Add a --symbolicate-wasm arg to profiler-edit. by mstange · Pull Request #6008 · firefox-devtools/profiler

mstange · 2026-05-07T19:29:06Z

This allows applying wasm symbols to existing profiles that were captured with a stripped wasm bundle.

The script looks for functions with names of the shape wasm-function[123], which is what Firefox uses when the wasm file doesn't have a names section.

Usage:

yarn build-node-tools && \
node node-tools-dist/profiler-edit.js -i input.json.gz \
--symbolicate-wasm http://host/a.wasm=./a-unstripped.wasm \
--symbolicate-wasm http://host/b.wasm=./b-unstripped.wasm \
-o out.json.gz

I've successfully used it to turn https://share.firefox.dev/4f9O7oh into https://share.firefox.dev/4nd6GKk .

codecov · 2026-05-07T19:33:41Z

Codecov Report

❌ Patch coverage is 77.14286% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.79%. Comparing base (642c1fd) to head (b4054d5).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/profile-logic/wasm-symbolication.ts	84.74%	17 Missing and 1 partial ⚠️
src/node-tools/profiler-edit.ts	36.36%	14 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #6008 +/- ##
==========================================
- Coverage 83.82% 83.79% -0.03% 
==========================================
Files 328 329 +1 Lines 34255 34395 +140 Branches 9572 9618 +46 ==========================================
+ Hits 28713 28821 +108 - Misses 5114 5145 +31 - Partials 428 429 +1

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canova

Nice, thanks for adding some tests! I added a bunch of nits to make things a bit clearer, but otherwise I don't see any issues.

This also made me look into the wasm spec a bit and learn more about it, so I think it was a good use of time 😄

This also made me think more about the source map support that I've been working on. These 2 things seem like solving it for 2 different use cases, so it seems very interesting. I didn't know about the name section in the wasm spec. I wonder how devtools handles it (or if it does). It looks like it's mostly looking at the dwarf info for now, but need to look deeper.

canova · 2026-05-08T13:52:16Z

+ const symbolicateWasm: WasmSymbolicationCliSpec[] = [];
+ const rawWasmArg = argv['symbolicate-wasm'];
+ let wasmArgs: unknown[];
+ if (rawWasmArg === undefined) {
+ wasmArgs = [];
+ } else if (Array.isArray(rawWasmArg)) {
+ wasmArgs = rawWasmArg;
+ } else {
+ wasmArgs = [rawWasmArg];
+ }
+ for (const arg of wasmArgs) {
+ if (typeof arg !== 'string' || arg === '') {
+ throw new Error('--symbolicate-wasm requires a value');
+ }
+ // Accept "<url>=<path>" if the LHS looks like a URL, otherwise treat the
+ // whole string as a path and infer the URL from the profile. Split on
+ // the last `=` so URLs containing `=` (e.g. in query strings) survive
+ // intact; this assumes file paths don't contain `=`.
+ const eqIndex = arg.lastIndexOf('=');
+ if (eqIndex !== -1 && /^[a-z]+:\/\//i.test(arg.slice(0, eqIndex))) {
+ symbolicateWasm.push({
+ url: arg.slice(0, eqIndex),
+ path: arg.slice(eqIndex + 1),
+ });
+ } else {
+ symbolicateWasm.push({ path: arg });
+ }
+ }


Not for this PR, but now that we have commander in the package.json, we can possibly simplify these things by using it.

canova · 2026-05-08T15:13:15Z

+// Parses the function-name subsection of a wasm "name" custom section and
+// returns a map from function index to name. Returns an empty map if the
+// module has no name section. The function index space includes imports
+// (imports come first) — same numbering used in `wasm-function[N]` strings.


Oh can we add a link to the Firefox source code where we generate this N number?

