MipsELFObjectWriter.cpp | Explore in Territory

//===-- MipsELFObjectWriter.cpp - Mips ELF Writer -------------------------===//
//
// 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 "MCTargetDesc/MipsFixupKinds.h"
#include "MCTargetDesc/MipsMCTargetDesc.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSymbolELF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <list>
#include <utility>

#define DEBUG_TYPE …

usingnamespacellvm;

namespace {

/// Holds additional information needed by the relocation ordering algorithm.
struct MipsRelocationEntry { … };

class MipsELFObjectWriter : public MCELFObjectTargetWriter { … };

/// The possible results of the Predicate function used by find_best.
enum FindBestPredicateResult { … };

} // end anonymous namespace

/// Copy elements in the range [First, Last) to d1 when the predicate is true or
/// d2 when the predicate is false. This is essentially both std::copy_if and
/// std::remove_copy_if combined into a single pass.
template <class InputIt, class OutputIt1, class OutputIt2, class UnaryPredicate>
static std::pair<OutputIt1, OutputIt2> copy_if_else(InputIt First, InputIt Last,
                                                    OutputIt1 d1, OutputIt2 d2,
                                                    UnaryPredicate Predicate) { … }

/// Find the best match in the range [First, Last).
///
/// An element matches when Predicate(X) returns FindBest_Match or
/// FindBest_PerfectMatch. A value of FindBest_PerfectMatch also terminates
/// the search. BetterThan(A, B) is a comparator that returns true when A is a
/// better match than B. The return value is the position of the best match.
///
/// This is similar to std::find_if but finds the best of multiple possible
/// matches.
template <class InputIt, class UnaryPredicate, class Comparator>
static InputIt find_best(InputIt First, InputIt Last, UnaryPredicate Predicate,
                         Comparator BetterThan) { … }

/// Determine the low relocation that matches the given relocation.
/// If the relocation does not need a low relocation then the return value
/// is ELF::R_MIPS_NONE.
///
/// The relocations that need a matching low part are
/// R_(MIPS|MICROMIPS|MIPS16)_HI16 for all symbols and
/// R_(MIPS|MICROMIPS|MIPS16)_GOT16 for local symbols only.
static unsigned getMatchingLoType(const ELFRelocationEntry &Reloc) { … }

// Determine whether a relocation X is a low-part and matches the high-part R
// perfectly by symbol and addend.
static bool isMatchingReloc(unsigned MatchingType, const ELFRelocationEntry &R,
                            const ELFRelocationEntry &X) { … }

MipsELFObjectWriter::MipsELFObjectWriter(uint8_t OSABI,
                                         bool HasRelocationAddend, bool Is64)
    : … { … }

unsigned MipsELFObjectWriter::getRelocType(MCContext &Ctx,
                                           const MCValue &Target,
                                           const MCFixup &Fixup,
                                           bool IsPCRel) const { … }

/// Sort relocation table entries by offset except where another order is
/// required by the MIPS ABI.
///
/// MIPS has a few relocations that have an AHL component in the expression used
/// to evaluate them. This AHL component is an addend with the same number of
/// bits as a symbol value but not all of our ABI's are able to supply a
/// sufficiently sized addend in a single relocation.
///
/// The O32 ABI for example, uses REL relocations which store the addend in the
/// section data. All the relocations with AHL components affect 16-bit fields
/// so the addend for a single relocation is limited to 16-bit. This ABI
/// resolves the limitation by linking relocations (e.g. R_MIPS_HI16 and
/// R_MIPS_LO16) and distributing the addend between the linked relocations. The
/// ABI mandates that such relocations must be next to each other in a
/// particular order (e.g. R_MIPS_HI16 must be immediately followed by a
/// matching R_MIPS_LO16) but the rule is less strict in practice.
///
/// The de facto standard is lenient in the following ways:
/// - 'Immediately following' does not refer to the next relocation entry but
///   the next matching relocation.
/// - There may be multiple high parts relocations for one low part relocation.
/// - There may be multiple low part relocations for one high part relocation.
/// - The AHL addend in each part does not have to be exactly equal as long as
///   the difference does not affect the carry bit from bit 15 into 16. This is
///   to allow, for example, the use of %lo(foo) and %lo(foo+4) when loading
///   both halves of a long long.
///
/// See getMatchingLoType() for a description of which high part relocations
/// match which low part relocations. One particular thing to note is that
/// R_MIPS_GOT16 and similar only have AHL addends if they refer to local
/// symbols.
///
/// It should also be noted that this function is not affected by whether
/// the symbol was kept or rewritten into a section-relative equivalent. We
/// always match using the expressions from the source.
void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
                                     std::vector<ELFRelocationEntry> &Relocs) { … }

bool MipsELFObjectWriter::needsRelocateWithSymbol(const MCValue &Val,
                                                  const MCSymbol &Sym,
                                                  unsigned Type) const { … }

std::unique_ptr<MCObjectTargetWriter>
llvm::createMipsELFObjectWriter(const Triple &TT, bool IsN32) { … }
llvm/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp
