LIBELF
Section: Libelf Programmer's Manual (3)
Updated: 202-1-18
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NAME
libelf - a library for accessing and manipulating ELF (Executable and Linkable
Format) files
LIBRARY
Elfutils library (
libelf,
libelf.so,
-lelf)
SYNOPSIS
#include <libelf.h>
DESCRIPTION
The
libelf library provides an API for reading, writing, and manipulating
ELF (Executable and Linkable Format) files. ELF is a standard format for object
files, shared libraries, core dumps, and executables. See
elf(5)
for more information regarding ELF.
libelf provides routines for working with ELF object file headers,
sections, symbol tables, relocation entries, and other key components.
The core of the library is based on
Elf
file descriptors representing ELF files, which can be read from, written to,
or updated i-place. The elf_begin function initializes access to an
ELF object, while additional functions like elf_getscn, elf_getdata,
and elf_ndxscn provide access to specific parts of the ELF file.
FILE VS MEMORY REPRESENTATION
The libelf library distinguishes between the file representation of an
ELF file and its memory representation.
File Representation refers to the format in which an ELF file is stored on disk.
The fields in the file may use specific sizes, alignment, and byte ordering
(endianness) that could be different from the native format used by the host
system.
Memory Representation refers to the way the ELF data is organized when loaded
into an application's memory. In memory, the data structures are typically
converted into the native format of the host system (e.g., the system's
endianness, word size, and alignment).
libelf provides the following functions to translate ELF data between
file and memory representations:
elf32_xlatetom,
elf64_xlatetom,
elf32_xlatetof,
and
elf64_xlatetof.
See
elf32_xlatetom(3)
for more information.
ELF VERSION
To account for the possibility of multiple versions of the ELF specification,
the ELF version number must be specified with the elf_version function
before any other libelf functions. This function sets libelf's ELF
version to the specified value. At this time the only supported ELF version is
EV_CURRENT.
DESCRIPTORS
Elf
descriptors the central
libelf object for accessing and manipulating
ELF files. They are created with the
elf_begin,
elf_clone,
and
elf_memory
functions and closed with the
elf_end
function.
libelf also provides
Elf_Scn
and
Elf_Data
descriptors for ELF sections and section contents, respectively. Members
of the
Elf_Data
struct are described below.
Members of the
Elf
and
Elf_Scn
structs are hidden from applications.
These descriptors can be acquired and modified using various
functions provided by libelf. See
libelf.h
for a complete list.
ERROR HANDLING
If a
libelf function encounters an error it will set an internal
error code that can be retrieved with
elf_errno.
Each thread maintains its own separate error code. The meaning of
each error code can be determined with
elf_errmsg,
which returns a string describing the error.
MEMORY MANAGEMENT
libelf manages all of the memory it allocates and frees it with
elf_end.
The application must not call
free
on any memory allocated by
libelf.
NAMESPACE
libelf uses the following prefix format. See
libelf.h for more
information.
-
-
-
- elf_
-
Functions usable with both 3-bit and 6-bit ELF files.
- elf32_
-
Functions usable with 3-bit ELF files.
- elf64_
-
Functions usable with 6-bit ELF files.
- Elf_
-
Type that represents data for both 3-bit and 6-bit ELF files.
- Elf32_
-
Type that represents data for 3-bit ELF files.
- Elf64_
-
Type that represents data for 6-bit ELF files.
- ELF_C_
-
Elf_Cmd
values used in functions such as
elf_flagset
and
elf_cntl.
- ELF_F_
-
Flags for ELF structures.
- ELF_K_
-
Elf_Kind
Identification values for recognized object file types.
- ELF_T_
-
Elf_Type
values representing the known types of ELF data such as
ELF_T_BYTE,
(unsigned char)
ELF_T_REL,
(relocation entry)
or
ELF_T_SYM
(symbol record).
DATA STRUCTURES
libelf implements the following data structures, in addition to including
the data structures given in the ELF specification (see
elf(5)
for more information).
Section Compression Header
typedef struct {
Elf32_Word ch_type;
Elf32_Word ch_size;
Elf32_Word ch_addralign;
} Elf32_Chdr;
typedef struct {
Elf64_Word ch_type;
Elf64_Word ch_reserved;
Elf64_Xword ch_size;
Elf64_Xword ch_addralign;
} Elf64_Chdr;
- ch_type
-
Compression format type. Legal values include
ELFCOMPRESS_ZLIB,
ELFCOMPRESS_ZSTD,
the inclusive range between
ELFCOMPRESS_LOOS
to
ELFCOMPRESS_HIOS
as well as the inclusive range between
ELFCOMPRESS_LOPROC
and
ELFCOMPRESS_HIPROC
-
-
-
ELFCOMPRESS_ZLIB
ZLIB/DEFLATE algorithm.
- ELFCOMPRESS_ZSTD
-
Zstandard algorithm.
- ELFCOMPRESS_LOOS
-
Start of O-specific compression types.
- ELFCOMPRESS_HIOS
-
End of O-specific compression types.
- ELFCOMPRESS_LOPROC
-
Start of processo-specific compression types.
- ELFCOMPRESS_HIPROC
-
End of processo-specific compression types.
- ch_reserved
-
Space reserved for use by libelf.
- ch_size
-
Data size of uncompressed section.
- ch_addralign
-
Alignment of uncompressed section.
Section Data
typedef struct {
void *d_buf;
Elf_Type d_type;
unsigned int d_version;
size_t d_size;
int64_t d_off;
size_t d_align;
} Elf_Data;
- d_buf
-
Pointer to the actual data.
Use
elf_getdata
to retrieve data in memory representation and
elf_rawdata
to retrieve data in file representation.
- d_type
-
The
Elf_Type
of this piece of data. See the
Elf_Type
enum in
libelf.h
for descriptions of each value.
- d_version
-
The ELF version for this data.
- d_size
-
The size in bytes of this data.
- d_off
-
The section offset of this data.
- d_align
-
The section alignment of this data.
Archive Member Header
typedef struct {
char *ar_name;
time_t ar_date;
uid_t ar_uid;
gid_t ar_gid;
mode_t ar_mode;
int64_t ar_size;
char *ar_rawname;
} Elf_Arhdr;
- ar_name
-
Name of archive member.
- ar_data
-
File date.
- ar_uid
-
User ID.
- ar_gid
-
Group ID.
- ar_mode
-
File mode.
- ar_size
-
File size.
- ar_rawname
-
Original name of archive member.
Archive Symbol Table Entry
typedef struct {
char *as_name;
size_t as_off;
unsigned long int as_hash;
} Elf_Arsym;
- as_name
-
Symbol name.
- as_off
-
Offset for this file in the archive.
- as_hash
-
Hash value of the name.
REPORTING BUGS
Report bugs to <
elfutil-devel@sourceware.org> or
https://sourceware.org/bugzilla/.
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- FILE VS MEMORY REPRESENTATION
-
- ELF VERSION
-
- DESCRIPTORS
-
- ERROR HANDLING
-
- MEMORY MANAGEMENT
-
- NAMESPACE
-
- DATA STRUCTURES
-
- Section Compression Header
-
- Section Data
-
- Archive Member Header
-
- Archive Symbol Table Entry
-
- REPORTING BUGS
-
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