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ELF(5)			  FreeBSD File Formats Manual			ELF(5)

NAME
     elf -- format of ELF executable binary files

SYNOPSIS
     #include <elf.h>

DESCRIPTION
     The header	file <elf.h> defines the format	of ELF executable binary
     files.  Amongst these files are normal executable files, relocatable
     object files, core	files and shared libraries.

     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.

     Applications which	wish to	process	ELF binary files for their native
     architecture only should include <elf.h> in their source code.  These
     applications should need to refer to all the types	and structures by
     their generic names ``Elf_xxx'' and to the	macros by ``ELF_xxx''.	Appli-
     cations written this way can be compiled on any architecture, regardless
     whether the host is 32-bit	or 64-bit.

     Should an application need	to process ELF files of	an unknown architec-
     ture then the application needs to	include	both <sys/elf32.h> and
     <sys/elf64.h> instead of <elf.h>.	Furthermore, all types and structures
     need to be	identified by either ``Elf32_xxx'' or ``Elf64_xxx''.  The
     macros need to be identified by ``ELF32_xxx'' or ``ELF64_xxx''.

     Whatever the system's architecture	is, it will always include
     <sys/elf_common.h>	as well	as <sys/elf_generic.h>.

     These header files	describe the above mentioned headers as	C structures
     and also include structures for dynamic sections, relocation sections and
     symbol tables.

     The following types are being used	for 32-bit architectures:

	   Elf32_Addr	   Unsigned program address
	   Elf32_Half	   Unsigned halfword field
	   Elf32_Off	   Unsigned file offset
	   Elf32_Sword	   Signed large	integer
	   Elf32_Word	   Field or unsigned large integer
	   Elf32_Size	   Unsigned object size

     For 64-bit	architectures we have the following types:

	   Elf64_Addr	   Unsigned program address
	   Elf64_Half	   Unsigned halfword field
	   Elf64_Off	   Unsigned file offset
	   Elf64_Sword	   Signed large	integer
	   Elf64_Word	   Field or unsigned large integer
	   Elf64_Size	   Unsigned object size
	   Elf64_Quarter   Unsigned quarterword	field

     All data structures that the file format defines follow the ``natural''
     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.

     The ELF header is described by the	type Elf32_Ehdr	or Elf64_Ehdr:

	   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;

	   typedef struct {
		   unsigned char   e_ident[EI_NIDENT];
		   Elf64_Quarter   e_type;
		   Elf64_Quarter   e_machine;
		   Elf64_Half	   e_version;
		   Elf64_Addr	   e_entry;
		   Elf64_Off	   e_phoff;
		   Elf64_Off	   e_shoff;
		   Elf64_Half	   e_flags;
		   Elf64_Quarter   e_ehsize;
		   Elf64_Quarter   e_phentsize;
		   Elf64_Quarter   e_phnum;
		   Elf64_Quarter   e_shentsize;
		   Elf64_Quarter   e_shnum;
		   Elf64_Quarter   e_shstrndx;
	   } Elf64_Ehdr;

     The fields	have the following meanings:

	   e_ident	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 EI_	and may	con-
			tain values which start	with the prefix	ELF.  The fol-
			lowing macros are defined:

			EI_MAG0	       The first byte of the magic number.  It
				       must be filled with ELFMAG0.
			EI_MAG1	       The second byte of the magic number.
				       It must be filled with ELFMAG1.
			EI_MAG2	       The third byte of the magic number.  It
				       must be filled with ELFMAG2.
			EI_MAG3	       The fourth byte of the magic number.
				       It must be filled with ELFMAG3.
			EI_CLASS       The fifth byte identifies the architec-
				       ture for	this binary:

				       ELFCLASSNONE  This class	is invalid.
				       ELFCLASS32    This defines the 32-bit
						     architecture.  It sup-
						     ports machines with files
						     and virtual address spa-
						     ces up to 4 Gigabytes.
				       ELFCLASS64    This defines the 64-bit
						     architecture.
			EI_DATA	       The sixth byte specifies	the data
				       encoding	of the processor-specific data
				       in the file.  Currently these encodings
				       are supported:

