illumos pointers are VA48, can allocate from the top of the 64-bit range as well.

Author: danmcd

deps/v8/src/codegen/code-stub-assembler.cc

@@ -1941,7 +1941,16 @@ TNode<Code> CodeStubAssembler::LoadCodeObjectFromJSDispatchTable(
   // The LSB is used as marking bit by the js dispatch table, so here we have
   // to set it using a bitwise OR as it may or may not be set.
   value = UncheckedCast<UintPtrT>(WordOr(
+#if defined(__illumos__) && defined(V8_HOST_ARCH_64_BIT)
+  // Pointers in illumos span both the low 2^47 range and the high 2^47 range
+  // as well. Checking the high bit being set in illumos means all higher bits
+  // need to be set to 1 after shifting right.
+  // Try WordSar() so any high-bit check wouldn't be necessary.
+      WordSar(UncheckedCast<IntPtrT>(value),
+	IntPtrConstant(JSDispatchEntry::kObjectPointerShift)),
+#else
       WordShr(value, UintPtrConstant(JSDispatchEntry::kObjectPointerShift)),
+#endif /* __illumos__ */
       UintPtrConstant(kHeapObjectTag)));
   return CAST(BitcastWordToTagged(value));
 }

deps/v8/src/sandbox/js-dispatch-table-inl.h

@@ -23,7 +23,9 @@ void JSDispatchEntry::MakeJSDispatchEntry(Address object, Address entrypoint,
                                           uint16_t parameter_count,
                                           bool mark_as_alive) {
   DCHECK_EQ(object & kHeapObjectTag, 0);
+#if !defined(__illumos__) || !defined(V8_TARGET_ARCH_64_BIT)
   DCHECK_EQ((object << kObjectPointerShift) >> kObjectPointerShift, object);
+#endif /* __illumos__ */
 
   Address payload =
       (object << kObjectPointerShift) | (parameter_count & kParameterCountMask);
@@ -49,7 +51,14 @@ Address JSDispatchEntry::GetCodePointer() const {
   // and so may be 0 or 1 here. As the return value is a tagged pointer, the
   // bit must be 1 when returned, so we need to set it here.
   Address payload = encoded_word_.load(std::memory_order_relaxed);
+#if defined(__illumos__) && defined(V8_TARGET_ARCH_64_BIT)
+  // Unsigned types won't sign-extend on shift-right, but we need to do
+  // this with illumos VA48 addressing.
+  return (Address)((intptr_t)payload >> (int)kObjectPointerShift) |
+    kHeapObjectTag;
+#else
   return (payload >> kObjectPointerShift) | kHeapObjectTag;
+#endif /* __illumos__ */
 }
 
 Tagged<Code> JSDispatchEntry::GetCode() const {
@@ -205,7 +214,12 @@ void JSDispatchEntry::MakeFreelistEntry(uint32_t next_entry_index) {
 bool JSDispatchEntry::IsFreelistEntry() const {
 #ifdef V8_TARGET_ARCH_64_BIT
   auto entrypoint = entrypoint_.load(std::memory_order_relaxed);
+#ifdef __illumos__
+  // See the illumos definition of kFreeEntryTag for why we have to do this.
+  return (entrypoint & 0xffff000000000000ull) == kFreeEntryTag;
+#else
   return (entrypoint & kFreeEntryTag) == kFreeEntryTag;
+#endif /* __illumos__ */
 #else
   return next_free_entry_.load(std::memory_order_relaxed) != 0;
 #endif

deps/v8/src/sandbox/js-dispatch-table.h

@@ -78,7 +78,22 @@ struct JSDispatchEntry {
 #if defined(V8_TARGET_ARCH_64_BIT)
   // Freelist entries contain the index of the next free entry in their lower 32
   // bits and are tagged with this tag.
+#ifdef __illumos__
+  // In illumos 64-bit apps, pointers are allocated both the bottom 2^47 range
+  // AND the top 2^47 range in the 64-bit space. Instead of 47 bits of VA space
+  // we have 48 bits. This means, however, the top 16-bits may be 0xffff. We
+  // therefore pick a different value for the kFreeEntryTag.  If/when we go to
+  // VA57, aka 5-level paging, we'll need to revisit this again, as will node
+  // by default, since the fixed-bits on the high end will shrink from top
+  // 16-bits to top 8-bits.
+  //
+  // Unless illumos ships an Oracle-Solaris-like VA47 link-time options to
+  // restrict pointers from allocating from above the Virtual Address hole,
+  // we need to be mindful of this.
+  static constexpr Address kFreeEntryTag = 0xfeed000000000000ull;
+#else
   static constexpr Address kFreeEntryTag = 0xffff000000000000ull;
+#endif /* __illumos__ */
 #ifdef V8_TARGET_BIG_ENDIAN
   // 2-byte parameter count is on the least significant side of encoded_word_.
   static constexpr int kBigEndianParamCountOffset =