path: root/static/freebsd/man5/elf.5 3.html

<table class="head">
  <tr>
    <td class="head-ltitle">ELF(5)</td>
    <td class="head-vol">File Formats Manual</td>
    <td class="head-rtitle">ELF(5)</td>
  </tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">elf</code> &#x2014; <span class="Nd">format of
    ELF executable binary files</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp"><code class="In">#include
  &lt;<a class="In">elf.h</a>&gt;</code></p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">The header file
    <code class="In">&lt;<a class="In">elf.h</a>&gt;</code> defines the format
    of ELF executable binary files. Amongst these files are normal executable
    files, relocatable object files, core files and shared libraries.</p>
<p class="Pp">An executable file using the ELF file format consists of an ELF
    header, followed by a program header table or a section header table, or
    both. The ELF header is always at offset zero of the file. The program
    header table and the section header table's offset in the file are defined
    in the ELF header. The two tables describe the rest of the particularities
    of the file.</p>
<p class="Pp">Applications which wish to process ELF binary files for their
    native architecture only should include
    <code class="In">&lt;<a class="In">elf.h</a>&gt;</code> in their source
    code. These applications should need to refer to all the types and
    structures by their generic names &#x201C;Elf_xxx&#x201D; and to the macros
    by &#x201C;ELF_xxx&#x201D;. Applications written this way can be compiled on
    any architecture, regardless whether the host is 32-bit or 64-bit.</p>
<p class="Pp">Should an application need to process ELF files of an unknown
    architecture then the application needs to include both
    <code class="In">&lt;<a class="In">sys/elf32.h</a>&gt;</code> and
    <code class="In">&lt;<a class="In">sys/elf64.h</a>&gt;</code> instead of
    <code class="In">&lt;<a class="In">elf.h</a>&gt;</code>. Furthermore, all
    types and structures need to be identified by either
    &#x201C;Elf32_xxx&#x201D; or &#x201C;Elf64_xxx&#x201D;. The macros need to
    be identified by &#x201C;ELF32_xxx&#x201D; or &#x201C;ELF64_xxx&#x201D;.</p>
<p class="Pp">Whatever the system's architecture is, it will always include
    <code class="In">&lt;<a class="In">sys/elf_common.h</a>&gt;</code> as well
    as <code class="In">&lt;<a class="In">sys/elf_generic.h</a>&gt;</code>.</p>
<p class="Pp">These header files describe the above mentioned headers as C
    structures and also include structures for dynamic sections, relocation
    sections and symbol tables.</p>
<p class="Pp">The following types are being used for 32-bit architectures:</p>
<div class="Bd Pp Bd-indent Li">
<pre>Elf32_Addr	Unsigned 32-bit program address
Elf32_Half	Unsigned 16-bit field
Elf32_Lword	Unsigned 64-bit field
Elf32_Off	Unsigned 32-bit file offset
Elf32_Sword	Signed 32-bit field or integer
Elf32_Word	Unsigned 32-bit field or integer</pre>
</div>
<p class="Pp">For 64-bit architectures we have the following types:</p>
<div class="Bd Pp Bd-indent Li">
<pre>Elf64_Addr	Unsigned 64-bit program address
Elf64_Half	Unsigned 16-bit field
Elf64_Lword	Unsigned 64-bit field
Elf64_Off	Unsigned 64-bit file offset
Elf64_Sword	Signed 32-bit field
Elf64_Sxword	Signed 64-bit field or integer
Elf64_Word	Unsigned 32-bit field
Elf64_Xword	Unsigned 64-bit field or integer</pre>
</div>
<p class="Pp">All data structures that the file format defines follow the
    &#x201C;natural&#x201D; size and alignment guidelines for the relevant
    class. If necessary, data structures contain explicit padding to ensure
    4-byte alignment for 4-byte objects, to force structure sizes to a multiple
    of 4, etc.</p>
<p class="Pp">The ELF header is described by the type Elf32_Ehdr or
  Elf64_Ehdr:</p>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
        unsigned char   e_ident[EI_NIDENT];
        Elf32_Half      e_type;
        Elf32_Half      e_machine;
        Elf32_Word      e_version;
        Elf32_Addr      e_entry;
        Elf32_Off       e_phoff;
        Elf32_Off       e_shoff;
        Elf32_Word      e_flags;
        Elf32_Half      e_ehsize;
        Elf32_Half      e_phentsize;
        Elf32_Half      e_phnum;
        Elf32_Half      e_shentsize;
        Elf32_Half      e_shnum;
        Elf32_Half      e_shstrndx;
} Elf32_Ehdr;</pre>
</div>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	unsigned char   e_ident[EI_NIDENT];
	Elf64_Half      e_type;
	Elf64_Half      e_machine;
	Elf64_Word      e_version;
	Elf64_Addr      e_entry;
	Elf64_Off       e_phoff;
	Elf64_Off       e_shoff;
	Elf64_Word      e_flags;
	Elf64_Half      e_ehsize;
	Elf64_Half      e_phentsize;
	Elf64_Half      e_phnum;
	Elf64_Half      e_shentsize;
	Elf64_Half      e_shnum;
	Elf64_Half      e_shstrndx;
} Elf64_Ehdr;</pre>
</div>
<p class="Pp">The fields have the following meanings:</p>
<p class="Pp"></p>
<div class="Bd-indent">
<dl class="Bl-tag Bl-compact">
  <dt id="e_ident"><a class="permalink" href="#e_ident"><code class="Dv">e_ident</code></a></dt>
  <dd>This array of bytes specifies to interpret the file, independent of the
      processor or the file's remaining contents. Within this array everything
      is named by macros, which start with the prefix
      <a class="permalink" href="#EI_"><b class="Sy" id="EI_">EI_</b></a> and
      may contain values which start with the prefix
      <a class="permalink" href="#ELF"><b class="Sy" id="ELF">ELF</b></a>. The
      following macros are defined:
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="EI_MAG0"><a class="permalink" href="#EI_MAG0"><code class="Dv">EI_MAG0</code></a></dt>
      <dd>The first byte of the magic number. It must be filled with
          <a class="permalink" href="#ELFMAG0"><b class="Sy" id="ELFMAG0">ELFMAG0</b></a>.</dd>
      <dt id="EI_MAG1"><a class="permalink" href="#EI_MAG1"><code class="Dv">EI_MAG1</code></a></dt>
      <dd>The second byte of the magic number. It must be filled with
          <a class="permalink" href="#ELFMAG1"><b class="Sy" id="ELFMAG1">ELFMAG1</b></a>.</dd>
      <dt id="EI_MAG2"><a class="permalink" href="#EI_MAG2"><code class="Dv">EI_MAG2</code></a></dt>
      <dd>The third byte of the magic number. It must be filled with
          <a class="permalink" href="#ELFMAG2"><b class="Sy" id="ELFMAG2">ELFMAG2</b></a>.</dd>
      <dt id="EI_MAG3"><a class="permalink" href="#EI_MAG3"><code class="Dv">EI_MAG3</code></a></dt>
      <dd>The fourth byte of the magic number. It must be filled with
          <a class="permalink" href="#ELFMAG3"><b class="Sy" id="ELFMAG3">ELFMAG3</b></a>.</dd>
      <dt id="EI_CLASS"><a class="permalink" href="#EI_CLASS"><code class="Dv">EI_CLASS</code></a></dt>
      <dd>The fifth byte identifies the architecture for this binary:
        <p class="Pp"></p>
        <dl class="Bl-tag Bl-compact">
          <dt id="ELFCLASSNONE"><a class="permalink" href="#ELFCLASSNONE"><code class="Dv">ELFCLASSNONE</code></a></dt>
          <dd>This class is invalid.</dd>
          <dt id="ELFCLASS32"><a class="permalink" href="#ELFCLASS32"><code class="Dv">ELFCLASS32</code></a></dt>
          <dd>This defines the 32-bit architecture. It supports machines with
              files and virtual address spaces up to 4 Gigabytes.</dd>
          <dt id="ELFCLASS64"><a class="permalink" href="#ELFCLASS64"><code class="Dv">ELFCLASS64</code></a></dt>
          <dd>This defines the 64-bit architecture.</dd>
        </dl>
      </dd>
      <dt id="EI_DATA"><a class="permalink" href="#EI_DATA"><code class="Dv">EI_DATA</code></a></dt>
      <dd>The sixth byte specifies the data encoding of the processor-specific
          data in the file. Currently these encodings are supported:
        <p class="Pp"></p>
        <dl class="Bl-tag Bl-compact">
          <dt id="ELFDATANONE"><a class="permalink" href="#ELFDATANONE"><code class="Dv">ELFDATANONE</code></a></dt>
          <dd>Unknown data format.</dd>
