[WebAssembly] Use __stack_pointer global when writing wasm binary

This ensures that symbolic relocations are generated for stack
pointer manipulations.

These relocations are of type R_WEBASSEMBLY_GLOBAL_INDEX_LEB.
This change also adds support for reading relocations of this
type in WasmObjectFile.cpp.

Since its a globally imported symbol this does mean that
the get_global/set_global instruction won't be valid until
the objects are linked that global used in no longer an
imported global.

Differential Revision: https://reviews.llvm.org/D34172

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305616 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineModuleInfoImpls.h

@@ -77,33 +77,6 @@ class MachineModuleInfoELF : public MachineModuleInfoImpl {
   SymbolListTy GetGVStubList() { return getSortedStubs(GVStubs); }
 };
 
-/// MachineModuleInfoWasm - This is a MachineModuleInfoImpl implementation
-/// for Wasm targets.
-class MachineModuleInfoWasm : public MachineModuleInfoImpl {
-  /// WebAssembly global variables defined by CodeGen.
-  std::vector<wasm::Global> Globals;
-
-  /// The WebAssembly global variable which is the stack pointer.
-  unsigned StackPointerGlobal;
-
-  virtual void anchor(); // Out of line virtual method.
-public:
-  MachineModuleInfoWasm(const MachineModuleInfo &)
-    : StackPointerGlobal(-1U) {}
-
-  void addGlobal(const wasm::Global &G) { Globals.push_back(G); }
-  const std::vector<wasm::Global> &getGlobals() const { return Globals; }
-
-  bool hasStackPointerGlobal() const {
-    return StackPointerGlobal != -1U;
-  }
-  unsigned getStackPointerGlobal() const {
-    assert(hasStackPointerGlobal() && "Stack ptr global hasn't been set");
-    return StackPointerGlobal;
-  }
-  void setStackPointerGlobal(unsigned Global) { StackPointerGlobal = Global; }
-};
-
 } // end namespace llvm
 
 #endif

lib/CodeGen/MachineModuleInfoImpls.cpp

@@ -23,7 +23,6 @@ using namespace llvm;
 // Out of line virtual method.
 void MachineModuleInfoMachO::anchor() {}
 void MachineModuleInfoELF::anchor() {}
-void MachineModuleInfoWasm::anchor() {}
 
 static int SortSymbolPair(const void *LHS, const void *RHS) {
   typedef std::pair<MCSymbol*, MachineModuleInfoImpl::StubValueTy> PairTy;

lib/MC/WasmObjectWriter.cpp

@@ -406,6 +406,8 @@ void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
   }
 
   assert(!IsPCRel);
+  assert(SymA);
+
   unsigned Type = getRelocType(Target, Fixup);
 
   WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
@@ -474,6 +476,7 @@ uint32_t WasmObjectWriter::getRelocationIndexValue(
     assert(IndirectSymbolIndices.count(RelEntry.Symbol));
     return IndirectSymbolIndices[RelEntry.Symbol];
   case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
+  case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
   case wasm::R_WEBASSEMBLY_GLOBAL_ADDR_LEB:
   case wasm::R_WEBASSEMBLY_GLOBAL_ADDR_SLEB:
   case wasm::R_WEBASSEMBLY_GLOBAL_ADDR_I32:
@@ -500,7 +503,8 @@ void WasmObjectWriter::applyRelocations(
     switch (RelEntry.Type) {
     case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
     case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
-    case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB: {
+    case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
+    case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB: {
       uint32_t Index = getRelocationIndexValue(RelEntry);
       WritePatchableSLEB(Stream, Index, Offset);
       break;
@@ -526,7 +530,7 @@ void WasmObjectWriter::applyRelocations(
       break;
     }
     default:
-      llvm_unreachable("unsupported relocation type");
+      llvm_unreachable("invalid relocation type");
     }
   }
 }

