path: root/lib/MC/MCDwarf.cpp

//===- lib/MC/MCDwarf.cpp - MCDwarf implementation ------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetAsmBackend.h"
using namespace llvm;

// Given a special op, return the address skip amount (in units of
// DWARF2_LINE_MIN_INSN_LENGTH.
#define SPECIAL_ADDR(op) (((op) - DWARF2_LINE_OPCODE_BASE)/DWARF2_LINE_RANGE)

// The maximum address skip amount that can be encoded with a special op.
#define MAX_SPECIAL_ADDR_DELTA		SPECIAL_ADDR(255)

// First special line opcode - leave room for the standard opcodes.
// Note: If you want to change this, you'll have to update the
// "standard_opcode_lengths" table that is emitted in DwarfFileTable::Emit().  
#define DWARF2_LINE_OPCODE_BASE		13

// Minimum line offset in a special line info. opcode.  This value
// was chosen to give a reasonable range of values.
#define DWARF2_LINE_BASE		-5

// Range of line offsets in a special line info. opcode.
# define DWARF2_LINE_RANGE		14

// Define the architecture-dependent minimum instruction length (in bytes).
// This value should be rather too small than too big.
# define DWARF2_LINE_MIN_INSN_LENGTH	1

// Note: when DWARF2_LINE_MIN_INSN_LENGTH == 1 which is the current setting,
// this routine is a nop and will be optimized away.
static inline uint64_t ScaleAddrDelta(uint64_t AddrDelta)
{
  if (DWARF2_LINE_MIN_INSN_LENGTH == 1)
    return AddrDelta;
  if (AddrDelta % DWARF2_LINE_MIN_INSN_LENGTH != 0) {
    // TODO: report this error, but really only once.
    ;
  }
  return AddrDelta / DWARF2_LINE_MIN_INSN_LENGTH;
}

//
// This is called when an instruction is assembled into the specified section
// and if there is information from the last .loc directive that has yet to have
// a line entry made for it is made.
//
void MCLineEntry::Make(MCStreamer *MCOS, const MCSection *Section) {
  if (!MCOS->getContext().getDwarfLocSeen())
    return;

  // Create a symbol at in the current section for use in the line entry.
  MCSymbol *LineSym = MCOS->getContext().CreateTempSymbol();
  // Set the value of the symbol to use for the MCLineEntry.
  MCOS->EmitLabel(LineSym);

  // Get the current .loc info saved in the context.
  const MCDwarfLoc &DwarfLoc = MCOS->getContext().getCurrentDwarfLoc();

  // Create a (local) line entry with the symbol and the current .loc info.
  MCLineEntry LineEntry(LineSym, DwarfLoc);

  // clear DwarfLocSeen saying the current .loc info is now used.
  MCOS->getContext().ClearDwarfLocSeen();

  // Get the MCLineSection for this section, if one does not exist for this
  // section create it.
  const DenseMap<const MCSection *, MCLineSection *> &MCLineSections =
    MCOS->getContext().getMCLineSections();
  MCLineSection *LineSection = MCLineSections.lookup(Section);
  if (!LineSection) {
    // Create a new MCLineSection.  This will be deleted after the dwarf line
    // table is created using it by iterating through the MCLineSections
    // DenseMap.
    LineSection = new MCLineSection;
    // Save a pointer to the new LineSection into the MCLineSections DenseMap.
    MCOS->getContext().addMCLineSection(Section, LineSection);
  }

  // Add the line entry to this section's entries.
  LineSection->addLineEntry(LineEntry);
}

//
// This helper routine returns an expression of End - Start + IntVal .
// 
static inline const MCExpr *MakeStartMinusEndExpr(MCStreamer *MCOS,
                                                  MCSymbol *Start,
                                                  MCSymbol *End, int IntVal) {
  MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
  const MCExpr *Res =
    MCSymbolRefExpr::Create(End, Variant, MCOS->getContext());
  const MCExpr *RHS =
    MCSymbolRefExpr::Create(Start, Variant, MCOS->getContext());
  const MCExpr *Res1 =
    MCBinaryExpr::Create(MCBinaryExpr::Sub, Res, RHS, MCOS->getContext());
  const MCExpr *Res2 =
    MCConstantExpr::Create(IntVal, MCOS->getContext());
  const MCExpr *Res3 =
    MCBinaryExpr::Create(MCBinaryExpr::Sub, Res1, Res2, MCOS->getContext());
  return Res3;
}

// 
// This emits an "absolute" address used in the start of a dwarf line number
// table.  This will result in a relocatation entry for the address.
//
static inline void EmitDwarfSetAddress(MCStreamer *MCOS,
                                       MCSymbol *Symbol,
                                       int PointerSize) {
  MCOS->EmitIntValue(dwarf::DW_LNS_extended_op, 1);

  MCOS->EmitULEB128IntValue(PointerSize + 1);

  MCOS->EmitIntValue(dwarf::DW_LNE_set_address, 1);
  MCOS->EmitSymbolValue(Symbol, PointerSize);
}

