Emit per-step linear-memory snapshots in the execution trace#123
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Debuggers need linear memory to resolve Rust variables that live in the shadow
stack (the majority at -O0, e.g. any fbreg-located local or parameter). Extend
the instruction trace record with a `mem` field: a full sparse snapshot of the
current module's linear memory, emitted only when it changed since the previous
snapshot (a `<prevMem>` cell holds the last one), else `null`.
The snapshot is a JSON array of `{ "addr", "bytes" }` runs — one per concrete
SparseBytes chunk, `bytes` lowercase hex via the Bytes2Hex hook — so only
written regions are carried; a consumer folds the most recent snapshot at or
before a step and treats unwritten bytes as 0. A `[traceInstr-nomem]` fallback
keeps tracing total for programs with no linear memory.
test_memory_tracing.py deploys the increment example and asserts the field is
present, snapshots are emitted on change (and omitted otherwise), and the folded
image is consistent.
bbyalcinkaya
approved these changes
Jul 17, 2026
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Debuggers need linear memory to resolve Rust variables that live in the shadow stack (the majority at optimization level
-O0, e.g., any fbreg-located local or parameter). Extend the instruction trace record with amemfield: a full sparse snapshot of the current module's linear memory, emitted only when it changed since the previous snapshot (a<prevMem>cell holds the last one), elsenull.The snapshot is a JSON array of
{ "addr", "bytes" }runs — one per concrete SparseBytes chunk,byteslowercase hex via the Bytes2Hex hook — so only written regions are carried; a consumer folds the most recent snapshot at or before a step and treats unwritten bytes as 0. A[traceInstr-nomem]fallback keeps tracing total for programs with no linear memory.test_memory_tracing.py deploys the increment example and asserts the field is present, snapshots are emitted on change (and omitted otherwise), and the folded image is consistent.