				       ELFDATANONE  Unknown data format.
				       ELFDATA2LSB  Two's complement, little-
						    endian.
				       ELFDATA2MSB  Two's complement, big-
						    endian.
			EI_VERSION     The version number of the ELF specifi-
				       cation:

				       EV_NONE	   Invalid version.
				       EV_CURRENT  Current version.
			EI_OSABI       This byte identifies the	operating sys-
				       tem and ABI to which the	object is tar-
				       geted.  Some fields in other ELF	struc-
				       tures have flags	and values that	have
				       platform	specific meanings; the inter-
				       pretation of those fields is determined
				       by the value of this byte.  The follow-
				       ing values are currently	defined:

				       ELFOSABI_SYSV	    UNIX System	V ABI.
				       ELFOSABI_HPUX	    HP-UX operating
							    system ABI.
				       ELFOSABI_NETBSD	    NetBSD operating
							    system ABI.
				       ELFOSABI_LINUX	    GNU/Linux operat-
							    ing	system ABI.
				       ELFOSABI_HURD	    GNU/Hurd operating
							    system ABI.
				       ELFOSABI_86OPEN	    86Open Common IA32
							    ABI.
				       ELFOSABI_SOLARIS	    Solaris operating
							    system ABI.
				       ELFOSABI_MONTEREY    Monterey project
							    ABI.
				       ELFOSABI_IRIX	    IRIX operating
							    system ABI.
				       ELFOSABI_FREEBSD	    FreeBSD operating
							    system ABI.
				       ELFOSABI_TRU64	    TRU64 UNIX operat-
							    ing	system ABI.
				       ELFOSABI_ARM	    ARM	architecture
							    ABI.
				       ELFOSABI_STANDALONE  Standalone (embed-
							    ded) ABI.
			EI_ABIVERSION  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 con-
				       forming to this specification use the
				       value 0.
			EI_PAD	       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.
			EI_BRAND       Start of	architecture identification.
			EI_NIDENT      The size	of the e_ident array.

	   e_type	This member of the structure identifies	the object
			file type:

			ET_NONE	 An unknown type.
			ET_REL	 A relocatable file.
			ET_EXEC	 An executable file.
			ET_DYN	 A shared object.
			ET_CORE	 A core	file.

	   e_machine	This member specifies the required architecture	for an
			individual file:

			EM_NONE		An unknown machine.
			EM_M32		AT&T WE	32100.
			EM_SPARC	Sun Microsystems SPARC.
			EM_386		Intel 80386.
			EM_68K		Motorola 68000.
			EM_88K		Motorola 88000.
			EM_486		Intel 80486.
			EM_860		Intel 80860.
			EM_MIPS		MIPS RS3000 (big-endian	only).
			EM_MIPS_RS4_BE	MIPS RS4000 (big-endian	only).
			EM_SPARC64	SPARC v9 64-bit	unofficial.
			EM_PARISC	HPPA.
			EM_PPC		PowerPC.
			EM_ALPHA	Compaq [DEC] Alpha.

	   e_version	This member identifies the file	version:

			EV_NONE	    Invalid version
			EV_CURRENT  Current version
	   e_entry	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.
	   e_phoff	This member holds the program header table's file off-
			set in bytes.  If the file has no program header ta-
			ble, this member holds zero.
	   e_shoff	This member holds the section header table's file off-
			set in bytes.  If the file has no section header table
			this member holds zero.
	   e_flags	This member holds processor-specific flags associated
			with the file.	Flag names take	the form
			EF_`machine_flag'. Currently no	flags have been
			defined.
	   e_ehsize	This member holds the ELF header's size	in bytes.
	   e_phentsize	This member holds the size in bytes of one entry in
			the file's program header table; all entries are the
			same size.
	   e_phnum	This member holds the number of	entries	in the program
			header table.  Thus the	product	of e_phentsize and
			e_phnum	gives the table's size in bytes.  If a file
			has no program header, e_phnum holds the value zero.
	   e_shentsize	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.
	   e_shnum	This member holds the number of	entries	in the section
			header table.  Thus the	product	of e_shentsize and
			e_shnum	gives the section header table's size in
			bytes.	If a file has no section header	table, e_shnum
			holds the value	of zero.
	   e_shstrndx	This member holds the section header table index of
			the entry associated with the section name string ta-
			ble.  If the file has no section name string table,
			this member holds the value SHN_UNDEF.