          <dt id="ELFDATA2LSB"><a class="permalink" href="#ELFDATA2LSB"><code class="Dv">ELFDATA2LSB</code></a></dt>
          <dd>Two's complement, little-endian.</dd>
          <dt id="ELFDATA2MSB"><a class="permalink" href="#ELFDATA2MSB"><code class="Dv">ELFDATA2MSB</code></a></dt>
          <dd>Two's complement, big-endian.</dd>
        </dl>
      </dd>
      <dt id="EI_VERSION"><a class="permalink" href="#EI_VERSION"><code class="Dv">EI_VERSION</code></a></dt>
      <dd>The version number of the ELF specification:
        <p class="Pp"></p>
        <dl class="Bl-tag Bl-compact">
          <dt id="EV_NONE"><a class="permalink" href="#EV_NONE"><code class="Dv">EV_NONE</code></a></dt>
          <dd>Invalid version.</dd>
          <dt id="EV_CURRENT"><a class="permalink" href="#EV_CURRENT"><code class="Dv">EV_CURRENT</code></a></dt>
          <dd>Current version.</dd>
        </dl>
      </dd>
      <dt id="EI_OSABI"><a class="permalink" href="#EI_OSABI"><code class="Dv">EI_OSABI</code></a></dt>
      <dd>This byte identifies the operating system and ABI to which the object
          is targeted. Some fields in other ELF structures have flags and values
          that have platform specific meanings; the interpretation of those
          fields is determined by the value of this byte. The following values
          are currently defined:
        <p class="Pp"></p>
        <dl class="Bl-tag Bl-compact">
          <dt id="ELFOSABI_SYSV"><a class="permalink" href="#ELFOSABI_SYSV"><code class="Dv">ELFOSABI_SYSV</code></a></dt>
          <dd>UNIX System V ABI.</dd>
          <dt id="ELFOSABI_HPUX"><a class="permalink" href="#ELFOSABI_HPUX"><code class="Dv">ELFOSABI_HPUX</code></a></dt>
          <dd>HP-UX operating system ABI.</dd>
          <dt id="ELFOSABI_NETBSD"><a class="permalink" href="#ELFOSABI_NETBSD"><code class="Dv">ELFOSABI_NETBSD</code></a></dt>
          <dd><span class="Ux">NetBSD</span> operating system ABI.</dd>
          <dt id="ELFOSABI_LINUX"><a class="permalink" href="#ELFOSABI_LINUX"><code class="Dv">ELFOSABI_LINUX</code></a></dt>
          <dd>GNU/Linux operating system ABI.</dd>
          <dt id="ELFOSABI_HURD"><a class="permalink" href="#ELFOSABI_HURD"><code class="Dv">ELFOSABI_HURD</code></a></dt>
          <dd>GNU/Hurd operating system ABI.</dd>
          <dt id="ELFOSABI_86OPEN"><a class="permalink" href="#ELFOSABI_86OPEN"><code class="Dv">ELFOSABI_86OPEN</code></a></dt>
          <dd>86Open Common IA32 ABI.</dd>
          <dt id="ELFOSABI_SOLARIS"><a class="permalink" href="#ELFOSABI_SOLARIS"><code class="Dv">ELFOSABI_SOLARIS</code></a></dt>
          <dd>Solaris operating system ABI.</dd>
          <dt id="ELFOSABI_MONTEREY"><a class="permalink" href="#ELFOSABI_MONTEREY"><code class="Dv">ELFOSABI_MONTEREY</code></a></dt>
          <dd>Monterey project ABI.</dd>
          <dt id="ELFOSABI_IRIX"><a class="permalink" href="#ELFOSABI_IRIX"><code class="Dv">ELFOSABI_IRIX</code></a></dt>
          <dd>IRIX operating system ABI.</dd>
          <dt id="ELFOSABI_FREEBSD"><a class="permalink" href="#ELFOSABI_FREEBSD"><code class="Dv">ELFOSABI_FREEBSD</code></a></dt>
          <dd><span class="Ux">FreeBSD</span> operating system ABI.</dd>
          <dt id="ELFOSABI_TRU64"><a class="permalink" href="#ELFOSABI_TRU64"><code class="Dv">ELFOSABI_TRU64</code></a></dt>
          <dd>TRU64 UNIX operating system ABI.</dd>
          <dt id="ELFOSABI_ARM"><a class="permalink" href="#ELFOSABI_ARM"><code class="Dv">ELFOSABI_ARM</code></a></dt>
          <dd>ARM architecture ABI.</dd>
          <dt id="ELFOSABI_STANDALONE"><a class="permalink" href="#ELFOSABI_STANDALONE"><code class="Dv">ELFOSABI_STANDALONE</code></a></dt>
          <dd>Standalone (embedded) ABI.</dd>
        </dl>
      </dd>
      <dt id="EI_ABIVERSION"><a class="permalink" href="#EI_ABIVERSION"><code class="Dv">EI_ABIVERSION</code></a></dt>
      <dd>This byte identifies the version of the ABI to which the object is
          targeted. This field is used to distinguish among incompatible
          versions of an ABI. The interpretation of this version number is
          dependent on the ABI identified by the EI_OSABI field. Applications
          conforming to this specification use the value 0.</dd>
      <dt id="EI_PAD"><a class="permalink" href="#EI_PAD"><code class="Dv">EI_PAD</code></a></dt>
      <dd>Start of padding. These bytes are reserved and set to zero. Programs
          which read them should ignore them. The value for EI_PAD will change
          in the future if currently unused bytes are given meanings.</dd>
      <dt id="EI_BRAND"><a class="permalink" href="#EI_BRAND"><code class="Dv">EI_BRAND</code></a></dt>
      <dd>Start of architecture identification.</dd>
      <dt id="EI_NIDENT"><a class="permalink" href="#EI_NIDENT"><code class="Dv">EI_NIDENT</code></a></dt>
      <dd>The size of the e_ident array.</dd>
    </dl>
    <p class="Pp"></p>
  </dd>
  <dt id="e_type"><a class="permalink" href="#e_type"><code class="Dv">e_type</code></a></dt>
  <dd>This member of the structure identifies the object file type:
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="ET_NONE"><a class="permalink" href="#ET_NONE"><code class="Dv">ET_NONE</code></a></dt>
      <dd>An unknown type.</dd>
      <dt id="ET_REL"><a class="permalink" href="#ET_REL"><code class="Dv">ET_REL</code></a></dt>
      <dd>A relocatable file.</dd>
      <dt id="ET_EXEC"><a class="permalink" href="#ET_EXEC"><code class="Dv">ET_EXEC</code></a></dt>
      <dd>An executable file.</dd>
      <dt id="ET_DYN"><a class="permalink" href="#ET_DYN"><code class="Dv">ET_DYN</code></a></dt>
      <dd>A shared object.</dd>
      <dt id="ET_CORE"><a class="permalink" href="#ET_CORE"><code class="Dv">ET_CORE</code></a></dt>
      <dd>A core file.</dd>
    </dl>
    <p class="Pp"></p>
  </dd>
  <dt id="e_machine"><a class="permalink" href="#e_machine"><code class="Dv">e_machine</code></a></dt>
  <dd>This member specifies the required architecture for an individual file:
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="EM_NONE"><a class="permalink" href="#EM_NONE"><code class="Dv">EM_NONE</code></a></dt>
      <dd>An unknown machine.</dd>
      <dt id="EM_M32"><a class="permalink" href="#EM_M32"><code class="Dv">EM_M32</code></a></dt>
      <dd>AT&amp;T WE 32100.</dd>
      <dt id="EM_SPARC"><a class="permalink" href="#EM_SPARC"><code class="Dv">EM_SPARC</code></a></dt>
      <dd>Sun Microsystems SPARC.</dd>
      <dt id="EM_386"><a class="permalink" href="#EM_386"><code class="Dv">EM_386</code></a></dt>
      <dd>Intel 80386.</dd>
      <dt id="EM_68K"><a class="permalink" href="#EM_68K"><code class="Dv">EM_68K</code></a></dt>
      <dd>Motorola 68000.</dd>
      <dt id="EM_88K"><a class="permalink" href="#EM_88K"><code class="Dv">EM_88K</code></a></dt>
      <dd>Motorola 88000.</dd>
      <dt id="EM_486"><a class="permalink" href="#EM_486"><code class="Dv">EM_486</code></a></dt>
      <dd>Intel 80486.</dd>
      <dt id="EM_860"><a class="permalink" href="#EM_860"><code class="Dv">EM_860</code></a></dt>
      <dd>Intel 80860.</dd>
      <dt id="EM_MIPS"><a class="permalink" href="#EM_MIPS"><code class="Dv">EM_MIPS</code></a></dt>
      <dd>MIPS RS3000 (big-endian only).</dd>
      <dt id="EM_MIPS_RS4_BE"><a class="permalink" href="#EM_MIPS_RS4_BE"><code class="Dv">EM_MIPS_RS4_BE</code></a></dt>
      <dd>MIPS RS4000 (big-endian only).</dd>
      <dt id="EM_SPARC64"><a class="permalink" href="#EM_SPARC64"><code class="Dv">EM_SPARC64</code></a></dt>
      <dd>SPARC v9 64-bit unofficial.</dd>
      <dt id="EM_PARISC"><a class="permalink" href="#EM_PARISC"><code class="Dv">EM_PARISC</code></a></dt>
      <dd>HPPA.</dd>
      <dt id="EM_PPC"><a class="permalink" href="#EM_PPC"><code class="Dv">EM_PPC</code></a></dt>
      <dd>PowerPC.</dd>
      <dt id="EM_ALPHA"><a class="permalink" href="#EM_ALPHA"><code class="Dv">EM_ALPHA</code></a></dt>
      <dd>Compaq [DEC] Alpha.</dd>
    </dl>
    <p class="Pp"></p>
  </dd>