//
// This emits the Dwarf line table for the specified section from the entries
// in the LineSection.
//
static inline void EmitDwarfLineTable(MCStreamer *MCOS,
                                      const MCSection *Section,
                                      const MCLineSection *LineSection,
                                      const MCSection *DwarfLineSection,
                                      MCSectionData *DLS,
                                      int PointerSize) {
  unsigned FileNum = 1;
  unsigned LastLine = 1;
  unsigned Column = 0;
  unsigned Flags = DWARF2_LINE_DEFAULT_IS_STMT ? DWARF2_FLAG_IS_STMT : 0;
  unsigned Isa = 0;
  MCSymbol *LastLabel = NULL;

  // Loop through each MCLineEntry and encode the dwarf line number table.
  for (MCLineSection::const_iterator
         it = LineSection->getMCLineEntries()->begin(),
         ie = LineSection->getMCLineEntries()->end(); it != ie; ++it) {

    if (FileNum != it->getFileNum()) {
      FileNum = it->getFileNum();
      MCOS->EmitIntValue(dwarf::DW_LNS_set_file, 1);
      MCOS->EmitULEB128IntValue(FileNum);
    }
    if (Column != it->getColumn()) {
      Column = it->getColumn();
      MCOS->EmitIntValue(dwarf::DW_LNS_set_column, 1);
      MCOS->EmitULEB128IntValue(Column);
    }
    if (Isa != it->getIsa()) {
      Isa = it->getIsa();
      MCOS->EmitIntValue(dwarf::DW_LNS_set_isa, 1);
      MCOS->EmitULEB128IntValue(Isa);
    }
    if ((it->getFlags() ^ Flags) & DWARF2_FLAG_IS_STMT) {
      Flags = it->getFlags();
      MCOS->EmitIntValue(dwarf::DW_LNS_negate_stmt, 1);
    }
    if (it->getFlags() & DWARF2_FLAG_BASIC_BLOCK)
      MCOS->EmitIntValue(dwarf::DW_LNS_set_basic_block, 1);
    if (it->getFlags() & DWARF2_FLAG_PROLOGUE_END)
      MCOS->EmitIntValue(dwarf::DW_LNS_set_prologue_end, 1);
    if (it->getFlags() & DWARF2_FLAG_EPILOGUE_BEGIN)
      MCOS->EmitIntValue(dwarf::DW_LNS_set_epilogue_begin, 1);

    int64_t LineDelta = static_cast<int64_t>(it->getLine()) - LastLine;
    MCSymbol *Label = it->getLabel();

    // At this point we want to emit/create the sequence to encode the delta in
    // line numbers and the increment of the address from the previous Label
    // and the current Label.
    if (LastLabel == NULL || DLS == NULL) {
      // emit the sequence to set the address
      EmitDwarfSetAddress(MCOS, Label, PointerSize);
      // emit the sequence for the LineDelta (from 1) and a zero address delta.
      MCDwarfLineAddr::Emit(MCOS, LineDelta, 0);
    }
    else {
      // Create an expression for the address delta from the LastLabel and
      // this Label (plus 0).
      const MCExpr *AddrDelta = MakeStartMinusEndExpr(MCOS, LastLabel, Label,0);
      // Create a Dwarf Line fragment for the LineDelta and AddrDelta.
      new MCDwarfLineAddrFragment(LineDelta, *AddrDelta, DLS);
    }

    LastLine = it->getLine();
    LastLabel = Label;
  }

  // Emit a DW_LNE_end_sequence for the end of the section.
  // Using the pointer Section create a temporary label at the end of the
  // section and use that and the LastLabel to compute the address delta
  // and use INT64_MAX as the line delta which is the signal that this is
  // actually a DW_LNE_end_sequence.

  // Switch to the section to be able to create a symbol at its end.
  MCOS->SwitchSection(Section);
  // Create a symbol at the end of the section.
  MCSymbol *SectionEnd = MCOS->getContext().CreateTempSymbol();
  // Set the value of the symbol, as we are at the end of the section.
  MCOS->EmitLabel(SectionEnd);

  // Switch back the the dwarf line section.
  MCOS->SwitchSection(DwarfLineSection);

  if (DLS == NULL) {
    // emit the sequence to set the address
    EmitDwarfSetAddress(MCOS, SectionEnd, PointerSize);
    // emit the sequence for the LineDelta (from 1) and a zero address delta.
    MCDwarfLineAddr::Emit(MCOS, INT64_MAX, 0);
  } else {
    // Create an expression for the address delta from the LastLabel and this
    // SectionEnd label.
    const MCExpr *AddrDelta = MakeStartMinusEndExpr(MCOS, LastLabel, SectionEnd,
                                                    0);
    // Create a Dwarf Line fragment for the LineDelta and AddrDelta.
    new MCDwarfLineAddrFragment(INT64_MAX, *AddrDelta, DLS);
  }
}

//
// This emits the Dwarf file and the line tables.
//
void MCDwarfFileTable::Emit(MCStreamer *MCOS,
                            const