lib/CodeGen/ELF.h

//===-- lib/CodeGen/ELF.h - ELF constants and data structures ---*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This header contains common, non-processor-specific data structures and
// constants for the ELF file format.
//
// The details of the ELF32 bits in this file are largely based on the Tool
// Interface Standard (TIS) Executable and Linking Format (ELF) Specification
// Version 1.2, May 1995. The ELF64 is based on HP/Intel definition of the
// ELF-64 object file format document, Version 1.5 Draft 2 May 27, 1998
//
//===----------------------------------------------------------------------===//

#ifndef CODEGEN_ELF_H
#define CODEGEN_ELF_H

#include "llvm/CodeGen/BinaryObject.h"
#include "llvm/CodeGen/MachineRelocation.h"
#include "llvm/Support/DataTypes.h"

namespace llvm {
  class GlobalValue;

  // Identification Indexes
  enum {
    EI_MAG0 = 0,
    EI_MAG1 = 1,
    EI_MAG2 = 2,
    EI_MAG3 = 3
  };

  // File types
  enum {
    ET_NONE   = 0,      // No file type
    ET_REL    = 1,      // Relocatable file
    ET_EXEC   = 2,      // Executable file
    ET_DYN    = 3,      // Shared object file
    ET_CORE   = 4,      // Core file
    ET_LOPROC = 0xff00, // Beginning of processor-specific codes
    ET_HIPROC = 0xffff  // Processor-specific
  };

  // Versioning
  enum {
    EV_NONE = 0,
    EV_CURRENT = 1
  };

  /// ELFSym - This struct contains information about each symbol that is
  /// added to logical symbol table for the module.  This is eventually
  /// turned into a real symbol table in the file.
  struct ELFSym {

    // ELF symbols are related to llvm ones by being one of the two llvm
    // types, for the other ones (section, file, func) a null pointer is
    // assumed.
    union {
      const GlobalValue *GV;  // If this is a pointer to a GV
      const char *Ext;  // If this is a pointer to a named symbol
    } Source;

    // Describes from which source type this ELF symbol comes from,
    // they can be GlobalValue, ExternalSymbol or neither.
    enum {
      isGV,      // The Source.GV field is valid.
      isExtSym,  // The Source.ExtSym field is valid.
      isOther    // Not a GlobalValue or External Symbol
    };
    unsigned SourceType;

    bool isGlobalValue() { return SourceType == isGV; }
    bool isExternalSym() { return SourceType == isExtSym; }

    // getGlobalValue - If this is a global value which originated the
    // elf symbol, return a reference to it.
    const GlobalValue *getGlobalValue() {
      assert(SourceType == isGV && "This is not a global value");
      return Source.GV;
    };

    // getExternalSym - If this is an external symbol which originated the
    // elf symbol, return a reference to it.
    const char *getExternalSymbol() {
      assert(SourceType == isExtSym && "This is not an external symbol");
      return Source.Ext;
    };

    // getGV - From a global value return a elf symbol to represent it
    static ELFSym *getGV(const GlobalValue *GV, unsigned Bind,
                         unsigned Type, unsigned Visibility) {
      ELFSym *Sym = new ELFSym();
      Sym->Source.GV = GV;
      Sym->setBind(Bind);
      Sym->setType(Type);
      Sym->setVisibility(Visibility);
      Sym->SourceType = isGV;
      return Sym;
    }

    // getExtSym - Create and return an elf symbol to represent an
    // external symbol
    static ELFSym *getExtSym(const char *Ext) {
      ELFSym *Sym = new ELFSym();
      Sym->Source.Ext = Ext;
      Sym->setBind(STB_GLOBAL);
      Sym->setType(STT_NOTYPE);
      Sym->setVisibility(STV_DEFAULT);
      Sym->SourceType = isExtSym;
      return Sym;
    }

