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llvm-project/llvm/lib/MC/MCDwarf.cpp

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//===- 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/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(MCObjectStreamer *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.
DenseMap<const MCSection *, MCLineSection *> &MCLineSections =
MCOS->getContext().getMCLineSections();
MCLineSection *LineSection = MCLineSections[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.
MCLineSections[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(MCObjectStreamer *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(MCObjectStreamer *MCOS,
MCSymbol *Symbol) {
MCOS->EmitIntValue(dwarf::DW_LNS_extended_op, 1);
int sizeof_address = MCOS->getAssembler().getBackend().getPointerSize();
MCOS->EmitULEB128Value(sizeof_address + 1);
MCOS->EmitIntValue(dwarf::DW_LNE_set_address, 1);
MCOS->EmitSymbolValue(Symbol, sizeof_address);
}
//
// This emits the Dwarf line table for the specified section from the entries
// in the LineSection.
//
static inline bool EmitDwarfLineTable(MCObjectStreamer *MCOS,
const MCSection *Section,
MCLineSection *LineSection,
const MCSection *DwarfLineSection) {
unsigned FileNum = 1;
unsigned LastLine = 1;
unsigned Column = 0;
unsigned Flags = DWARF2_LINE_DEFAULT_IS_STMT ? DWARF2_FLAG_IS_STMT : 0;
unsigned Isa = 0;
bool EmittedLineTable = false;
MCSymbol *LastLabel = NULL;
MCSectionData &DLS =
MCOS->getAssembler().getOrCreateSectionData(*DwarfLineSection);
// Loop through each MCLineEntry and encode the dwarf line number table.
for (MCLineSection::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->EmitULEB128Value(FileNum);
}
if (Column != it->getColumn()) {
Column = it->getColumn();
MCOS->EmitIntValue(dwarf::DW_LNS_set_column, 1);
MCOS->EmitULEB128Value(Column);
}
if (Isa != it->getIsa()) {
Isa = it->getIsa();
MCOS->EmitIntValue(dwarf::DW_LNS_set_isa, 1);
MCOS->EmitULEB128Value(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 = 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) {
// emit the sequence to set the address
EmitDwarfSetAddress(MCOS, Label);
// 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;
EmittedLineTable = true;
}
// 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);
// 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);
return EmittedLineTable;
}
//
// This emits the Dwarf file and the line tables.
//
void MCDwarfFileTable::Emit(MCObjectStreamer *MCOS,
const MCSection *DwarfLineSection) {
// Switch to the section where the table will be emitted into.
MCOS->SwitchSection(DwarfLineSection);
// Create a symbol at the beginning of this section.
MCSymbol *LineStartSym = MCOS->getContext().CreateTempSymbol();
// Set the value of the symbol, as we are at the start of the section.
MCOS->EmitLabel(LineStartSym);
// Create a symbol for the end of the section (to be set when we get there).
MCSymbol *LineEndSym = MCOS->getContext().CreateTempSymbol();
// The first 4 bytes is the total length of the information for this
// compilation unit (not including these 4 bytes for the length).
MCOS->EmitValue(MakeStartMinusEndExpr(MCOS, LineStartSym, LineEndSym, 4),
4, 0);
// Next 2 bytes is the Version, which is Dwarf 2.
MCOS->EmitIntValue(2, 2);
// Create a symbol for the end of the prologue (to be set when we get there).
MCSymbol *ProEndSym = MCOS->getContext().CreateTempSymbol(); // Lprologue_end
// Length of the prologue, is the next 4 bytes. Which is the start of the
// section to the end of the prologue. Not including the 4 bytes for the
// total length, the 2 bytes for the version, and these 4 bytes for the
// length of the prologue.
MCOS->EmitValue(MakeStartMinusEndExpr(MCOS, LineStartSym, ProEndSym,
(4 + 2 + 4)),
4, 0);
// Parameters of the state machine, are next.
