llvm/lib/MC/GOFFObjectWriter.cpp

   1 //===- lib/MC/GOFFObjectWriter.cpp - GOFF File Writer ---------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements GOFF object file writer information.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/BinaryFormat/GOFF.h"
  14 #include "llvm/MC/MCAssembler.h"
  15 #include "llvm/MC/MCGOFFObjectWriter.h"
  16 #include "llvm/MC/MCValue.h"
  17 #include "llvm/Support/Debug.h"
  18 #include "llvm/Support/Endian.h"
  19 #include "llvm/Support/Path.h"
  20 #include "llvm/Support/raw_ostream.h"
  21
  22 using namespace llvm;
  23
  24 #define DEBUG_TYPE "goff-writer"
  25
  26 namespace {
  27
  28 // The standard System/390 convention is to name the high-order (leftmost) bit
  29 // in a byte as bit zero. The Flags type helps to set bits in a byte according
  30 // to this numeration order.
  31 class Flags {
  32   uint8_t Val;
  33
  34   constexpr static uint8_t bits(uint8_t BitIndex, uint8_t Length, uint8_t Value,
  35                                 uint8_t OldValue) {
  36     assert(BitIndex < 8 && "Bit index out of bounds!");
  37     assert(Length + BitIndex <= 8 && "Bit length too long!");
  38
  39     uint8_t Mask = ((1 << Length) - 1) << (8 - BitIndex - Length);
  40     Value = Value << (8 - BitIndex - Length);
  41     assert((Value & Mask) == Value && "Bits set outside of range!");
  42
  43     return (OldValue & ~Mask) | Value;
  44   }
  45
  46 public:
  47   constexpr Flags() : Val(0) {}
  48   constexpr Flags(uint8_t BitIndex, uint8_t Length, uint8_t Value)
  49       : Val(bits(BitIndex, Length, Value, 0)) {}
  50
  51   void set(uint8_t BitIndex, uint8_t Length, uint8_t Value) {
  52     Val = bits(BitIndex, Length, Value, Val);
  53   }
  54
  55   constexpr operator uint8_t() const { return Val; }
  56 };
  57
  58 // Common flag values on records.
  59
  60 // Flag: This record is continued.
  61 constexpr uint8_t RecContinued = Flags(7, 1, 1);
  62
  63 // Flag: This record is a continuation.
  64 constexpr uint8_t RecContinuation = Flags(6, 1, 1);
  65
  66 // The GOFFOstream is responsible to write the data into the fixed physical
  67 // records of the format. A user of this class announces the start of a new
  68 // logical record and the size of its content. While writing the content, the
  69 // physical records are created for the data. Possible fill bytes at the end of
  70 // a physical record are written automatically. In principle, the GOFFOstream
  71 // is agnostic of the endianness of the content. However, it also supports
  72 // writing data in big endian byte order.
  73 class GOFFOstream : public raw_ostream {
  74   /// The underlying raw_pwrite_stream.
  75   raw_pwrite_stream &OS;
  76
  77   /// The remaining size of this logical record, including fill bytes.
  78   size_t RemainingSize;
  79
  80 #ifndef NDEBUG
  81   /// The number of bytes needed to fill up the last physical record.
  82   size_t Gap = 0;
  83 #endif
  84
  85   /// The number of logical records emitted to far.
  86   uint32_t LogicalRecords;
  87
  88   /// The type of the current (logical) record.
  89   GOFF::RecordType CurrentType;
  90
  91   /// Signals start of new record.
  92   bool NewLogicalRecord;
  93
  94   /// Static allocated buffer for the stream, used by the raw_ostream class. The
  95   /// buffer is sized to hold the content of a physical record.
  96   char Buffer[GOFF::RecordContentLength];
  97
  98   // Return the number of bytes left to write until next physical record.
  99   // Please note that we maintain the total numbers of byte left, not the
 100   // written size.
 101   size_t bytesToNextPhysicalRecord() {
 102     size_t Bytes = RemainingSize % GOFF::RecordContentLength;
 103     return Bytes ? Bytes : GOFF::RecordContentLength;
 104   }
 105
 106   /// Write the record prefix of a physical record, using the given record type.
