mozglue/linker/Elfxx.h
author Noemi Erli <nerli@mozilla.com>
Tue, 18 Jan 2022 17:41:19 +0200
changeset 604772 310661795ca22ab62de923ce9fc3b36850e6d72d
parent 573028 4c3d3c0ed93d5356fa63cd22803543bb44dfb120
permissions -rw-r--r--
Merge autoland to mozilla-central. a=merge

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef Elfxx_h
#define Elfxx_h

#include "Utils.h"

/**
 * Android system headers have two different elf.h file. The one under linux/
 * is the most complete on older Android API versions without unified headers.
 */
#if defined(ANDROID) && __ANDROID_API__ < 21 && !defined(__ANDROID_API_L__)
#  include <linux/elf.h>
#else
#  include <elf.h>
#endif
#include <endian.h>

#if defined(__ARM_EABI__) && !defined(PT_ARM_EXIDX)
#  define PT_ARM_EXIDX 0x70000001
#endif

/**
 * Generic ELF macros for the target system
 */
#ifdef __LP64__
#  define Elf_(type) Elf64_##type
#  define ELFCLASS ELFCLASS64
#  define ELF_R_TYPE ELF64_R_TYPE
#  define ELF_R_SYM ELF64_R_SYM
#  ifndef ELF_ST_BIND
#    define ELF_ST_BIND ELF64_ST_BIND
#  endif
#else
#  define Elf_(type) Elf32_##type
#  define ELFCLASS ELFCLASS32
#  define ELF_R_TYPE ELF32_R_TYPE
#  define ELF_R_SYM ELF32_R_SYM
#  ifndef ELF_ST_BIND
#    define ELF_ST_BIND ELF32_ST_BIND
#  endif
#endif

#ifndef __BYTE_ORDER
#  error Cannot find endianness
#endif

#if __BYTE_ORDER == __LITTLE_ENDIAN
#  define ELFDATA ELFDATA2LSB
#elif __BYTE_ORDER == __BIG_ENDIAN
#  define ELFDATA ELFDATA2MSB
#endif

#ifdef __linux__
#  define ELFOSABI ELFOSABI_LINUX
#  ifdef EI_ABIVERSION
#    define ELFABIVERSION 0
#  endif
#else
#  error Unknown ELF OSABI
#endif

#if defined(__i386__)
#  define ELFMACHINE EM_386

// Doing this way probably doesn't scale to other architectures
#  define R_ABS R_386_32
#  define R_GLOB_DAT R_386_GLOB_DAT
#  define R_JMP_SLOT R_386_JMP_SLOT
#  define R_RELATIVE R_386_RELATIVE
#  define RELOC(n) DT_REL##n
#  define UNSUPPORTED_RELOC(n) DT_RELA##n
#  define STR_RELOC(n) "DT_REL" #  n
#  define Reloc Rel

#elif defined(__x86_64__)
#  define ELFMACHINE EM_X86_64

#  define R_ABS R_X86_64_64
#  define R_GLOB_DAT R_X86_64_GLOB_DAT
#  define R_JMP_SLOT R_X86_64_JUMP_SLOT
#  define R_RELATIVE R_X86_64_RELATIVE
#  define RELOC(n) DT_RELA##n
#  define UNSUPPORTED_RELOC(n) DT_REL##n
#  define STR_RELOC(n) "DT_RELA" #  n
#  define Reloc Rela

#elif defined(__arm__)
#  define ELFMACHINE EM_ARM

#  ifndef R_ARM_ABS32
#    define R_ARM_ABS32 2
#  endif
#  ifndef R_ARM_GLOB_DAT
#    define R_ARM_GLOB_DAT 21
#  endif
#  ifndef R_ARM_JUMP_SLOT
#    define R_ARM_JUMP_SLOT 22
#  endif
#  ifndef R_ARM_RELATIVE
#    define R_ARM_RELATIVE 23
#  endif

#  define R_ABS R_ARM_ABS32
#  define R_GLOB_DAT R_ARM_GLOB_DAT
#  define R_JMP_SLOT R_ARM_JUMP_SLOT
#  define R_RELATIVE R_ARM_RELATIVE
#  define RELOC(n) DT_REL##n
#  define UNSUPPORTED_RELOC(n) DT_RELA##n
#  define STR_RELOC(n) "DT_REL" #  n
#  define Reloc Rel

