Imported and defined globals share an index space, but previously the decoder...

Imported and defined globals share an index space, but previously the decoder clobbered the imported global indices with the defined globals.

BUG=none

Review-Url: https://codereview.chromium.org/2410953003
Cr-Commit-Position: refs/heads/master@{#40230}

src/wasm/module-decoder.cc

@@ -406,7 +406,13 @@ class ModuleDecoder : public Decoder {
     // ===== Global section ==================================================
     if (section_iter.section_code() == kGlobalSectionCode) {
       uint32_t globals_count = consume_u32v("globals count");
-      module->globals.reserve(SafeReserve(globals_count));
+      uint32_t imported_globals = static_cast<uint32_t>(module->globals.size());
+      if (!IsWithinLimit(std::numeric_limits<int32_t>::max(), globals_count,
+                         imported_globals)) {
+        error(pos, pos, "too many imported+defined globals: %u + %u",
+              imported_globals, globals_count);
+      }
+      module->globals.reserve(SafeReserve(imported_globals + globals_count));
       for (uint32_t i = 0; ok() && i < globals_count; ++i) {
         TRACE("DecodeGlobal[%d] module+%d\n", i,
               static_cast<int>(pc_ - start_));
@@ -414,7 +420,7 @@ class ModuleDecoder : public Decoder {
         module->globals.push_back(
             {kAstStmt, false, WasmInitExpr(), 0, false, false});
         WasmGlobal* global = &module->globals.back();
-        DecodeGlobalInModule(module, i, global);
+        DecodeGlobalInModule(module, i + imported_globals, global);
       }
       section_iter.advance();
     }
@@ -675,7 +681,10 @@ class ModuleDecoder : public Decoder {
       case WasmInitExpr::kGlobalIndex: {
         uint32_t other_index = global->init.val.global_index;
         if (other_index >= index) {
-          error("invalid global index in init expression");
+          error(pos, pos,
+                "invalid global index in init expression, "
+                "index %u, other_index %u",
+                index, other_index);
         } else if (module->globals[other_index].type != global->type) {
           error(pos, pos,
                 "type mismatch in global initialization "

src/wasm/wasm-module.cc

@@ -1544,6 +1544,9 @@ class WasmInstanceBuilder {
 
       uint32_t source_size =
           static_cast<uint32_t>(segment->get_int(kSourceSize));
+      // TODO(titzer): These should be runtime errors and not CHECKs if
+      // dest_addr is global (and therefore initialized at linktime to an
+      // possibly-invalid value).
       CHECK_LT(dest_addr, mem_size);
       CHECK_LE(source_size, mem_size);
       CHECK_LE(dest_addr, mem_size - source_size);

test/mjsunit/wasm/globals.js

@@ -64,3 +64,25 @@ function TestImportedExported(type, val, expected) {
 TestImportedExported(kAstI32, 415.5, 415);
 TestImportedExported(kAstF32, -979.34343, Math.fround(-979.34343));
 TestImportedExported(kAstF64, 81347.66666, 81347.66666);
+
+function TestGlobalIndexSpace(type, val) {
+  print("TestGlobalIndexSpace(" + val + ") = " + val);
+  var builder = new WasmModuleBuilder();
+  var im = builder.addImportedGlobal("foo", undefined, type);
+  assertEquals(0, im);
+  var def = builder.addGlobal(type, false);
+  assertEquals(1, def.index);
+  def.init_index = im;
+
+  var sig = makeSig([], [type]);
+  builder.addFunction("main", sig)
+    .addBody([kExprGetGlobal, def.index])
+    .exportAs("main");
+
+  var instance = builder.instantiate({foo: val});
+  assertEquals(val, instance.exports.main());
+}
+
+TestGlobalIndexSpace(kAstI32, 123);
+TestGlobalIndexSpace(kAstF32, 54321.125);
+TestGlobalIndexSpace(kAstF64, 12345.678);