ELF/Target.h

//===- Target.h -------------------------------------------------*- C++ -*-===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef LLD_ELF_TARGET_H
#define LLD_ELF_TARGET_H

#include "InputSection.h"
#include "lld/Common/ErrorHandler.h"
#include "llvm/Object/ELF.h"
#include "llvm/Support/MathExtras.h"
#include <array>

namespace lld {
std::string toString(elf::RelType Type);

namespace elf {
class Defined;
class InputFile;
class Symbol;

class TargetInfo {
public:
  virtual uint32_t calcEFlags() const { return 0; }
  virtual RelType getDynRel(RelType Type) const { return Type; }
  virtual void writeGotPltHeader(uint8_t *Buf) const {}
  virtual void writeGotHeader(uint8_t *Buf) const {}
  virtual void writeGotPlt(uint8_t *Buf, const Symbol &S) const {};
  virtual void writeIgotPlt(uint8_t *Buf, const Symbol &S) const;
  virtual int64_t getImplicitAddend(const uint8_t *Buf, RelType Type) const;

  // If lazy binding is supported, the first entry of the PLT has code
  // to call the dynamic linker to resolve PLT entries the first time
  // they are called. This function writes that code.
  virtual void writePltHeader(uint8_t *Buf) const {}

  virtual void writePlt(uint8_t *Buf, uint64_t GotEntryAddr,
                        uint64_t PltEntryAddr, int32_t Index,
                        unsigned RelOff) const {}
  virtual void addPltHeaderSymbols(InputSection &IS) const {}
  virtual void addPltSymbols(InputSection &IS, uint64_t Off) const {}

  // Returns true if a relocation only uses the low bits of a value such that
  // all those bits are in the same page. For example, if the relocation
  // only uses the low 12 bits in a system with 4k pages. If this is true, the
  // bits will always have the same value at runtime and we don't have to emit
  // a dynamic relocation.
  virtual bool usesOnlyLowPageBits(RelType Type) const;

  // Decide whether a Thunk is needed for the relocation from File
  // targeting S.
  virtual bool needsThunk(RelExpr Expr, RelType RelocType,
                          const InputFile *File, uint64_t BranchAddr,
                          const Symbol &S) const;

  // On systems with range extensions we place collections of Thunks at
  // regular spacings that enable the majority of branches reach the Thunks.
  // a value of 0 means range extension thunks are not supported.
  virtual uint32_t getThunkSectionSpacing() const { return 0; }

  // The function with a prologue starting at Loc was compiled with
  // -fsplit-stack and it calls a function compiled without. Adjust the prologue
  // to do the right thing. See https://gcc.gnu.org/wiki/SplitStacks.
  // The symbols st_other flags are needed on PowerPC64 for determining the
  // offset to the split-stack prologue.
  virtual bool adjustPrologueForCrossSplitStack(uint8_t *Loc, uint8_t *End,
                                                uint8_t StOther) const;

  // Return true if we can reach Dst from Src with Relocation RelocType
  virtual bool inBranchRange(RelType Type, uint64_t Src,
                             uint64_t Dst) const;
  virtual RelExpr getRelExpr(RelType Type, const Symbol &S,
                             const uint8_t *Loc) const = 0;

  virtual void relocateOne(uint8_t *Loc, RelType Type, uint64_t Val) const = 0;

  virtual ~TargetInfo();

  unsigned TlsGdRelaxSkip = 1;
  unsigned PageSize = 4096;
  unsigned DefaultMaxPageSize = 4096;

  uint64_t getImageBase();

  // Offset of _GLOBAL_OFFSET_TABLE_ from base of .got or .got.plt section.
  uint64_t GotBaseSymOff = 0;
  // True if _GLOBAL_OFFSET_TABLE_ is relative to .got.plt, false if .got.
  bool GotBaseSymInGotPlt = true;

  RelType CopyRel;
  RelType GotRel;
  RelType NoneRel;
  RelType PltRel;
  RelType RelativeRel;
  RelType IRelativeRel;
  RelType TlsDescRel;
  RelType TlsGotRel;
  RelType TlsModuleIndexRel;
  RelType TlsOffsetRel;
  unsigned GotEntrySize = 0;
  unsigned GotPltEntrySize = 0;
  unsigned PltEntrySize;
  unsigned PltHeaderSize;

  // At least on x86_64 positions 1 and 2 are used by the first plt entry
  // to support lazy loading.
  unsigned GotPltHeaderEntriesNum = 3;

  // On PPC ELF V2 abi, the first entry in the .got is the .TOC.
  unsigned GotHeaderEntriesNum = 0;

  bool NeedsThunks = false;

  // A 4-byte field corresponding to one or more trap instructions, used to pad
  // executable OutputSections.
  std::array<uint8_t, 4> TrapInstr;

  // If a target needs to rewrite calls to __morestack to instead call
  // __morestack_non_split when a split-stack enabled caller calls a
  // non-split-stack callee this will return true. Otherwise returns false.
  bool NeedsMoreStackNonSplit = true;

  virtual RelExpr adjustRelaxExpr(RelType Type, const uint8_t *Data,
                                  RelExpr Expr) const;
  virtual void relaxGot(uint8_t *Loc, uint64_t Val) const;
  virtual void relaxTlsGdToIe(uint8_t *Loc, RelType Type, uint64_t Val) const;
  virtual void relaxTlsGdToLe(uint8_t *Loc, RelType Type, uint64_t Val) const;
  virtual void relaxTlsIeToLe(uint8_t *Loc, RelType Type, uint64_t Val) const;
  virtual void relaxTlsLdToLe(uint8_t *Loc, RelType Type, uint64_t Val) const;

protected:
  // On FreeBSD x86_64 the first page cannot be mmaped.
  // On Linux that is controled by vm.mmap_min_addr. At least on some x86_64
  // installs that is 65536, so the first 15 pages cannot be used.
  // Given that, the smallest value that can be used in here is 0x10000.
  uint64_t DefaultImageBase = 0x10000;
};

