[WebAssembly] Define WebAssembly-specific relocation codes.

Currently WebAssembly has two kinds of relocations; data addresses and
function addresses. This adds ELF relocations for them, as well as an
MC symbol kind to indicate which type of relocation is needed.

llvm-svn: 257416

5 files changed, 58 insertions, 15 deletions

diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyELFObjectWriter.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyELFObjectWriter.cpp
index c47a3d9094e..f9012d8fb77 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyELFObjectWriter.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyELFObjectWriter.cpp
@@ -41,8 +41,23 @@ WebAssemblyELFObjectWriter::WebAssemblyELFObjectWriter(bool Is64Bit,
 unsigned WebAssemblyELFObjectWriter::GetRelocType(const MCValue &Target,
                                                   const MCFixup &Fixup,
                                                   bool IsPCRel) const {
-  // FIXME: Do we need our own relocs?
-  return Fixup.getKind();
+  // WebAssembly functions are not allocated in the address space. To resolve a
+  // pointer to a function, we must use a special relocation type.
+  if (const MCSymbolRefExpr *SyExp =
+          dyn_cast<MCSymbolRefExpr>(Fixup.getValue()))
+    if (SyExp->getKind() == MCSymbolRefExpr::VK_WebAssembly_FUNCTION)
+      return ELF::R_WEBASSEMBLY_FUNCTION;
+
+  switch (Fixup.getKind()) {
+  case FK_Data_4:
+    assert(!is64Bit() && "4-byte relocations only supported on wasm32");
+    return ELF::R_WEBASSEMBLY_DATA;
+  case FK_Data_8:
+    assert(is64Bit() && "8-byte relocations only supported on wasm64");
+    return ELF::R_WEBASSEMBLY_DATA;
+  default:
+    llvm_unreachable("unimplemented fixup kind");
+  }
 }
 
 MCObjectWriter *llvm::createWebAssemblyELFObjectWriter(raw_pwrite_stream &OS,
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
index 6c1ef40b0cc..8d84901b3a2 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -70,6 +70,7 @@ private:
   void EmitConstantPool() override;
   void EmitFunctionBodyStart() override;
   void EmitInstruction(const MachineInstr *MI) override;
+  const MCExpr *lowerConstant(const Constant *CV) override;
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,
                        raw_ostream &OS) override;
@@ -221,6 +222,14 @@ void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   }
 }
 
+const MCExpr *WebAssemblyAsmPrinter::lowerConstant(const Constant *CV) {
+  if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV))
+    if (GV->getValueType()->isFunctionTy())
+      return MCSymbolRefExpr::create(
+          getSymbol(GV), MCSymbolRefExpr::VK_WebAssembly_FUNCTION, OutContext);
+  return AsmPrinter::lowerConstant(CV);
+}
+
 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
                                             unsigned OpNo, unsigned AsmVariant,
                                             const char *ExtraCode,
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index 7a89f788c1a..e9933b09298 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -573,7 +573,8 @@ SDValue WebAssemblyTargetLowering::LowerGlobalAddress(SDValue Op,
   SDLoc DL(Op);
   const auto *GA = cast<GlobalAddressSDNode>(Op);
   EVT VT = Op.getValueType();
-  assert(GA->getTargetFlags() == 0 && "WebAssembly doesn't set target flags");
+  assert(GA->getTargetFlags() == 0 &&
+         "Unexpected target flags on generic GlobalAddressSDNode");
   if (GA->getAddressSpace() != 0)
     fail(DL, DAG, "WebAssembly only expects the 0 address space");
   return DAG.getNode(
@@ -587,9 +588,16 @@ WebAssemblyTargetLowering::LowerExternalSymbol(SDValue Op,
   SDLoc DL(Op);
   const auto *ES = cast<ExternalSymbolSDNode>(Op);
   EVT VT = Op.getValueType();
-  assert(ES->getTargetFlags() == 0 && "WebAssembly doesn't set target flags");
+  assert(ES->getTargetFlags() == 0 &&
+         "Unexpected target flags on generic ExternalSymbolSDNode");
+  // Set the TargetFlags to 0x1 which indicates that this is a "function"
+  // symbol rather than a data symbol. We do this unconditionally even though
+  // we don't know anything about the symbol other than its name, because all
+  // external symbols used in target-independent SelectionDAG code are for
+  // functions.
   return DAG.getNode(WebAssemblyISD::Wrapper, DL, VT,
-                     DAG.getTargetExternalSymbol(ES->getSymbol(), VT));
+                     DAG.getTargetExternalSymbol(ES->getSymbol(), VT,
+                                                 /*TargetFlags=*/0x1));
 }
 
