[wasm] Simplify init by adding SetRawMemory() to WasmContext.

Bug: 
Change-Id: I1f4a9d06e91a0523e590a77f8073800d6f1994d6
Reviewed-on: https://chromium-review.googlesource.com/830393
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50140}

src/wasm/wasm-objects.cc

@@ -399,8 +399,8 @@ Handle<JSArrayBuffer> GrowMemoryBuffer(Isolate* isolate,
 void SetInstanceMemory(Isolate* isolate, Handle<WasmInstanceObject> instance,
                        Handle<JSArrayBuffer> buffer) {
   auto wasm_context = instance->wasm_context()->get();
-  wasm_context->mem_start = reinterpret_cast<byte*>(buffer->backing_store());
-  wasm_context->mem_size = buffer->byte_length()->Number();
+  wasm_context->SetRawMemory(reinterpret_cast<byte*>(buffer->backing_store()),
+                             buffer->byte_length()->Number());
 #if DEBUG
   // To flush out bugs earlier, in DEBUG mode, check that all pages of the
   // memory are accessible by reading and writing one byte on each page.
@@ -563,8 +563,7 @@ Handle<WasmInstanceObject> WasmInstanceObject::New(
       reinterpret_cast<WasmInstanceObject*>(*instance_object), isolate);
 
   auto wasm_context = Managed<WasmContext>::Allocate(isolate);
-  wasm_context->get()->mem_start = nullptr;
-  wasm_context->get()->mem_size = 0;
+  wasm_context->get()->SetRawMemory(nullptr, 0);
   wasm_context->get()->globals_start = nullptr;
   instance->set_wasm_context(*wasm_context);
 

src/wasm/wasm-objects.h

@@ -59,10 +59,18 @@ class WasmInstanceObject;
 // grow_memory). The address of the WasmContext is provided to the wasm entry
 // functions using a RelocatableIntPtrConstant, then the address is passed as
 // parameter to the other wasm functions.
+// Note that generated code can directly read from instances of this struct.
 struct WasmContext {
-  byte* mem_start;
-  uint32_t mem_size;
-  byte* globals_start;
+  byte* mem_start = nullptr;
+  uint32_t mem_size = 0;  // TODO(titzer): uintptr_t?
+  byte* globals_start = nullptr;
+
+  inline void SetRawMemory(void* mem_start, size_t mem_size) {
+    DCHECK_LE(mem_size,
+              wasm::kV8MaxWasmMemoryPages * wasm::kSpecMaxWasmMemoryPages);
+    this->mem_start = static_cast<byte*>(mem_start);
+    this->mem_size = static_cast<uint32_t>(mem_size);
+  }
 };
 
 // Representation of a WebAssembly.Module JavaScript-level object.

test/cctest/compiler/test-run-wasm-machops.cc

@@ -50,7 +50,8 @@ static void RunLoadStoreRelocation(MachineType rep) {
   CType new_buffer[kNumElems];
   byte* raw = reinterpret_cast<byte*>(buffer);
   byte* new_raw = reinterpret_cast<byte*>(new_buffer);
-  WasmContext wasm_context = {raw, sizeof(buffer), nullptr};
+  WasmContext wasm_context;
+  wasm_context.SetRawMemory(raw, sizeof(buffer));
   for (size_t i = 0; i < sizeof(buffer); i++) {
     raw[i] = static_cast<byte>((i + sizeof(CType)) ^ 0xAA);
     new_raw[i] = static_cast<byte>((i + sizeof(CType)) ^ 0xAA);
@@ -70,8 +71,7 @@ static void RunLoadStoreRelocation(MachineType rep) {
   CHECK(buffer[0] != buffer[1]);
   CHECK_EQ(OK, m.Call());
   CHECK(buffer[0] == buffer[1]);
-  wasm_context.mem_size = sizeof(new_buffer);
-  wasm_context.mem_start = new_raw;
+  wasm_context.SetRawMemory(new_raw, sizeof(new_buffer));
   CHECK(new_buffer[0] != new_buffer[1]);
   CHECK_EQ(OK, m.Call());
   CHECK(new_buffer[0] == new_buffer[1]);
@@ -101,7 +101,7 @@ static void RunLoadStoreRelocationOffset(MachineType rep) {
     int32_t y = kNumElems - x - 1;
     // initialize the buffer with raw data.
     byte* raw = reinterpret_cast<byte*>(buffer);
-    wasm_context = {raw, sizeof(buffer), nullptr};
+    wasm_context.SetRawMemory(raw, sizeof(buffer));
     for (size_t i = 0; i < sizeof(buffer); i++) {
       raw[i] = static_cast<byte>((i + sizeof(buffer)) ^ 0xAA);
     }
@@ -130,8 +130,7 @@ static void RunLoadStoreRelocationOffset(MachineType rep) {
       new_raw[i] = static_cast<byte>((i + sizeof(buffer)) ^ 0xAA);
     }
 
