[ubsan] Turn on full -fsanitize=undefined

The build config inherited from Chromium only enables a subset
of the checks that UBSan supports. We want them all, so this
patch overrides what "is_ubsan" means for V8.

Bug: v8:3770
Change-Id: I1d0a7d994279272f13ff1d4ac9ed235fcbfc0951
Reviewed-on: https://chromium-review.googlesource.com/c/1443502
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59222}

BUILD.gn

@@ -656,6 +656,11 @@ config("toolchain") {
       "-Wno-return-type",
     ]
   }
+
+  # Chromium uses a hand-picked subset of UBSan coverage. We want everything.
+  if (is_ubsan) {
+    cflags += [ "-fsanitize=undefined" ]
+  }
 }
 
 # Configs for code coverage with gcov. Separate configs for cflags and ldflags

test/common/wasm/wasm-module-runner.cc

@@ -72,7 +72,10 @@ bool InterpretWasmModuleForTesting(Isolate* isolate,
   size_t param_count = signature->parameter_count();
   std::unique_ptr<WasmValue[]> arguments(new WasmValue[param_count]);
 
-  memcpy(arguments.get(), args, std::min(param_count, argc));
+  size_t arg_count = std::min(param_count, argc);
+  if (arg_count > 0) {
+    memcpy(arguments.get(), args, arg_count);
+  }
 
   // Fill the parameters up with default values.
   for (size_t i = argc; i < param_count; ++i) {