[wasm] Prefer source map over DWARF info if present

Some tools that transform Wasm today, already support encoding the
transforms and correctly updating locations in source maps, but not yet
in DWARF (although this is being worked on).

Until they catch up, it's best to consistently prefer source maps over
DWARF when both are present, and not just rely on order of sections as
accidentally done in the previous CL that introduced DWARF info.

Ref: crrev.com/c/v8/v8/+/1834341
Bug: chromium:1016772
Change-Id: I769311e2096ae0e4ca304bef0a0453c7e0776aae
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1888930
Commit-Queue: Ingvar Stepanyan <rreverser@google.com>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64647}

src/wasm/module-decoder.cc

@@ -460,7 +460,10 @@ class ModuleDecoderImpl : public Decoder {
         DecodeSourceMappingURLSection();
         break;
       case kDebugInfoSectionCode:
+        // If there is an explicit source map, prefer it over DWARF info.
+        if (!has_seen_unordered_section(kSourceMappingURLSectionCode)) {
           module_->source_map_url.assign("wasm://dwarf");
+        }
         consume_bytes(static_cast<uint32_t>(end_ - start_), ".debug_info");
         break;
       case kCompilationHintsSectionCode:

test/inspector/debugger/wasm-scripts-expected.txt

@@ -4,8 +4,14 @@ Session #1: Script #0 parsed. URL: wasm://wasm/wasm-f608ae1e/wasm-f608ae1e-0. So
 Session #1: Script #1 parsed. URL: wasm://wasm/wasm-f608ae1e/wasm-f608ae1e-1. Source map URL:
 Session #2: Script #0 parsed. URL: wasm://wasm/wasm-f608ae1e/wasm-f608ae1e-0. Source map URL:
 Session #2: Script #1 parsed. URL: wasm://wasm/wasm-f608ae1e/wasm-f608ae1e-1. Source map URL:
-Session #1: Script #2 parsed. URL: wasm://wasm/wasm-ef526f5e. Source map URL: wasm://dwarf
-Session #2: Script #2 parsed. URL: wasm://wasm/wasm-ef526f5e. Source map URL: wasm://dwarf
+Session #1: Script #2 parsed. URL: wasm://wasm/wasm-74f86b7e. Source map URL: wasm://dwarf
+Session #2: Script #2 parsed. URL: wasm://wasm/wasm-74f86b7e. Source map URL: wasm://dwarf
+Session #1: Script #3 parsed. URL: wasm://wasm/wasm-3754e3fe. Source map URL: abc
+Session #2: Script #3 parsed. URL: wasm://wasm/wasm-3754e3fe. Source map URL: abc
+Session #1: Script #4 parsed. URL: wasm://wasm/wasm-2bd2e40e. Source map URL: abc
+Session #2: Script #4 parsed. URL: wasm://wasm/wasm-2bd2e40e. Source map URL: abc
+Session #1: Script #5 parsed. URL: wasm://wasm/wasm-f568e726. Source map URL: abc
+Session #2: Script #5 parsed. URL: wasm://wasm/wasm-f568e726. Source map URL: abc
 Session #1: Source for wasm://wasm/wasm-f608ae1e/wasm-f608ae1e-0:
 func $nopFunction
   nop
@@ -32,11 +38,35 @@ func $main
   end
 end
 
-Session #1: Source for wasm://wasm/wasm-ef526f5e:
-Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 0c 0b 2e 64 65 62 75 67 5f 69 6e 66 6f 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
+Session #1: Source for wasm://wasm/wasm-74f86b7e:
+Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 11 0b 2e 64 65 62 75 67 5f 69 6e 66 6f 01 02 03 04 05 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
 Imports: []
 Exports: [main: function]
-Session #2: Source for wasm://wasm/wasm-ef526f5e:
-Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 0c 0b 2e 64 65 62 75 67 5f 69 6e 66 6f 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
+Session #2: Source for wasm://wasm/wasm-74f86b7e:
+Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 11 0b 2e 64 65 62 75 67 5f 69 6e 66 6f 01 02 03 04 05 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
+Imports: []
+Exports: [main: function]
+Session #1: Source for wasm://wasm/wasm-3754e3fe:
+Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 15 10 73 6f 75 72 63 65 4d 61 70 70 69 6e 67 55 52 4c 03 61 62 63 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
+Imports: []
+Exports: [main: function]
+Session #2: Source for wasm://wasm/wasm-3754e3fe:
+Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 15 10 73 6f 75 72 63 65 4d 61 70 70 69 6e 67 55 52 4c 03 61 62 63 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
+Imports: []
+Exports: [main: function]
+Session #1: Source for wasm://wasm/wasm-2bd2e40e:
+Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 11 0b 2e 64 65 62 75 67 5f 69 6e 66 6f 01 02 03 04 05 00 15 10 73 6f 75 72 63 65 4d 61 70 70 69 6e 67 55 52 4c 03 61 62 63 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
+Imports: []
+Exports: [main: function]
+Session #2: Source for wasm://wasm/wasm-2bd2e40e:
+Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 11 0b 2e 64 65 62 75 67 5f 69 6e 66 6f 01 02 03 04 05 00 15 10 73 6f 75 72 63 65 4d 61 70 70 69 6e 67 55 52 4c 03 61 62 63 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
+Imports: []
+Exports: [main: function]
+Session #1: Source for wasm://wasm/wasm-f568e726:
+Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 15 10 73 6f 75 72 63 65 4d 61 70 70 69 6e 67 55 52 4c 03 61 62 63 00 11 0b 2e 64 65 62 75 67 5f 69 6e 66 6f 01 02 03 04 05 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
+Imports: []
+Exports: [main: function]
+Session #2: Source for wasm://wasm/wasm-f568e726:
+Raw: 00 61 73 6d 01 00 00 00 01 07 02 60 00 00 60 00 00 03 03 02 00 01 07 08 01 04 6d 61 69 6e 00 01 0a 0e 02 03 00 01 0b 08 00 02 40 41 02 1a 0b 0b 00 15 10 73 6f 75 72 63 65 4d 61 70 70 69 6e 67 55 52 4c 03 61 62 63 00 11 0b 2e 64 65 62 75 67 5f 69 6e 66 6f 01 02 03 04 05 00 1b 04 6e 61 6d 65 01 14 02 00 0b 6e 6f 70 46 75 6e 63 74 69 6f 6e 01 04 6d 61 69 6e
 Imports: []
 Exports: [main: function]

