Subzero. Enables moar complex relocation offsets.

Makefile.standalone

@@ -142,8 +142,8 @@ ifdef FORCEASM
   # resulting nexe.  So we just disable those tests for now.
   FORCEASM_XTEST_EXCLUDES = -e x8632,sandbox,test_sync_atomic
   FORCEASM_LIT_PARAM = --param=FORCEASM
-  # x86 sandboxing lit tests are disabled because llvm-mc uses different
-  # relocations for pushing return addresses onto the stack.
+  # x86 sandboxing lit tests are disabled because filetype=asm does not
+  # handle bundle_lock pad-to-end correctly.
   # TODO(jpp): fix this.
   FORCEASM_LIT_TEST_EXCLUDES = --filter='^(?!.*/x86/sandboxing.ll).*'
 else

src/IceAssembler.h

@@ -238,9 +238,6 @@ class Assembler {
   Assembler &operator=(const Assembler &) = delete;
 
 public:
-  using InternalRelocationList =
-      std::vector<std::pair<const IceString, const SizeT>>;
-
   enum AssemblerKind {
     Asm_ARM32,
     Asm_MIPS32,
@@ -328,23 +325,12 @@ public:
 
   AssemblerKind getKind() const { return Kind; }
 
-  void addRelocationAtCurrentPosition(const IceString &RelocName) {
-    if (!getPreliminary()) {
-      InternalRelocs.emplace_back(RelocName, getBufferSize());
-    }
-  }
-
-  const InternalRelocationList &getInternalRelocations() const {
-    return InternalRelocs;
-  }
-
 protected:
   explicit Assembler(AssemblerKind Kind)
       : Kind(Kind), Allocator(), Buffer(*this) {}
 
 private:
   const AssemblerKind Kind;
-  InternalRelocationList InternalRelocs;
 
   ArenaAllocator<32 * 1024> Allocator;
   /// FunctionName and IsInternal are transferred from the original Cfg object,

src/IceAssemblerX86Base.h

@@ -171,6 +171,7 @@ public:
   Label *getOrCreateCfgNodeLabel(SizeT Number);
   Label *getOrCreateLocalLabel(SizeT Number);
   void bindLocalLabel(SizeT Number);
+  void bindRelocOffset(RelocOffset *Offset);
 
   bool fixupIsPCRel(FixupKind Kind) const override {
     // Currently assuming this is the only PC-rel relocation type used.

src/IceAssemblerX86BaseImpl.h

@@ -106,6 +106,13 @@ void AssemblerX86Base<TraitsType>::bindLocalLabel(SizeT Number) {
 }
 
 template <typename TraitsType>
+void AssemblerX86Base<TraitsType>::bindRelocOffset(RelocOffset *Offset) {
+  if (!getPreliminary()) {
+    Offset->setOffset(Buffer.getPosition());
+  }
+}
+
+template <typename TraitsType>
 void AssemblerX86Base<TraitsType>::call(GPRRegister reg) {
   AssemblerBuffer::EnsureCapacity ensured(&Buffer);
   emitRexB(RexTypeIrrelevant, reg);

src/IceDefs.h

@@ -309,6 +309,8 @@ enum RandomizationPassesEnum {
   RPE_num
 };
 
+using RelocOffsetArray = llvm::SmallVector<class RelocOffset *, 4>;
+
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEDEFS_H

src/IceELFObjectWriter.cpp

@@ -256,15 +256,6 @@ void ELFObjectWriter::writeFunctionCode(const IceString &FuncName,
   SymTab->createDefinedSym(FuncName, SymbolType, SymbolBinding, Section,
                            OffsetInSection, SymbolSize);
   StrTab->add(FuncName);
-  for (const auto &InternalReloc : Asm->getInternalRelocations()) {
-    const IceString &RelocName = InternalReloc.first;
-    constexpr uint8_t RelocSymbolType = STT_NOTYPE;
-    constexpr uint8_t RelocSymbolBinding = STB_LOCAL;
-    const SizeT RelocOffsetInSection = OffsetInSection + InternalReloc.second;
-    SymTab->createDefinedSym(RelocName, RelocSymbolType, RelocSymbolBinding,
-                             Section, RelocOffsetInSection, SymbolSize);
-    StrTab->add(RelocName);
-  }
 
