[arm64] Assembler support for internal references.

src/arm64/assembler-arm64.cc

Index: src/arm64/assembler-arm64.cc
diff --git a/src/arm64/assembler-arm64.cc b/src/arm64/assembler-arm64.cc
index 93d1d25a6c7747628d51c0c4466432ad9e749fd8..d0724336333d87476e610c65a9bc2796ffabb4f3 100644
--- a/src/arm64/assembler-arm64.cc
+++ b/src/arm64/assembler-arm64.cc
@@ -171,7 +171,7 @@ CPURegList CPURegList::GetSafepointSavedRegisters() {
 // -----------------------------------------------------------------------------
 // Implementation of RelocInfo
 
-const int RelocInfo::kApplyMask = 0;
+const int RelocInfo::kApplyMask = 1 << RelocInfo::INTERNAL_REFERENCE;
 
 
 bool RelocInfo::IsCodedSpecially() {
@@ -732,7 +732,15 @@ void Assembler::bind(Label* label) {
     DCHECK(prevlinkoffset >= 0);
 
     // Update the link to point to the label.
-    link->SetImmPCOffsetTarget(reinterpret_cast<Instruction*>(pc_));
+    if (link->IsUnresolvedInternalReference()) {
+      // Internal references do not get patched to an instruction but directly
+      // to an address.
+      internal_reference_positions_.push_back(linkoffset);
+      PatchingAssembler patcher(link, 2);
+      patcher.dc64(reinterpret_cast<uintptr_t>(pc_));
+    } else {
+      link->SetImmPCOffsetTarget(reinterpret_cast<Instruction*>(pc_));
+    }
 
     // Link the label to the previous link in the chain.
     if (linkoffset - prevlinkoffset == kStartOfLabelLinkChain) {
@@ -2060,6 +2068,50 @@ void Assembler::ucvtf(const FPRegister& fd,
 }
 
 
+void Assembler::dcptr(Label* label) {
+  RecordRelocInfo(RelocInfo::INTERNAL_REFERENCE);
+  if (label->is_bound()) {
+    // The label is bound, so it does not need to be updated and the internal
+    // reference should be emitted.
+    //
+    // In this case, label->pos() returns the offset of the label from the
+    // start of the buffer.
+    internal_reference_positions_.push_back(pc_offset());
+    dc64(reinterpret_cast<uintptr_t>(buffer_ + label->pos()));
+  } else {
+    int32_t offset;
+    if (label->is_linked()) {
+      // The label is linked, so the internal reference should be added
+      // onto the end of the label's link chain.
+      //
+      // In this case, label->pos() returns the offset of the last linked
+      // instruction from the start of the buffer.
+      offset = label->pos() - pc_offset();
+      DCHECK(offset != kStartOfLabelLinkChain);
+    } else {
+      // The label is unused, so it now becomes linked and the internal
+      // reference is at the start of the new link chain.
+      offset = kStartOfLabelLinkChain;
+    }
+    // The instruction at pc is now the last link in the label's chain.
+    label->link_to(pc_offset());
+
+    // Traditionally the offset to the previous instruction in the chain is
+    // encoded in the instruction payload (e.g. branch range) but internal
+    // references are not instructions so while unbound they are encoded as
+    // two consecutive brk instructions. The two 16-bit immediates are used
+    // to encode the offset.
+    offset >>= kInstructionSizeLog2;
+    DCHECK(is_int32(offset));
+    uint32_t high16 = unsigned_bitextract_32(31, 16, offset);
+    uint32_t low16 = unsigned_bitextract_32(15, 0, offset);
+
+    brk(high16);
+    brk(low16);
+  }
+}
+
+
 // Note:
 // Below, a difference in case for the same letter indicates a
 // negated bit.
@@ -2819,6 +2871,12 @@ void Assembler::GrowBuffer() {
   // buffer nor pc absolute pointing inside the code buffer, so there is no need
   // to relocate any emitted relocation entries.
 
+  // Relocate internal references.
+  for (auto pos : internal_reference_positions_) {
+    intptr_t* p = reinterpret_cast<intptr_t*>(buffer_ + pos);
+    *p += pc_delta;
+  }
+
   // Pending relocation entries are also relative, no need to relocate.
 }
 
@@ -2828,6 +2886,7 @@ void Assembler::RecordRelocInfo(RelocInfo::Mode rmode, intptr_t data) {
   RelocInfo rinfo(reinterpret_cast<byte*>(pc_), rmode, data, NULL);
   if (((rmode >= RelocInfo::JS_RETURN) &&
        (rmode <= RelocInfo::DEBUG_BREAK_SLOT)) ||
+      (rmode == RelocInfo::INTERNAL_REFERENCE) ||
       (rmode == RelocInfo::CONST_POOL) ||
       (rmode == RelocInfo::VENEER_POOL) ||
       (rmode == RelocInfo::DEOPT_REASON)) {
@@ -2837,6 +2896,7 @@ void Assembler::RecordRelocInfo(RelocInfo::Mode rmode, intptr_t data) {
            || RelocInfo::IsComment(rmode)
            || RelocInfo::IsDeoptReason(rmode)
            || RelocInfo::IsPosition(rmode)
+           || RelocInfo::IsInternalReference(rmode)
            || RelocInfo::IsConstPool(rmode)
            || RelocInfo::IsVeneerPool(rmode));
     // These modes do not need an entry in the constant pool.