lib/Object/WasmObjectFile.cpp

@@ -325,14 +325,16 @@ Error WasmObjectFile::parseRelocSection(StringRef Name, const uint8_t *Ptr,
     case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
     case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
     case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
+    case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
       break;
     case wasm::R_WEBASSEMBLY_GLOBAL_ADDR_LEB:
     case wasm::R_WEBASSEMBLY_GLOBAL_ADDR_SLEB:
     case wasm::R_WEBASSEMBLY_GLOBAL_ADDR_I32:
       Reloc.Addend = readVarint32(Ptr);
       break;
     default:
-      return make_error<GenericBinaryError>("Bad relocation type",
+      return make_error<GenericBinaryError>("Bad relocation type: " +
+                                                Twine(Reloc.Type),
                                             object_error::parse_failed);
     }
     Section->Relocations.push_back(Reloc);

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp

@@ -36,7 +36,6 @@ STATISTIC(MCNumFixups, "Number of MC fixups created.");
 namespace {
 class WebAssemblyMCCodeEmitter final : public MCCodeEmitter {
   const MCInstrInfo &MCII;
-  MCContext &Ctx;
 
   // Implementation generated by tablegen.
   uint64_t getBinaryCodeForInstr(const MCInst &MI,
@@ -48,14 +47,12 @@ class WebAssemblyMCCodeEmitter final : public MCCodeEmitter {
                          const MCSubtargetInfo &STI) const override;
 
 public:
-  WebAssemblyMCCodeEmitter(const MCInstrInfo &mcii, MCContext &ctx)
-      : MCII(mcii), Ctx(ctx) {}
+  WebAssemblyMCCodeEmitter(const MCInstrInfo &mcii) : MCII(mcii) {}
 };
 } // end anonymous namespace
 
-MCCodeEmitter *llvm::createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII,
-                                                    MCContext &Ctx) {
-  return new WebAssemblyMCCodeEmitter(MCII, Ctx);
+MCCodeEmitter *llvm::createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII) {
+  return new WebAssemblyMCCodeEmitter(MCII);
 }
 
 void WebAssemblyMCCodeEmitter::encodeInstruction(
@@ -89,11 +86,7 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
         } else if (Info.OperandType == WebAssembly::OPERAND_I64IMM) {
           encodeSLEB128(int64_t(MO.getImm()), OS);
         } else if (Info.OperandType == WebAssembly::OPERAND_GLOBAL) {
-          Fixups.push_back(MCFixup::create(
-              OS.tell() - Start, MCConstantExpr::create(MO.getImm(), Ctx),
-              MCFixupKind(WebAssembly::fixup_code_global_index), MI.getLoc()));
-          ++MCNumFixups;
-          encodeULEB128(uint64_t(MO.getImm()), OS);
+          llvm_unreachable("wasm globals should only be accessed symbolicly");
         } else if (Info.OperandType == WebAssembly::OPERAND_SIGNATURE) {
           encodeSLEB128(int64_t(MO.getImm()), OS);
         } else {
@@ -135,6 +128,9 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
                  Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
         FixupKind = MCFixupKind(WebAssembly::fixup_code_uleb128_i32);
         PaddedSize = 5;
+      } else if (Info.OperandType == WebAssembly::OPERAND_GLOBAL) {
+        FixupKind = MCFixupKind(WebAssembly::fixup_code_global_index);
+        PaddedSize = 5;
       } else {
         llvm_unreachable("unexpected symbolic operand kind");
       }

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.cpp

@@ -74,7 +74,7 @@ static MCInstPrinter *createMCInstPrinter(const Triple & /*T*/,
 static MCCodeEmitter *createCodeEmitter(const MCInstrInfo &MCII,
                                         const MCRegisterInfo & /*MRI*/,
                                         MCContext &Ctx) {
-  return createWebAssemblyMCCodeEmitter(MCII, Ctx);
+  return createWebAssemblyMCCodeEmitter(MCII);
 }
 
 static MCAsmBackend *createAsmBackend(const Target & /*T*/,

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h

@@ -35,8 +35,7 @@ class raw_pwrite_stream;
 Target &getTheWebAssemblyTarget32();
 Target &getTheWebAssemblyTarget64();
 
