feat(dwarf): capture per-instruction machine-offset → wasm-op source map (VCR-DBG-001, #242) - #427
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…map (VCR-DBG-001, #242, #394) PR A of the v0.12.0 DWARF `.debug_line` release: close the encoder machine-offset gap so a later step can emit source-line debug info. `compile_wasm_to_arm` now captures a `LineMap = Vec<(machine_offset, wasm_op_index)>` during the encode loop — `code.len()` immediately before each `encode()` is the instruction's final offset within the function's `.text` (the trailing literal pool is appended at the end and the LDR patch is in-place, so earlier offsets never shift). Carried on `CompiledFunction.line_map`. Frozen-safe by construction: the map is captured but NEVER serialized, so the emitted `.text` is byte-identical with or without it. Proven by the existing differential fixtures staying green plus `test_line_map_is_wellformed_dbg001`, which asserts monotonic, in-bounds offsets and that recompilation yields identical code. ARM only; the RISC-V backend carries an empty map (DWARF emit there is a follow-up). Next (PR B): gimli as a production dep (auto-picked up by Bazel via from_cargo, #422), read the input wasm's `.debug_line`, and emit a non-ALLOC `.debug_line` section behind a `--debug-line` flag, gated by an additivity byte-diff oracle. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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This was referenced Jun 22, 2026
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, #394) (#440) First release of the north-star verified-codegen campaign. Pin sweep 0.11.51 -> 0.12.0 (workspace + all path-dep versions + MODULE.bazel + Cargo.lock), CHANGELOG, and VCR-DBG-001 roadmap status -> implemented. Ships: - VCR-DBG-001 `--debug-line` DWARF emission (PR A #427 / B #429 / C #430): debugger-readable .debug_* mapping ARM .text -> wasm source lines, with .rel.debug_* relocations verified end-to-end against arm-none-eabi-ld. Purely additive; default build bit-identical. - VCR-MEM-001 layer-2 frozen-safe budget decision logic + oracles (#421-#425). - gimli 0.33 adaptation (#439) + wast 252 (#438). Minor bump: new user-facing `--debug-line` feature (semver-correct). Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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What — PR A of v0.12.0 (DWARF
.debug_line)Closes the encoder machine-offset gap that blocked DWARF line emission.
compile_wasm_to_armnow captures aLineMap = Vec<(machine_offset, wasm_op_index)>during the encode loop and carries it onCompiledFunction.line_map.The offset is
code.len()taken immediately before eachencode()— the instruction's final position in the function's.text, because nothing after the loop shifts earlier instructions (the literal pool is appended at the end; the LDR placeholder patch is in-place/length-preserving).Frozen-safe by construction
The map is captured but never serialized in this PR, so the emitted
.textis byte-identical with or without it. Proven by:test_line_map_is_wellformed_dbg001— asserts monotonic, in-bounds offsets and that recompilation yields identical code (the side-table doesn't perturb output).ARM only; the RISC-V backend carries an empty map (its DWARF emit is a VCR-DBG-001 follow-up).
Where this sits
This is the first of two PRs for v0.12.0. Next (PR B):
gimlias a production dep (auto-resolved by Bazel via from_cargo #422), read the input wasm's.debug_line, and emit a non-ALLOC.debug_linesection behind a--debug-lineflag — gated by an additivity byte-diff oracle (flag-on vs flag-off: only.debug_linediffers;.text/.data/.bssidentical).Verification
cargo test -p synth-backend --lib→ 204 pass (incl. the new test); integration fixtures greencargo clippy --all-targets -- -D warningsclean (added aLineMaptype alias for the return tuple);cargo fmt --checkcleanrivet checkzero non-xref errors; roadmap VCR-DBG-001 step-5a progress recordedRefs #242, #394.
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