    // getSectionSym - Returns a elf symbol to represent an elf section
    static ELFSym *getSectionSym() {
      ELFSym *Sym = new ELFSym();
      Sym->setBind(ELFSym::STB_LOCAL);
      Sym->setType(ELFSym::STT_SECTION);
      Sym->setVisibility(ELFSym::STV_DEFAULT);
      Sym->SourceType = isOther;
      return Sym;
    }

    // ELF specific fields
    unsigned NameIdx;         // Index in .strtab of name, once emitted.
    uint64_t Value;
    unsigned Size;
    uint8_t Info;
    uint8_t Other;
    unsigned short SectionIdx;

    // Symbol index into the Symbol table
    unsigned SymTabIdx;

    enum {
      STB_LOCAL = 0,  // Local sym, not visible outside obj file containing def
      STB_GLOBAL = 1, // Global sym, visible to all object files being combined
      STB_WEAK = 2    // Weak symbol, like global but lower-precedence
    };

    enum {
      STT_NOTYPE = 0,  // Symbol's type is not specified
      STT_OBJECT = 1,  // Symbol is a data object (variable, array, etc.)
      STT_FUNC = 2,    // Symbol is executable code (function, etc.)
      STT_SECTION = 3, // Symbol refers to a section
      STT_FILE = 4     // Local, absolute symbol that refers to a file
    };

    enum {
      STV_DEFAULT = 0,  // Visibility is specified by binding type
      STV_INTERNAL = 1, // Defined by processor supplements
      STV_HIDDEN = 2,   // Not visible to other components
      STV_PROTECTED = 3 // Visible in other components but not preemptable
    };

    ELFSym() : SourceType(isOther), NameIdx(0), Value(0),
               Size(0), Info(0), Other(STV_DEFAULT), SectionIdx(0),
               SymTabIdx(0) {}

    unsigned getBind() const { return (Info >> 4) & 0xf; }
    unsigned getType() const { return Info & 0xf; }
    bool isLocalBind() const { return getBind() == STB_LOCAL; }

    void setBind(unsigned X) {
      assert(X == (X & 0xF) && "Bind value out of range!");
      Info = (Info & 0x0F) | (X << 4);
    }

    void setType(unsigned X) {
      assert(X == (X & 0xF) && "Type value out of range!");
      Info = (Info & 0xF0) | X;
    }

    void setVisibility(unsigned V) {
      assert(V == (V & 0x3) && "Visibility value out of range!");
      Other = V;
    }
  };

  /// ELFSection - This struct contains information about each section that is
  /// emitted to the file.  This is eventually turned into the section header
  /// table at the end of the file.
  class ELFSection : public BinaryObject {
    public:
    // ELF specific fields
    unsigned NameIdx;   // sh_name - .shstrtab idx of name, once emitted.
    unsigned Type;      // sh_type - Section contents & semantics 
    unsigned Flags;     // sh_flags - Section flags.
    uint64_t Addr;      // sh_addr - The mem addr this section is in.
    unsigned Offset;    // sh_offset - Offset from the file start
    unsigned Size;      // sh_size - The section size.
    unsigned Link;      // sh_link - Section header table index link.
    unsigned Info;      // sh_info - Auxillary information.
    unsigned Align;     // sh_addralign - Alignment of section.
    unsigned EntSize;   // sh_entsize - Size of entries in the section e

    // Section Header Flags
    enum {
      SHF_WRITE            = 1 << 0, // Writable
      SHF_ALLOC            = 1 << 1, // Mapped into the process addr space
      SHF_EXECINSTR        = 1 << 2, // Executable
      SHF_MERGE            = 1 << 4, // Might be merged if equal
      SHF_STRINGS          = 1 << 5, // Contains null-terminated strings
      SHF_INFO_LINK        = 1 << 6, // 'sh_info' contains SHT index
      SHF_LINK_ORDER       = 1 << 7, // Preserve order after combining
      SHF_OS_NONCONFORMING = 1 << 8, // nonstandard OS support required
      SHF_GROUP            = 1 << 9, // Section is a member of a group
      SHF_TLS              = 1 << 10 // Section holds thread-local data
    };

