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doc/libelf.3
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Aaron Merey
doc: Update libelf.3 with gelf.h information
15 апр 2026, 05:39
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15 апр 2026, 05:39
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.TH LIBELF 3 2024-10-18 "Libelf" "Libelf Programmer's Manual" .SH NAME libelf \- a library for accessing and manipulating ELF (Executable and Linkable Format) files .SH LIBRARY Elfutils library (\fBlibelf\fP, \fBlibelf.so\fP, \fB-lelf\fP) .SH SYNOPSIS .nf .B #include <libelf.h> .B #include <gelf.h> .SH DESCRIPTION The \fBlibelf\fP 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 .BR elf (5) for more information regarding ELF. \fBlibelf\fP 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 .I Elf file descriptors representing ELF files, which can be read from, written to, or updated in-place. The \fBelf_begin\fP function initializes access to an ELF object, while additional functions like \fBelf_getscn\fP, \fBelf_getdata\fP, and \fBelf_ndxscn\fP provide access to specific parts of the ELF file. .SH GELF INTERFACE \fB<gelf.h>\fP provides a class-independent interface to \fBlibelf\fP that transparently handles both \fBELFCLASS32\fP and \fBELFCLASS64\fP binaries. This allows callers to avoid selecting \fBlibelf\fP functions that are specialized for working with a particular class of ELF binary. \fIGElf_\fP types defined in \fB<gelf.h>\fP are aliases for their \fIElf64_\fP equivalents. Any conversions to \fIElf32_\fP types are handled internally by \fBgelf_\fP functions. See \fBGELF DATA STRUCTURES\fP and \fBGELF MACROS\fP for more information. When using \fBgelf_\fP functions that modify data structure values for \fBELFCLASS32\fP binaries, the size of the value should not exceed the maximum size of the \fBELFCLASS32\fP equivalent. .SH FILE VS MEMORY REPRESENTATION The \fBlibelf\fP library distinguishes between the file representation of an ELF file and its memory representation. .PP 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. .PP 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). .PP \fBlibelf\fP provides the following functions to translate ELF data between file and memory representations: .BR elf32_xlatetom , .BR elf64_xlatetom , .BR elf32_xlatetof , and .BR elf64_xlatetof . \fB<gelf.h>\fP provides .B gelf_xlatetom and .B gelf_xlatetof for class-independent translation between file and memory representations. See .BR elf32_xlatetom (3) for more information. .SH ELF VERSION To account for the possibility of multiple versions of the ELF specification, the ELF version number must be specified with the \fBelf_version\fP function before any other \fBlibelf\fP functions. This function sets \fBlibelf\fP's ELF version to the specified value. At this time the only supported ELF version is \fBEV_CURRENT\fP. .SH DESCRIPTORS .I Elf descriptors the central \fBlibelf\fP object for accessing and manipulating ELF files. They are created with the .BR elf_begin , .BR elf_clone , and .B elf_memory functions and closed with the .B elf_end function. \fBlibelf\fP also provides .I Elf_Scn and .I Elf_Data descriptors for ELF sections and section contents, respectively. Members of the .I Elf_Data struct are described below. Members of the .I Elf and .I Elf_Scn structs are hidden from applications. These descriptors can be acquired and modified using various functions provided by \fBlibelf\fP. See .B libelf.h for a complete list. .SH ERROR HANDLING If a \fBlibelf\fP function encounters an error it will set an internal error code that can be retrieved with .BR elf_errno . Each thread maintains its own separate error code. The meaning of each error code can be determined with .BR elf_errmsg, which returns a string describing the error. \fBlibelf\fP functions returning a pointer return NULL on failure. .SH MEMORY MANAGEMENT \fBlibelf\fP manages all of the memory it allocates and frees it with .BR elf_end . The application must not call .B free on any memory allocated by \fBlibelf\fP. .SH NAMESPACE \fBlibelf\fP uses the following prefix format. See \fBlibelf.h\fP and \fBgelf.h\fP for more information. .RS .TP .PD 0 .TP .B elf_ Functions usable with both 32-bit and 64-bit ELF files. .TP .B elf32_ Functions usable with 32-bit ELF files. .TP .B elf64_ Functions usable with 64-bit ELF