   // Copy the fixup information from per-function Assembler memory to the
   // object writer's memory, for writing later.

src/IceGlobalContext.cpp

@@ -44,8 +44,18 @@
 namespace std {
 template <> struct hash<Ice::RelocatableTuple> {
   size_t operator()(const Ice::RelocatableTuple &Key) const {
+    if (!Key.EmitString.empty()) {
+      return hash<Ice::IceString>()(Key.EmitString);
+    }
+
+    assert(!Key.OffsetExpr.empty());
+    if (Key.OffsetExpr[0]->hasOffset()) {
+      return hash<Ice::IceString>()(Key.Name) +
+             hash<Ice::RelocOffsetT>()(Key.OffsetExpr[0]->getOffset());
+    }
+
     return hash<Ice::IceString>()(Key.Name) +
-           hash<Ice::RelocOffsetT>()(Key.Offset);
+           hash<std::size_t>()(Key.OffsetExpr.size());
   }
 };
 } // end of namespace std
@@ -785,18 +795,28 @@ Constant *GlobalContext::getConstantDouble(double ConstantDouble) {
   return getConstPool()->Doubles.getOrAdd(this, ConstantDouble);
 }
 
-Constant *GlobalContext::getConstantSym(RelocOffsetT Offset,
+Constant *GlobalContext::getConstantSym(const RelocOffsetArray &Offset,
                                         const IceString &Name,
+                                        const IceString &EmitString,
                                         bool SuppressMangling) {
   return getConstPool()->Relocatables.getOrAdd(
-      this, RelocatableTuple(Offset, Name, SuppressMangling));
+      this, RelocatableTuple(Offset, Name, EmitString, SuppressMangling));
+}
+
+Constant *GlobalContext::getConstantSym(RelocOffsetT Offset,
+                                        const IceString &Name,
+                                        bool SuppressMangling) {
+  constexpr char EmptyEmitString[] = "";
+  return getConstantSym({RelocOffset::create(this, Offset)}, Name,
+                        EmptyEmitString, SuppressMangling);
 }
 
 Constant *GlobalContext::getConstantExternSym(const IceString &Name) {
   constexpr RelocOffsetT Offset = 0;
   constexpr bool SuppressMangling = true;
   return getConstPool()->ExternRelocatables.getOrAdd(
-      this, RelocatableTuple(Offset, Name, SuppressMangling));
+      this, RelocatableTuple({RelocOffset::create(this, Offset)}, Name,
+                             SuppressMangling));
 }
 
 Constant *GlobalContext::getConstantUndef(Type Ty) {

src/IceGlobalContext.h

@@ -200,6 +200,9 @@ public:
   Constant *getConstantFloat(float Value);
   Constant *getConstantDouble(double Value);
   /// Returns a symbolic constant.
+  Constant *getConstantSym(const RelocOffsetArray &Offset,
+                           const IceString &Name, const IceString &EmitString,
+                           bool SuppressMangling);
   Constant *getConstantSym(RelocOffsetT Offset, const IceString &Name,
                            bool SuppressMangling);
   Constant *getConstantExternSym(const IceString &Name);

src/IceInstX86Base.h

@@ -337,13 +337,13 @@ template <typename TraitsType> struct InstImpl {
     void emit(const Cfg *Func) const override;
     void emitIAS(const Cfg *Func) const override;
     void dump(const Cfg *Func) const override;
-    void setIsReturnLocation(bool Value) { IsReturnLocation = Value; }
+    void setRelocOffset(RelocOffset *Value) { OffsetReloc = Value; }
 
   private:
     InstX86Label(Cfg *Func, TargetLowering *Target);
 
     SizeT Number; // used for unique label generation.
-    bool IsReturnLocation = false;
+    RelocOffset *OffsetReloc = nullptr;
   };
 
   /// Conditional and unconditional branch instruction.

