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