    // Section Types
    enum {
      SHT_NULL     = 0,  // No associated section (inactive entry).
      SHT_PROGBITS = 1,  // Program-defined contents.
      SHT_SYMTAB   = 2,  // Symbol table.
      SHT_STRTAB   = 3,  // String table.
      SHT_RELA     = 4,  // Relocation entries; explicit addends.
      SHT_HASH     = 5,  // Symbol hash table.
      SHT_DYNAMIC  = 6,  // Information for dynamic linking.
      SHT_NOTE     = 7,  // Information about the file.
      SHT_NOBITS   = 8,  // Data occupies no space in the file.
      SHT_REL      = 9,  // Relocation entries; no explicit addends.
      SHT_SHLIB    = 10, // Reserved.
      SHT_DYNSYM   = 11, // Symbol table.
      SHT_LOPROC   = 0x70000000, // Lowest processor arch-specific type.
      SHT_HIPROC   = 0x7fffffff, // Highest processor arch-specific type.
      SHT_LOUSER   = 0x80000000, // Lowest type reserved for applications.
      SHT_HIUSER   = 0xffffffff  // Highest type reserved for applications.
    };

    // Special section indices.
    enum {
      SHN_UNDEF     = 0,      // Undefined, missing, irrelevant
      SHN_LORESERVE = 0xff00, // Lowest reserved index
      SHN_LOPROC    = 0xff00, // Lowest processor-specific index
      SHN_HIPROC    = 0xff1f, // Highest processor-specific index
      SHN_ABS       = 0xfff1, // Symbol has absolute value; no relocation
      SHN_COMMON    = 0xfff2, // FORTRAN COMMON or C external global variables
      SHN_HIRESERVE = 0xffff  // Highest reserved index
    };

    /// SectionIdx - The number of the section in the Section Table.
    unsigned short SectionIdx;

    /// Sym - The symbol to represent this section if it has one.
    ELFSym *Sym;

    /// getSymIndex - Returns the symbol table index of the symbol
    /// representing this section.
    unsigned getSymbolTableIndex() const {
      assert(Sym && "section not present in the symbol table");
      return Sym->SymTabIdx;
    }

    ELFSection(const std::string &name, bool isLittleEndian, bool is64Bit)
      : BinaryObject(name, isLittleEndian, is64Bit), Type(0), Flags(0), Addr(0),
        Offset(0), Size(0), Link(0), Info(0), Align(0), EntSize(0), Sym(0) {}
  };

  /// ELFRelocation - This class contains all the information necessary to
  /// to generate any 32-bit or 64-bit ELF relocation entry.
  class ELFRelocation {
    uint64_t r_offset;    // offset in the section of the object this applies to
    uint32_t r_symidx;    // symbol table index of the symbol to use
    uint32_t r_type;      // machine specific relocation type
    int64_t  r_add;       // explicit relocation addend
    bool     r_rela;      // if true then the addend is part of the entry
                          // otherwise the addend is at the location specified
                          // by r_offset
  public:
    uint64_t getInfo(bool is64Bit) const {
      if (is64Bit)
        return ((uint64_t)r_symidx << 32) + ((uint64_t)r_type & 0xFFFFFFFFL);
      else
        return (r_symidx << 8)  + (r_type & 0xFFL);
    }

    uint64_t getOffset() const { return r_offset; }
    int64_t getAddend() const { return r_add; }

    ELFRelocation(uint64_t off, uint32_t sym, uint32_t type,
                  bool rela = true, int64_t addend = 0) :
      r_offset(off), r_symidx(sym), r_type(type),
      r_add(addend), r_rela(rela) {}
  };

} // end namespace llvm

#endif