 107   static void writeRecordPrefix(raw_ostream &OS, GOFF::RecordType Type,
 108                                 size_t RemainingSize,
 109                                 uint8_t Flags = RecContinuation);
 110
 111   /// Fill the last physical record of a logical record with zero bytes.
 112   void fillRecord();
 113
 114   /// See raw_ostream::write_impl.
 115   void write_impl(const char *Ptr, size_t Size) override;
 116
 117   /// Return the current position within the stream, not counting the bytes
 118   /// currently in the buffer.
 119   uint64_t current_pos() const override { return OS.tell(); }
 120
 121 public:
 122   explicit GOFFOstream(raw_pwrite_stream &OS)
 123       : OS(OS), RemainingSize(0), LogicalRecords(0), NewLogicalRecord(false) {
 124     SetBuffer(Buffer, sizeof(Buffer));
 125   }
 126
 127   ~GOFFOstream() { finalize(); }
 128
 129   raw_pwrite_stream &getOS() { return OS; }
 130
 131   void newRecord(GOFF::RecordType Type, size_t Size);
 132
 133   void finalize() { fillRecord(); }
 134
 135   uint32_t logicalRecords() { return LogicalRecords; }
 136
 137   // Support for endian-specific data.
 138   template <typename value_type> void writebe(value_type Value) {
 139     Value =
 140         support::endian::byte_swap<value_type>(Value, llvm::endianness::big);
 141     write(reinterpret_cast<const char *>(&Value), sizeof(value_type));
 142   }
 143 };
 144
 145 void GOFFOstream::writeRecordPrefix(raw_ostream &OS, GOFF::RecordType Type,
 146                                     size_t RemainingSize, uint8_t Flags) {
 147   uint8_t TypeAndFlags = Flags | (Type << 4);
 148   if (RemainingSize > GOFF::RecordLength)
 149     TypeAndFlags |= RecContinued;
 150   OS << static_cast<unsigned char>(GOFF::PTVPrefix) // Record Type
 151      << static_cast<unsigned char>(TypeAndFlags)    // Continuation
 152      << static_cast<unsigned char>(0);              // Version
 153 }
 154
 155 void GOFFOstream::newRecord(GOFF::RecordType Type, size_t Size) {
 156   fillRecord();
 157   CurrentType = Type;
 158   RemainingSize = Size;
 159 #ifdef NDEBUG
 160   size_t Gap;
 161 #endif
 162   Gap = (RemainingSize % GOFF::RecordContentLength);
 163   if (Gap) {
 164     Gap = GOFF::RecordContentLength - Gap;
 165     RemainingSize += Gap;
 166   }
 167   NewLogicalRecord = true;
 168   ++LogicalRecords;
 169 }
 170
 171 void GOFFOstream::fillRecord() {
 172   assert((GetNumBytesInBuffer() <= RemainingSize) &&
 173          "More bytes in buffer than expected");
 174   size_t Remains = RemainingSize - GetNumBytesInBuffer();
 175   if (Remains) {
 176     assert(Remains == Gap && "Wrong size of fill gap");
 177     assert((Remains < GOFF::RecordLength) &&
 178            "Attempt to fill more than one physical record");
 179     raw_ostream::write_zeros(Remains);
 180   }
 181   flush();
 182   assert(RemainingSize == 0 && "Not fully flushed");
 183   assert(GetNumBytesInBuffer() == 0 && "Buffer not fully empty");
 184 }
 185
 186 // This function is called from the raw_ostream implementation if:
 187 // - The internal buffer is full. Size is excactly the size of the buffer.
 188 // - Data larger than the internal buffer is written. Size is a multiple of the
 189 //   buffer size.
 190 // - flush() has been called. Size is at most the buffer size.
 191 // The GOFFOstream implementation ensures that flush() is called before a new
 192 // logical record begins. Therefore it is sufficient to check for a new block
 193 // only once.