files. .TP .B Elf_ Type that represents data for both 32-bit and 64-bit ELF files. .TP .B Elf32_ Type that represents data for 32-bit ELF files. .TP .B Elf64_ Type that represents data for 64-bit ELF files. .TP .B ELF_C_ .I Elf_Cmd values used in functions such as .B elf_flagset and .BR elf_cntl . .TP .B ELF_F_ Flags for ELF structures. .TP .B ELF_K_ .I Elf_Kind Identification values for recognized object file types. .TP .B ELF_T_ .I Elf_Type values representing the known types of ELF data such as .BR ELF_T_BYTE , (unsigned char) .BR ELF_T_REL , (relocation entry) or .B ELF_T_SYM (symbol record). .TP .B gelf_ Class-independent functions. .TP .B GElf_ Class-independent types. .TP .B GELF_ Class-independent macros. .fi .PD .RE .SH DATA STRUCTURES \fBlibelf\fP implements the following data structures, in addition to including the data structures given in the ELF specification (see .BR elf (5) for more information). .SS Section Compression Header .nf .in +4 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; .fi .TP .I ch_type Compression format type. Legal values include .BR ELFCOMPRESS_ZLIB , .BR ELFCOMPRESS_ZSTD , the inclusive range between .B ELFCOMPRESS_LOOS to .B ELFCOMPRESS_HIOS as well as the inclusive range between .B ELFCOMPRESS_LOPROC and .B ELFCOMPRESS_HIPROC .RS .TP .PD 0 .B ELFCOMPRESS_ZLIB ZLIB/DEFLATE algorithm. .TP .B ELFCOMPRESS_ZSTD Zstandard algorithm. .TP .B ELFCOMPRESS_LOOS Start of OS-specific compression types. .TP .B ELFCOMPRESS_HIOS End of OS-specific compression types. .TP .B ELFCOMPRESS_LOPROC Start of processor-specific compression types. .TP .B ELFCOMPRESS_HIPROC End of processor-specific compression types. .PD .RE .TP .I ch_reserved Space reserved for use by \fBlibelf\fP. .TP .I ch_size Data size of uncompressed section. .TP .I ch_addralign Alignment of uncompressed section. .SS Section Data .nf .in +4 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; .fi .TP .I d_buf Pointer to the actual data. Use .B elf_getdata to retrieve data in memory representation and .B elf_rawdata to retrieve data in file representation. .TP .I d_type The .I Elf_Type of this piece of data. See the .I Elf_Type enum in .B libelf.h for descriptions of each value. .TP .I d_version The ELF version for this data. .TP .I d_size The size in bytes of this data. .TP .I d_off The section offset of this data. .TP .I d_align The section alignment of this data. .SS Archive Member Header .nf .in +4 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; .fi .TP .I ar_name Name of archive member. .TP .I ar_data File date. .TP .I ar_uid User ID. .TP .I ar_gid Group ID. .TP .I ar_mode File mode. .TP .I ar_size File size. .TP .I ar_rawname Original name of archive member. .SS Archive Symbol Table Entry .nf .in +4 typedef struct { char *as_name; size_t as_off; unsigned long int as_hash; } Elf_Arsym; .fi .TP .I as_name Symbol name. .TP .I as_off Offset for this file in the archive. .TP .I as_hash Hash value of the name. .SH GELF DATA STRUCTURES \fIGElf_\fP types are aliases for their \fIElf64_\fP equivalents. See .B elf(5) for more information regarding the underlying types. .TS tab(:); lB lB l l. GElf type:Underlying 64-bit type _ GElf_Half:Elf64_Half GElf_Word:Elf64_Word GElf_Sword:Elf64_Sword GElf_Xword:Elf64_Xword GElf_Sxword:Elf64_Sxword GElf_Addr:Elf64_Addr GElf_Off:Elf64_Off GElf_Ehdr:Elf64_Ehdr GElf_Shdr:Elf64_Shdr GElf_Section:Elf64_Section GElf_Sym:Elf64_Sym GElf_Syminfo:Elf64_Syminfo GElf_Rel:Elf64_Rel GElf_Rela:Elf64_Rela GElf_Relr:Elf64_Relr GElf_Phdr:Elf64_Phdr GElf_Chdr:Elf64_Chdr GElf_Dyn:Elf64_Dyn GElf_Verdef:Elf64_Verdef GElf_Verdaux:Elf64_Verdaux GElf_Verneed:Elf64_Verneed GElf_Vernaux:Elf64_Vernaux GElf_Versym:Elf64_Versym GElf_auxv_t:Elf64_auxv_t GElf_Nhdr:Elf64_Nhdr GElf_Move:Elf64_Move GElf_Lib:Elf64_Lib .TE .SH GELF MACROS All \fBGELF_\fP macros are aliases for their \fBELF64_\fP equivalents. See .B elf(5) for more information regarding the underlying macros. .TS tab(:); lB lB l l. GElf macro:Underlying 64-bit macro _ GELF_ST_BIND:ELF64_ST_BIND GELF_ST_TYPE:ELF64_ST_TYPE GELF_ST_INFO:ELF64_ST_INFO GELF_ST_VISIBILITY:ELF64_ST_VISIBILITY GELF_M_INFO:ELF64_M_INFO GELF_M_SIZE:ELF64_M_SIZE GELF_M_SYM:ELF64_M_SYM GELF_R_INFO:ELF64_R_INFO GELF_R_TYPE:ELF64_R_TYPE GELF_R_SYM:ELF64_R_SYM .TE .SH REPORTING BUGS Report bugs to <elfutils-devel@sourceware.org> or https://sourceware.org/bugzilla/.