test/inspector/debugger/wasm-scripts.js

@@ -17,16 +17,18 @@ let sessions = [
 
 utils.load('test/mjsunit/wasm/wasm-module-builder.js');
 
-// Add two empty functions. Both should be registered as individual scripts at
-// module creation time.
-var builder = new WasmModuleBuilder();
-builder.addFunction('nopFunction', kSig_v_v).addBody([kExprNop]);
-builder.addFunction('main', kSig_v_v)
+// Create module with given custom sections.
+function createModule(...customSections) {
+  var builder = new WasmModuleBuilder();
+  builder.addFunction('nopFunction', kSig_v_v).addBody([kExprNop]);
+  builder.addFunction('main', kSig_v_v)
       .addBody([kExprBlock, kWasmStmt, kExprI32Const, 2, kExprDrop, kExprEnd])
       .exportAs('main');
-var module_bytes = builder.toArray();
-builder.addCustomSection('.debug_info', []);
-var module_bytes_with_dwarf = builder.toArray();
+  for (var { name, value } of customSections) {
+    builder.addCustomSection(name, value);
+  }
+  return builder.toArray();
+}
 
 function testFunction(bytes) {
   // Compilation triggers registration of wasm scripts.
@@ -34,16 +36,37 @@ function testFunction(bytes) {
 }
 
 contextGroup.addScript(testFunction.toString(), 0, 0, 'v8://test/testFunction');
-contextGroup.addScript('var module_bytes = ' + JSON.stringify(module_bytes));
-contextGroup.addScript('var module_bytes_with_dwarf = ' + JSON.stringify(module_bytes_with_dwarf));
 
 InspectorTest.log(
     'Check that each inspector gets two wasm scripts at module creation time.');
 
+// Sample .debug_info section.
+// Content doesn't matter, as we don't try to parse it in V8,
+// but should be non-empty to check that we're skipping it correctly.
+const dwarfSection = { name: '.debug_info', value: [1, 2, 3, 4, 5] };
+
+// Sample sourceMappingURL section set to "abc".
+const sourceMapSection = { name: 'sourceMappingURL', value: [3, 97, 98, 99] };
+
 sessions[0].Protocol.Runtime
     .evaluate({
-      'expression': '//# sourceURL=v8://test/runTestRunction\n' +
-          'testFunction(module_bytes); testFunction(module_bytes_with_dwarf);'
+      'expression': `//# sourceURL=v8://test/runTestRunction
+
+      // no debug info
+      testFunction([${createModule()}]);
+
+      // DWARF
+      testFunction([${createModule(dwarfSection)}]);
+
+      // Source map
+      testFunction([${createModule(sourceMapSection)}]);
+
+      // DWARF + source map
+      testFunction([${createModule(dwarfSection, sourceMapSection)}]);
+
+      // Source map + DWARF (different order)
+      testFunction([${createModule(sourceMapSection, dwarfSection)}]);
+      `
     })
     .then(() => (
       // At this point all scripts were parsed.
@@ -89,7 +112,7 @@ function trackScripts(debuggerParams) {
   async function loadScript({url, scriptId, sourceMapURL}) {
     InspectorTest.log(`Session #${sessionId}: Script #${scripts.length} parsed. URL: ${url}. Source map URL: ${sourceMapURL}`);
     let scriptSource;
-    if (sourceMapURL === "wasm://dwarf") {
+    if (sourceMapURL) {
       let {result: {bytecode}} = await Protocol.Debugger.getWasmBytecode({scriptId});
       // Binary value is represented as base64 in JSON, decode it.
       bytecode = decodeBase64(bytecode);