			SHN_UNDEF      This value marks	an undefined, missing,
				       irrelevant, or otherwise	meaningless
				       section reference.  For example,	a sym-
				       bol ``defined'' relative	to section
				       number SHN_UNDEF	is an undefined	sym-
				       bol.
			SHN_LORESERVE  This value specifies the	lower bound of
				       the range of reserved indexes.
			SHN_LOPROC     This value up to	and including
				       SHN_HIPROC are reserved for processor-
				       specific	semantics.
			SHN_HIPROC     This value down to and including
				       SHN_LOPROC are reserved for processor-
				       specific	semantics.
			SHN_ABS	       This value specifies absolute values
				       for the corresponding reference.	 For
				       example,	symbols	defined	relative to
				       section number SHN_ABS have absolute
				       values and are not affected by reloca-
				       tion.
			SHN_COMMON     Symbols defined relative	to this	sec-
				       tion are	common symbols,	such as	For-
				       tran COMMON or unallocated C external
				       variables.
			SHN_HIRESERVE  This value specifies the	upper bound of
				       the range of the	range of reserved
				       indices between SHN_LORESERVE and
				       SHN_HIRESERVE, inclusive; the values do
				       not reference the section header	table.
				       That is,	the section header table does
				       not contain entries for the reserved
				       indices.

     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 segment con-
     tains one or more sections.  Program headers are meaningful only for exe-
     cutable and shared	object files.  A file specifies	its own	program	header
     size with the ELF header's	e_phentsize and	e_phnum	members.  As with the
     Elf executable header, the	program	header also has	different versions
     depending on the architecture:

	   typedef struct {
		   Elf32_Word	   p_type;
		   Elf32_Off	   p_offset;
		   Elf32_Addr	   p_vaddr;
		   Elf32_Addr	   p_paddr;
		   Elf32_Size	   p_filesz;
		   Elf32_Size	   p_memsz;
		   Elf32_Word	   p_flags;
		   Elf32_Size	   p_align;
	   } Elf32_Phdr;

	   typedef struct {
		   Elf64_Half	   p_type;
		   Elf64_Half	   p_flags;
		   Elf64_Off	   p_offset;
		   Elf64_Addr	   p_vaddr;
		   Elf64_Addr	   p_paddr;
		   Elf64_Size	   p_filesz;
		   Elf64_Size	   p_memsz;
		   Elf64_Size	   p_align;
	   } Elf64_Phdr;

     The main difference between the 32-bit and	the 64-bit program header lies
     only in the location of a p_flags member in the total struct.

	   p_type    This member of the	Phdr struct tells what kind of segment
		     this array	element	describes or how to interpret the
		     array element's information.

		     PT_NULL	 The array element is unused and the other
				 members' values are undefined.	 This lets the
				 program header	have ignored entries.
		     PT_LOAD	 The array element specifies a loadable	seg-
				 ment, described by p_filesz and p_memsz.  The
				 bytes from the	file are mapped	to the begin-
				 ning of the memory segment.  If the segment's
				 memory	size (p_memsz) is larger than the file
				 size (p_filesz), the ``extra''	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 p_vaddr member.
		     PT_DYNAMIC	 The array element specifies dynamic linking
				 information.
		     PT_INTERP	 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.
		     PT_NOTE	 The array element specifies the location and
				 size for auxiliary information.
		     PT_SHLIB	 This segment type is reserved but has unspec-
				 ified semantics.  Programs that contain an
				 array element of this type do not conform to
				 the ABI.
		     PT_PHDR	 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.  More-
				 over, it may only occur if the	program	header
				 table is part of the memory image of the pro-
				 gram.	If it is present it must precede any
				 loadable segment entry.
		     PT_LOPROC	 This value up to and including	PT_HIPROC are
				 reserved for processor-specific semantics.
		     PT_HIPROC	 This value down to and	including PT_LOPROC
				 are reserved for processor-specific seman-
				 tics.

	   p_offset  This member holds the offset from the beginning of	the
		     file at which the first byte of the segment resides.
	   p_vaddr   This member holds the virtual address at which the	first
		     byte of the segment resides in memory.
	   p_paddr   On	systems	for which physical addressing is relevant,
		     this member is reserved for the segment's physical
		     address.  Under BSD this member is	not used and must be
		     zero.
	   p_filesz  This member holds the number of bytes in the file image
		     of	the segment.  It may be	zero.
	   p_memsz   This member holds the number of bytes in the memory image
		     of	the segment.  It may be	zero.
	   p_flags   This member holds flags relevant to the segment:

		     PF_X  An executable segment.
		     PF_W  A writable segment.
		     PF_R  A readable segment.

		     A text segment commonly has the flags PF_X	and PF_R.  A
		     data segment commonly has PF_X, PF_W and PF_R.
	   p_align   This member holds the value to which the segments are
		     aligned in	memory and in the file.	 Loadable process seg-
		     ments must	have congruent values for p_vaddr and
		     p_offset, modulo the page size.  Values of	zero and one
		     mean no alignment is required.  Otherwise,	p_align	should
		     be	a positive, integral power of two, and p_vaddr should
		     equal p_offset, modulo p_align.

     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 struc-
     tures.  The ELF header's e_shoff member gives the byte offset from	the
     beginning of the file to the section header table.	 e_shnum holds the
     number of entries the section header table	contains.  e_shentsize holds
     the size in bytes of each entry.

     A section header table index is a subscript into this array.  Some	sec-
     tion header table indices are reserved.  An object	file does not have
     sections for these	special	indices:

     SHN_UNDEF	    This value marks an	undefined, missing, irrelevant or oth-
		    erwise meaningless section reference.
     SHN_LORESERVE  This value specifies the lower bound of the	range of
		    reserved indices.
     SHN_LOPROC	    This value up to and including SHN_HIPROC are reserved for
		    processor-specific semantics.
     SHN_HIPROC	    This value down to and including SHN_LOPROC	are reserved
		    for	processor-specific semantics.
     SHN_ABS	    This value specifies absolute values for the corresponding
		    reference.	For example, symbols defined relative to sec-
		    tion number	SHN_ABS	have absolute values and are not
		    affected by	relocation.
     SHN_COMMON	    Symbols defined relative to	this section are common	sym-
		    bols, such as FORTRAN COMMON or unallocated	C external
		    variables.
     SHN_HIRESERVE  This value specifies the upper bound of the	range of
		    reserved indices.  The system reserves indices between
		    SHN_LORESERVE and SHN_HIRESERVE, inclusive.	 The section
		    header table does not contain entries for the reserved
		    indices.

     The section header	has the	following structure:

	   typedef struct {
		   Elf32_Word	   sh_name;
		   Elf32_Word	   sh_type;
		   Elf32_Word	   sh_flags;
		   Elf32_Addr	   sh_addr;
		   Elf32_Off	   sh_offset;
		   Elf32_Size	   sh_size;
		   Elf32_Word	   sh_link;
		   Elf32_Word	   sh_info;
		   Elf32_Size	   sh_addralign;
		   Elf32_Size	   sh_entsize;
	   } Elf32_Shdr;

	   typedef struct {
		   Elf64_Half	   sh_name;
		   Elf64_Half	   sh_type;
		   Elf64_Size	   sh_flags;
		   Elf64_Addr	   sh_addr;
		   Elf64_Off	   sh_offset;
		   Elf64_Size	   sh_size;
		   Elf64_Half	   sh_link;
		   Elf64_Half	   sh_info;
		   Elf64_Size	   sh_addralign;
		   Elf64_Size	   sh_entsize;
	   } Elf64_Shdr;

     sh_name	   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.
     sh_type	   This	member categorizes the section's contents and seman-
		   tics.