src/IceInstX86BaseImpl.h

@@ -459,10 +459,10 @@ void InstImpl<TraitsType>::InstX86Label::emit(const Cfg *Func) const {
 template <typename TraitsType>
 void InstImpl<TraitsType>::InstX86Label::emitIAS(const Cfg *Func) const {
   Assembler *Asm = Func->getAssembler<Assembler>();
-  if (IsReturnLocation) {
-    Asm->addRelocationAtCurrentPosition(getName(Func));
-  }
   Asm->bindLocalLabel(Number);
+  if (OffsetReloc != nullptr) {
+    Asm->bindRelocOffset(OffsetReloc);
+  }
 }
 
 template <typename TraitsType>

src/IceOperand.cpp

@@ -24,7 +24,66 @@
 namespace Ice {
 
 bool operator==(const RelocatableTuple &A, const RelocatableTuple &B) {
-  return A.Offset == B.Offset && A.Name == B.Name;
+  // A and B are the same if:
+  //   (1) they have the same name; and
+  //   (2) they have the same offset.
+  //
+  // (1) is trivial to check, but (2) requires some care.
+  //
+  // For (2):
+  //  if A and B have known offsets (i.e., no symbolic references), then
+  //     A == B -> A.Offset == B.Offset.
+  //  else each element i in A.OffsetExpr[i] must be the same (or have the same
+  //    value) as B.OffsetExpr[i].
+  if (A.Name != B.Name) {
+    return false;
+  }
+
+  bool BothHaveKnownOffsets = true;
+  RelocOffsetT OffsetA = 0;
+  RelocOffsetT OffsetB = 0;
+  for (SizeT i = 0; i < A.OffsetExpr.size() && BothHaveKnownOffsets; ++i) {
+    BothHaveKnownOffsets = A.OffsetExpr[i]->hasOffset();
+    if (BothHaveKnownOffsets) {
+      OffsetA += A.OffsetExpr[i]->getOffset();
+    }
+  }
+  for (SizeT i = 0; i < B.OffsetExpr.size() && BothHaveKnownOffsets; ++i) {
+    BothHaveKnownOffsets = B.OffsetExpr[i]->hasOffset();
+    if (BothHaveKnownOffsets) {
+      OffsetB += B.OffsetExpr[i]->getOffset();
+    }
+  }
+  if (BothHaveKnownOffsets) {
+    // Both have known offsets (i.e., no unresolved symbolic references), so
+    // A == B -> A.Offset == B.Offset.
+    return OffsetA == OffsetB;
+  }
+
+  // Otherwise, A and B are not the same if their OffsetExpr's have different
+  // sizes.
+  if (A.OffsetExpr.size() != B.OffsetExpr.size()) {
+    return false;
+  }
+
+  // If the OffsetExprs' sizes are the same, then
+  // for each i in OffsetExprSize:
+  for (SizeT i = 0; i < A.OffsetExpr.size(); ++i) {
+    const auto *const RelocOffsetA = A.OffsetExpr[i];
+    const auto *const RelocOffsetB = B.OffsetExpr[i];
+    if (RelocOffsetA->hasOffset() && RelocOffsetB->hasOffset()) {
+      // A.OffsetExpr[i].Offset == B.OffsetExpr[i].Offset iff they are both
+      // defined;
+      if (RelocOffsetA->getOffset() != RelocOffsetB->getOffset()) {
+        return false;
+      }
+    } else if (RelocOffsetA != RelocOffsetB) {
+      // or, if they are undefined, then the RelocOffsets must be the same.
+      return false;
+    }
+  }
+
+  return true;
 }
 
 bool operator<(const RegWeight &A, const RegWeight &B) {
@@ -501,8 +560,13 @@ void ConstantRelocatable::dump(const Cfg *Func, Ostream &Str) const {
   } else {
     Str << Name;
   }
-  if (Offset)
-    Str << "+" << Offset;
+  const RelocOffsetT Offset = getOffset();
+  if (Offset) {
+    if (Offset >= 0) {
+      Str << "+";
+    }
+    Str << Offset;
+  }
 }
 
 void ConstantUndef::emit(TargetLowering *Target) const { Target->emit(this); }

src/IceOperand.h

@@ -26,6 +26,8 @@
 
 #include "llvm/Support/Format.h"
 
+#include <limits>
+
 namespace Ice {
 
 class Operand {
@@ -247,6 +249,43 @@ inline void ConstantInteger64::dump(const Cfg *, Ostream &Str) const {
   Str << static_cast<int64_t>(getValue());
 }
 
