RuntimeDyldELF/AArch64: Implement basic GOT support

This patch implements two GOT relocations:
R_AARCH64_ADR_GOT_PAGE and R_AARCH64_LD64_GOT_LO12_NC

Differential revision: https://reviews.llvm.org/D28571

llvm-svn: 294191

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

@@ -484,6 +484,14 @@ Error RuntimeDyldImpl::computeTotalAllocSize(const ObjectFile &Obj,
     }
   }
 
+  // Compute Global Offset Table size. If it is not zero we
+  // also update alignment, which is equal to a size of a
+  // single GOT entry.
+  if (unsigned GotSize = computeGOTSize(Obj)) {
+    RWSectionSizes.push_back(GotSize);
+    RWDataAlign = std::max<uint32_t>(RWDataAlign, getGOTEntrySize());
+  }
+
   // Compute the size of all common symbols
   uint64_t CommonSize = 0;
   uint32_t CommonAlign = 1;
@@ -518,6 +526,24 @@ Error RuntimeDyldImpl::computeTotalAllocSize(const ObjectFile &Obj,
   return Error::success();
 }
 
+// compute GOT size
+unsigned RuntimeDyldImpl::computeGOTSize(const ObjectFile &Obj) {
+  size_t GotEntrySize = getGOTEntrySize();
+  if (!GotEntrySize)
+    return 0;
+
+  size_t GotSize = 0;
+  for (section_iterator SI = Obj.section_begin(), SE = Obj.section_end();
+       SI != SE; ++SI) {
+
+    for (const RelocationRef &Reloc : SI->relocations())
+      if (relocationNeedsGot(Reloc))
+        GotSize += GotEntrySize;
+  }
+
+  return GotSize;
+}
+
 // compute stub buffer size for the given section
 unsigned RuntimeDyldImpl::computeSectionStubBufSize(const ObjectFile &Obj,
                                                     const SectionRef &Section) {

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp

@@ -961,6 +961,61 @@ bool RuntimeDyldELF::resolveAArch64ShortBranch(
   return true;
 }
 
+void RuntimeDyldELF::resolveAArch64Branch(unsigned SectionID,
+                                          const RelocationValueRef &Value,
+                                          relocation_iterator RelI,
+                                          StubMap &Stubs) {
+
+  DEBUG(dbgs() << "\t\tThis is an AArch64 branch relocation.");
+  SectionEntry &Section = Sections[SectionID];
+
+  uint64_t Offset = RelI->getOffset();
+  unsigned RelType = RelI->getType();
+  // Look for an existing stub.
+  StubMap::const_iterator i = Stubs.find(Value);
+  if (i != Stubs.end()) {
+    resolveRelocation(Section, Offset,
+                      (uint64_t)Section.getAddressWithOffset(i->second),
+                      RelType, 0);
+    DEBUG(dbgs() << " Stub function found\n");
+  } else if (!resolveAArch64ShortBranch(SectionID, RelI, Value)) {
+    // Create a new stub function.
+    DEBUG(dbgs() << " Create a new stub function\n");
+    Stubs[Value] = Section.getStubOffset();
+    uint8_t *StubTargetAddr = createStubFunction(
+        Section.getAddressWithOffset(Section.getStubOffset()));
+
+    RelocationEntry REmovz_g3(SectionID, StubTargetAddr - Section.getAddress(),
+                              ELF::R_AARCH64_MOVW_UABS_G3, Value.Addend);
+    RelocationEntry REmovk_g2(SectionID,
+                              StubTargetAddr - Section.getAddress() + 4,
+                              ELF::R_AARCH64_MOVW_UABS_G2_NC, Value.Addend);
+    RelocationEntry REmovk_g1(SectionID,
+                              StubTargetAddr - Section.getAddress() + 8,
+                              ELF::R_AARCH64_MOVW_UABS_G1_NC, Value.Addend);
+    RelocationEntry REmovk_g0(SectionID,
+                              StubTargetAddr - Section.getAddress() + 12,
+                              ELF::R_AARCH64_MOVW_UABS_G0_NC, Value.Addend);
+
+    if (Value.SymbolName) {
+      addRelocationForSymbol(REmovz_g3, Value.SymbolName);
+      addRelocationForSymbol(REmovk_g2, Value.SymbolName);
+      addRelocationForSymbol(REmovk_g1, Value.SymbolName);
+      addRelocationForSymbol(REmovk_g0, Value.SymbolName);
+    } else {
+      addRelocationForSection(REmovz_g3, Value.SectionID);
+      addRelocationForSection(REmovk_g2, Value.SectionID);
+      addRelocationForSection(REmovk_g1, Value.SectionID);
+      addRelocationForSection(REmovk_g0, Value.SectionID);
+    }
+    resolveRelocation(Section, Offset,
+                      reinterpret_cast<uint64_t>(Section.getAddressWithOffset(
+                          Section.getStubOffset())),
+                      RelType, 0);
+    Section.advanceStubOffset(getMaxStubSize());
+  }
+}
+
 Expected<relocation_iterator>
 RuntimeDyldELF::processRelocationRef(
     unsigned SectionID, relocation_iterator RelI, const ObjectFile &O,
@@ -1055,55 +1110,22 @@ RuntimeDyldELF::processRelocationRef(
 
