WIP: wasm oob trap handling experiments

src/wasm/wasm-js.cc

Index: src/wasm/wasm-js.cc
diff --git a/src/wasm/wasm-js.cc b/src/wasm/wasm-js.cc
index 853a77f3ccaedfdb094c22b462885392812112a3..372df4056dc1304d312633fb819c445b16107452 100644
--- a/src/wasm/wasm-js.cc
+++ b/src/wasm/wasm-js.cc
@@ -2,6 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <setjmp.h>
+#include <signal.h>
+#include <stdio.h>
+
+#include <iostream>
+
 #include "src/api-natives.h"
 #include "src/api.h"
 #include "src/asmjs/asm-js.h"
@@ -9,6 +15,8 @@
 #include "src/asmjs/asm-wasm-builder.h"
 #include "src/assert-scope.h"
 #include "src/ast/ast.h"
+#include "src/ast/scopes.h"
+#include "src/code-stubs.h"
 #include "src/execution.h"
 #include "src/factory.h"
 #include "src/handles.h"
@@ -339,6 +347,64 @@ static Handle<JSFunction> InstallFunc(Isolate* isolate, Handle<JSObject> object,
   return function;
 }
 
+static void TrapHandler(int signum, siginfo_t* info, void* arg) {
+  ucontext_t* uc = reinterpret_cast<ucontext_t*>(arg);
+
+  fprintf(stderr, "Return address was %p\n",
+          reinterpret_cast<void*>(uc->uc_mcontext.gregs[REG_RIP]));
+
+  auto fault_addr = uc->uc_mcontext.gregs[REG_RIP];
+
+  Code* code = nullptr;
+
+  // Check if this is a wasm fault.
+  if (nullptr == wasm::gTrapHandlers) {
+    std::cerr << "No handler data" << std::endl;
+  }
+  for (auto* handler_data = wasm::gTrapHandlers; handler_data;
+       handler_data = handler_data->next) {
+    std::cerr << "Testing fault against "
+              << reinterpret_cast<void*>(
+                     handler_data->code->instruction_start())
+              << " - "
+              << reinterpret_cast<void*>(handler_data->code->instruction_end())
+              << std::endl;
+
+    if (handler_data->code->contains(reinterpret_cast<byte*>(fault_addr))) {
+      code = handler_data->code;
+      break;
+    }
+  }
+
+  if (nullptr != code) {
+    for (RelocIterator it(code, -1); !it.done(); it.next()) {
+      auto* rinfo = it.rinfo();
+      // rinfo->Print(isolate, std::cerr);
+      fprintf(stderr, "  = %p\n", reinterpret_cast<void*>(rinfo->data()));
+
+      if (reinterpret_cast<intptr_t>(rinfo->pc()) == fault_addr) {
+        auto jmp_offset = rinfo->data();
+        auto landing_addr = fault_addr + jmp_offset;
+
+        uc->uc_mcontext.gregs[REG_RIP] = reinterpret_cast<greg_t>(landing_addr);
+        return;
+      }
+    }
+
+    // So this is a weird thing. If we got here, we decided the fault
+    // was in WASM code, but we couldn't find an entry in the
+    // RelocInfo for its address. This is bad.
+    __builtin_trap();
+  }
+
+  // If we get here, it's not a wasm fault, so we go to the next handler.
+  //
+  // TODO(eholk): we simulate going to the next handler by trapping
+  // here instead. We need to actually save the old handler and then
+  // call it.
+  __builtin_trap();
+}
+
 void WasmJs::Install(Isolate* isolate, Handle<JSGlobalObject> global) {
   if (!FLAG_expose_wasm && !FLAG_validate_asm) {
     return;
@@ -411,6 +477,24 @@ void WasmJs::Install(Isolate* isolate, Handle<JSGlobalObject> global) {
 
   context->set_wasm_module_constructor(*module_constructor);
   context->set_wasm_instance_constructor(*instance_constructor);
+
+  {
+    // Add the Wasm.experimentalVersion property.
+    Handle<String> name = v8_str(isolate, "experimentalVersion");
+    PropertyAttributes attributes =
+        static_cast<PropertyAttributes>(DONT_DELETE | READ_ONLY);
+    Handle<Smi> value = Handle<Smi>(Smi::FromInt(wasm::kWasmVersion), isolate);
+    JSObject::AddProperty(wasm_object, name, value, attributes);
+  }
+
+  {
+    struct sigaction action;
+    action.sa_sigaction = TrapHandler;
+    action.sa_flags = SA_SIGINFO;
+    sigemptyset(&action.sa_mask);
+    // TODO(eholk): check the return value
+    sigaction(SIGSEGV, &action, NULL);
+  }
 }
 
 void WasmJs::InstallWasmFunctionMap(Isolate* isolate, Handle<Context> context) {