  <dt id="e_version"><a class="permalink" href="#e_version"><code class="Dv">e_version</code></a></dt>
  <dd>This member identifies the file version:
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="EV_NONE~2"><a class="permalink" href="#EV_NONE~2"><code class="Dv">EV_NONE</code></a></dt>
      <dd>Invalid version</dd>
      <dt id="EV_CURRENT~2"><a class="permalink" href="#EV_CURRENT~2"><code class="Dv">EV_CURRENT</code></a></dt>
      <dd>Current version</dd>
    </dl>
  </dd>
  <dt id="e_entry"><a class="permalink" href="#e_entry"><code class="Dv">e_entry</code></a></dt>
  <dd>This member gives the virtual address to which the system first transfers
      control, thus starting the process. If the file has no associated entry
      point, this member holds zero.</dd>
  <dt id="e_phoff"><a class="permalink" href="#e_phoff"><code class="Dv">e_phoff</code></a></dt>
  <dd>This member holds the program header table's file offset in bytes. If the
      file has no program header table, this member holds zero.</dd>
  <dt id="e_shoff"><a class="permalink" href="#e_shoff"><code class="Dv">e_shoff</code></a></dt>
  <dd>This member holds the section header table's file offset in bytes. If the
      file has no section header table this member holds zero.</dd>
  <dt id="e_flags"><a class="permalink" href="#e_flags"><code class="Dv">e_flags</code></a></dt>
  <dd>This member holds processor-specific flags associated with the file. Flag
      names take the form EF_`machine_flag'. Currently no flags have been
      defined.</dd>
  <dt id="e_ehsize"><a class="permalink" href="#e_ehsize"><code class="Dv">e_ehsize</code></a></dt>
  <dd>This member holds the ELF header's size in bytes.</dd>
  <dt id="e_phentsize"><a class="permalink" href="#e_phentsize"><code class="Dv">e_phentsize</code></a></dt>
  <dd>This member holds the size in bytes of one entry in the file's program
      header table; all entries are the same size.</dd>
  <dt id="e_phnum"><a class="permalink" href="#e_phnum"><code class="Dv">e_phnum</code></a></dt>
  <dd>This member holds the number of entries in the program header table. If
      the file is using extended program header numbering, then the
      <b class="Sy">e_phnum</b> member will contain the value
      <code class="Dv">PN_XNUM</code> and the actual number of program header
      table entries will be stored in the <b class="Sy">sh_info</b> member of
      the section header at index <code class="Dv">SHN_UNDEF</code>. The product
      of <b class="Sy">e_phentsize</b> and the number of program header table
      entries gives the program header table's size in bytes. If a file has no
      program header, <b class="Sy">e_phnum</b> holds the value zero.</dd>
  <dt id="e_shentsize"><a class="permalink" href="#e_shentsize"><code class="Dv">e_shentsize</code></a></dt>
  <dd>This member holds a sections header's size in bytes. A section header is
      one entry in the section header table; all entries are the same size.</dd>
  <dt id="e_shnum"><a class="permalink" href="#e_shnum"><code class="Dv">e_shnum</code></a></dt>
  <dd>This member holds the number of entries in the section header table. If
      the file is using extended section numbering, then the
      <b class="Sy">e_shnum</b> member will be zero and the actual section
      number will be stored in the <b class="Sy">sh_size</b> member of the
      section header at index <code class="Dv">SHN_UNDEF</code>. If a file has
      no section header table, both the <b class="Sy">e_shnum</b> and the
      <b class="Sy">e_shoff</b> fields of the ELF header will be zero. The
      product of <b class="Sy">e_shentsize</b> and the number of sections in the
      file gives the section header table's size in bytes.</dd>
  <dt id="e_shstrndx"><a class="permalink" href="#e_shstrndx"><code class="Dv">e_shstrndx</code></a></dt>
  <dd>This member holds the section header table index of the entry associated
      with the section name string table. If extended section numbering is being
      used, this field will hold the value
      <a class="permalink" href="#SHN_XINDEX"><b class="Sy" id="SHN_XINDEX">SHN_XINDEX</b></a>,
      and the actual section header table index will be present in the
      <b class="Sy">sh_link</b> field of the section header entry at index
      <code class="Dv">SHN_UNDEF</code>. If the file has no section name string
      table, this member holds the value <b class="Sy">SHN_UNDEF</b>.</dd>
</dl>
</div>
<p class="Pp" id="segment">An executable or shared object file's program header
    table is an array of structures, each describing a segment or other
    information the system needs to prepare the program for execution. An object
    file <a class="permalink" href="#segment"><i class="Em">segment</i></a>
    contains one or more
    <a class="permalink" href="#sections"><i class="Em" id="sections">sections</i></a>.
    Program headers are meaningful only for executable and shared object files.
    A file specifies its own program header size with the ELF header's
    <b class="Sy">e_phentsize</b> and <b class="Sy">e_phnum</b> members. As with
    the Elf executable header, the program header also has different versions
    depending on the architecture:</p>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
        Elf32_Word      p_type;
        Elf32_Off       p_offset;
        Elf32_Addr      p_vaddr;
        Elf32_Addr      p_paddr;
        Elf32_Word      p_filesz;
        Elf32_Word      p_memsz;
        Elf32_Word      p_flags;
        Elf32_Word      p_align;
} Elf32_Phdr;</pre>
</div>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
        Elf64_Word      p_type;
        Elf64_Word      p_flags;
        Elf64_Off       p_offset;
        Elf64_Addr      p_vaddr;
        Elf64_Addr      p_paddr;
        Elf64_Xword     p_filesz;
        Elf64_Xword     p_memsz;
        Elf64_Xword     p_align;
} Elf64_Phdr;</pre>
</div>
<p class="Pp">The main difference between the 32-bit and the 64-bit program
    header lies only in the location of a <b class="Sy">p_flags</b> member in
    the total struct.</p>
<p class="Pp"></p>
<div class="Bd-indent">
<dl class="Bl-tag Bl-compact">
  <dt id="p_type"><a class="permalink" href="#p_type"><code class="Dv">p_type</code></a></dt>
  <dd>This member of the Phdr struct tells what kind of segment this array
      element describes or how to interpret the array element's information.
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="PT_NULL"><a class="permalink" href="#PT_NULL"><code class="Dv">PT_NULL</code></a></dt>
      <dd>The array element is unused and the other members' values are
          undefined. This lets the program header have ignored entries.</dd>
      <dt id="PT_LOAD"><a class="permalink" href="#PT_LOAD"><code class="Dv">PT_LOAD</code></a></dt>
      <dd>The array element specifies a loadable segment, described by
          <b class="Sy">p_filesz</b> and <b class="Sy">p_memsz</b>. The bytes
          from the file are mapped to the beginning of the memory segment. If
          the segment's memory size (<b class="Sy">p_memsz</b>) is larger than
          the file size (<b class="Sy">p_filesz</b>), the &#x201C;extra&#x201D;
          bytes are defined to hold the value 0 and to follow the segment's
          initialized area. The file size may not be larger than the memory
          size. Loadable segment entries in the program header table appear in
          ascending order, sorted on the <b class="Sy">p_vaddr</b> member.</dd>
      <dt id="PT_DYNAMIC"><a class="permalink" href="#PT_DYNAMIC"><code class="Dv">PT_DYNAMIC</code></a></dt>
      <dd>The array element specifies dynamic linking information.</dd>
      <dt id="PT_INTERP"><a class="permalink" href="#PT_INTERP"><code class="Dv">PT_INTERP</code></a></dt>
      <dd>The array element specifies the location and size of a null-terminated
          path name to invoke as an interpreter. This segment type is meaningful
          only for executable files (though it may occur for shared objects).
