sir: flat memory with guarded stores - #23
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Flat memory adds an in-bounds obligation on mstore32 to the progress theorems, alongside the control-point disjunction and the allocation obligations that already carry names. Written out at every use it makes the statements unreadable, so it becomes Program.StoreInBounds in Spec/Step.lean, next to the step relation whose precondition it is. It unfolds definitionally, so no proof changed.
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superseded by #26 |
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Memory becomes a flat byte store with allocations as write authority:
mload32reads it directly andmstore32fires only inside a provisioned region.What changed
Allocationdrops itsbytespayload for{ offset, size }, andMemoryStatecarriesstore : Nat → UInt8besideprovisioned.MemoryState.emptyzero-fills; an arbitraryMemoryStateanswers anything outside its allocations.mload32loses itsVector UInt8 32oracle and reads 32 bytes from the store, soStmt.isMemOracleshrinks tomallocUninitandDecoder.NoMloaddisappears from the dialogue. Memory-reading programs come inside theMemOracleFreedeterminism family;bareLoad_deterministicwitnesses one that was outside it before.mstore32throws.storeOutOfBoundsunless a single provisioned allocation contains the whole 32-byte range. This narrows the step relation. A 32-byte store straddling two abutting allocations used to execute and write both halves; it is now rejected, and a program whose first store is out of bounds is deterministic by being stuck.Program.StoreInBounds, a premise about the statement at the current control point. Every other export is byte-identical while quantifying over the smaller relation.