   DEBUG(dbgs() << "\t\tSectionID: " << SectionID << " Offset: " << Offset
                << "\n");
-  if ((Arch == Triple::aarch64 || Arch == Triple::aarch64_be) &&
+  if ((Arch == Triple::aarch64 || Arch == Triple::aarch64_be)) {
-      (RelType == ELF::R_AARCH64_CALL26 || RelType == ELF::R_AARCH64_JUMP26)) {
+    if (RelType == ELF::R_AARCH64_CALL26 || RelType == ELF::R_AARCH64_JUMP26) {
-    // This is an AArch64 branch relocation, need to use a stub function.
+      resolveAArch64Branch(SectionID, Value, RelI, Stubs);
-    DEBUG(dbgs() << "\t\tThis is an AArch64 branch relocation.");
+    } else if (RelType == ELF::R_AARCH64_ADR_GOT_PAGE) {
-    SectionEntry &Section = Sections[SectionID];
+      // Craete new GOT entry or find existing one. If GOT entry is
+      // to be created, then we also emit ABS64 relocation for it.
+      uint64_t GOTOffset = findOrAllocGOTEntry(Value, ELF::R_AARCH64_ABS64);
+      resolveGOTOffsetRelocation(SectionID, Offset, GOTOffset + Addend,
+                                 ELF::R_AARCH64_ADR_PREL_PG_HI21);
 
-    // Look for an existing stub.
+    } else if (RelType == ELF::R_AARCH64_LD64_GOT_LO12_NC) {
-    StubMap::const_iterator i = Stubs.find(Value);
+      uint64_t GOTOffset = findOrAllocGOTEntry(Value, ELF::R_AARCH64_ABS64);
-    if (i != Stubs.end()) {
+      resolveGOTOffsetRelocation(SectionID, Offset, GOTOffset + Addend,
-      resolveRelocation(Section, Offset,
+                                 ELF::R_AARCH64_LDST64_ABS_LO12_NC);
-                        (uint64_t)Section.getAddressWithOffset(i->second),
+    } else {
-                        RelType, 0);
+      processSimpleRelocation(SectionID, Offset, RelType, Value);
-      DEBUG(dbgs() << " Stub function found\n");
-    } else if (!resolveAArch64ShortBranch(SectionID, RelI, Value)) {
-      // Create a new stub function.
-      DEBUG(dbgs() << " Create a new stub function\n");
-      Stubs[Value] = Section.getStubOffset();
-      uint8_t *StubTargetAddr = createStubFunction(
-          Section.getAddressWithOffset(Section.getStubOffset()));
-
-      RelocationEntry REmovz_g3(SectionID,
-                                StubTargetAddr - Section.getAddress(),
-                                ELF::R_AARCH64_MOVW_UABS_G3, Value.Addend);
-      RelocationEntry REmovk_g2(SectionID, StubTargetAddr -
-                                               Section.getAddress() + 4,
-                                ELF::R_AARCH64_MOVW_UABS_G2_NC, Value.Addend);
-      RelocationEntry REmovk_g1(SectionID, StubTargetAddr -
-                                               Section.getAddress() + 8,
-                                ELF::R_AARCH64_MOVW_UABS_G1_NC, Value.Addend);
-      RelocationEntry REmovk_g0(SectionID, StubTargetAddr -
-                                               Section.getAddress() + 12,
-                                ELF::R_AARCH64_MOVW_UABS_G0_NC, Value.Addend);
-
-      if (Value.SymbolName) {
-        addRelocationForSymbol(REmovz_g3, Value.SymbolName);
-        addRelocationForSymbol(REmovk_g2, Value.SymbolName);
-        addRelocationForSymbol(REmovk_g1, Value.SymbolName);
-        addRelocationForSymbol(REmovk_g0, Value.SymbolName);
-      } else {
-        addRelocationForSection(REmovz_g3, Value.SectionID);
-        addRelocationForSection(REmovk_g2, Value.SectionID);
-        addRelocationForSection(REmovk_g1, Value.SectionID);
-        addRelocationForSection(REmovk_g0, Value.SectionID);
-      }
-      resolveRelocation(Section, Offset,
-                        reinterpret_cast<uint64_t>(Section.getAddressWithOffset(
-                            Section.getStubOffset())),
-                        RelType, 0);
-      Section.advanceStubOffset(getMaxStubSize());
     }
   } else if (Arch == Triple::arm) {
     if (RelType == ELF::R_ARM_PC24 || RelType == ELF::R_ARM_CALL ||
@@ -1252,7 +1274,7 @@ RuntimeDyldELF::processRelocationRef(
       if (i != GOTSymbolOffsets.end())
         RE.SymOffset = i->second;
       else {
-        RE.SymOffset = allocateGOTEntries(SectionID, 1);
+        RE.SymOffset = allocateGOTEntries(1);
         GOTSymbolOffsets[TargetName] = RE.SymOffset;
       }
     }
@@ -1509,14 +1531,15 @@ RuntimeDyldELF::processRelocationRef(
           Section.advanceStubOffset(getMaxStubSize());
 