          However it may not occur more than once in a file. If it is present it
          must precede any loadable segment entry.</dd>
      <dt id="PT_NOTE"><a class="permalink" href="#PT_NOTE"><code class="Dv">PT_NOTE</code></a></dt>
      <dd>The array element specifies the location and size for auxiliary
          information.</dd>
      <dt id="PT_SHLIB"><a class="permalink" href="#PT_SHLIB"><code class="Dv">PT_SHLIB</code></a></dt>
      <dd>This segment type is reserved but has unspecified semantics. Programs
          that contain an array element of this type do not conform to the
        ABI.</dd>
      <dt id="PT_PHDR"><a class="permalink" href="#PT_PHDR"><code class="Dv">PT_PHDR</code></a></dt>
      <dd>The array element, if present, specifies the location and size of the
          program header table itself, both in the file and in the memory image
          of the program. This segment type may not occur more than once in a
          file. Moreover, it may only occur if the program header table is part
          of the memory image of the program. If it is present it must precede
          any loadable segment entry.</dd>
      <dt id="PT_LOPROC"><a class="permalink" href="#PT_LOPROC"><code class="Dv">PT_LOPROC</code></a></dt>
      <dd>This value up to and including <b class="Sy">PT_HIPROC</b> are
          reserved for processor-specific semantics.</dd>
      <dt id="PT_HIPROC"><a class="permalink" href="#PT_HIPROC"><code class="Dv">PT_HIPROC</code></a></dt>
      <dd>This value down to and including <b class="Sy">PT_LOPROC</b> are
          reserved for processor-specific semantics.</dd>
    </dl>
    <p class="Pp"></p>
  </dd>
  <dt id="p_offset"><a class="permalink" href="#p_offset"><code class="Dv">p_offset</code></a></dt>
  <dd>This member holds the offset from the beginning of the file at which the
      first byte of the segment resides.</dd>
  <dt id="p_vaddr"><a class="permalink" href="#p_vaddr"><code class="Dv">p_vaddr</code></a></dt>
  <dd>This member holds the virtual address at which the first byte of the
      segment resides in memory.</dd>
  <dt id="p_paddr"><a class="permalink" href="#p_paddr"><code class="Dv">p_paddr</code></a></dt>
  <dd>On systems for which physical addressing is relevant, this member is
      reserved for the segment's physical address. Under
      <span class="Ux">BSD</span> this member is not used and must be zero.</dd>
  <dt id="p_filesz"><a class="permalink" href="#p_filesz"><code class="Dv">p_filesz</code></a></dt>
  <dd>This member holds the number of bytes in the file image of the segment. It
      may be zero.</dd>
  <dt id="p_memsz"><a class="permalink" href="#p_memsz"><code class="Dv">p_memsz</code></a></dt>
  <dd>This member holds the number of bytes in the memory image of the segment.
      It may be zero.</dd>
  <dt id="p_flags"><a class="permalink" href="#p_flags"><code class="Dv">p_flags</code></a></dt>
  <dd>This member holds flags relevant to the segment:
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="PF_X"><a class="permalink" href="#PF_X"><code class="Dv">PF_X</code></a></dt>
      <dd>An executable segment.</dd>
      <dt id="PF_W"><a class="permalink" href="#PF_W"><code class="Dv">PF_W</code></a></dt>
      <dd>A writable segment.</dd>
      <dt id="PF_R"><a class="permalink" href="#PF_R"><code class="Dv">PF_R</code></a></dt>
      <dd>A readable segment.</dd>
    </dl>
    <p class="Pp">A text segment commonly has the flags <b class="Sy">PF_X</b>
        and <b class="Sy">PF_R</b>. A data segment commonly has
        <b class="Sy">PF_X</b>, <b class="Sy">PF_W</b> and
        <b class="Sy">PF_R</b>.</p>
  </dd>
  <dt id="p_align"><a class="permalink" href="#p_align"><code class="Dv">p_align</code></a></dt>
  <dd>This member holds the value to which the segments are aligned in memory
      and in the file. Loadable process segments must have congruent values for
      <b class="Sy">p_vaddr</b> and <b class="Sy">p_offset</b>, modulo the page
      size. Values of zero and one mean no alignment is required. Otherwise,
      <b class="Sy">p_align</b> should be a positive, integral power of two, and
      <b class="Sy">p_vaddr</b> should equal <b class="Sy">p_offset</b>, modulo
      <b class="Sy">p_align</b>.</dd>
</dl>
</div>
<p class="Pp">An file's section header table lets one locate all the file's
    sections. The section header table is an array of Elf32_Shdr or Elf64_Shdr
    structures. The ELF header's <b class="Sy">e_shoff</b> member gives the byte
    offset from the beginning of the file to the section header table.
    <b class="Sy">e_shnum</b> holds the number of entries the section header
    table contains. <b class="Sy">e_shentsize</b> holds the size in bytes of
    each entry.</p>
<p class="Pp">A section header table index is a subscript into this array. Some
    section header table indices are reserved. An object file does not have
    sections for these special indices:</p>
<p class="Pp"></p>
<dl class="Bl-tag Bl-compact">
  <dt id="SHN_UNDEF"><a class="permalink" href="#SHN_UNDEF"><code class="Dv">SHN_UNDEF</code></a></dt>
  <dd>This value marks an undefined, missing, irrelevant, or otherwise
      meaningless section reference. For example, a symbol
      &#x201C;defined&#x201D; relative to section number
      <b class="Sy">SHN_UNDEF</b> is an undefined symbol.</dd>
  <dt id="SHN_LORESERVE"><a class="permalink" href="#SHN_LORESERVE"><code class="Dv">SHN_LORESERVE</code></a></dt>
  <dd>This value specifies the lower bound of the range of reserved
    indices.</dd>
  <dt id="SHN_LOPROC"><a class="permalink" href="#SHN_LOPROC"><code class="Dv">SHN_LOPROC</code></a></dt>
  <dd>This value up to and including <b class="Sy">SHN_HIPROC</b> are reserved
      for processor-specific semantics.</dd>
  <dt id="SHN_HIPROC"><a class="permalink" href="#SHN_HIPROC"><code class="Dv">SHN_HIPROC</code></a></dt>
  <dd>This value down to and including <b class="Sy">SHN_LOPROC</b> are reserved
      for processor-specific semantics.</dd>
  <dt id="SHN_ABS"><a class="permalink" href="#SHN_ABS"><code class="Dv">SHN_ABS</code></a></dt>
  <dd>This value specifies absolute values for the corresponding reference. For
      example, symbols defined relative to section number
      <b class="Sy">SHN_ABS</b> have absolute values and are not affected by
      relocation.</dd>
  <dt id="SHN_COMMON"><a class="permalink" href="#SHN_COMMON"><code class="Dv">SHN_COMMON</code></a></dt>
  <dd>Symbols defined relative to this section are common symbols, such as
      FORTRAN COMMON or unallocated C external variables.</dd>
  <dt id="SHN_HIRESERVE"><a class="permalink" href="#SHN_HIRESERVE"><code class="Dv">SHN_HIRESERVE</code></a></dt>
  <dd>This value specifies the upper bound of the range of reserved indices. The
      system reserves indices between <b class="Sy">SHN_LORESERVE</b> and
      <b class="Sy">SHN_HIRESERVE</b>, inclusive. The section header table does
      not contain entries for the reserved indices.</dd>
</dl>
<p class="Pp">The section header has the following structure:</p>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf32_Word      sh_name;
	Elf32_Word      sh_type;
	Elf32_Word      sh_flags;
	Elf32_Addr      sh_addr;
	Elf32_Off       sh_offset;
	Elf32_Word      sh_size;
	Elf32_Word      sh_link;
	Elf32_Word      sh_info;
	Elf32_Word      sh_addralign;
	Elf32_Word      sh_entsize;
} Elf32_Shdr;</pre>
</div>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf64_Word      sh_name;
	Elf64_Word      sh_type;
	Elf64_Xword     sh_flags;
	Elf64_Addr      sh_addr;
	Elf64_Off       sh_offset;
	Elf64_Xword     sh_size;
	Elf64_Word      sh_link;
	Elf64_Word      sh_info;
	Elf64_Xword     sh_addralign;
	Elf64_Xword     sh_entsize;
} Elf64_Shdr;</pre>
</div>
<p class="Pp"></p>
<dl class="Bl-tag Bl-compact">
  <dt id="sh_name"><a class="permalink" href="#sh_name"><code class="Dv">sh_name</code></a></dt>
  <dd>This member specifies the name of the section. Its value is an index into
      the section header string table section, giving the location of a
      null-terminated string.</dd>
  <dt id="sh_type"><a class="permalink" href="#sh_type"><code class="Dv">sh_type</code></a></dt>
  <dd>This member categorizes the section's contents and semantics.