MCOS->EmitIntValue(DWARF2_LINE_MIN_INSN_LENGTH, 1);
MCOS->EmitIntValue(DWARF2_LINE_DEFAULT_IS_STMT, 1);
MCOS->EmitIntValue(DWARF2_LINE_BASE, 1);
MCOS->EmitIntValue(DWARF2_LINE_RANGE, 1);
MCOS->EmitIntValue(DWARF2_LINE_OPCODE_BASE, 1);
// Standard opcode lengths
MCOS->EmitIntValue(0, 1); // length of DW_LNS_copy
MCOS->EmitIntValue(1, 1); // length of DW_LNS_advance_pc
MCOS->EmitIntValue(1, 1); // length of DW_LNS_advance_line
MCOS->EmitIntValue(1, 1); // length of DW_LNS_set_file
MCOS->EmitIntValue(1, 1); // length of DW_LNS_set_column
MCOS->EmitIntValue(0, 1); // length of DW_LNS_negate_stmt
MCOS->EmitIntValue(0, 1); // length of DW_LNS_set_basic_block
MCOS->EmitIntValue(0, 1); // length of DW_LNS_const_add_pc
MCOS->EmitIntValue(1, 1); // length of DW_LNS_fixed_advance_pc
MCOS->EmitIntValue(0, 1); // length of DW_LNS_set_prologue_end
MCOS->EmitIntValue(0, 1); // length of DW_LNS_set_epilogue_begin
MCOS->EmitIntValue(1, 1); // DW_LNS_set_isa
// Put out the directory and file tables.
// First the directory table.
const std::vector<StringRef> &MCDwarfDirs =
MCOS->getContext().getMCDwarfDirs();
for (unsigned i = 0; i < MCDwarfDirs.size(); i++) {
MCOS->EmitBytes(MCDwarfDirs[i], 0); // the DirectoryName
MCOS->EmitBytes(StringRef("\0", 1), 0); // the null term. of the string
}
MCOS->EmitIntValue(0, 1); // Terminate the directory list
// Second the file table.
const std::vector<MCDwarfFile *> &MCDwarfFiles =
MCOS->getContext().getMCDwarfFiles();
for (unsigned i = 1; i < MCDwarfFiles.size(); i++) {
MCOS->EmitBytes(MCDwarfFiles[i]->getName(), 0); // FileName
MCOS->EmitBytes(StringRef("\0", 1), 0); // the null term. of the string
MCOS->EmitULEB128Value(MCDwarfFiles[i]->getDirIndex()); // the Directory num
MCOS->EmitIntValue(0, 1); // last modification timestamp (always 0)
MCOS->EmitIntValue(0, 1); // filesize (always 0)
}
MCOS->EmitIntValue(0, 1); // Terminate the file list
// This is the end of the prologue, so set the value of the symbol at the
// end of the prologue (that was used in a previous expression).
MCOS->EmitLabel(ProEndSym);
// Put out the line tables.
bool EmittedLineTable = false;
DenseMap<const MCSection *, MCLineSection *> &MCLineSections =
MCOS->getContext().getMCLineSections();
for (DenseMap<const MCSection *, MCLineSection *>::iterator it =
MCLineSections.begin(), ie = MCLineSections.end(); it != ie; ++it) {
EmittedLineTable = EmitDwarfLineTable(MCOS, it->first, it->second,
DwarfLineSection);
// Now delete the MCLineSections that were created in MCLineEntry::Make()
// and used to emit the line table.
delete it->second;
}
// If there are no line tables emited then we emit:
// The following DW_LNE_set_address sequence to set the address to zero and
// the DW_LNE_end_sequence.
if (EmittedLineTable == false) {
if (MCOS->getAssembler().getBackend().getPointerSize() == 8) {
// This is the DW_LNE_set_address sequence for 64-bit code.
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(9, 1);
MCOS->EmitIntValue(2, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
}
else {
// This is the DW_LNE_set_address sequence for 32-bit code.
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(5, 1);
MCOS->EmitIntValue(2, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
MCOS->EmitIntValue(0, 1);
}
// Lastly emit the DW_LNE_end_sequence which consists of 3 bytes '00 01 01'
// (00 is the code for extended opcodes, followed by a ULEB128 length of the
// extended opcode (01), and the DW_LNE_end_sequence (01).
MCOS->EmitIntValue(0, 1); // DW_LNS_extended_op
MCOS->EmitIntValue(1, 1); // ULEB128 length of the extended opcode
MCOS->EmitIntValue(1, 1); // DW_LNE_end_sequence
}
// This is the end of the section, so set the value of the symbol at the end
// of this section (that was used in a previous expression).
