[WebAssembly] Add skeleton MC support for the Wasm container format

This just adds the basic skeleton for supporting a new object file format.
All of the actual encoding will be implemented in followup patches.

Differential Revision: https://reviews.llvm.org/D26722

llvm-svn: 295803

1 files changed, 119 insertions, 0 deletions

diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
new file mode 100644
index 00000000000..cb11bab01eb
--- /dev/null
+++ b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -0,0 +1,119 @@
+//===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements Wasm object file writer information.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCAsmLayout.h"
+#include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCFixupKindInfo.h"
+#include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCSectionWasm.h"
+#include "llvm/MC/MCSymbolWasm.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/MC/MCWasmObjectWriter.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/StringSaver.h"
+#include <vector>
+
+using namespace llvm;
+
+#undef DEBUG_TYPE
+#define DEBUG_TYPE "reloc-info"
+
+namespace {
+typedef DenseMap<const MCSectionWasm *, uint32_t> SectionIndexMapTy;
+
+class WasmObjectWriter : public MCObjectWriter {
+  /// Helper struct for containing some precomputed information on symbols.
+  struct WasmSymbolData {
+    const MCSymbolWasm *Symbol;
+    StringRef Name;
+
+    // Support lexicographic sorting.
+    bool operator<(const WasmSymbolData &RHS) const { return Name < RHS.Name; }
+  };
+
+  /// The target specific Wasm writer instance.
+  std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
+
+  // TargetObjectWriter wrappers.
+  bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
+  unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
+                        const MCFixup &Fixup, bool IsPCRel) const {
+    return TargetObjectWriter->getRelocType(Ctx, Target, Fixup, IsPCRel);
+  }
+
+public:
+  WasmObjectWriter(MCWasmObjectTargetWriter *MOTW, raw_pwrite_stream &OS)
+      : MCObjectWriter(OS, /*IsLittleEndian=*/true), TargetObjectWriter(MOTW) {}
+
+  void reset() override {
+    MCObjectWriter::reset();
+  }
+
+  ~WasmObjectWriter() override;
+
+  void writeHeader(const MCAssembler &Asm);
+
+  void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
+                        const MCFragment *Fragment, const MCFixup &Fixup,
+                        MCValue Target, bool &IsPCRel,
+                        uint64_t &FixedValue) override;
+
+  void executePostLayoutBinding(MCAssembler &Asm,
+                                const MCAsmLayout &Layout) override;
+
+  void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
+};
+} // end anonymous namespace
+
+WasmObjectWriter::~WasmObjectWriter() {}
+
+// Emit the Wasm header.
+void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
+  // TODO: write the magic cookie and the version.
+}
+
+void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
+                                                const MCAsmLayout &Layout) {
+}
+
+void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
+                                        const MCAsmLayout &Layout,
+                                        const MCFragment *Fragment,
+                                        const MCFixup &Fixup, MCValue Target,
+                                        bool &IsPCRel, uint64_t &FixedValue) {
+  // TODO: Implement
+}
+
+void WasmObjectWriter::writeObject(MCAssembler &Asm,
+                                   const MCAsmLayout &Layout) {
+  // Write out the Wasm header.
+  writeHeader(Asm);
+
+  // TODO: Write the contents.
+}
+
+MCObjectWriter *llvm::createWasmObjectWriter(MCWasmObjectTargetWriter *MOTW,
+                                             raw_pwrite_stream &OS) {
+  return new WasmObjectWriter(MOTW, OS);
+}