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="SHT_NULL"><a class="permalink" href="#SHT_NULL"><code class="Dv">SHT_NULL</code></a></dt>
      <dd>This value marks the section header as inactive. It does not have an
          associated section. Other members of the section header have undefined
          values.</dd>
      <dt id="SHT_PROGBITS"><a class="permalink" href="#SHT_PROGBITS"><code class="Dv">SHT_PROGBITS</code></a></dt>
      <dd>The section holds information defined by the program, whose format and
          meaning are determined solely by the program.</dd>
      <dt id="SHT_SYMTAB"><a class="permalink" href="#SHT_SYMTAB"><code class="Dv">SHT_SYMTAB</code></a></dt>
      <dd>This section holds a symbol table. Typically,
          <b class="Sy">SHT_SYMTAB</b> provides symbols for link editing, though
          it may also be used for dynamic linking. As a complete symbol table,
          it may contain many symbols unnecessary for dynamic linking. An object
          file can also contain a
          <a class="permalink" href="#SHN_DYNSYM"><b class="Sy" id="SHN_DYNSYM">SHN_DYNSYM</b></a>
          section.</dd>
      <dt id="SHT_STRTAB"><a class="permalink" href="#SHT_STRTAB"><code class="Dv">SHT_STRTAB</code></a></dt>
      <dd>This section holds a string table. An object file may have multiple
          string table sections.</dd>
      <dt id="SHT_RELA"><a class="permalink" href="#SHT_RELA"><code class="Dv">SHT_RELA</code></a></dt>
      <dd>This section holds relocation entries with explicit addends, such as
          type
          <a class="permalink" href="#Elf32_Rela"><b class="Sy" id="Elf32_Rela">Elf32_Rela</b></a>
          for the 32-bit class of object files. An object may have multiple
          relocation sections.</dd>
      <dt id="SHT_HASH"><a class="permalink" href="#SHT_HASH"><code class="Dv">SHT_HASH</code></a></dt>
      <dd>This section holds a symbol hash table. All object participating in
          dynamic linking must contain a symbol hash table. An object file may
          have only one hash table.</dd>
      <dt id="SHT_DYNAMIC"><a class="permalink" href="#SHT_DYNAMIC"><code class="Dv">SHT_DYNAMIC</code></a></dt>
      <dd>This section holds information for dynamic linking. An object file may
          have only one dynamic section.</dd>
      <dt id="SHT_NOTE"><a class="permalink" href="#SHT_NOTE"><code class="Dv">SHT_NOTE</code></a></dt>
      <dd>This section holds information that marks the file in some way.</dd>
      <dt id="SHT_NOBITS"><a class="permalink" href="#SHT_NOBITS"><code class="Dv">SHT_NOBITS</code></a></dt>
      <dd>A section of this type occupies no space in the file but otherwise
          resembles
          <a class="permalink" href="#SHN_PROGBITS"><b class="Sy" id="SHN_PROGBITS">SHN_PROGBITS</b></a>.
          Although this section contains no bytes, the
          <b class="Sy">sh_offset</b> member contains the conceptual file
          offset.</dd>
      <dt id="SHT_REL"><a class="permalink" href="#SHT_REL"><code class="Dv">SHT_REL</code></a></dt>
      <dd>This section holds relocation offsets without explicit addends, such
          as type
          <a class="permalink" href="#Elf32_Rel"><b class="Sy" id="Elf32_Rel">Elf32_Rel</b></a>
          for the 32-bit class of object files. An object file may have multiple
          relocation sections.</dd>
      <dt id="SHT_SHLIB"><a class="permalink" href="#SHT_SHLIB"><code class="Dv">SHT_SHLIB</code></a></dt>
      <dd>This section is reserved but has unspecified semantics.</dd>
      <dt id="SHT_DYNSYM"><a class="permalink" href="#SHT_DYNSYM"><code class="Dv">SHT_DYNSYM</code></a></dt>
      <dd>This section holds a minimal set of dynamic linking symbols. An object
          file can also contain a
          <a class="permalink" href="#SHN_SYMTAB"><b class="Sy" id="SHN_SYMTAB">SHN_SYMTAB</b></a>
          section.</dd>
      <dt id="SHT_LOPROC"><a class="permalink" href="#SHT_LOPROC"><code class="Dv">SHT_LOPROC</code></a></dt>
      <dd>This value up to and including <b class="Sy">SHT_HIPROC</b> are
          reserved for processor-specific semantics.</dd>
      <dt id="SHT_HIPROC"><a class="permalink" href="#SHT_HIPROC"><code class="Dv">SHT_HIPROC</code></a></dt>
      <dd>This value down to and including <b class="Sy">SHT_LOPROC</b> are
          reserved for processor-specific semantics.</dd>
      <dt id="SHT_LOUSER"><a class="permalink" href="#SHT_LOUSER"><code class="Dv">SHT_LOUSER</code></a></dt>
      <dd>This value specifies the lower bound of the range of indices reserved
          for application programs.</dd>
      <dt id="SHT_HIUSER"><a class="permalink" href="#SHT_HIUSER"><code class="Dv">SHT_HIUSER</code></a></dt>
      <dd>This value specifies the upper bound of the range of indices reserved
          for application programs. Section types between
          <b class="Sy">SHT_LOUSER</b> and <b class="Sy">SHT_HIUSER</b> may be
          used by the application, without conflicting with current or future
          system-defined section types.</dd>
    </dl>
    <p class="Pp"></p>
  </dd>
  <dt id="sh_flags"><a class="permalink" href="#sh_flags"><code class="Dv">sh_flags</code></a></dt>
  <dd>Sections support one-bit flags that describe miscellaneous attributes. If
      a flag bit is set in <b class="Sy">sh_flags</b>, the attribute is
      &#x201C;on&#x201D; for the section. Otherwise, the attribute is
      &#x201C;off&#x201D; or does not apply. Undefined attributes are set to
      zero.
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="SHF_WRITE"><a class="permalink" href="#SHF_WRITE"><code class="Dv">SHF_WRITE</code></a></dt>
      <dd>This section contains data that should be writable during process
          execution.</dd>
      <dt id="SHF_ALLOC"><a class="permalink" href="#SHF_ALLOC"><code class="Dv">SHF_ALLOC</code></a></dt>
      <dd>The section occupies memory during process execution. Some control
          sections do not reside in the memory image of an object file. This
          attribute is off for those sections.</dd>
      <dt id="SHF_EXECINSTR"><a class="permalink" href="#SHF_EXECINSTR"><code class="Dv">SHF_EXECINSTR</code></a></dt>
      <dd>The section contains executable machine instructions.</dd>
      <dt id="SHF_MASKPROC"><a class="permalink" href="#SHF_MASKPROC"><code class="Dv">SHF_MASKPROC</code></a></dt>
      <dd>All bits included in this mask are reserved for processor-specific
          semantics.</dd>
      <dt id="SHF_COMPRESSED"><a class="permalink" href="#SHF_COMPRESSED"><code class="Dv">SHF_COMPRESSED</code></a></dt>
      <dd>The section data is compressed.</dd>
    </dl>
    <p class="Pp"></p>
  </dd>
  <dt id="sh_addr"><a class="permalink" href="#sh_addr"><code class="Dv">sh_addr</code></a></dt>
  <dd>If the section will appear in the memory image of a process, this member
      holds the address at which the section's first byte should reside.
      Otherwise, the member contains zero.</dd>
  <dt id="sh_offset"><a class="permalink" href="#sh_offset"><code class="Dv">sh_offset</code></a></dt>
  <dd>This member's value holds the byte offset from the beginning of the file
      to the first byte in the section. One section type,
      <b class="Sy">SHT_NOBITS</b>, occupies no space in the file, and its
      <b class="Sy">sh_offset</b> member locates the conceptual placement in the
      file.</dd>
  <dt id="sh_size"><a class="permalink" href="#sh_size"><code class="Dv">sh_size</code></a></dt>
  <dd>This member holds the section's size in bytes. Unless the section type is
      <b class="Sy">SHT_NOBITS</b>, the section occupies
      <b class="Sy">sh_size</b> bytes in the file. A section of type
      <b class="Sy">SHT_NOBITS</b> may have a non-zero size, but it occupies no
      space in the file.</dd>
  <dt id="sh_link"><a class="permalink" href="#sh_link"><code class="Dv">sh_link</code></a></dt>
  <dd>This member holds a section header table index link, whose interpretation
      depends on the section type.</dd>
  <dt id="sh_info"><a class="permalink" href="#sh_info"><code class="Dv">sh_info</code></a></dt>
  <dd>This member holds extra information, whose interpretation depends on the
      section type.</dd>
  <dt id="sh_addralign"><a class="permalink" href="#sh_addralign"><code class="Dv">sh_addralign</code></a></dt>
  <dd>Some sections have address alignment constraints. If a section holds a
      doubleword, the system must ensure doubleword alignment for the entire
      section. That is, the value of <b class="Sy">sh_addr</b> must be congruent
      to zero, modulo the value of <b class="Sy">sh_addralign</b>. Only zero and
      positive integral powers of two are allowed. Values of zero or one mean
      the section has no alignment constraints.</dd>
  <dt id="sh_entsize"><a class="permalink" href="#sh_entsize"><code class="Dv">sh_entsize</code></a></dt>
  <dd>Some sections hold a table of fixed-sized entries, such as a symbol table.
      For such a section, this member gives the size in bytes for each entry.