+/// RelocOffset allows symbolic references in ConstantRelocatables' offsets,
+/// e.g., 8 + LabelOffset, where label offset is the location (code or data)
+/// of a Label that is only determinable during ELF emission.
+class RelocOffset final {
+  RelocOffset(const RelocOffset &) = delete;
+  RelocOffset &operator=(const RelocOffset &) = delete;
+
+public:
+  static RelocOffset *create(GlobalContext *Ctx) {
+    return new (Ctx->allocate<RelocOffset>()) RelocOffset();
+  }
+
+  static RelocOffset *create(GlobalContext *Ctx, RelocOffsetT Value) {
+    return new (Ctx->allocate<RelocOffset>()) RelocOffset(Value);
+  }
+
+  bool hasOffset() const { return HasOffset; }
+
+  RelocOffsetT getOffset() const {
+    assert(HasOffset);
+    return Offset;
+  }
+
+  void setOffset(const RelocOffsetT Value) {
+    assert(!HasOffset);
+    Offset = Value;
+    HasOffset = true;
+  }
+
+private:
+  RelocOffset() = default;
+  explicit RelocOffset(RelocOffsetT Offset) { setOffset(Offset); }
+
+  bool HasOffset = false;
+  RelocOffsetT Offset;
+};
+
 /// RelocatableTuple bundles the parameters that are used to construct an
 /// ConstantRelocatable. It is done this way so that ConstantRelocatable can fit
 /// into the global constant pool template mechanism.
@@ -255,14 +294,22 @@ class RelocatableTuple {
   RelocatableTuple &operator=(const RelocatableTuple &) = delete;
 
 public:
-  RelocatableTuple(const RelocOffsetT Offset, const IceString &Name,
+  RelocatableTuple(const RelocOffsetArray &OffsetExpr, const IceString &Name,
                    bool SuppressMangling)
-      : Offset(Offset), Name(Name), SuppressMangling(SuppressMangling) {}
+      : OffsetExpr(OffsetExpr), Name(Name), SuppressMangling(SuppressMangling) {
+  }
+
+  RelocatableTuple(const RelocOffsetArray &OffsetExpr, const IceString &Name,
+                   const IceString &EmitString, bool SuppressMangling)
+      : OffsetExpr(OffsetExpr), Name(Name), EmitString(EmitString),
+        SuppressMangling(SuppressMangling) {}
+
   RelocatableTuple(const RelocatableTuple &) = default;
 
-  const RelocOffsetT Offset;
+  const RelocOffsetArray OffsetExpr;
   const IceString Name;
-  bool SuppressMangling;
+  const IceString EmitString;
+  const bool SuppressMangling;
 };
 
 bool operator==(const RelocatableTuple &A, const RelocatableTuple &B);
@@ -277,13 +324,22 @@ class ConstantRelocatable : public Constant {
 public:
   static ConstantRelocatable *create(GlobalContext *Ctx, Type Ty,
                                      const RelocatableTuple &Tuple) {
-    return new (Ctx->allocate<ConstantRelocatable>()) ConstantRelocatable(
-        Ty, Tuple.Offset, Tuple.Name, Tuple.SuppressMangling);
+    return new (Ctx->allocate<ConstantRelocatable>())
+        ConstantRelocatable(Ty, Tuple.OffsetExpr, Tuple.Name, Tuple.EmitString,
+                            Tuple.SuppressMangling);
   }
 
-  RelocOffsetT getOffset() const { return Offset; }
+  RelocOffsetT getOffset() const {
+    RelocOffsetT Offset = 0;
+    for (const auto *const OffsetReloc : OffsetExpr) {
+      Offset += OffsetReloc->getOffset();
+    }
+    return Offset;
+  }
+
+  const IceString &getEmitString() const { return EmitString; }
+
   const IceString &getName() const { return Name; }
-  void setSuppressMangling(bool Value) { SuppressMangling = Value; }
   bool getSuppressMangling() const { return SuppressMangling; }
   using Constant::emit;
   void emit(TargetLowering *Target) const final;
@@ -298,13 +354,16 @@ public:
   }
 
 private:
-  ConstantRelocatable(Type Ty, RelocOffsetT Offset, const IceString &Name,
+  ConstantRelocatable(Type Ty, const RelocOffsetArray &OffsetExpr,
+                      const IceString &Name, const IceString &EmitString,
                       bool SuppressMangling)
-      : Constant(kConstRelocatable, Ty), Offset(Offset), Name(Name),
-        SuppressMangling(SuppressMangling) {}
-  const RelocOffsetT Offset; /// fixed offset to add
+      : Constant(kConstRelocatable, Ty), OffsetExpr(OffsetExpr), Name(Name),
+        EmitString(EmitString), SuppressMangling(SuppressMangling) {}
+
+  const RelocOffsetArray OffsetExpr; /// fixed offset to add
   const IceString Name;              /// optional for debug/dump
-  bool SuppressMangling;
+  const IceString EmitString;        /// optional for textual emission
+  const bool SuppressMangling;
 };
 