-    wasm_context.mem_size = sizeof(new_buffer);
-    wasm_context.mem_start = new_raw;
+    wasm_context.SetRawMemory(new_raw, sizeof(new_buffer));
 
     CHECK(new_buffer[x] != new_buffer[y]);
     CHECK_EQ(OK, m.Call());
@@ -154,7 +153,8 @@ TEST(RunLoadStoreRelocationOffset) {
 TEST(Uint32LessThanMemoryRelocation) {
   RawMachineAssemblerTester<uint32_t> m;
   RawMachineLabel within_bounds, out_of_bounds;
-  WasmContext wasm_context = {reinterpret_cast<Address>(1234), 0x200, nullptr};
+  WasmContext wasm_context;
+  wasm_context.SetRawMemory(reinterpret_cast<void*>(1234), 0x200);
   Node* index = m.Int32Constant(0x200);
   Node* wasm_context_node =
       m.RelocatableIntPtrConstant(reinterpret_cast<uintptr_t>(&wasm_context),
@@ -169,7 +169,7 @@ TEST(Uint32LessThanMemoryRelocation) {
   m.Return(m.Int32Constant(0xDEADBEEF));
   // Check that index is out of bounds with current size
   CHECK_EQ(0xDEADBEEF, m.Call());
-  wasm_context.mem_size = 0x400;
+  wasm_context.SetRawMemory(wasm_context.mem_start, 0x400);
   // Check that after limit is increased, index is within bounds.
   CHECK_EQ(0xACEDu, m.Call());
 }

test/cctest/wasm/test-run-wasm-relocation.cc

@@ -36,8 +36,8 @@ WASM_COMPILED_EXEC_TEST(RunPatchWasmContext) {
       reinterpret_cast<Address>(old_wasm_context);
 
   uint32_t new_global_data[3] = {0, 0, 0};
-  WasmContext new_wasm_context = {0, 0,
-                                  reinterpret_cast<byte*>(new_global_data)};
+  WasmContext new_wasm_context;
+  new_wasm_context.globals_start = reinterpret_cast<byte*>(new_global_data);
 
   {
     // TODO(6792): No longer needed once WebAssembly code is off heap.

test/cctest/wasm/wasm-run-utils.cc

@@ -61,8 +61,7 @@ byte* TestingModuleBuilder::AddMemory(uint32_t size) {
   // TODO(wasm): Delete the following two lines when test-run-wasm will use a
   // multiple of kPageSize as memory size. At the moment, the effect of these
   // two lines is used to shrink the memory for testing purposes.
-  instance_object_->wasm_context()->get()->mem_start = mem_start_;
-  instance_object_->wasm_context()->get()->mem_size = mem_size_;
+  instance_object_->wasm_context()->get()->SetRawMemory(mem_start_, mem_size_);
   return mem_start_;
 }