      This member contains zero if the section does not hold a table of
      fixed-size entries.</dd>
</dl>
<p class="Pp">Various sections hold program and control information:</p>
<dl class="Bl-tag Bl-compact">
  <dt>.bss</dt>
  <dd>(Block Started by Symbol) This section holds uninitialized data that
      contributes to the program's memory image. By definition, the system
      initializes the data with zeros when the program begins to run. This
      section is of type <b class="Sy">SHT_NOBITS</b>. The attributes types are
      <b class="Sy">SHF_ALLOC</b> and <b class="Sy">SHF_WRITE</b>.</dd>
  <dt>.comment</dt>
  <dd>This section holds version control information. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. No attribute types are used.</dd>
  <dt>.ctors</dt>
  <dd>This legacy section holds pointers to initialization routines, executed
      before calling the main program entry point. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. The attributes used are
      <b class="Sy">SHF_ALLOC</b>.</dd>
  <dt>.data</dt>
  <dd>This section holds initialized data that contribute to the program's
      memory image. This section is of type <b class="Sy">SHT_PROGBITS</b>. The
      attribute types are <b class="Sy">SHF_ALLOC</b> and
      <b class="Sy">SHF_WRITE</b>.</dd>
  <dt>.data1</dt>
  <dd>This section holds initialized data that contribute to the program's
      memory image. This section is of type <b class="Sy">SHT_PROGBITS</b>. The
      attribute types are <b class="Sy">SHF_ALLOC</b> and
      <b class="Sy">SHF_WRITE</b>.</dd>
  <dt>.debug</dt>
  <dd>This section holds information for symbolic debugging. The contents are
      unspecified. This section is of type <b class="Sy">SHT_PROGBITS</b>. No
      attribute types are used.</dd>
  <dt>.dtors</dt>
  <dd>This legacy section holds pointers to finalization routines, executed when
      the program exits normally. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. The attributes used are
      <b class="Sy">SHF_ALLOC</b>.</dd>
  <dt>.dynamic</dt>
  <dd>This section holds dynamic linking information. The section's attributes
      will include the <b class="Sy">SHF_ALLOC</b> bit. Whether the
      <b class="Sy">SHF_WRITE</b> bit is set is processor-specific. This section
      is of type <b class="Sy">SHT_DYNAMIC</b>. See the attributes above.</dd>
  <dt>.dynstr</dt>
  <dd>This section holds strings needed for dynamic linking, most commonly the
      strings that represent the names associated with symbol table entries.
      This section is of type <b class="Sy">SHT_STRTAB</b>. The attribute type
      used is <b class="Sy">SHF_ALLOC</b>.</dd>
  <dt>.dynsym</dt>
  <dd>This section holds the dynamic linking symbol table. This section is of
      type <b class="Sy">SHT_DYNSYM</b>. The attribute used is
      <b class="Sy">SHF_ALLOC</b>.</dd>
  <dt>.fini</dt>
  <dd>This legacy section holds executable instructions that contribute to the
      process termination code. When a program exits normally the system
      arranges to execute the code in this section. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. The attributes used are
      <b class="Sy">SHF_ALLOC</b> and <b class="Sy">SHF_EXECINSTR</b>.</dd>
  <dt id="SHT_FINI_ARRAY">.fini_array</dt>
  <dd>This section holds pointers to finalization routines. When a program exits
      normally <a class="Xr">rtld(1)</a> executes the code referenced by this
      section. This section is of type
      <a class="permalink" href="#SHT_FINI_ARRAY"><b class="Sy">SHT_FINI_ARRAY</b></a>.
      The attributes used are <b class="Sy">SHF_ALLOC</b>. Refer to
      <code class="Dv">NT_FREEBSD_NOINIT_TAG</code> (below) for a description of
      how initialization and finalization code is invoked.</dd>
  <dt>.got</dt>
  <dd>This section holds the global offset table. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. The attributes are
    processor-specific.</dd>
  <dt>.hash</dt>
  <dd>This section holds a symbol hash table. This section is of type
      <b class="Sy">SHT_HASH</b>. The attribute used is
      <b class="Sy">SHF_ALLOC</b>.</dd>
  <dt>.init</dt>
  <dd>This legacy section holds executable instructions that contribute to the
      process initialization code. When a program starts to run the system
      arranges to execute the code in this section before calling the main
      program entry point. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. The attributes used are
      <b class="Sy">SHF_ALLOC</b> and <b class="Sy">SHF_EXECINSTR</b>.</dd>
  <dt id="SHT_INIT_ARRAY">.init_array</dt>
  <dd>This section holds pointers to initialization routines. When a program
      starts to run <a class="Xr">rtld(1)</a> executes the code referenced by
      this section before calling the program entry point. This section is of
      type
      <a class="permalink" href="#SHT_INIT_ARRAY"><b class="Sy">SHT_INIT_ARRAY</b></a>.
      The attributes used are <b class="Sy">SHF_ALLOC</b>. Refer to
      <code class="Dv">NT_FREEBSD_NOINIT_TAG</code> (below) for a description of
      how initialization and finalization code is invoked.</dd>
  <dt>.interp</dt>
  <dd>This section holds the pathname of a program interpreter. If the file has
      a loadable segment that includes the section, the section's attributes
      will include the <b class="Sy">SHF_ALLOC</b> bit. Otherwise, that bit will
      be off. This section is of type <b class="Sy">SHT_PROGBITS</b>.</dd>
  <dt>.line</dt>
  <dd>This section holds line number information for symbolic debugging, which
      describes the correspondence between the program source and the machine
      code. The contents are unspecified. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. No attribute types are used.</dd>
  <dt>.note</dt>
  <dd>This section holds information in the &#x201C;Note Section&#x201D; format
      described below. This section is of type <b class="Sy">SHT_NOTE</b>. No
      attribute types are used.</dd>
  <dt>.plt</dt>
  <dd>This section holds the procedure linkage table. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. The attributes are
    processor-specific.</dd>
  <dt id=".rel.text">.relNAME</dt>
  <dd>This section holds relocation information as described below. If the file
      has a loadable segment that includes relocation, the section's attributes
      will include the <b class="Sy">SHF_ALLOC</b> bit. Otherwise the bit will
      be off. By convention, &#x201C;NAME&#x201D; is supplied by the section to
      which the relocations apply. Thus a relocation section for
      <b class="Sy">.text</b> normally would have the name
      <a class="permalink" href="#.rel.text"><b class="Sy">.rel.text</b></a>.
      This section is of type <b class="Sy">SHT_REL</b>.</dd>
  <dt id=".rela.text">.relaNAME</dt>
  <dd>This section holds relocation information as described below. If the file
      has a loadable segment that includes relocation, the section's attributes
      will include the <b class="Sy">SHF_ALLOC</b> bit. Otherwise the bit will
      be off. By convention, &#x201C;NAME&#x201D; is supplied by the section to
      which the relocations apply. Thus a relocation section for
      <b class="Sy">.text</b> normally would have the name
      <a class="permalink" href="#.rela.text"><b class="Sy">.rela.text</b></a>.
      This section is of type <b class="Sy">SHT_RELA</b>.</dd>
  <dt>.rodata</dt>
  <dd>This section holds read-only data that typically contributes to a
      non-writable segment in the process image. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. The attribute used is
      <b class="Sy">SHF_ALLOC</b>.</dd>
  <dt>.rodata1</dt>
  <dd>This section holds read-only data that typically contributes to a
      non-writable segment in the process image. This section is of type
      <b class="Sy">SHT_PROGBITS</b>. The attribute used is
      <b class="Sy">SHF_ALLOC</b>.</dd>
  <dt>.shstrtab</dt>
  <dd>This section holds section names. This section is of type
      <b class="Sy">SHT_STRTAB</b>. No attribute types are used.</dd>
  <dt>.strtab</dt>
  <dd>This section holds strings, most commonly the strings that represent the
      names associated with symbol table entries. If the file has a loadable
      segment that includes the symbol string table, the section's attributes
      will include the <b class="Sy">SHF_ALLOC</b> bit. Otherwise the bit will
      be off. This section is of type <b class="Sy">SHT_STRTAB</b>.</dd>
  <dt>.symtab</dt>
  <dd>This section holds a symbol table. If the file has a loadable segment that
      includes the symbol table, the section's attributes will include the
      <b class="Sy">SHF_ALLOC</b> bit. Otherwise the bit will be off. This
      section is of type <b class="Sy">SHT_SYMTAB</b>.</dd>
  <dt>.text</dt>
  <dd>This section holds the &#x201C;text&#x201D;, or executable instructions,
      of a program. This section is of type <b class="Sy">SHT_PROGBITS</b>. The
      attributes used are <b class="Sy">SHF_ALLOC</b> and
      <b class="Sy">SHF_EXECINSTR</b>.</dd>
  <dt>.jcr</dt>
  <dd>This section holds information about Java classes that must be registered.
      It is obsolete and binaries created for <span class="Ux">FreeBSD 15</span>
      or later do not process it.</dd>
  <dt>.eh_frame</dt>
  <dd>This section holds information used for C++ exception-handling.</dd>
</dl>
<p class="Pp">A section with the <code class="Dv">SHF_COMPRESSED</code> flag set
    contains a compressed copy of the section data. Compressed section data
    begins with an <var class="Vt">Elf64_Chdr</var> or
    <var class="Vt">Elf32_Chdr structure</var> which encodes the compression
    algorithm and some characteristics of the uncompressed data.</p>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf32_Word    ch_type;
	Elf32_Word    ch_size;
	Elf32_Word    ch_addralign;
} Elf32_Chdr;</pre>
</div>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf64_Word    ch_type;
	Elf64_Word    ch_reserved;
	Elf64_Xword   ch_size;
	Elf64_Xword   ch_addralign;
} Elf64_Chdr;</pre>
</div>
<p class="Pp"></p>
<dl class="Bl-tag Bl-compact">
  <dt id="ch_type"><a class="permalink" href="#ch_type"><code class="Dv">ch_type</code></a></dt>
  <dd>The compression algorithm used. A value of
      <code class="Dv">ELFCOMPRESS_ZLIB</code> indicates that the data is
      compressed using <a class="Xr">zlib(3)</a>. A value of
      <code class="Dv">ELFCOMPRESS_ZSTD</code> indicates that the data is
      compressed using Zstandard.</dd>
  <dt id="ch_size"><a class="permalink" href="#ch_size"><code class="Dv">ch_size</code></a></dt>
  <dd>The size, in bytes, of the uncompressed section data. This corresponds to
      the <b class="Sy">sh_size</b> field of a section header containing
      uncompressed data.</dd>
  <dt id="ch_addralign"><a class="permalink" href="#ch_addralign"><code class="Dv">ch_addralign</code></a></dt>
  <dd>The address alignment of the uncompressed section data. This corresponds
      to the <b class="Sy">sh_addralign</b> field of a section header containing
      uncompressed data.</dd>
</dl>
<p class="Pp">String table sections hold null-terminated character sequences,
    commonly called strings. The object file uses these strings to represent
    symbol and section names. One references a string as an index into the
    string table section. The first byte, which is index zero, is defined to
    hold a null character. Similarly, a string table's last byte is defined to
    hold a null character, ensuring null termination for all strings.</p>
<p class="Pp">An object file's symbol table holds information needed to locate
    and relocate a program's symbolic definitions and references. A symbol table
    index is a subscript into this array.</p>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf32_Word      st_name;
	Elf32_Addr      st_value;
	Elf32_Word      st_size;
	unsigned char   st_info;
	unsigned char   st_other;
	Elf32_Half      st_shndx;
} Elf32_Sym;</pre>
</div>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf64_Word      st_name;
	unsigned char   st_info;
	unsigned char   st_other;
	Elf64_Half      st_shndx;
	Elf64_Addr      st_value;
	Elf64_Xword     st_size;
} Elf64_Sym;</pre>
</div>
<p class="Pp"></p>
<dl class="Bl-tag Bl-compact">
  <dt id="st_name"><a class="permalink" href="#st_name"><code class="Dv">st_name</code></a></dt>
  <dd>This member holds an index into the object file's symbol string table,
      which holds character representations of the symbol names. If the value is
      non-zero, it represents a string table index that gives the symbol name.
      Otherwise, the symbol table has no name.</dd>
  <dt id="st_value"><a class="permalink" href="#st_value"><code class="Dv">st_value</code></a></dt>
  <dd>This member gives the value of the associated symbol.</dd>
  <dt id="st_size"><a class="permalink" href="#st_size"><code class="Dv">st_size</code></a></dt>
  <dd>Many symbols have associated sizes. This member holds zero if the symbol
      has no size or an unknown size.</dd>
  <dt id="st_info"><a class="permalink" href="#st_info"><code class="Dv">st_info</code></a></dt>
  <dd>This member specifies the symbol's type and binding attributes:
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="STT_NOTYPE"><a class="permalink" href="#STT_NOTYPE"><code class="Dv">STT_NOTYPE</code></a></dt>
      <dd>The symbol's type is not defined.</dd>
      <dt id="STT_OBJECT"><a class="permalink" href="#STT_OBJECT"><code class="Dv">STT_OBJECT</code></a></dt>
      <dd>The symbol is associated with a data object.</dd>
      <dt id="STT_FUNC"><a class="permalink" href="#STT_FUNC"><code class="Dv">STT_FUNC</code></a></dt>
      <dd>The symbol is associated with a function or other executable
        code.</dd>
      <dt id="STT_SECTION"><a class="permalink" href="#STT_SECTION"><code class="Dv">STT_SECTION</code></a></dt>
      <dd>The symbol is associated with a section. Symbol table entries of this
          type exist primarily for relocation and normally have
          <b class="Sy">STB_LOCAL</b> bindings.</dd>
      <dt id="STT_FILE"><a class="permalink" href="#STT_FILE"><code class="Dv">STT_FILE</code></a></dt>
      <dd>By convention the symbol's name gives the name of the source file
          associated with the object file. A file symbol has
          <b class="Sy">STB_LOCAL</b> bindings, its section index is
          <b class="Sy">SHN_ABS</b>, and it precedes the other
          <b class="Sy">STB_LOCAL</b> symbols of the file, if it is
        present.</dd>
      <dt id="STT_LOPROC"><a class="permalink" href="#STT_LOPROC"><code class="Dv">STT_LOPROC</code></a></dt>
      <dd>This value up to and including <b class="Sy">STT_HIPROC</b> are
          reserved for processor-specific semantics.</dd>
      <dt id="STT_HIPROC"><a class="permalink" href="#STT_HIPROC"><code class="Dv">STT_HIPROC</code></a></dt>
      <dd>This value down to and including <b class="Sy">STT_LOPROC</b> are
          reserved for processor-specific semantics.</dd>
    </dl>
    <p class="Pp"></p>
    <dl class="Bl-tag Bl-compact">
      <dt id="STB_LOCAL"><a class="permalink" href="#STB_LOCAL"><code class="Dv">STB_LOCAL</code></a></dt>
      <dd>Local symbols are not visible outside the object file containing their
          definition. Local symbols of the same name may exist in multiple file
          without interfering with each other.</dd>
      <dt id="STB_GLOBAL"><a class="permalink" href="#STB_GLOBAL"><code class="Dv">STB_GLOBAL</code></a></dt>
      <dd>Global symbols are visible to all object files being combined. One
          file's definition of a global symbol will satisfy another file's
          undefined reference to the same symbol.</dd>
      <dt id="STB_WEAK"><a class="permalink" href="#STB_WEAK"><code class="Dv">STB_WEAK</code></a></dt>
      <dd>Weak symbols resemble global symbols, but their definitions have lower
          precedence.</dd>
      <dt id="STB_LOPROC"><a class="permalink" href="#STB_LOPROC"><code class="Dv">STB_LOPROC</code></a></dt>
      <dd>This value up to and including <b class="Sy">STB_HIPROC</b> are
          reserved for processor-specific semantics.</dd>
      <dt id="STB_HIPROC"><a class="permalink" href="#STB_HIPROC"><code class="Dv">STB_HIPROC</code></a></dt>
      <dd>This value down to and including <b class="Sy">STB_LOPROC</b> are
          reserved for processor-specific semantics.
        <p class="Pp">There are macros for packing and unpacking the binding and
            type fields:</p>
        <p class="Pp"></p>
        <dl class="Bl-tag Bl-compact">
          <dt id="ELF32_ST_BIND"><a class="permalink" href="#ELF32_ST_BIND"><code class="Fn">ELF32_ST_BIND</code></a>(<var class="Fa">info</var>)</dt>
          <dd>or
              <a class="permalink" href="#ELF64_ST_BIND"><code class="Fn" id="ELF64_ST_BIND">ELF64_ST_BIND</code></a>(<var class="Fa">info</var>)
              extract a binding from an st_info value.</dd>
          <dt id="ELF64_ST_TYPE"><a class="permalink" href="#ELF64_ST_TYPE"><code class="Fn">ELF64_ST_TYPE</code></a>(<var class="Fa">info</var>)</dt>
          <dd>or
              <a class="permalink" href="#ELF32_ST_TYPE"><code class="Fn" id="ELF32_ST_TYPE">ELF32_ST_TYPE</code></a>(<var class="Fa">info</var>)
              extract a type from an st_info value.</dd>
          <dt id="ELF32_ST_INFO"><a class="permalink" href="#ELF32_ST_INFO"><code class="Fn">ELF32_ST_INFO</code></a>(<var class="Fa">bind</var>,
            <var class="Fa">type</var>)</dt>
          <dd>or
              <a class="permalink" href="#ELF64_ST_INFO"><code class="Fn" id="ELF64_ST_INFO">ELF64_ST_INFO</code></a>(<var class="Fa">bind</var>,
              <var class="Fa">type</var>) convert a binding and a type into an
              st_info value.</dd>
        </dl>
      </dd>
    </dl>
    <p class="Pp"></p>
  </dd>
  <dt id="st_other"><a class="permalink" href="#st_other"><code class="Dv">st_other</code></a></dt>
  <dd>This member currently holds zero and has no defined meaning.</dd>
  <dt id="st_shndx"><a class="permalink" href="#st_shndx"><code class="Dv">st_shndx</code></a></dt>
  <dd>Every symbol table entry is &#x201C;defined&#x201D; in relation to some
      section. This member holds the relevant section header table index.</dd>
</dl>
<p class="Pp">Relocation is the process of connecting symbolic references with
    symbolic definitions. Relocatable files must have information that describes
    how to modify their section contents, thus allowing executable and shared
    object files to hold the right information for a process' program image.