		   SHT_NULL	 This value marks the section header as	inac-
				 tive.	It does	not have an associated sec-
				 tion.	Other members of the section header
				 have undefined	values.
		   SHT_PROGBITS	 The section holds information defined by the
				 program, whose	format and meaning are deter-
				 mined solely by the program.
		   SHT_SYMTAB	 This section holds a symbol table.  Typi-
				 cally,	SHT_SYMTAB 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 SHN_DYNSYM section.
		   SHT_STRTAB	 This section holds a string table.  An	object
				 file may have multiple	string table sections.
		   SHT_RELA	 This section holds relocation entries with
				 explicit addends, such	as type	Elf32_Rela for
				 the 32-bit class of object files.  An object
				 may have multiple relocation sections.
		   SHT_HASH	 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.
		   SHT_DYNAMIC	 This section holds information	for dynamic
				 linking.  An object file may have only	one
				 dynamic section.
		   SHT_NOTE	 This section holds information	that marks the
				 file in some way.
		   SHT_NOBITS	 A section of this type	occupies no space in
				 the file but otherwise	resembles
				 SHN_PROGBITS.	Although this section contains
				 no bytes, the sh_offset member	contains the
				 conceptual file offset.
		   SHT_REL	 This section holds relocation offsets without
				 explicit addends, such	as type	Elf32_Rel for
				 the 32-bit class of object files.  An object
				 file may have multiple	relocation sections.
		   SHT_SHLIB	 This section is reserved but has unspecified
				 semantics.
		   SHT_DYNSYM	 This section holds a minimal set of dynamic
				 linking symbols.  An object file can also
				 contain a SHN_SYMTAB section.
		   SHT_LOPROC	 This value up to and including	SHT_HIPROC are
				 reserved for processor-specific semantics.
		   SHT_HIPROC	 This value down to and	including SHT_LOPROC
				 are reserved for processor-specific seman-
				 tics.
		   SHT_LOUSER	 This value specifies the lower	bound of the
				 range of indices reserved for application
				 programs.
		   SHT_HIUSER	 This value specifies the upper	bound of the
				 range of indices reserved for application
				 programs.  Section types between SHT_LOUSER
				 and SHT_HIUSER	may be used by the applica-
				 tion, without conflicting with	current	or
				 future	system-defined section types.

     sh_flags	   Sections support one-bit flags that describe	miscellaneous
		   attributes.	If a flag bit is set in	sh_flags, the
		   attribute is	``on'' for the section.	 Otherwise, the
		   attribute is	``off''	or does	not apply.  Undefined
		   attributes are set to zero.

		   SHF_WRITE	  This section contains	data that should be
				  writable during process execution.
		   SHF_ALLOC	  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 sec-
				  tions.
		   SHF_EXECINSTR  The section contains executable machine
				  instructions.
		   SHF_MASKPROC	  All bits included in this mask are reserved
				  for processor-specific semantics.

     sh_addr	   If the section will appear in the memory image of a
		   process, this member	holds the address at which the sec-
		   tion's first	byte should reside.  Otherwise,	the member
		   contains zero.
     sh_offset	   This	member's value holds the byte offset from the begin-
		   ning	of the file to the first byte in the section.  One
		   section type, SHT_NOBITS, occupies no space in the file,
		   and its sh_offset member locates the	conceptual placement
		   in the file.
     sh_size	   This	member holds the section's size	in bytes.  Unless the
		   section type	is SHT_NOBITS, the section occupies sh_size
		   bytes in the	file.  A section of type SHT_NOBITS may	have a
		   non-zero size, but it occupies no space in the file.
     sh_link	   This	member holds a section header table index link,	whose
		   interpretation depends on the section type.
     sh_info	   This	member holds extra information,	whose interpretation
		   depends on the section type.
     sh_addralign  Some	sections have address alignment	constraints.  If a
		   section holds a doubleword, the system must ensure double-
		   word	alignment for the entire section.  That	is, the	value
		   of sh_addr must be congruent	to zero, modulo	the value of
		   sh_addralign.  Only zero and	positive integral powers of
		   two are allowed.  Values of zero or one mean	the section
		   has no alignment constraints.
     sh_entsize	   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.

