differences in integer type declarations). I have not be able to track down the reason for the differences, so I cannot commit the generated code.
My apologies, please disregard. Marcel, thank you for doing the code generation :-)
Dave
On Thu, Jun 02, 2022 at 01:21:29PM -0700, David T Lewis wrote:
@marceltaeumel the fix inVMMaker.oscog-dtl.3185 is trivial, but I need someone else (you or Eliot) to do the code generation this time. The reason is that my generated code has differences that I cannot account for (specifically one value in the primitiveMetadataTable array is generated as 0x100 but should be 0x200, and in several places there are differences in integer type declarations). I have not be able to track down the reason for the differences, so I cannot commit the generated code.
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Closed #638 as completed.
Reopened #638.
Wow. This is not over. Next issue is in `imageSegmentVersion`. I will try to fix this on the image side for now. But this is still a bug in the VM primitve 98 `primitiveStoreImageSegment`... :-(
The biggest issue for an image-side discrimination is that the VMMaker-specific constant `512 ... MultipleBytecodeSetsBitmask` is not part of the regular image code. Which is a good thing, I suppose. Still ...
For my understanding - is the concern with imageSegmentVersion a problem for practical reasons (something does not work as expected)? It certainly makes sense that an image segment should have a format number that matches the image from which it was saved, but as a practical matter does anything bad happen if this is not the case?
In the extreme case, surely it could mean that the data was in a completely non-acceptable format?
On 2022-06-07, at 4:26 PM, David T Lewis notifications@github.com wrote:
For my understanding - is the concern with imageSegmentVersion a problem for practical reasons (something does not work as expected)? It certainly makes sense that an image segment should have a format number that matches the image from which it was saved, but as a practical matter does anything bad happen if this is not the case?
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tim -- tim Rowledge; tim@rowledge.org; http://www.rowledge.org/tim Useful random insult:- A prime candidate for natural deselection.
I am trying to understand the real-world scenario in which this matters. I have an image running Sista bytecodes and my image format is 68533. I save an image segment to disk, and that image segment contains objects that contain compiled code that contain Sista bytecodes. The saved image segment records itself with format number 68021 (not 68533). Later on, someone loads that image segment using a VM that is a year or two old, so the VM does not know about 68533. But the VM probably does know how to run Sista bytecodes because it is only a year or two old. Everything still works, so as a practical matter what is the problem?
Regarding image side code and MultipleBytecodeSetsBitmask in VMMaker, on the image side you would use this (only if necessary, and hopefully it is not necessary):
(ImageFormat fromInteger: 68021) requiresMultipleBytecodeSupport ==> false (ImageFormat fromInteger: 68533) requiresMultipleBytecodeSupport ==> true
[...] is the concern with imageSegmentVersion a problem for practical reasons [...] I am trying to understand the real-world scenario in which this matters. [...]
Well, loads of tests fail or err at the moment. Maybe we should just fix the image-side load code for image segments to also accept 68021, even if the `imageFormatForSnapshot` is 68533.
I committed a quickfix via System-mt.1355. Yet, this topic might need more discussion.
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