MCOS->EmitLabel(LineEndSym);
}
/// Utility function to compute the size of the encoding.
uint64_t MCDwarfLineAddr::ComputeSize(int64_t LineDelta, uint64_t AddrDelta) {
SmallString<256> Tmp;
raw_svector_ostream OS(Tmp);
MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OS);
return OS.GetNumBytesInBuffer();
}
/// Utility function to write the encoding to an object writer.
void MCDwarfLineAddr::Write(MCObjectWriter *OW, int64_t LineDelta,
uint64_t AddrDelta) {
SmallString<256> Tmp;
raw_svector_ostream OS(Tmp);
MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OS);
OW->WriteBytes(OS.str());
}
/// Utility function to emit the encoding to a streamer.
void MCDwarfLineAddr::Emit(MCObjectStreamer *MCOS, int64_t LineDelta,
uint64_t AddrDelta) {
SmallString<256> Tmp;
raw_svector_ostream OS(Tmp);
MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OS);
MCOS->EmitBytes(OS.str(), /*AddrSpace=*/0);
}
/// Utility function to encode a Dwarf pair of LineDelta and AddrDeltas.
void MCDwarfLineAddr::Encode(int64_t LineDelta, uint64_t AddrDelta,
raw_ostream &OS) {
uint64_t Temp, Opcode;
bool NeedCopy = false;
// Scale the address delta by the minimum instruction length.
AddrDelta = ScaleAddrDelta(AddrDelta);
// A LineDelta of INT64_MAX is a signal that this is actually a
// DW_LNE_end_sequence. We cannot use special opcodes here, since we want the
// end_sequence to emit the matrix entry.
if (LineDelta == INT64_MAX) {
if (AddrDelta == MAX_SPECIAL_ADDR_DELTA)
OS << char(dwarf::DW_LNS_const_add_pc);
else {
OS << char(dwarf::DW_LNS_advance_pc);
SmallString<32> Tmp;
raw_svector_ostream OSE(Tmp);
MCObjectWriter::EncodeULEB128(AddrDelta, OSE);
OS << OSE.str();
}
OS << char(dwarf::DW_LNS_extended_op);
OS << char(1);
OS << char(dwarf::DW_LNE_end_sequence);
return;
}
// Bias the line delta by the base.
Temp = LineDelta - DWARF2_LINE_BASE;
// If the line increment is out of range of a special opcode, we must encode
// it with DW_LNS_advance_line.
if (Temp >= DWARF2_LINE_RANGE) {
OS << char(dwarf::DW_LNS_advance_line);
SmallString<32> Tmp;
raw_svector_ostream OSE(Tmp);
MCObjectWriter::EncodeSLEB128(LineDelta, OSE);
OS << OSE.str();
LineDelta = 0;
Temp = 0 - DWARF2_LINE_BASE;
NeedCopy = true;
}
// Use DW_LNS_copy instead of a "line +0, addr +0" special opcode.
if (LineDelta == 0 && AddrDelta == 0) {
OS << char(dwarf::DW_LNS_copy);
return;
}
// Bias the opcode by the special opcode base.
Temp += DWARF2_LINE_OPCODE_BASE;
// Avoid overflow when addr_delta is large.
if (AddrDelta < 256 + MAX_SPECIAL_ADDR_DELTA) {
// Try using a special opcode.
Opcode = Temp + AddrDelta * DWARF2_LINE_RANGE;
if (Opcode <= 255) {
OS << char(Opcode);
return;
}
// Try using DW_LNS_const_add_pc followed by special op.
Opcode = Temp + (AddrDelta - MAX_SPECIAL_ADDR_DELTA) * DWARF2_LINE_RANGE;
if (Opcode <= 255) {
OS << char(dwarf::DW_LNS_const_add_pc);
OS << char(Opcode);
return;
}
}
// Otherwise use DW_LNS_advance_pc.
OS << char(dwarf::DW_LNS_advance_pc);
SmallString<32> Tmp;
raw_svector_ostream OSE(Tmp);
MCObjectWriter::EncodeULEB128(AddrDelta, OSE);
OS << OSE.str();
if (NeedCopy)
OS << char(dwarf::DW_LNS_copy);
else
OS << char(Temp);
}
void MCDwarfFile::print(raw_ostream &OS) const {
OS << '"' << getName() << '"';
}
void MCDwarfFile::dump() const {
print(dbgs());
}
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