-MCCodeEmitter *createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII,
-                                              MCContext &Ctx);
+MCCodeEmitter *createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII);
 
 MCAsmBackend *createWebAssemblyAsmBackend(const Triple &TT);
 

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp

@@ -68,6 +68,8 @@ WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
   bool IsFunction = IsFunctionExpr(Fixup.getValue());
 
   switch (unsigned(Fixup.getKind())) {
+  case WebAssembly::fixup_code_global_index:
+    return wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB;
   case WebAssembly::fixup_code_sleb128_i32:
     if (IsFunction)
       return wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB;

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

@@ -96,13 +96,6 @@ void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
                                MCConstantExpr::create(Size, OutContext));
     }
   }
-
-  if (!TM.getTargetTriple().isOSBinFormatELF()) {
-    MachineModuleInfoWasm &MMIW = MMI->getObjFileInfo<MachineModuleInfoWasm>();
-    getTargetStreamer()->emitGlobal(MMIW.getGlobals());
-    if (MMIW.hasStackPointerGlobal())
-      getTargetStreamer()->emitStackPointer(MMIW.getStackPointerGlobal());
-  }
 }
 
 void WebAssemblyAsmPrinter::EmitConstantPool() {

lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp

@@ -104,10 +104,10 @@ static void writeSPToMemory(unsigned SrcReg, MachineFunction &MF,
                             const DebugLoc &DL) {
   const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
 
+  const char *ES = "__stack_pointer";
+  auto *SPSymbol = MF.createExternalSymbolName(ES);
   if (MF.getSubtarget<WebAssemblySubtarget>()
         .getTargetTriple().isOSBinFormatELF()) {
-    const char *ES = "__stack_pointer";
-    auto *SPSymbol = MF.createExternalSymbolName(ES);
     MachineRegisterInfo &MRI = MF.getRegInfo();
     const TargetRegisterClass *PtrRC =
         MRI.getTargetRegisterInfo()->getPointerRegClass(MF);
@@ -125,10 +125,8 @@ static void writeSPToMemory(unsigned SrcReg, MachineFunction &MF,
         .addReg(SrcReg)
         .addMemOperand(MMO);
   } else {
-    MachineModuleInfoWasm &MMIW =
-        MF.getMMI().getObjFileInfo<MachineModuleInfoWasm>();
     BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::SET_GLOBAL_I32))
-        .addImm(MMIW.getStackPointerGlobal())
+        .addExternalSymbol(SPSymbol)
         .addReg(SrcReg);
   }
 }
@@ -171,10 +169,11 @@ void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
   unsigned SPReg = WebAssembly::SP32;
   if (StackSize)
     SPReg = MRI.createVirtualRegister(PtrRC);
+
+  const char *ES = "__stack_pointer";
+  auto *SPSymbol = MF.createExternalSymbolName(ES);
   if (MF.getSubtarget<WebAssemblySubtarget>()
         .getTargetTriple().isOSBinFormatELF()) {
-    const char *ES = "__stack_pointer";
-    auto *SPSymbol = MF.createExternalSymbolName(ES);
     unsigned Zero = MRI.createVirtualRegister(PtrRC);
 
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), Zero)
@@ -189,22 +188,8 @@ void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
         .addReg(Zero)    // addr
         .addMemOperand(LoadMMO);
   } else {
-    auto &MMIW = MF.getMMI().getObjFileInfo<MachineModuleInfoWasm>();
-    if (!MMIW.hasStackPointerGlobal()) {
-      MMIW.setStackPointerGlobal(MMIW.getGlobals().size());
-
-      // Create the stack-pointer global. For now, just use the
-      // Emscripten/Binaryen ABI names.
-      wasm::Global G;
-      G.Type = wasm::ValType::I32;
-      G.Mutable = true;
-      G.InitialValue = 0;
-      G.InitialModule = "env";
-      G.InitialName = "STACKTOP";
-      MMIW.addGlobal(G);
-    }
     BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::GET_GLOBAL_I32), SPReg)
-        .addImm(MMIW.getStackPointerGlobal());
+        .addExternalSymbol(SPSymbol);
   }
 
   bool HasBP = hasBP(MF);

lib/Target/WebAssembly/WebAssemblyRegStackify.cpp

@@ -170,28 +170,16 @@ static void Query(const MachineInstr &MI, AliasAnalysis &AA, bool &Read,
   if (MI.mayStore()) {
     Write = true;
 
