refactor/fix: Use object offsets instead of field indexes for precise object scanning #3736
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WojciechMazur
commented
Feb 8, 2024
Comment on lines
-35
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| nir.Val.Long( | ||
| (offset - sizeOfHeader) / MemoryLayout.BYTES_IN_LONG | ||
| ) |
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This way on calculating reference field indexes could have lead to runtime issues in 32-bit runtime. It would lead to having double indexes (eg. offset=16 & offset=20 would point to the same index) and might omit scanning some of misaligned fields.
<3 |
kubukoz
reviewed
Feb 8, 2024
Co-authored-by: Jakub Kozłowski <kubukoz@gmail.com>
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Immix and Commix scan objects precisely based on array of indexes containing possible references. Previously this list was populate by indexes of fields, now it's a list of offsets starting from object address (also known as start of object header) to make the code more readable.
It also can possibly some issues on 32-bit CPU architectures, see code comment below.
As an additional improvement used when debugging we're adding an utility to extract Class name as wide-string allowing to show it in debug information from the GC (best effort, no guarantess about String object layout)