     Various sections hold program and control information:
     .bss	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 sec-
		tion is	of type	SHT_NOBITS.  The attributes types are
		SHF_ALLOC and SHF_WRITE.
     .comment	This section holds version control information.	 This section
		is of type SHT_PROGBITS.  No attribute types are used.
     .data	This section holds initialized data that contribute to the
		program's memory image.	 This section is of type SHT_PROGBITS.
		The attribute types are	SHF_ALLOC and SHF_WRITE.
     .data1	This section holds initialized data that contribute to the
		program's memory image.	 This section is of type SHT_PROGBITS.
		The attribute types are	SHF_ALLOC and SHF_WRITE.
     .debug	This section holds information for symbolic debugging.	The
		contents are unspecified.  This	section	is of type
		SHT_PROGBITS.  No attribute types are used.
     .dynamic	This section holds dynamic linking information.	 The section's
		attributes will	include	the SHF_ALLOC bit.  Whether the
		SHF_WRITE bit is set is	processor-specific.  This section is
		of type	SHT_DYNAMIC.  See the attributes above.
     .dynstr	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 SHT_STRTAB.
		The attribute type used	is SHF_ALLOC.
     .dynsym	This section holds the dynamic linking symbol table.  This
		section	is of type SHT_DYNSYM.	The attribute used is
		SHF_ALLOC.
     .fini	This 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 SHT_PROGBITS.  The attributes used are
		SHF_ALLOC and SHF_EXECINSTR.
     .got	This section holds the global offset table.  This section is
		of type	SHT_PROGBITS.  The attributes are processor-specific.
     .hash	This section holds a symbol hash table.	 This section is of
		type SHT_HASH.	The attribute used is SHF_ALLOC.
     .init	This 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
		SHT_PROGBITS.  The attributes used are SHF_ALLOC and
		SHF_EXECINSTR.
     .interp	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 SHF_ALLOC	bit.  Other-
		wise, that bit will be off.  This section is of	type
		SHT_PROGBITS.
     .line	This section holds line	number information for symbolic	debug-
		ging, which describes the correspondence between the program
		source and the machine code.  The contents are unspecified.
		This section is	of type	SHT_PROGBITS.  No attribute types are
		used.
     .note	This section holds information in the ``Note Section'' format
		described below.  This section is of type SHT_NOTE.  No
		attribute types	are used.
     .plt	This section holds the procedure linkage table.	 This section
		is of type SHT_PROGBITS.  The attributes are processor-spe-
		cific.
     .relNAME	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 SHF_ALLOC bit.  Oth-
		erwise the bit will be off.  By	convention, ``NAME'' is	sup-
		plied by the section to	which the relocations apply.  Thus a
		relocation section for .text normally would have the name
		.rel.text.  This section is of type SHT_REL.
     .relaNAME	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 SHF_ALLOC bit.  Oth-
		erwise the bit will be off.  By	convention, ``NAME'' is	sup-
		plied by the section to	which the relocations apply.  Thus a
		relocation section for .text normally would have the name
		.rela.text.  This section is of	type SHT_RELA.
     .rodata	This section holds read-only data that typically contributes
		to a non-writable segment in the process image.	 This section
		is of type SHT_PROGBITS.  The attribute	used is	SHF_ALLOC.
     .rodata1	This section hold read-only data that typically	contributes to
		a non-writable segment in the process image.  This section is
		of type	SHT_PROGBITS.  The attribute used is SHF_ALLOC.
     .shstrtab	This section holds section names.  This	section	is of type
		SHT_STRTAB.  No	attribute types	are used.
     .strtab	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
		SHF_ALLOC bit.	Otherwise the bit will be off.	This section
		is of type SHT_STRTAB.
     .symtab	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 SHF_ALLOC bit.  Otherwise the bit
		will be	off.  This section is of type SHT_SYMTAB.
     .text	This section holds the ``text'', or executable instructions,
		of a program.  This section is of type SHT_PROGBITS.  The
		attributes used	are SHF_ALLOC and SHF_EXECINSTR.
     .jcr	This section holds information about Java classes that must be
		registered.
     .eh_frame	This section holds information used for	C++ exception-han-
		dling.

     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.