           // Allocate a GOT Entry
-          uint64_t GOTOffset = allocateGOTEntries(SectionID, 1);
+          uint64_t GOTOffset = allocateGOTEntries(1);
 
           // The load of the GOT address has an addend of -4
-          resolveGOTOffsetRelocation(SectionID, StubOffset + 2, GOTOffset - 4);
+          resolveGOTOffsetRelocation(SectionID, StubOffset + 2, GOTOffset - 4,
+                                     ELF::R_X86_64_PC32);
 
           // Fill in the value of the symbol we're targeting into the GOT
           addRelocationForSymbol(
-              computeGOTOffsetRE(SectionID, GOTOffset, 0, ELF::R_X86_64_64),
+              computeGOTOffsetRE(GOTOffset, 0, ELF::R_X86_64_64),
               Value.SymbolName);
         }
 
@@ -1531,11 +1554,13 @@ RuntimeDyldELF::processRelocationRef(
     } else if (RelType == ELF::R_X86_64_GOTPCREL ||
                RelType == ELF::R_X86_64_GOTPCRELX ||
                RelType == ELF::R_X86_64_REX_GOTPCRELX) {
-      uint64_t GOTOffset = allocateGOTEntries(SectionID, 1);
+      uint64_t GOTOffset = allocateGOTEntries(1);
-      resolveGOTOffsetRelocation(SectionID, Offset, GOTOffset + Addend);
+      resolveGOTOffsetRelocation(SectionID, Offset, GOTOffset + Addend,
+                                 ELF::R_X86_64_PC32);
 
       // Fill in the value of the symbol we're targeting into the GOT
-      RelocationEntry RE = computeGOTOffsetRE(SectionID, GOTOffset, Value.Offset, ELF::R_X86_64_64);
+      RelocationEntry RE =
+          computeGOTOffsetRE(GOTOffset, Value.Offset, ELF::R_X86_64_64);
       if (Value.SymbolName)
         addRelocationForSymbol(RE, Value.SymbolName);
       else
@@ -1593,9 +1618,7 @@ size_t RuntimeDyldELF::getGOTEntrySize() {
   return Result;
 }
 
-uint64_t RuntimeDyldELF::allocateGOTEntries(unsigned SectionID, unsigned no)
+uint64_t RuntimeDyldELF::allocateGOTEntries(unsigned no) {
-{
-  (void)SectionID; // The GOT Section is the same for all section in the object file
   if (GOTSectionID == 0) {
     GOTSectionID = Sections.size();
     // Reserve a section id. We'll allocate the section later
@@ -1607,17 +1630,38 @@ uint64_t RuntimeDyldELF::allocateGOTEntries(unsigned SectionID, unsigned no)
   return StartOffset;
 }
 