 SDValue WebAssemblyTargetLowering::LowerJumpTable(SDValue Op,
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
index a953f824700..eaba53e46ed 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
@@ -36,15 +36,17 @@ MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
   return Printer.GetExternalSymbolSymbol(MO.getSymbolName());
 }
 
-MCOperand WebAssemblyMCInstLower::LowerSymbolOperand(const MachineOperand &MO,
-                                                     MCSymbol *Sym) const {
-  assert(MO.getTargetFlags() == 0 && "WebAssembly does not use target flags");
+MCOperand WebAssemblyMCInstLower::LowerSymbolOperand(MCSymbol *Sym,
+                                                     int64_t Offset,
+                                                     bool IsFunc) const {
+  MCSymbolRefExpr::VariantKind VK =
+      IsFunc ? MCSymbolRefExpr::VK_WebAssembly_FUNCTION
+             : MCSymbolRefExpr::VK_None;
+  const MCExpr *Expr = MCSymbolRefExpr::create(Sym, VK, Ctx);
 
-  const MCExpr *Expr = MCSymbolRefExpr::create(Sym, Ctx);
-
-  int64_t Offset = MO.getOffset();
   if (Offset != 0) {
-    assert(!MO.isJTI() && "Unexpected offset with jump table index");
+    if (IsFunc)
+      report_fatal_error("Function addresses with offsets not supported");
     Expr =
         MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, Ctx), Ctx);
   }
@@ -94,10 +96,18 @@ void WebAssemblyMCInstLower::Lower(const MachineInstr *MI,
           MCSymbolRefExpr::create(MO.getMBB()->getSymbol(), Ctx));
       break;
     case MachineOperand::MO_GlobalAddress:
-      MCOp = LowerSymbolOperand(MO, GetGlobalAddressSymbol(MO));
+      assert(MO.getTargetFlags() == 0 &&
+             "WebAssembly does not use target flags on GlobalAddresses");
+      MCOp = LowerSymbolOperand(GetGlobalAddressSymbol(MO), MO.getOffset(),
+                                MO.getGlobal()->getValueType()->isFunctionTy());
       break;
     case MachineOperand::MO_ExternalSymbol:
-      MCOp = LowerSymbolOperand(MO, GetExternalSymbolSymbol(MO));
+      // The target flag indicates whether this is a symbol for a
+      // variable or a function.
+      assert((MO.getTargetFlags() & -2) == 0 &&
+             "WebAssembly uses only one target flag bit on ExternalSymbols");
+      MCOp = LowerSymbolOperand(GetExternalSymbolSymbol(MO), /*Offset=*/0,
+                                MO.getTargetFlags() & 1);
       break;
     }
 
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.h b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.h
index 6d704704f57..ab4ba1c28d5 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.h
@@ -31,9 +31,10 @@ class LLVM_LIBRARY_VISIBILITY WebAssemblyMCInstLower {
   MCContext &Ctx;
   AsmPrinter &Printer;
 
-  MCOperand LowerSymbolOperand(const MachineOperand &MO, MCSymbol *Sym) const;
   MCSymbol *GetGlobalAddressSymbol(const MachineOperand &MO) const;
   MCSymbol *GetExternalSymbolSymbol(const MachineOperand &MO) const;
+  MCOperand LowerSymbolOperand(MCSymbol *Sym, int64_t Offset,
+                               bool IsFunc) const;
 
 public:
   WebAssemblyMCInstLower(MCContext &ctx, AsmPrinter &printer)