TargetInfo *getAArch64TargetInfo();
TargetInfo *getAMDGPUTargetInfo();
TargetInfo *getARMTargetInfo();
TargetInfo *getAVRTargetInfo();
TargetInfo *getHexagonTargetInfo();
TargetInfo *getMSP430TargetInfo();
TargetInfo *getPPC64TargetInfo();
TargetInfo *getPPCTargetInfo();
TargetInfo *getRISCVTargetInfo();
TargetInfo *getSPARCV9TargetInfo();
TargetInfo *getX32TargetInfo();
TargetInfo *getX86TargetInfo();
TargetInfo *getX86_64TargetInfo();
template <class ELFT> TargetInfo *getMipsTargetInfo();

struct ErrorPlace {
  InputSectionBase *IS;
  std::string Loc;
};

// Returns input section and corresponding source string for the given location.
ErrorPlace getErrorPlace(const uint8_t *Loc);

static inline std::string getErrorLocation(const uint8_t *Loc) {
  return getErrorPlace(Loc).Loc;
}

// In the PowerPC64 Elf V2 abi a function can have 2 entry points.  The first is
// a global entry point (GEP) which typically is used to intiailzie the TOC
// pointer in general purpose register 2.  The second is a local entry
// point (LEP) which bypasses the TOC pointer initialization code. The
// offset between GEP and LEP is encoded in a function's st_other flags.
// This function will return the offset (in bytes) from the global entry-point
// to the local entry-point.
unsigned getPPC64GlobalEntryToLocalEntryOffset(uint8_t StOther);

uint64_t getPPC64TocBase();
uint64_t getAArch64Page(uint64_t Expr);

extern TargetInfo *Target;
TargetInfo *getTarget();

template <class ELFT> bool isMipsPIC(const Defined *Sym);

static inline void reportRangeError(uint8_t *Loc, RelType Type, const Twine &V,
                                    int64_t Min, uint64_t Max) {
  ErrorPlace ErrPlace = getErrorPlace(Loc);
  StringRef Hint;
  if (ErrPlace.IS && ErrPlace.IS->Name.startswith(".debug"))
    Hint = "; consider recompiling with -fdebug-types-section to reduce size "
           "of debug sections";

  errorOrWarn(ErrPlace.Loc + "relocation " + lld::toString(Type) +
              " out of range: " + V.str() + " is not in [" + Twine(Min).str() +
              ", " + Twine(Max).str() + "]" + Hint);
}

inline unsigned getPltEntryOffset(unsigned Idx) {
  return Target->PltHeaderSize + Target->PltEntrySize * Idx;
}

// Make sure that V can be represented as an N bit signed integer.
inline void checkInt(uint8_t *Loc, int64_t V, int N, RelType Type) {
  if (V != llvm::SignExtend64(V, N))
    reportRangeError(Loc, Type, Twine(V), llvm::minIntN(N), llvm::maxIntN(N));
}

// Make sure that V can be represented as an N bit unsigned integer.
inline void checkUInt(uint8_t *Loc, uint64_t V, int N, RelType Type) {
  if ((V >> N) != 0)
    reportRangeError(Loc, Type, Twine(V), 0, llvm::maxUIntN(N));
}

// Make sure that V can be represented as an N bit signed or unsigned integer.
inline void checkIntUInt(uint8_t *Loc, uint64_t V, int N, RelType Type) {
  // For the error message we should cast V to a signed integer so that error
  // messages show a small negative value rather than an extremely large one
  if (V != (uint64_t)llvm::SignExtend64(V, N) && (V >> N) != 0)
    reportRangeError(Loc, Type, Twine((int64_t)V), llvm::minIntN(N),
                     llvm::maxIntN(N));
}

inline void checkAlignment(uint8_t *Loc, uint64_t V, int N, RelType Type) {
  if ((V & (N - 1)) != 0)
    error(getErrorLocation(Loc) + "improper alignment for relocation " +
          lld::toString(Type) + ": 0x" + llvm::utohexstr(V) +
          " is not aligned to " + Twine(N) + " bytes");
}

// Endianness-aware read/write.
inline uint16_t read16(const void *P) {
  return llvm::support::endian::read16(P, Config->Endianness);
}

inline uint32_t read32(const void *P) {
  return llvm::support::endian::read32(P, Config->Endianness);
}

inline uint64_t read64(const void *P) {
  return llvm::support::endian::read64(P, Config->Endianness);
}

inline void write16(void *P, uint16_t V) {
  llvm::support::endian::write16(P, V, Config->Endianness);
}

inline void write32(void *P, uint32_t V) {
  llvm::support::endian::write32(P, V, Config->Endianness);
}

inline void write64(void *P, uint64_t V) {
  llvm::support::endian::write64(P, V, Config->Endianness);
}
} // namespace elf
} // namespace lld

#endif