     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.

	   typedef struct {
		   Elf32_Word	   st_name;
		   Elf32_Addr	   st_value;
		   Elf32_Size	   st_size;
		   unsigned char   st_info;
		   unsigned char   st_other;
		   Elf32_Half	   st_shndx;
	   } Elf32_Sym;

	   typedef struct {
		   Elf64_Half	   st_name;
		   unsigned char   st_info;
		   unsigned char   st_other;
		   Elf64_Quarter   st_shndx;
		   Elf64_Addr	   st_value;
		   Elf64_Size	   st_size;
	   } Elf64_Sym;

     st_name   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.
     st_value  This member gives the value of the associated symbol.
     st_size   Many symbols have associated sizes.  This member	holds zero if
	       the symbol has no size or an unknown size.
     st_info   This member specifies the symbol's type and binding attributes:

	       STT_NOTYPE   The	symbol's type is not defined.
	       STT_OBJECT   The	symbol is associated with a data object.
	       STT_FUNC	    The	symbol is associated with a function or	other
			    executable code.
	       STT_SECTION  The	symbol is associated with a section.  Symbol
			    table entries of this type exist primarily for
			    relocation and normally have STB_LOCAL bindings.
	       STT_FILE	    By convention the symbol's name gives the name of
			    the	source file associated with the	object file.
			    A file symbol has STB_LOCAL	bindings, its section
			    index is SHN_ABS, and it precedes the other
			    STB_LOCAL symbols of the file, if it is present.
	       STT_LOPROC   This value up to and including STT_HIPROC are
			    reserved for processor-specific semantics.
	       STT_HIPROC   This value down to and including STT_LOPROC	are
			    reserved for processor-specific semantics.

	       STB_LOCAL   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.
	       STB_GLOBAL  Global symbols are visible to all object files
			   being combined.  One	file's definition of a global
			   symbol will satisfy another file's undefined	refer-
			   ence	to the same symbol.
	       STB_WEAK	   Weak	symbols	resemble global	symbols, but their
			   definitions have lower precedence.
	       STB_LOPROC  This	value up to and	including STB_HIPROC are
			   reserved for	processor-specific semantics.
	       STB_HIPROC  This	value down to and including STB_LOPROC are
			   reserved for	processor-specific semantics.

			   There are macros for	packing	and unpacking the
			   binding and type fields:

			   ELF32_ST_BIND(info)	      or ELF64_ST_BIND(info)
						      extract a	binding	from
						      an st_info value.
			   ELF64_ST_TYPE(info)	      or ELF32_ST_TYPE(info)
						      extract a	type from an
						      st_info value.
			   ELF32_ST_INFO(bind, type)  or ELF64_ST_INFO(bind,
						      type) convert a binding
						      and a type into an
						      st_info value.

     st_other  This member currently holds zero	and has	no defined meaning.
     st_shndx  Every symbol table entry	is ``defined'' in relation to some
	       section.	 This member holds the relevant	section	header table
	       index.

     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.

     Relocation	structures that	do not need an addend:

	   typedef struct {
		   Elf32_Addr	   r_offset;
		   Elf32_Word	   r_info;
	   } Elf32_Rel;

	   typedef struct {
		   Elf64_Addr	   r_offset;
		   Elf64_Size	   r_info;
	   } Elf64_Rel;

     Relocation	structures that	need an	addend:

	   typedef struct {
		   Elf32_Addr	   r_offset;
		   Elf32_Word	   r_info;
		   Elf32_Sword	   r_addend;
	   } Elf32_Rela;

	   typedef struct {
		   Elf64_Addr	   r_offset;
		   Elf64_Size	   r_info;
		   Elf64_Off	   r_addend;
	   } Elf64_Rela;

     r_offset  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.
     r_info    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 ELF_[32|64]_R_TYPE or
	       ELF[32|64]_R_SYM, respectively to the entry's r_info member.
     r_addend  This member specifies a constant	addend used to compute the
	       value to	be stored into the relocatable field.

SEE ALSO
     as(1), gdb(1), ld(1), objdump(1), execve(2), core(5)

     Hewlett Packard, Elf-64 Object File Format.

     Santa Cruz	Operation, System V Application	Binary Interface.

     Unix System Laboratories, "Object Files", Executable and Linking Format
     (ELF).

HISTORY
     The ELF header files made their appearance	in FreeBSD 2.2.6.  ELF in
     itself first appeared in AT&T System V UNIX.  The ELF format is an
     adopted standard.

AUTHORS
     This manual page was written by Jeroen Ruigrok van	der Werven
     <asmodai@FreeBSD.org> with	inspiration from BSDi's	BSD/OS elf(5) manpage.

FreeBSD	9.2			 July 31, 1999			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | AUTHORS

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