 /// ConstantUndef represents an unspecified bit pattern. Although it is legal to

src/IceTargetLowering.cpp

@@ -704,6 +704,13 @@ void TargetLowering::emitWithoutPrefix(const ConstantRelocatable *C,
   if (!BuildDefs::dump())
     return;
   Ostream &Str = Ctx->getStrEmit();
+  const IceString &EmitStr = C->getEmitString();
+  if (!EmitStr.empty()) {
+    // C has a custom emit string, so we use it instead of the canonical
+    // Name + Offset form.
+    Str << EmitStr;
+    return;
+  }
   if (C->getSuppressMangling())
     Str << C->getName();
   else

src/IceTargetLoweringX8664.cpp

@@ -598,15 +598,44 @@ Inst *TargetX8664::emitCallToTarget(Operand *CallTarget, Variable *ReturnReg) {
   Inst *NewCall = nullptr;
   auto *CallTargetR = llvm::dyn_cast<Variable>(CallTarget);
   if (NeedSandboxing) {
+    // In NaCl sandbox, calls are replaced by a push/jmp pair:
+    //
+    //     push .after_call
+    //     jmp CallTarget
+    //     .align bundle_size
+    // after_call:
+    //
+    // In order to emit this sequence, we need a temporary label ("after_call",
+    // in this example.)
+    //
+    // The operand to push is a ConstantRelocatable. The easy way to implement
+    // this sequence is to create a ConstantRelocatable(0, "after_call"), but
+    // this ends up creating more relocations for the linker to resolve.
+    // Therefore, we create a ConstantRelocatable from the name of the function
+    // being compiled (i.e., ConstantRelocatable(after_call - Func, Func).
+    //
+    // By default, ConstantRelocatables are emitted (in textual output) as
+    //
+    //  ConstantName + Offset
+    //
+    // ReturnReloc has an offset that is only known during binary emission.
+    // Therefore, we set a custom emit string for ReturnReloc that will be
+    // used instead. In this particular case, the code will be emitted as
+    //
+    //  push .after_call
     InstX86Label *ReturnAddress = InstX86Label::create(Func, this);
-    ReturnAddress->setIsReturnLocation(true);
+    auto *ReturnRelocOffset = RelocOffset::create(Ctx);
+    ReturnAddress->setRelocOffset(ReturnRelocOffset);
     constexpr bool SuppressMangling = true;
+    const IceString EmitString = ReturnAddress->getName(Func);
+    auto *ReturnReloc = llvm::cast<ConstantRelocatable>(Ctx->getConstantSym(
+        {ReturnRelocOffset}, Ctx->mangleName(Func->getFunctionName()),
+        EmitString, SuppressMangling));
     /* AutoBundle scoping */ {
       std::unique_ptr<AutoBundle> Bundler;
       if (CallTargetR == nullptr) {
         Bundler = makeUnique<AutoBundle>(this, InstBundleLock::Opt_PadToEnd);
-        _push(Ctx->getConstantSym(0, ReturnAddress->getName(Func),
-                                  SuppressMangling));
+        _push(ReturnReloc);
       } else {
         Variable *T = makeReg(IceType_i32);
         Variable *T64 = makeReg(IceType_i64);
@@ -615,8 +644,7 @@ Inst *TargetX8664::emitCallToTarget(Operand *CallTarget, Variable *ReturnReg) {
 
