mac/arm64: When cross-building the snapshot, use page size of the target ISA instead of the host.

Bug: chromium:1107945
Change-Id: I0f721ccaf06c7ddaf0213448c29f48f5c57ccc6e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2310575
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69000}

src/base/platform/platform-posix.cc

@@ -111,6 +111,13 @@ const int kMmapFd = VM_MAKE_TAG(255);
 const int kMmapFd = -1;
 #endif  // !V8_OS_MACOSX
 
+#if defined(__APPLE__) && V8_TARGET_ARCH_ARM64
+// During snapshot generation in cross builds, sysconf() runs on the Intel
+// host and returns host page size, while the snapshot needs to use the
+// target page size.
+constexpr int kAppleArmPageSize = 1 << 14;
+#endif
+
 const int kMmapFdOffset = 0;
 
 // TODO(v8:10026): Add the right permission flag to make executable pages
@@ -226,12 +233,20 @@ int OS::ActivationFrameAlignment() {
 
 // static
 size_t OS::AllocatePageSize() {
+#if defined(__APPLE__) && V8_TARGET_ARCH_ARM64
+  return kAppleArmPageSize;
+#else
   return static_cast<size_t>(sysconf(_SC_PAGESIZE));
+#endif
 }
 
 // static
 size_t OS::CommitPageSize() {
+#if defined(__APPLE__) && V8_TARGET_ARCH_ARM64
+  static size_t page_size = kAppleArmPageSize;
+#else
   static size_t page_size = getpagesize();
+#endif
   return page_size;
 }
 
@@ -250,12 +265,10 @@ void* OS::GetRandomMmapAddr() {
     MutexGuard guard(rng_mutex.Pointer());
     GetPlatformRandomNumberGenerator()->NextBytes(&raw_addr, sizeof(raw_addr));
   }
-#if defined(__APPLE__)
-#if V8_TARGET_ARCH_ARM64
+#if defined(__APPLE__) && V8_TARGET_ARCH_ARM64
   DCHECK_EQ(1 << 14, AllocatePageSize());
   raw_addr = RoundDown(raw_addr, 1 << 14);
 #endif
-#endif
 #if defined(V8_USE_ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
     defined(THREAD_SANITIZER) || defined(LEAK_SANITIZER)
   // If random hint addresses interfere with address ranges hard coded in
@@ -265,7 +278,7 @@ void* OS::GetRandomMmapAddr() {
   raw_addr &= 0x007fffff0000ULL;
   raw_addr += 0x7e8000000000ULL;
 #else
-#if V8_TARGET_ARCH_X64
+#if V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64
   // Currently available CPUs have 48 bits of virtual addressing.  Truncate
   // the hint address to 46 bits to give the kernel a fighting chance of
   // fulfilling our placement request.