js-20261012-wasm-dwarf-inline-origin-stacktrace-reconstruction

Answer

Done. Here's what I diagnosed and delivered.

Root cause

The problem isn't a single bug — it's a set of coordinate/identity mismatches that a naive "scan every DIE for low ≤ addr < high" resolver gets wrong:

1. Address spaces — V8 reports Wasm offsets as module file offsets, DWARF uses an origin at the first function body. Missing this maps to the wrong source line.
2. Relocations — .o files store R_WASM_FUNCTION_OFFSET_I32 / R_WASM_SECTION_OFFSET_I32; without applying them every low_pc is wrong.
3. Tombstones — wasm-ld rewrites dead functions to 0xfffffffe/0xffffffff; if treated as live ranges they corrupt the whole index (I actually hit and fixed this).
4. Inline nesting is DIE ancestry, not the range list, and outer-frame locations come from the child's call site.
5. Overlapping ranges need a deterministic total order + structured ambiguity.
6. Cyclic abstract_origin can hang a naive walker.
7. Per-query scans are quadratic; a static centered interval tree fixes it.

The fix

• solution/wasm-dwarf-inline.js (1551 lines, dependency-free): Wasm section/reloc/linking parser, DWARF 2–5 parser (line, ranges, rnglists, addr, str_offsets, split .dwo merge), abstract-origin cycle guard, tombstone filtering, centered interval tree, GNU call-site/tail-call handling, frame reconstruction with deterministic tie-breaking and structured ambiguity, plus a CLI.
• solution/test.js: differential harness that compiles real Wasm with clang --target=wasm32 -g (DWARF 4 and 5), links with wasm-ld, and compares every line-table row / range boundary against llvm-addr2line -f -i.
• SOLUTION.md: the requested writeup with root-cause analysis, exact fix, and verification.

Verification (all green)

PASS linked.wasm (multi-CU, DWARF4)  (26/26)
PASS linked5.wasm (multi-CU, DWARF5) (26/26)
PASS trap.wasm (nested inline)       (8/8)
PASS call.wasm (call sites)          (27/27)
PASS inline.o / inline5.o relocation equivalence + addr2line (14/14 each)
PASS split-DWARF5 .dwo merge         (10/10)
PASS tail-call call-site metadata
PASS cyclic abstract-origin handling
PASS overlapping-range structured ambiguity
PASS 100k queries in ~56 ms (non-quadratic)
PASS runtime V8 offset 0x40 -> DWARF 0x4 -> [inner > middle > guarded]
PASS dead-code tombstones excluded
==> pass=87 fail=0

Run it yourself: cd ~/solution && node test.js.