llvm/lib/MC/MCSymbol.cpp

//===- lib/MC/MCSymbol.cpp - MCSymbol implementation ----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "llvm/MC/MCSymbol.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstddef>

using namespace llvm;

// There are numerous MCSymbol objects, so keeping sizeof(MCSymbol) small is
// crucial for minimizing peak memory usage.
static_assert(sizeof(MCSymbol) <= 24, "Keep the base symbol small");

// Only the address of this fragment is ever actually used.
static MCFragment SentinelFragment;

// Sentinel value for the absolute pseudo fragment.
MCFragment *MCSymbol::AbsolutePseudoFragment = &SentinelFragment;

void *MCSymbol::operator new(size_t s, const MCSymbolTableEntry *Name,
                             MCContext &Ctx) {
  // We may need more space for a Name to account for alignment.  So allocate
  // space for the storage type and not the name pointer.
  size_t Size = s + (Name ? sizeof(NameEntryStorageTy) : 0);

  // For safety, ensure that the alignment of a pointer is enough for an
  // MCSymbol.  This also ensures we don't need padding between the name and
  // symbol.
  static_assert((unsigned)alignof(MCSymbol) <= alignof(NameEntryStorageTy),
                "Bad alignment of MCSymbol");
  void *Storage = Ctx.allocate(Size, alignof(NameEntryStorageTy));
  NameEntryStorageTy *Start = static_cast<NameEntryStorageTy*>(Storage);
  NameEntryStorageTy *End = Start + (Name ? 1 : 0);
  return End;
}

void MCSymbol::setVariableValue(const MCExpr *Value) {
  assert(Value && "Invalid equated expression");
  assert((kind == Kind::Regular || kind == Kind::Equated) &&
         "Cannot equate a common symbol");
  this->Value = Value;
  kind = Kind::Equated;
  Fragment = nullptr;
}

void MCSymbol::print(raw_ostream &OS, const MCAsmInfo *MAI) const {
  // The name for this MCSymbol is required to be a valid target name.  However,
  // some targets support quoting names with funny characters.  If the name
  // contains a funny character, then print it quoted.
  StringRef Name = getName();
  if (!MAI || MAI->isValidUnquotedName(Name)) {
    OS << Name;
    return;
  }

  if (MAI && !MAI->supportsNameQuoting())
    report_fatal_error("Symbol name with unsupported characters");

  OS << '"';
  for (char C : Name) {
    if (C == '\n')
      OS << "\\n";
    else if (C == '"')
      OS << "\\\"";
    else if (C == '\\')
      OS << "\\\\";
    else
      OS << C;
  }
  OS << '"';
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void MCSymbol::dump() const { dbgs() << *this; }
#endif

// Determine whether the offset between two labels can change at link time.
// Currently, this function is used only in DWARF info emission logic, where it
// helps generate more optimal debug info when the offset between labels is
// constant at link time.
bool llvm::isRangeRelaxable(const MCSymbol *Begin, const MCSymbol *End) {
  assert(Begin && "Range without a begin symbol?");
  assert(End && "Range without an end symbol?");
  for (const auto *Fragment = Begin->getFragment();
       Fragment != End->getFragment(); Fragment = Fragment->getNext()) {
    assert(Fragment);
    if (Fragment->isLinkerRelaxable())
      return true;
  }
  return false;
}