[ext-code-space] Fix external code space on Windows

... and introduce CodeRange::GetWritableReservedAreaSize() as a
bottleneck for calculating a size of the writable area used for unwind
information.

Bug: v8:11880
Change-Id: Ifa2a3f74ce994cffb6bb8bef12ab17b69dabd706
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3244409
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77555}

BUILD.gn

@@ -507,6 +507,9 @@ assert(!v8_enable_map_packing || !v8_enable_pointer_compression,
 assert(!v8_enable_map_packing || v8_current_cpu == "x64",
        "Map packing is only supported on x64")
 
+assert(!v8_enable_external_code_space || v8_enable_pointer_compression,
+       "External code space feature requires pointer compression")
+
 assert(!v8_enable_heap_sandbox || v8_enable_pointer_compression,
        "V8 Heap Sandbox requires pointer compression")
 

src/heap/code-range.cc

@@ -86,6 +86,11 @@ void CodeRangeAddressHint::NotifyFreedCodeRange(Address code_range_start,
 
 CodeRange::~CodeRange() { Free(); }
 
+// static
+size_t CodeRange::GetWritableReservedAreaSize() {
+  return kReservedCodeRangePages * MemoryAllocator::GetCommitPageSize();
+}
+
 bool CodeRange::InitReservation(v8::PageAllocator* page_allocator,
                                 size_t requested) {
   DCHECK_NE(requested, 0);
@@ -96,8 +101,7 @@ bool CodeRange::InitReservation(v8::PageAllocator* page_allocator,
   if (requested <= kMinimumCodeRangeSize) {
     requested = kMinimumCodeRangeSize;
   }
-  const size_t reserved_area =
-      kReservedCodeRangePages * MemoryAllocator::GetCommitPageSize();
+  const size_t reserved_area = GetWritableReservedAreaSize();
   if (requested < (kMaximalCodeRangeSize - reserved_area)) {
     requested += RoundUp(reserved_area, MemoryChunk::kPageSize);
     // Fullfilling both reserved pages requirement and huge code area
@@ -113,14 +117,15 @@ bool CodeRange::InitReservation(v8::PageAllocator* page_allocator,
   // base_alignment should be kAnyBaseAlignment when V8_ENABLE_NEAR_CODE_RANGE
   // is enabled so that InitReservation would not break the alignment in
   // GetAddressHint().
+  const size_t allocate_page_size = page_allocator->AllocatePageSize();
   params.base_alignment =
       V8_EXTERNAL_CODE_SPACE_BOOL
           ? base::bits::RoundUpToPowerOfTwo(requested)
           : VirtualMemoryCage::ReservationParams::kAnyBaseAlignment;
-  params.base_bias_size = reserved_area;
+  params.base_bias_size = RoundUp(reserved_area, allocate_page_size);
   params.page_size = MemoryChunk::kPageSize;
-  params.requested_start_hint = GetCodeRangeAddressHint()->GetAddressHint(
-      requested, page_allocator->AllocatePageSize());
+  params.requested_start_hint =
+      GetCodeRangeAddressHint()->GetAddressHint(requested, allocate_page_size);
 
   if (!VirtualMemoryCage::InitReservation(params)) return false;
 

src/heap/code-range.h

@@ -68,7 +68,11 @@ class CodeRangeAddressHint {
 // 4) |base()| is CommitPageSize()-aligned
 class CodeRange final : public VirtualMemoryCage {
  public:
-  V8_EXPORT_PRIVATE ~CodeRange();
+  V8_EXPORT_PRIVATE ~CodeRange() override;
+
+  // Returns the size of the initial area of a code-range, which is marked
+  // writable and reserved to contain unwind information.
+  static size_t GetWritableReservedAreaSize();
 
   uint8_t* embedded_blob_code_copy() const {
     // remap_embedded_builtins_mutex_ is designed to protect write contention to

src/heap/heap.cc

@@ -3045,7 +3045,7 @@ int Heap::GetFillToAlign(Address address, AllocationAlignment alignment) {
 }
 
 size_t Heap::GetCodeRangeReservedAreaSize() {
-  return kReservedCodeRangePages * MemoryAllocator::GetCommitPageSize();
+  return CodeRange::GetWritableReservedAreaSize();
 }
 
 HeapObject Heap::PrecedeWithFiller(HeapObject object, int filler_size) {