[traphandler] Fix simulator test for Mac

On Mac we handle SIGBUS, not SIGSEGV, so the test should access a valid
but inaccessible pointer to trigger the right signal.

R=jkummerow@chromium.org

Bug: v8:11955, v8:12249
Change-Id: I25b93ce40bccc24ef5e84694a7c03c465eb4c51e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3168344
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76984}

test/unittests/wasm/trap-handler-simulator-unittest.cc

@@ -4,6 +4,8 @@
 
 #include "src/trap-handler/trap-handler-simulator.h"
 
+#include <cstdint>
+
 #include "include/v8-initialization.h"
 #include "src/codegen/macro-assembler-inl.h"
 #include "src/execution/simulator.h"
@@ -23,6 +25,14 @@ constexpr uintptr_t kFakePc = 11;
 
 class SimulatorTrapHandlerTest : public TestWithIsolate {
  public:
+  ~SimulatorTrapHandlerTest() {
+    if (inaccessible_memory_) {
+      auto* page_allocator = GetPlatformPageAllocator();
+      CHECK(page_allocator->FreePages(inaccessible_memory_,
+                                      page_allocator->AllocatePageSize()));
+    }
+  }
+
   void SetThreadInWasm() {
     EXPECT_EQ(0, *thread_in_wasm);
     *thread_in_wasm = 1;
@@ -33,7 +43,23 @@ class SimulatorTrapHandlerTest : public TestWithIsolate {
     *thread_in_wasm = 0;
   }
 
+  uintptr_t InaccessibleMemoryPtr() {
+    if (!inaccessible_memory_) {
+      auto* page_allocator = GetPlatformPageAllocator();
+      size_t page_size = page_allocator->AllocatePageSize();
+      inaccessible_memory_ =
+          reinterpret_cast<uint8_t*>(page_allocator->AllocatePages(
+              nullptr, /* size */ page_size, /* align */ page_size,
+              PageAllocator::kNoAccess));
+      CHECK_NOT_NULL(inaccessible_memory_);
+    }
+    return reinterpret_cast<uintptr_t>(inaccessible_memory_);
+  }
+
   int* thread_in_wasm = trap_handler::GetThreadInWasmThreadLocalAddress();
+
+ private:
+  uint8_t* inaccessible_memory_ = nullptr;
 };
 
 TEST_F(SimulatorTrapHandlerTest, ProbeMemorySuccess) {
@@ -41,24 +67,26 @@ TEST_F(SimulatorTrapHandlerTest, ProbeMemorySuccess) {
   EXPECT_EQ(0u, ProbeMemory(reinterpret_cast<uintptr_t>(&x), kFakePc));
 }
 
-TEST_F(SimulatorTrapHandlerTest, ProbeMemoryFail) {
+TEST_F(SimulatorTrapHandlerTest, ProbeMemoryFailNullptr) {
   constexpr uintptr_t kNullAddress = 0;
   EXPECT_DEATH_IF_SUPPORTED(ProbeMemory(kNullAddress, kFakePc), "");
 }
 
+TEST_F(SimulatorTrapHandlerTest, ProbeMemoryFailInaccessible) {
+  EXPECT_DEATH_IF_SUPPORTED(ProbeMemory(InaccessibleMemoryPtr(), kFakePc), "");
+}
+
 TEST_F(SimulatorTrapHandlerTest, ProbeMemoryFailWhileInWasm) {
   // Test that we still crash if the trap handler is set up and the "thread in
   // wasm" flag is set, but the PC is not registered as a protected instruction.
   constexpr bool kUseDefaultHandler = true;
   CHECK(v8::V8::EnableWebAssemblyTrapHandler(kUseDefaultHandler));
 
-  constexpr uintptr_t kNullAddress = 0;
   SetThreadInWasm();
-  EXPECT_DEATH_IF_SUPPORTED(ProbeMemory(kNullAddress, kFakePc), "");
+  EXPECT_DEATH_IF_SUPPORTED(ProbeMemory(InaccessibleMemoryPtr(), kFakePc), "");
 }
 
 TEST_F(SimulatorTrapHandlerTest, ProbeMemoryWithTrapHandled) {
-  constexpr uintptr_t kNullAddress = 0;
   constexpr uintptr_t kFakeLandingPad = 19;
 
   constexpr bool kUseDefaultHandler = true;
@@ -69,7 +97,7 @@ TEST_F(SimulatorTrapHandlerTest, ProbeMemoryWithTrapHandled) {
       RegisterHandlerData(0, 128, 1, &fake_protected_instruction);
 
   SetThreadInWasm();
-  EXPECT_EQ(kFakeLandingPad, ProbeMemory(kNullAddress, kFakePc));
+  EXPECT_EQ(kFakeLandingPad, ProbeMemory(InaccessibleMemoryPtr(), kFakePc));
 
   // Reset everything.
   ResetThreadInWasm();
@@ -87,9 +115,9 @@ TEST_F(SimulatorTrapHandlerTest, ProbeMemoryWithLandingPad) {
   MacroAssembler masm(nullptr, AssemblerOptions{}, CodeObjectRequired::kNo,
                       buffer->CreateView());
   // Generate an illegal memory access.
-  masm.Mov(scratch, 0);
+  masm.Mov(scratch, InaccessibleMemoryPtr());
   uint32_t crash_offset = masm.pc_offset();
-  masm.Str(scratch, MemOperand(scratch, 0));  // nullptr access
+  masm.Str(scratch, MemOperand(scratch, 0));  // load from inaccessible memory.
   uint32_t recovery_offset = masm.pc_offset();
   // Return.
   masm.Ret();