         _mov(T, CallTargetR);
         Bundler = makeUnique<AutoBundle>(this, InstBundleLock::Opt_PadToEnd);
-        _push(Ctx->getConstantSym(0, ReturnAddress->getName(Func),
-                                  SuppressMangling));
+        _push(ReturnReloc);
         const SizeT BundleSize =
             1 << Func->getAssembler<>()->getBundleAlignLog2Bytes();
         _and(T, Ctx->getConstantInt32(~(BundleSize - 1)));

src/IceTargetLoweringX8664Traits.h

@@ -74,7 +74,7 @@ struct TargetX8664Traits {
       RegX8664::Encoded_Reg_eax;
   static constexpr GPRRegister Encoded_Reg_Counter = RegX8664::Encoded_Reg_ecx;
   static constexpr FixupKind FK_PcRel = llvm::ELF::R_X86_64_PC32;
-  static constexpr FixupKind FK_Abs = llvm::ELF::R_X86_64_32;
+  static constexpr FixupKind FK_Abs = llvm::ELF::R_X86_64_32S;
   static constexpr FixupKind FK_Gotoff = llvm::ELF::R_X86_64_GOTOFF64;
   static constexpr FixupKind FK_GotPC = llvm::ELF::R_X86_64_GOTPC32;
 

tests_lit/assembler/x86/sandboxing.ll

@@ -28,9 +28,8 @@ entry:
 ; CHECK: 1b: {{.*}} call 1c
 ; CHECK-NEXT: 20:
 ; X8664-LABEL: test_direct_call
-; X8664: push {{.*}}$local$__0
+; X8664: push {{.*}} R_X86_64_32S test_direct_call+{{.*}}20
 ; X8664: jmp {{.*}} call_target
-; X8664: {{0+}}20 <{{.*}}$local$__0>:
 
 ; An indirect call sequence uses the right mask and register-call sequence.
 define internal void @test_indirect_call(i32 %target) {
@@ -46,11 +45,10 @@ entry:
 ; CHECK-NEXT: call [[REG]]
 ; CHECk-NEXT: 20:
 ; X8664-LABEL: test_indirect_call
-; X8664: push {{.*}}$local$__0
+; X8664: push {{.*}} R_X86_64_32S test_indirect_call+{{.*}}20
 ; X8664: {{.*}} and e[[REG:..]],0xffffffe0
 ; X8664: add r[[REG]],r15
 ; X8664: jmp r[[REG]]
-; X8664: {{0+}}20 <{{.*}}$local$__0>:
 
 ; A return sequence uses the right pop / mask / jmp sequence.
 define internal void @test_ret() {
@@ -271,8 +269,7 @@ define internal void @bundle_lock_pad_to_end_padding_0(i32 %arg0, i32 %arg1,
   ; bundle boundary
   ret void
 }
-; X8664-LABEL: bundle_lock_pad_to_end_padding_0$local$__0
-; X8664: 56: {{.*}} push {{.*}}$local$__1
+; X8664: 56: {{.*}} push {{.*}} R_X86_64_32S bundle_lock_pad_to_end_padding_0+{{.*}}60
 ; X8664: 5b: {{.*}} jmp {{.*}} call_target
 ; X8664: 60: {{.*}} add
 
@@ -289,8 +286,7 @@ define internal void @bundle_lock_pad_to_end_padding_11(i32 %arg0, i32 %arg1,
   ; bundle boundary
   ret void
 }
-; X8664-LABEL: bundle_lock_pad_to_end_padding_11$local$__0
-; X8664: 4b: {{.*}} push {{.*}}$local$__1
+; X8664: 4b: {{.*}} push {{.*}} R_X86_64_32S bundle_lock_pad_to_end_padding_11+{{.*}}60
 ; X8664: 50: {{.*}} jmp {{.*}} call_target
 ; X8664: 55: {{.*}} nop
 ; X8664: 5d: {{.*}} nop
@@ -308,8 +304,7 @@ define internal void @bundle_lock_pad_to_end_padding_22(i32 %arg0, i32 %arg1,
   ; bundle boundary
   ret void
 }
-; X8664-LABEL: bundle_lock_pad_to_end_padding_22$local$__0
-; X8664: 40: {{.*}} push {{.*}}$local$__1
+; X8664: 40: {{.*}} push {{.*}} R_X86_64_32S bundle_lock_pad_to_end_padding_22+{{.*}}60
 ; X8664: 45: {{.*}} jmp {{.*}} call_target
 ; X8664: 4a: {{.*}} nop
 ; X8664: 52: {{.*}} nop