[ext-code-space] Allocate external code space near embedded builtins

Bug: v8:11880
Change-Id: I9a936c293e261142111e235c041e3526680d9629
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3240828Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77519}

src/common/globals.h

@@ -104,7 +104,8 @@ STATIC_ASSERT(V8_DEFAULT_STACK_SIZE_KB* KB +
                   kStackLimitSlackForDeoptimizationInBytes <=
               MB);
 
-#if defined(V8_SHORT_BUILTIN_CALLS) && !defined(V8_COMPRESS_POINTERS)
+#if defined(V8_SHORT_BUILTIN_CALLS) && \
+    (!defined(V8_COMPRESS_POINTERS) || defined(V8_EXTERNAL_CODE_SPACE))
 #define V8_ENABLE_NEAR_CODE_RANGE_BOOL true
 #else
 #define V8_ENABLE_NEAR_CODE_RANGE_BOOL false

src/execution/isolate.cc

@@ -364,10 +364,13 @@ uint32_t Isolate::CurrentEmbeddedBlobDataSize() {
 }
 
 base::AddressRegion Isolate::GetShortBuiltinsCallRegion() {
-  DCHECK(V8_ENABLE_NEAR_CODE_RANGE_BOOL);
   DCHECK_LT(CurrentEmbeddedBlobCodeSize(), kShortBuiltinCallsBoundary);
   Address embedded_blob_code_start =
       reinterpret_cast<Address>(CurrentEmbeddedBlobCode());
+  if (embedded_blob_code_start == kNullAddress) {
+    // Return empty region if there's no embedded blob.
+    return base::AddressRegion(kNullAddress, 0);
+  }
   Address embedded_blob_code_end =
       embedded_blob_code_start + CurrentEmbeddedBlobCodeSize();
   Address region_start =

src/execution/isolate.h

@@ -1627,6 +1627,8 @@ class V8_EXPORT_PRIVATE Isolate final : private HiddenFactory {
     return V8_SHORT_BUILTIN_CALLS_BOOL && is_short_builtin_calls_enabled_;
   }
 
+  // Returns a region from which it's possible to make short calls/jumps to
+  // embedded builtins or empty region if there's no embedded blob.
   static base::AddressRegion GetShortBuiltinsCallRegion();
 
   void set_array_buffer_allocator(v8::ArrayBuffer::Allocator* allocator) {

src/heap/code-range.cc

@@ -35,16 +35,19 @@ Address CodeRangeAddressHint::GetAddressHint(size_t code_range_size,
                                              size_t alignment) {
   base::MutexGuard guard(&mutex_);
 
+  // Try to allocate code range in the preferred region where we can use
+  // short instructions for calling/jumping to embedded builtins.
+  base::AddressRegion preferred_region = Isolate::GetShortBuiltinsCallRegion();
+
   Address result = 0;
   auto it = recently_freed_.find(code_range_size);
   // No recently freed region has been found, try to provide a hint for placing
-  // a code region
+  // a code region.
   if (it == recently_freed_.end() || it->second.empty()) {
-    if (V8_ENABLE_NEAR_CODE_RANGE_BOOL) {
-      base::AddressRegion region = Isolate::GetShortBuiltinsCallRegion();
-      DCHECK_LT(region.begin(), region.end());
+    if (V8_ENABLE_NEAR_CODE_RANGE_BOOL && !preferred_region.is_empty()) {
       auto memory_ranges = base::OS::GetFreeMemoryRangesWithin(
-          region.begin(), region.end(), code_range_size, alignment);
+          preferred_region.begin(), preferred_region.end(), code_range_size,
+          alignment);
       if (!memory_ranges.empty()) {
         result = memory_ranges.front().start;
         CHECK(IsAligned(result, alignment));
@@ -56,13 +59,12 @@ Address CodeRangeAddressHint::GetAddressHint(size_t code_range_size,
   }
 
   // Try to reuse near code range first.
-  if (V8_ENABLE_NEAR_CODE_RANGE_BOOL) {
-    base::AddressRegion region = Isolate::GetShortBuiltinsCallRegion();
+  if (V8_ENABLE_NEAR_CODE_RANGE_BOOL && !preferred_region.is_empty()) {
     auto freed_regions_for_size = it->second;
     for (auto it_freed = freed_regions_for_size.rbegin();
          it_freed != freed_regions_for_size.rend(); ++it_freed) {
       Address code_range_start = *it_freed;
-      if (region.contains(code_range_start, code_range_size)) {
+      if (preferred_region.contains(code_range_start, code_range_size)) {
         CHECK(IsAligned(code_range_start, alignment));
         freed_regions_for_size.erase((it_freed + 1).base());
         return code_range_start;