 194 void GOFFOstream::write_impl(const char *Ptr, size_t Size) {
 195   assert((RemainingSize >= Size) && "Attempt to write too much data");
 196   assert(RemainingSize && "Logical record overflow");
 197   if (!(RemainingSize % GOFF::RecordContentLength)) {
 198     writeRecordPrefix(OS, CurrentType, RemainingSize,
 199                       NewLogicalRecord ? 0 : RecContinuation);
 200     NewLogicalRecord = false;
 201   }
 202   assert(!NewLogicalRecord &&
 203          "New logical record not on physical record boundary");
 204
 205   size_t Idx = 0;
 206   while (Size > 0) {
 207     size_t BytesToWrite = bytesToNextPhysicalRecord();
 208     if (BytesToWrite > Size)
 209       BytesToWrite = Size;
 210     OS.write(Ptr + Idx, BytesToWrite);
 211     Idx += BytesToWrite;
 212     Size -= BytesToWrite;
 213     RemainingSize -= BytesToWrite;
 214     if (Size)
 215       writeRecordPrefix(OS, CurrentType, RemainingSize);
 216   }
 217 }
 218
 219 class GOFFObjectWriter : public MCObjectWriter {
 220   // The target specific GOFF writer instance.
 221   std::unique_ptr<MCGOFFObjectTargetWriter> TargetObjectWriter;
 222
 223   // The stream used to write the GOFF records.
 224   GOFFOstream OS;
 225
 226 public:
 227   GOFFObjectWriter(std::unique_ptr<MCGOFFObjectTargetWriter> MOTW,
 228                    raw_pwrite_stream &OS)
 229       : TargetObjectWriter(std::move(MOTW)), OS(OS) {}
 230
 231   ~GOFFObjectWriter() override {}
 232
 233   // Write GOFF records.
 234   void writeHeader();
 235   void writeEnd();
 236
 237   // Implementation of the MCObjectWriter interface.
 238   void recordRelocation(MCAssembler &Asm, const MCFragment *Fragment,
 239                         const MCFixup &Fixup, MCValue Target,
 240                         uint64_t &FixedValue) override {}
 241   uint64_t writeObject(MCAssembler &Asm) override;
 242 };
 243 } // end anonymous namespace
 244
 245 void GOFFObjectWriter::writeHeader() {
 246   OS.newRecord(GOFF::RT_HDR, /*Size=*/57);
 247   OS.write_zeros(1);       // Reserved
 248   OS.writebe<uint32_t>(0); // Target Hardware Environment
 249   OS.writebe<uint32_t>(0); // Target Operating System Environment
 250   OS.write_zeros(2);       // Reserved
 251   OS.writebe<uint16_t>(0); // CCSID
 252   OS.write_zeros(16);      // Character Set name
 253   OS.write_zeros(16);      // Language Product Identifier
 254   OS.writebe<uint32_t>(1); // Architecture Level
 255   OS.writebe<uint16_t>(0); // Module Properties Length
 256   OS.write_zeros(6);       // Reserved
 257 }
 258
 259 void GOFFObjectWriter::writeEnd() {
 260   uint8_t F = GOFF::END_EPR_None;
 261   uint8_t AMODE = 0;
 262   uint32_t ESDID = 0;
 263
 264   // TODO Set Flags/AMODE/ESDID for entry point.
 265
 266   OS.newRecord(GOFF::RT_END, /*Size=*/13);
 267   OS.writebe<uint8_t>(Flags(6, 2, F)); // Indicator flags
 268   OS.writebe<uint8_t>(AMODE);          // AMODE
 269   OS.write_zeros(3);                   // Reserved
 270   // The record count is the number of logical records. In principle, this value
 271   // is available as OS.logicalRecords(). However, some tools rely on this field
 272   // being zero.
 273   OS.writebe<uint32_t>(0);     // Record Count
 274   OS.writebe<uint32_t>(ESDID); // ESDID (of entry point)
 275   OS.finalize();
 276 }
 277
 278 uint64_t GOFFObjectWriter::writeObject(MCAssembler &Asm) {
 279   uint64_t StartOffset = OS.tell();
 280
 281   writeHeader();
 282   writeEnd();
 283
 284   LLVM_DEBUG(dbgs() << "Wrote " << OS.logicalRecords() << " logical records.");
 285
 286   return OS.tell() - StartOffset;
 287 }
 288
 289 std::unique_ptr<MCObjectWriter>
 290 llvm::createGOFFObjectWriter(std::unique_ptr<MCGOFFObjectTargetWriter> MOTW,
 291                              raw_pwrite_stream &OS) {
 292   return std::make_unique<GOFFObjectWriter>(std::move(MOTW), OS);
 293 }