Added link to https://searchfox.org/firefox-main/rev/69a6da6b2f5f8f6bdb90cd6dd70a024f460f12ca/js/src/wasm/WasmMetadata.cpp#209

This allows applying wasm symbols to existing profiles that were captured with a stripped wasm bundle. The script looks for functions with names of the shape `wasm-function[123]`, which is what Firefox uses when the wasm file doesn't have a names section. Usage: ``` yarn build-node-tools && \ node node-tools-dist/profiler-edit.js -i input.json.gz \ --symbolicate-wasm http://host/a.wasm=./a-unstripped.wasm \ --symbolicate-wasm http://host/b.wasm=./b-unstripped.wasm \ -o out.json.gz ```

Changes: [fatadel] Remove unused dependencies from package.json (#6010) [Nazım Can Altınova] Make profiler-cli work in sandboxed environments (#6003) [Markus Stange] Make profiler-edit run profile compacting before writing out the file (#6015) [Markus Stange] Migrate from prettier to oxfmt (#5986) [Markus Stange] Add a --symbolicate-wasm arg to profiler-edit. (#6008) [Markus Stange] Build and upload the cli artifact in PRs (#6020) [Markus Stange] Use @streamparser/json if the input is too large to fit in a V8 string (#6016) [Nazım Can Altınova] Print also the status output right after cli `load` command (#6019) [Nicolas Chevobbe] Update devtools-reps to 0.27.7 (#6030) [Nazım Can Altınova] Include `--search` option in `pq filter push` (#6026) [Nazım Can Altınova] Update all Yarn dependencies (2026-05-20) (#6033) [fatadel] Translate URL track-index state through profile sanitization (#6000) [Markus Stange] Make withSize use a wrapper element so that it can stop calling findDOMNode (#5988) [Markus Stange] Fix dhat importer (#6036) [Nazım Can Altınova] Annotate inlined frames in CLI call trees and stacks (#6041) [Nazım Can Altınova] Use proper types in cli tests instead of custom inline types (#6038) [Nazım Can Altınova] Fix text truncation for frames named after Object.prototype methods (#6044) [Nazım Can Altınova] Add missing key props to CodeErrorOverlay error list items (#6047) [depfu[bot]] ⬆️ Update oxfmt to version 0.51.0 (#6054) [Nazım Can Altınova] 🔃 Sync: l10n -> main (May 26, 2026) (#6058) [Nazım Can Altınova] Use URL-state symbol server for `profiler-cli function annotate` (#6051) [Nazım Can Altınova] Bump profiler-cli version to 0.2.0 (#6059) And special thanks to our localizers: fr: YD sr: Марко Костић (Marko Kostić) tr: Ali Demirtaş zh-CN: Olvcpr423 zh-CN: wxie

mstange force-pushed the symbolicate-wasm-script branch from 52ba22e to ab1e4b6Compare May 7, 2026 19:31

mstange force-pushed the symbolicate-wasm-script branch 3 times, most recently from 0202adf to be15b28Compare May 7, 2026 19:49

mstange requested a review from canova May 7, 2026 19:49

mstange force-pushed the symbolicate-wasm-script branch 2 times, most recently from a70577c to a8608c4Compare May 7, 2026 21:54

canova approved these changes May 11, 2026
View reviewed changes

mstange force-pushed the symbolicate-wasm-script branch from a8608c4 to f845b5bCompare May 11, 2026 21:48

mstange added 2 commits May 11, 2026 17:52

Allow downloading profiler-node-tools zip files from PRs.
b4054d5

mstange force-pushed the symbolicate-wasm-script branch from f845b5b to b4054d5Compare May 11, 2026 21:53

mstange enabled auto-merge May 11, 2026 21:53

mstange merged commit d03a0cf into firefox-devtools:mainMay 11, 2026
21 checks passed

canova mentioned this pull request May 26, 2026
Deploy May 26, 2026 #6061
Merged

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Add a --symbolicate-wasm arg to profiler-edit. - #6008

Add a --symbolicate-wasm arg to profiler-edit.#6008
mstange merged 2 commits into
firefox-devtools:mainfrom
mstange:symbolicate-wasm-script

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mstange commented May 7, 2026•
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