-    const MachineFunction &MF = *MI.getParent()->getParent();
-    if (MF.getSubtarget<WebAssemblySubtarget>()
-          .getTargetTriple().isOSBinFormatELF()) {
-      // Check for stores to __stack_pointer.
-      for (auto MMO : MI.memoperands()) {
-        const MachinePointerInfo &MPI = MMO->getPointerInfo();
-        if (MPI.V.is<const PseudoSourceValue *>()) {
-          auto PSV = MPI.V.get<const PseudoSourceValue *>();
-          if (const ExternalSymbolPseudoSourceValue *EPSV =
-                  dyn_cast<ExternalSymbolPseudoSourceValue>(PSV))
-            if (StringRef(EPSV->getSymbol()) == "__stack_pointer")
-              StackPointer = true;
-        }
-      }
-    } else {
-      // Check for sets of the stack pointer.
-      const MachineModuleInfoWasm &MMIW =
-          MF.getMMI().getObjFileInfo<MachineModuleInfoWasm>();
-      if ((MI.getOpcode() == WebAssembly::SET_LOCAL_I32 ||
-           MI.getOpcode() == WebAssembly::SET_LOCAL_I64) &&
-          MI.getOperand(0).getImm() == MMIW.getStackPointerGlobal()) {
-        StackPointer = true;
+    // Check for stores to __stack_pointer.
+    for (auto MMO : MI.memoperands()) {
+      const MachinePointerInfo &MPI = MMO->getPointerInfo();
+      if (MPI.V.is<const PseudoSourceValue *>()) {
+        auto PSV = MPI.V.get<const PseudoSourceValue *>();
+        if (const ExternalSymbolPseudoSourceValue *EPSV =
+                dyn_cast<ExternalSymbolPseudoSourceValue>(PSV))
+          if (StringRef(EPSV->getSymbol()) == "__stack_pointer") {
+            StackPointer = true;
+          }
       }
     }
   } else if (MI.hasOrderedMemoryRef()) {