-void RuntimeDyldELF::resolveGOTOffsetRelocation(unsigned SectionID, uint64_t Offset, uint64_t GOTOffset)
+uint64_t RuntimeDyldELF::findOrAllocGOTEntry(const RelocationValueRef &Value,
-{
+                                             unsigned GOTRelType) {
+  auto E = GOTOffsetMap.insert({Value, 0});
+  if (E.second) {
+    uint64_t GOTOffset = allocateGOTEntries(1);
+
+    // Create relocation for newly created GOT entry
+    RelocationEntry RE =
+        computeGOTOffsetRE(GOTOffset, Value.Offset, GOTRelType);
+    if (Value.SymbolName)
+      addRelocationForSymbol(RE, Value.SymbolName);
+    else
+      addRelocationForSection(RE, Value.SectionID);
+
+    E.first->second = GOTOffset;
+  }
+
+  return E.first->second;
+}
+
+void RuntimeDyldELF::resolveGOTOffsetRelocation(unsigned SectionID,
+                                                uint64_t Offset,
+                                                uint64_t GOTOffset,
+                                                uint32_t Type) {
   // Fill in the relative address of the GOT Entry into the stub
-  RelocationEntry GOTRE(SectionID, Offset, ELF::R_X86_64_PC32, GOTOffset);
+  RelocationEntry GOTRE(SectionID, Offset, Type, GOTOffset);
   addRelocationForSection(GOTRE, GOTSectionID);
 }
 
-RelocationEntry RuntimeDyldELF::computeGOTOffsetRE(unsigned SectionID, uint64_t GOTOffset, uint64_t SymbolOffset,
+RelocationEntry RuntimeDyldELF::computeGOTOffsetRE(uint64_t GOTOffset,
-                                                   uint32_t Type)
+                                                   uint64_t SymbolOffset,
-{
+                                                   uint32_t Type) {
-  (void)SectionID; // The GOT Section is the same for all section in the object file
   return RelocationEntry(GOTSectionID, GOTOffset, Type, SymbolOffset);
 }
 
@@ -1683,6 +1727,19 @@ bool RuntimeDyldELF::isCompatibleFile(const object::ObjectFile &Obj) const {
   return Obj.isELF();
 }
 
+bool RuntimeDyldELF::relocationNeedsGot(const RelocationRef &R) const {
+  unsigned RelTy = R.getType();
+  if (Arch == Triple::aarch64 || Arch == Triple::aarch64_be)
+    return RelTy == ELF::R_AARCH64_ADR_GOT_PAGE ||
+           RelTy == ELF::R_AARCH64_LD64_GOT_LO12_NC;
+
+  if (Arch == Triple::x86_64)
+    return RelTy == ELF::R_X86_64_GOTPCREL ||
+           RelTy == ELF::R_X86_64_GOTPCRELX ||
+           RelTy == ELF::R_X86_64_REX_GOTPCRELX;
+  return false;
+}
+
 bool RuntimeDyldELF::relocationNeedsStub(const RelocationRef &R) const {
   if (Arch != Triple::x86_64)
     return true;  // Conservative answer

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h

@@ -43,6 +43,9 @@ class RuntimeDyldELF : public RuntimeDyldImpl {
   bool resolveAArch64ShortBranch(unsigned SectionID, relocation_iterator RelI,
                                  const RelocationValueRef &Value);
 
+  void resolveAArch64Branch(unsigned SectionID, const RelocationValueRef &Value,
+                            relocation_iterator RelI, StubMap &Stubs);
+
   void resolveARMRelocation(const SectionEntry &Section, uint64_t Offset,
                             uint32_t Value, uint32_t Type, int32_t Addend);
 
@@ -88,24 +91,26 @@ class RuntimeDyldELF : public RuntimeDyldImpl {
                             ObjSectionToIDMap &LocalSections,
                             RelocationValueRef &Rel);
 protected:
-  size_t getGOTEntrySize();
+  size_t getGOTEntrySize() override;
 
 private:
   SectionEntry &getSection(unsigned SectionID) { return Sections[SectionID]; }
 
   // Allocate no GOT entries for use in the given section.
-  uint64_t allocateGOTEntries(unsigned SectionID, unsigned no);
+  uint64_t allocateGOTEntries(unsigned no);
+
+  // Find GOT entry corresponding to relocation or create new one.
+  uint64_t findOrAllocGOTEntry(const RelocationValueRef &Value,
+                               unsigned GOTRelType);
 
   // Resolve the relvative address of GOTOffset in Section ID and place
   // it at the given Offset
   void resolveGOTOffsetRelocation(unsigned SectionID, uint64_t Offset,
-                                  uint64_t GOTOffset);
+                                  uint64_t GOTOffset, uint32_t Type);
 
   // For a GOT entry referenced from SectionID, compute a relocation entry
   // that will place the final resolved value in the GOT slot
-  RelocationEntry computeGOTOffsetRE(unsigned SectionID,
+  RelocationEntry computeGOTOffsetRE(uint64_t GOTOffset, uint64_t SymbolOffset,
-                                     uint64_t GOTOffset,
-                                     uint64_t SymbolOffset,
                                      unsigned Type);
 