    Relocation entries are these data.</p>
<p class="Pp">Relocation structures that do not need an addend:</p>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf32_Addr      r_offset;
	Elf32_Word      r_info;
} Elf32_Rel;</pre>
</div>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf64_Addr      r_offset;
	Elf64_Xword     r_info;
} Elf64_Rel;</pre>
</div>
<p class="Pp">Relocation structures that need an addend:</p>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf32_Addr      r_offset;
	Elf32_Word      r_info;
	Elf32_Sword     r_addend;
} Elf32_Rela;</pre>
</div>
<div class="Bd Pp Bd-indent Li">
<pre>typedef struct {
	Elf64_Addr      r_offset;
	Elf64_Xword     r_info;
	Elf64_Sxword    r_addend;
} Elf64_Rela;</pre>
</div>
<p class="Pp"></p>
<dl class="Bl-tag Bl-compact">
  <dt id="r_offset"><a class="permalink" href="#r_offset"><code class="Dv">r_offset</code></a></dt>
  <dd>This member gives the location at which to apply the relocation action.
      For a relocatable file, the value is the byte offset from the beginning of
      the section to the storage unit affected by the relocation. For an
      executable file or shared object, the value is the virtual address of the
      storage unit affected by the relocation.</dd>
  <dt id="r_info"><a class="permalink" href="#r_info"><code class="Dv">r_info</code></a></dt>
  <dd>This member gives both the symbol table index with respect to which the
      relocation must be made and the type of relocation to apply. Relocation
      types are processor-specific. When the text refers to a relocation entry's
      relocation type or symbol table index, it means the result of applying
      <a class="permalink" href="#ELF__32_64__R_TYPE"><b class="Sy" id="ELF__32_64__R_TYPE">ELF_[32|64]_R_TYPE</b></a>
      or
      <a class="permalink" href="#ELF_32_64__R_SYM"><b class="Sy" id="ELF_32_64__R_SYM">ELF[32|64]_R_SYM</b></a>,
      respectively to the entry's <b class="Sy">r_info</b> member.</dd>
  <dt id="r_addend"><a class="permalink" href="#r_addend"><code class="Dv">r_addend</code></a></dt>
  <dd>This member specifies a constant addend used to compute the value to be
      stored into the relocatable field.</dd>
</dl>
<section class="Ss">
<h2 class="Ss" id="Note_Section"><a class="permalink" href="#Note_Section">Note
  Section</a></h2>
<p class="Pp">ELF note sections consist of entries with the following
  format:</p>
<table class="Bl-column Bd-indent">
  <tr id="Field">
    <td><a class="permalink" href="#Field"><b class="Sy">Field</b></a></td>
    <td><a class="permalink" href="#Size"><b class="Sy" id="Size">Size</b></a></td>
    <td><a class="permalink" href="#Description"><b class="Sy" id="Description">Description</b></a></td>
  </tr>
  <tr id="namesz">
    <td><var class="Va">namesz</var></td>
    <td>32 bits</td>
    <td>Size of name</td>
  </tr>
  <tr id="descsz">
    <td><var class="Va">descsz</var></td>
    <td>32 bits</td>
    <td>Size of desc</td>
  </tr>
  <tr id="type">
    <td><var class="Va">type</var></td>
    <td>32 bits</td>
    <td>OS-dependent note type</td>
  </tr>
  <tr id="name">
    <td><var class="Va">name</var></td>
    <td><var class="Va">namesz</var></td>
    <td>Null-terminated originator name</td>
  </tr>
  <tr id="desc">
    <td><var class="Va">desc</var></td>
    <td><var class="Va">descsz</var></td>
    <td>OS-dependent note data</td>
  </tr>
</table>
<p class="Pp">The <var class="Va">name</var> and <var class="Va">desc</var>
    fields are padded to ensure 4-byte alignment. <var class="Va">namesz</var>
    and <var class="Va">descsz</var> specify the unpadded length.</p>
<p class="Pp"><span class="Ux">FreeBSD</span> defines the following ELF note
    types (with corresponding interpretation of <var class="Va">desc</var>):</p>
<dl class="Bl-tag">
  <dt id="NT_FREEBSD_ABI_TAG"><a class="permalink" href="#NT_FREEBSD_ABI_TAG"><code class="Dv">NT_FREEBSD_ABI_TAG</code></a>
    (Value: 1)</dt>
  <dd>Indicates the OS ABI version in a form of a 32-bit integer containing
      expected ABI version (i.e.,
    <code class="Dv">__FreeBSD_version</code>).</dd>
  <dt id="NT_FREEBSD_NOINIT_TAG"><a class="permalink" href="#NT_FREEBSD_NOINIT_TAG"><code class="Dv">NT_FREEBSD_NOINIT_TAG</code></a>
    (Value: 2)</dt>
  <dd>Indicates that the C startup does not call initialization routines, and
      thus <a class="Xr">rtld(1)</a> must do so. <var class="Va">desc</var> is
      ignored.</dd>
  <dt id="NT_FREEBSD_ARCH_TAG"><a class="permalink" href="#NT_FREEBSD_ARCH_TAG"><code class="Dv">NT_FREEBSD_ARCH_TAG</code></a>
    (Value: 3)</dt>
  <dd>Contains the MACHINE_ARCH that the executable was built for.</dd>
  <dt id="NT_FREEBSD_FEATURE_CTL"><a class="permalink" href="#NT_FREEBSD_FEATURE_CTL"><code class="Dv">NT_FREEBSD_FEATURE_CTL</code></a>
    (Value: 4)</dt>
  <dd>Contains a bitmask of mitigations and features to enable:
    <dl class="Bl-tag">
      <dt>NT_FREEBSD_FCTL_ASLR_DISABLE (Value: 0x01)</dt>
      <dd>Request that address randomization (ASLR) not be performed. See
          <a class="Xr">security(7)</a>.</dd>
      <dt>NT_FREEBSD_FCTL_PROTMAX_DISABLE (Value: 0x02)</dt>
      <dd>Request that <a class="Xr">mmap(2)</a> calls not set PROT_MAX to the
          initial value of the <var class="Fa">prot</var> argument.</dd>
      <dt>NT_FREEBSD_FCTL_STKGAP_DISABLE (Value: 0x04)</dt>
      <dd>Disable stack gap.</dd>
      <dt>NT_FREEBSD_FCTL_WXNEEDED (Value: 0x08)</dt>
      <dd>Indicate that the binary requires mappings that are simultaneously
          writeable and executable.</dd>
      <dt>NT_FREEBSD_FCTL_LA48 (Value: 0x10)</dt>
      <dd>Request 48-bit linear address space on amd64.</dd>
      <dt>NT_FREEBSD_FCTL_LA57 (Value: 0x40)</dt>
      <dd>Accept 57-bit linear address space on amd64.</dd>
    </dl>
  </dd>
</dl>
</section>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
  ALSO</a></h1>
<p class="Pp"><a class="Xr">as(1)</a>, <a class="Xr">gdb(1)</a>
    (<span class="Pa">ports/devel/gdb</span>), <a class="Xr">ld(1)</a>,
    <a class="Xr">objdump(1)</a>, <a class="Xr">readelf(1)</a>,
    <a class="Xr">execve(2)</a>, <a class="Xr">zlib(3)</a>,
    <a class="Xr">ar(5)</a>, <a class="Xr">core(5)</a></p>
<p class="Pp"><cite class="Rs"><span class="RsA">Hewlett Packard</span>,
    <i class="RsB">Elf-64 Object File Format</i>.</cite></p>
<p class="Pp"><cite class="Rs"><span class="RsA">Santa Cruz Operation</span>,
    <i class="RsB">System V Application Binary Interface</i>.</cite></p>
<p class="Pp"><cite class="Rs"><span class="RsA">Unix System
    Laboratories</span>, <span class="RsT">Object Files</span>,
    <i class="RsB">Executable and Linking Format (ELF)</i>.</cite></p>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">The ELF header files made their appearance in
    <span class="Ux">FreeBSD 2.2.6</span>. ELF in itself first appeared in
    <span class="Ux">AT&amp;T System&#x00A0;V UNIX</span>. The ELF format is an
    adopted standard.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="AUTHORS"><a class="permalink" href="#AUTHORS">AUTHORS</a></h1>
<p class="Pp">This manual page was written by <span class="An">Jeroen Ruigrok
    van der Werven</span>
    &lt;<a class="Mt" href="mailto:asmodai@FreeBSD.org">asmodai@FreeBSD.org</a>&gt;
    with inspiration from BSDi's <span class="Ux">BSD/OS</span>
    <code class="Nm">elf</code> manpage.</p>
</section>
</div>
<table class="foot">
  <tr>
    <td class="foot-date">May 26, 2025</td>
    <td class="foot-os">FreeBSD 15.0</td>
  </tr>
</table>