test/CodeGen/WebAssembly/byval.ll

@@ -24,12 +24,12 @@ declare void @ext_byval_func_empty(%EmptyStruct* byval)
 define void @byval_arg(%SmallStruct* %ptr) {
  ; CHECK: .param i32
  ; Subtract 16 from SP (SP is 16-byte aligned)
- ; CHECK-NEXT: get_global $push[[L2:.+]]=, 0
+ ; CHECK-NEXT: get_global $push[[L2:.+]]=, __stack_pointer
  ; CHECK-NEXT: i32.const $push[[L3:.+]]=, 16
  ; CHECK-NEXT: i32.sub $push[[L11:.+]]=, $pop[[L2]], $pop[[L3]]
  ; Ensure SP is stored back before the call
  ; CHECK-NEXT: tee_local $push[[L10:.+]]=, $[[SP:.+]]=, $pop[[L11]]{{$}}
- ; CHECK-NEXT: set_global 0, $pop[[L10]]{{$}}
+ ; CHECK-NEXT: set_global __stack_pointer, $pop[[L10]]{{$}}
  ; Copy the SmallStruct argument to the stack (SP+12, original SP-4)
  ; CHECK-NEXT: i32.load $push[[L0:.+]]=, 0($0)
  ; CHECK-NEXT: i32.store 12($[[SP]]), $pop[[L0]]
@@ -41,7 +41,7 @@ define void @byval_arg(%SmallStruct* %ptr) {
  ; Restore the stack
  ; CHECK-NEXT: i32.const $push[[L6:.+]]=, 16
  ; CHECK-NEXT: i32.add $push[[L8:.+]]=, $[[SP]], $pop[[L6]]
- ; CHECK-NEXT: set_global 0, $pop[[L8]]
+ ; CHECK-NEXT: set_global __stack_pointer, $pop[[L8]]
  ; CHECK-NEXT: return
  ret void
 }
@@ -53,7 +53,7 @@ define void @byval_arg_align8(%SmallStruct* %ptr) {
  ; CHECK: i32.const $push[[L1:.+]]=, 16
  ; CHECK-NEXT: i32.sub $push[[L11:.+]]=, {{.+}}, $pop[[L1]]
  ; CHECK-NEXT: tee_local $push[[L10:.+]]=, $[[SP:.+]]=, $pop[[L11]]{{$}}
- ; CHECK-NEXT: set_global 0, $pop[[L10]]{{$}}
+ ; CHECK-NEXT: set_global __stack_pointer, $pop[[L10]]{{$}}
  ; Copy the SmallStruct argument to the stack (SP+8, original SP-8)
  ; CHECK-NEXT: i32.load $push[[L0:.+]]=, 0($0){{$}}
  ; CHECK-NEXT: i32.store 8($[[SP]]), $pop[[L0]]{{$}}
@@ -72,7 +72,7 @@ define void @byval_arg_double(%AlignedStruct* %ptr) {
  ; CHECK: i32.const $push[[L1:.+]]=, 16
  ; CHECK-NEXT: i32.sub $push[[L14:.+]]=, {{.+}}, $pop[[L1]]
  ; CHECK-NEXT: tee_local $push[[L13:.+]]=, $[[SP:.+]]=, $pop[[L14]]
- ; CHECK-NEXT: set_global 0, $pop[[L13]]
+ ; CHECK-NEXT: set_global __stack_pointer, $pop[[L13]]
  ; Copy the AlignedStruct argument to the stack (SP+0, original SP-16)
  ; Just check the last load/store pair of the memcpy
  ; CHECK: i64.load $push[[L4:.+]]=, 0($0)
@@ -110,11 +110,11 @@ define void @byval_empty_callee(%EmptyStruct* byval %ptr) {
 
 ; Call memcpy for "big" byvals.
 ; CHECK-LABEL: big_byval:
-; CHECK:      get_global $push[[L2:.+]]=, 0{{$}}
+; CHECK:      get_global $push[[L2:.+]]=, __stack_pointer{{$}}
 ; CHECK-NEXT: i32.const $push[[L3:.+]]=, 131072
 ; CHECK-NEXT: i32.sub $push[[L11:.+]]=, $pop[[L2]], $pop[[L3]]
 ; CHECK-NEXT: tee_local $push[[L10:.+]]=, $[[SP:.+]]=, $pop[[L11]]{{$}}
-; CHECK-NEXT: set_global 0, $pop[[L10]]{{$}}
+; CHECK-NEXT: set_global __stack_pointer, $pop[[L10]]{{$}}
 ; CHECK-NEXT: i32.const $push[[L0:.+]]=, 131072
 ; CHECK-NEXT: i32.call       $push[[L11:.+]]=, memcpy@FUNCTION, $[[SP]], ${{.+}}, $pop{{.+}}
 ; CHECK-NEXT: tee_local      $push[[L9:.+]]=, $[[SP:.+]]=, $pop[[L11]]{{$}}

test/CodeGen/WebAssembly/reg-stackify.ll

@@ -448,7 +448,7 @@ bb10:                                             ; preds = %bb9, %bb
 
 ; CHECK-LABEL: stackpointer_dependency:
 ; CHECK:      call {{.+}}, stackpointer_callee@FUNCTION,
-; CHECK-NEXT: set_global 0,
+; CHECK-NEXT: set_global __stack_pointer,
 declare i32 @stackpointer_callee(i8* readnone, i8* readnone)
 declare i8* @llvm.frameaddress(i32)
 define i32 @stackpointer_dependency(i8* readnone) {