   // Compute the address in memory where we can find the placeholder
@@ -146,6 +151,10 @@ private:
   SmallVector<SID, 2> UnregisteredEHFrameSections;
   SmallVector<SID, 2> RegisteredEHFrameSections;
 
+  // Map between GOT relocation value and corresponding GOT offset
+  std::map<RelocationValueRef, uint64_t> GOTOffsetMap;
+
+  bool relocationNeedsGot(const RelocationRef &R) const override;
   bool relocationNeedsStub(const RelocationRef &R) const override;
 
 public:

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h

@@ -213,7 +213,7 @@ public:
   }
 };
 
-/// @brief Symbol info for RuntimeDyld. 
+/// @brief Symbol info for RuntimeDyld.
 class SymbolTableEntry {
 public:
   SymbolTableEntry()
@@ -426,6 +426,9 @@ protected:
                               uint64_t &RODataSize, uint32_t &RODataAlign,
                               uint64_t &RWDataSize, uint32_t &RWDataAlign);
 
+  // \brief Compute GOT size
+  unsigned computeGOTSize(const ObjectFile &Obj);
+
   // \brief Compute the stub buffer size required for a section
   unsigned computeSectionStubBufSize(const ObjectFile &Obj,
                                      const SectionRef &Section);
@@ -433,6 +436,14 @@ protected:
   // \brief Implementation of the generic part of the loadObject algorithm.
   Expected<ObjSectionToIDMap> loadObjectImpl(const object::ObjectFile &Obj);
 
+  // \brief Return size of Global Offset Table (GOT) entry
+  virtual size_t getGOTEntrySize() { return 0; }
+
+  // \brief Return true if the relocation R may require allocating a GOT entry.
+  virtual bool relocationNeedsGot(const RelocationRef &R) const {
+    return false;
+  }
+
   // \brief Return true if the relocation R may require allocating a stub.
   virtual bool relocationNeedsStub(const RelocationRef &R) const {
     return true;    // Conservative answer

llvm/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_PIC_relocations.s

@@ -0,0 +1,46 @@
+# RUN: llvm-mc -triple=arm64-none-linux-gnu -filetype=obj -o %T/pic-reloc.o %s
+# RUN: llvm-rtdyld -triple=arm64-none-linux-gnu -verify  -check=%s %T/pic-reloc.o \
+# RUN:    -map-section pic-reloc.o,.got=0x20000 -dummy-extern f=0x1234 -dummy-extern g=0x5678
+
+_s:
+  nop
+_a1:
+	adrp	x8, :got:f
+_a2:
+	adrp	x9, :got:g
+_a3:
+  adrp  x10, :got:_s
+_l1:
+  ldr x8, [x8, :got_lo12:f]
+_l2:
+  ldr x9, [x9, :got_lo12:g]
+_l3:
+  ldr x10, [x10, :got_lo12:_s]
+
+
+## We'll end up having two sections .text and .got,
+## each is located on the start of a memory page
+
+## Test that .got section has three entries pointing to f, g and _s
+# *{8}section_addr(pic-reloc.o, .got) = f
+# *{8}(section_addr(pic-reloc.o, .got) + 8) = g
+# *{8}(section_addr(pic-reloc.o, .got) + 16) = _s
+
+## Test that first adrp instruction really takes address of 
+## the .got section (_s label is on the start of a page)
+# rtdyld-check: _s + (((*{4}_a1)[30:29] + ((*{4}_a1)[23:5] << 2)) << 12) = section_addr(pic-reloc.o, .got)
+
+## Test that second adrp takes address of .got
+# rtdyld-check: _s + (((*{4}_a2)[30:29] + ((*{4}_a2)[23:5] << 2)) << 12) = section_addr(pic-reloc.o, .got)
+
+## Test that third adrp takes address of .got
+# rtdyld-check: _s + (((*{4}_a3)[30:29] + ((*{4}_a3)[23:5] << 2)) << 12) = section_addr(pic-reloc.o, .got)
+
+## Test that first ldr immediate value is 0 >> 3 = 0 (1st .got entry)
+# rtdyld-check: (*{4}_l1)[21:10] = 0
+
+## Test that second ldr immediate value is 8 >> 3 = 1 (2nd .got entry)
+# rtdyld-check: (*{4}_l2)[21:10] = 1
+
+## Test that third ldr immediate value is 16 >> 3 = 2 (3rd .got entry, addend is 0)
+# rtdyld-check: (*{4}_l3)[21:10] = 2