More table safety improvements #11255
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This is some more progress on bytecodealliance#11179 aimed at improving the safety of management of tables internally within Wasmtime: * `Instance::table_index` is removed as it can be replaced with data stored directly in the `VMTableImport` now. * `Instance::get_table` now returns `&mut Table` * `Instance::get_defined_table_with_lazy_init` now returns `&mut Table` * `Instance::with_defined_table_index_and_instance` now directly returns `DefinedTableIndex` plus `Pin<&mut Instance>`, codifying the ability to "laterally move" between instances. * `Instance::table_init_segment` was refactored to "take" the tables during initialization and replace them afterwards, resolving the split borrow issue and removing an `unsafe` block in the function. cc bytecodealliance#11179
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This commit fixes an issue in the previous commit with respect to Miri and Stacked Borrows. This does so by improving the safety of the `Table::copy`-related functions to all work mostly on safe code rather than unsafe references. Some minor amount of unsafety is still present but it is now clearly documented and easier to verify.
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The Miri violation of stacked borrows is I believe legitimate, so I've added a new commit which improves the safety situation around |
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The `match` makes the cases a lot more clear IMO, and additionally the conditions asserted in each branch become trivially obvious (they are exactly what was matched upon for their associated branch) so I removed them. I also made some minor copy-edit tweaks to some comments while I was here. This would have just been a nitpick review comment on bytecodealliance#11255 but I was traveling and didn't get a chance to leave review comments in a reasonable amount of time, so instead I am just fixing them up myself in this follow up.
This was referenced Jul 24, 2025
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The `match` makes the cases a lot more clear IMO, and additionally the conditions asserted in each branch become trivially obvious (they are exactly what was matched upon for their associated branch) so I removed them. I also made some minor copy-edit tweaks to some comments while I was here. This would have just been a nitpick review comment on #11255 but I was traveling and didn't get a chance to leave review comments in a reasonable amount of time, so instead I am just fixing them up myself in this follow up.
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* More table safety improvements This is some more progress on bytecodealliance#11179 aimed at improving the safety of management of tables internally within Wasmtime: * `Instance::table_index` is removed as it can be replaced with data stored directly in the `VMTableImport` now. * `Instance::get_table` now returns `&mut Table` * `Instance::get_defined_table_with_lazy_init` now returns `&mut Table` * `Instance::with_defined_table_index_and_instance` now directly returns `DefinedTableIndex` plus `Pin<&mut Instance>`, codifying the ability to "laterally move" between instances. * `Instance::table_init_segment` was refactored to "take" the tables during initialization and replace them afterwards, resolving the split borrow issue and removing an `unsafe` block in the function. cc bytecodealliance#11179 * Improve safety of `Table::copy` This commit fixes an issue in the previous commit with respect to Miri and Stacked Borrows. This does so by improving the safety of the `Table::copy`-related functions to all work mostly on safe code rather than unsafe references. Some minor amount of unsafety is still present but it is now clearly documented and easier to verify. * Fix tests
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Oct 20, 2025
The `match` makes the cases a lot more clear IMO, and additionally the conditions asserted in each branch become trivially obvious (they are exactly what was matched upon for their associated branch) so I removed them. I also made some minor copy-edit tweaks to some comments while I was here. This would have just been a nitpick review comment on bytecodealliance#11255 but I was traveling and didn't get a chance to leave review comments in a reasonable amount of time, so instead I am just fixing them up myself in this follow up.
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This is some more progress on #11179 aimed at improving the safety of management of tables internally within Wasmtime:
Instance::table_indexis removed as it can be replaced with data stored directly in theVMTableImportnow.Instance::get_tablenow returns&mut TableInstance::get_defined_table_with_lazy_initnow returns&mut TableInstance::with_defined_table_index_and_instancenow directly returnsDefinedTableIndexplusPin<&mut Instance>, codifying the ability to "laterally move" between instances.Instance::table_init_segmentwas refactored to "take" the tables during initialization and replace them afterwards, resolving the split borrow issue and removing anunsafeblock in the function.Closes #11179