From 1a9ebde7e0930343823f20aae07ddb64ed33d0fb Mon Sep 17 00:00:00 2001
From: Lang Hames <lhames@gmail.com>
Date: Thu, 21 Jan 2016 21:59:50 +0000
Subject: [PATCH] [RuntimeDyld][AArch64] Add support for the MachO
 ARM64_RELOC_SUBTRACTOR reloc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@258438 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../Targets/RuntimeDyldMachOAArch64.h         | 54 ++++++++++++++++++-
 .../AArch64/MachO_ARM64_relocations.s         |  5 ++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/lib/ExecutionEngine/RuntimeDyld/Targets/RuntimeDyldMachOAArch64.h b/lib/ExecutionEngine/RuntimeDyld/Targets/RuntimeDyldMachOAArch64.h
index dbca37747ce..ea2a7a2953b 100644
--- a/lib/ExecutionEngine/RuntimeDyld/Targets/RuntimeDyldMachOAArch64.h
+++ b/lib/ExecutionEngine/RuntimeDyld/Targets/RuntimeDyldMachOAArch64.h
@@ -270,6 +270,9 @@ public:
       RelInfo = Obj.getRelocation(RelI->getRawDataRefImpl());
     }
 
+    if (Obj.getAnyRelocationType(RelInfo) == MachO::ARM64_RELOC_SUBTRACTOR)
+      return processSubtractRelocation(SectionID, RelI, Obj, ObjSectionToID);
+
     RelocationEntry RE(getRelocationEntry(SectionID, Obj, RelI));
     RE.Addend = decodeAddend(RE);
 
@@ -349,7 +352,15 @@ public:
       encodeAddend(LocalAddress, /*Size=*/4, RelType, Value);
       break;
     }
-    case MachO::ARM64_RELOC_SUBTRACTOR:
+    case MachO::ARM64_RELOC_SUBTRACTOR: {
+      uint64_t SectionABase = Sections[RE.Sections.SectionA].getLoadAddress();
+      uint64_t SectionBBase = Sections[RE.Sections.SectionB].getLoadAddress();
+      assert((Value == SectionABase || Value == SectionBBase) &&
+             "Unexpected SUBTRACTOR relocation value.");
+      Value = SectionABase - SectionBBase + RE.Addend;
+      writeBytesUnaligned(Value, LocalAddress, 1 << RE.Size);
+      break;
+    }
     case MachO::ARM64_RELOC_POINTER_TO_GOT:
     case MachO::ARM64_RELOC_TLVP_LOAD_PAGE21:
     case MachO::ARM64_RELOC_TLVP_LOAD_PAGEOFF12:
@@ -398,6 +409,47 @@ private:
                              RE.IsPCRel, RE.Size);
     addRelocationForSection(TargetRE, RE.SectionID);
   }
+
+  relocation_iterator
+  processSubtractRelocation(unsigned SectionID, relocation_iterator RelI,
+                            const ObjectFile &BaseObjT,
+                            ObjSectionToIDMap &ObjSectionToID) {
+    const MachOObjectFile &Obj =
+        static_cast<const MachOObjectFile&>(BaseObjT);
+    MachO::any_relocation_info RE =
+        Obj.getRelocation(RelI->getRawDataRefImpl());
+
+    unsigned Size = Obj.getAnyRelocationLength(RE);
+    uint64_t Offset = RelI->getOffset();
+    uint8_t *LocalAddress = Sections[SectionID].getAddressWithOffset(Offset);
+    unsigned NumBytes = 1 << Size;
+
+    ErrorOr<StringRef> SubtrahendNameOrErr = RelI->getSymbol()->getName();
+    if (auto EC = SubtrahendNameOrErr.getError())
+      report_fatal_error(EC.message());
+    auto SubtrahendI = GlobalSymbolTable.find(*SubtrahendNameOrErr);
+    unsigned SectionBID = SubtrahendI->second.getSectionID();
+    uint64_t SectionBOffset = SubtrahendI->second.getOffset();
+    int64_t Addend =
+      SignExtend64(readBytesUnaligned(LocalAddress, NumBytes), NumBytes * 8);
+
+    ++RelI;
+    ErrorOr<StringRef> MinuendNameOrErr = RelI->getSymbol()->getName();
+    if (auto EC = MinuendNameOrErr.getError())
+      report_fatal_error(EC.message());
+    auto MinuendI = GlobalSymbolTable.find(*MinuendNameOrErr);
+    unsigned SectionAID = MinuendI->second.getSectionID();
+    uint64_t SectionAOffset = MinuendI->second.getOffset();
+
+    RelocationEntry R(SectionID, Offset, MachO::ARM64_RELOC_SUBTRACTOR, (uint64_t)Addend,
+                      SectionAID, SectionAOffset, SectionBID, SectionBOffset,
+                      false, Size);
+
+    addRelocationForSection(R, SectionAID);
+
+    return ++RelI;
+  }
+
 };
 }
 
diff --git a/test/ExecutionEngine/RuntimeDyld/AArch64/MachO_ARM64_relocations.s b/test/ExecutionEngine/RuntimeDyld/AArch64/MachO_ARM64_relocations.s
index 0387b932f1c..b29418783d6 100644
--- a/test/ExecutionEngine/RuntimeDyld/AArch64/MachO_ARM64_relocations.s
+++ b/test/ExecutionEngine/RuntimeDyld/AArch64/MachO_ARM64_relocations.s
@@ -77,3 +77,8 @@ tgt:
     .fill 4096, 1, 0
 _ptr:
     .quad _foo
+
+# Test ARM64_RELOC_SUBTRACTOR.
+# rtdyld-check: *{8}_subtractor_result = _test_branch_reloc - _foo
+_subtractor_result:
+    .quad _test_branch_reloc - _foo