#elif defined(__aarch64__)
#  define ELFMACHINE EM_AARCH64

#  define R_ABS R_AARCH64_ABS64
#  define R_GLOB_DAT R_AARCH64_GLOB_DAT
#  define R_JMP_SLOT R_AARCH64_JUMP_SLOT
#  define R_RELATIVE R_AARCH64_RELATIVE
#  define RELOC(n) DT_RELA##n
#  define UNSUPPORTED_RELOC(n) DT_REL##n
#  define STR_RELOC(n) "DT_RELA" #  n
#  define Reloc Rela

#else
#  error Unknown ELF machine type
#endif

/**
 * Android system headers don't have all definitions
 */
#ifndef STN_UNDEF
#  define STN_UNDEF 0
#endif
#ifndef DT_INIT_ARRAY
#  define DT_INIT_ARRAY 25
#endif
#ifndef DT_FINI_ARRAY
#  define DT_FINI_ARRAY 26
#endif
#ifndef DT_INIT_ARRAYSZ
#  define DT_INIT_ARRAYSZ 27
#endif
#ifndef DT_FINI_ARRAYSZ
#  define DT_FINI_ARRAYSZ 28
#endif
#ifndef DT_RELACOUNT
#  define DT_RELACOUNT 0x6ffffff9
#endif
#ifndef DT_RELCOUNT
#  define DT_RELCOUNT 0x6ffffffa
#endif
#ifndef DT_VERSYM
#  define DT_VERSYM 0x6ffffff0
#endif
#ifndef DT_VERDEF
#  define DT_VERDEF 0x6ffffffc
#endif
#ifndef DT_VERDEFNUM
#  define DT_VERDEFNUM 0x6ffffffd
#endif
#ifndef DT_VERNEED
#  define DT_VERNEED 0x6ffffffe
#endif
#ifndef DT_VERNEEDNUM
#  define DT_VERNEEDNUM 0x6fffffff
#endif
#ifndef DT_FLAGS_1
#  define DT_FLAGS_1 0x6ffffffb
#endif
#ifndef DT_FLAGS
#  define DT_FLAGS 30
#endif
#ifndef DF_SYMBOLIC
#  define DF_SYMBOLIC 0x00000002
#endif
#ifndef DF_TEXTREL
#  define DF_TEXTREL 0x00000004
#endif

namespace Elf {

/**
 * Define a few basic Elf Types
 */
typedef Elf_(Phdr) Phdr;
typedef Elf_(Dyn) Dyn;
typedef Elf_(Sym) Sym;
typedef Elf_(Addr) Addr;
typedef Elf_(Word) Word;
typedef Elf_(Half) Half;

/**
 * Helper class around the standard Elf header struct
 */
struct Ehdr : public Elf_(Ehdr) {
  /**
   * Equivalent to reinterpret_cast<const Ehdr *>(buf), but additionally
   * checking that this is indeed an Elf header and that the Elf type
   * corresponds to that of the system
   */
  static const Ehdr* validate(const void* buf);
};

/**
 * Elf String table
 */
class Strtab : public UnsizedArray<const char> {
 public:
  /**
   * Returns the string at the given index in the table
   */
  const char* GetStringAt(off_t index) const {
    return &UnsizedArray<const char>::operator[](index);
  }
};

/**
 * Helper class around Elf relocation.
 */
struct Rel : public Elf_(Rel) {
  /**
   * Returns the addend for the relocation, which is the value stored
   * at r_offset.
   */
  Addr GetAddend(void* base) const {
    return *(reinterpret_cast<const Addr*>(reinterpret_cast<const char*>(base) +
                                           r_offset));
  }
};

/**
 * Helper class around Elf relocation with addend.
 */
struct Rela : public Elf_(Rela) {
  /**
   * Returns the addend for the relocation.
   */
  Addr GetAddend(void* base) const { return r_addend; }
};

} /* namespace Elf */

#endif /* Elfxx_h */