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diff --git a/lib/libelf/elf.3 b/lib/libelf/elf.3 new file mode 100644 index 00000000000..93a072bb4ec --- /dev/null +++ b/lib/libelf/elf.3 @@ -0,0 +1,616 @@ +.\" Copyright (c) 2006-2008,2011 Joseph Koshy. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" This software is provided by Joseph Koshy ``as is'' and +.\" any express or implied warranties, including, but not limited to, the +.\" implied warranties of merchantability and fitness for a particular purpose +.\" are disclaimed. in no event shall Joseph Koshy be liable +.\" for any direct, indirect, incidental, special, exemplary, or consequential +.\" damages (including, but not limited to, procurement of substitute goods +.\" or services; loss of use, data, or profits; or business interruption) +.\" however caused and on any theory of liability, whether in contract, strict +.\" liability, or tort (including negligence or otherwise) arising in any way +.\" out of the use of this software, even if advised of the possibility of +.\" such damage. +.\" +.\" $Id: elf.3,v 1.1 2019/02/01 05:27:37 jsg Exp $ +.\" +.Dd October 10, 2018 +.Dt ELF 3 +.Os +.Sh NAME +.Nm elf +.Nd API for manipulating ELF objects +.Sh LIBRARY +.Lb libelf +.Sh SYNOPSIS +.In libelf.h +.Sh DESCRIPTION +The +.Lb libelf +provides functions that allow an application to read and manipulate +ELF object files, and to read +.Xr ar 1 +archives. +The library allows the manipulation of ELF objects in a byte ordering +and word-size independent way, allowing an application to read and +create ELF objects for 32 and 64 bit architectures and for little- +and big-endian machines. +The library is capable of processing ELF objects that use extended +section numbering. +.Pp +This manual page serves to provide an overview of the functionality in +the ELF library. +Further information may found in the manual pages for individual +.Xr ELF 3 +functions that comprise the library. +.Ss ELF Concepts +As described in +.Xr elf 5 , +ELF files contain several data structures that are laid out in a +specific way. +ELF files begin with an +.Dq Executable Header , +and may contain an optional +.Dq Program Header Table , +and optional data in the form of ELF +.Dq sections . +A +.Dq Section Header Table +describes the content of the data in these sections. +.Pp +ELF objects have an associated +.Dq "ELF class" +which denotes the natural machine word size for the architecture +the object is associated with. +Objects for 32 bit architectures have an ELF class of +.Dv ELFCLASS32 . +Objects for 64 bit architectures have an ELF class of +.Dv ELFCLASS64 . +.Pp +ELF objects also have an associated +.Dq endianness +which denotes the endianness of the machine architecture associated +with the object. +This may be +.Dv ELFDATA2LSB +for little-endian architectures and +.Dv ELFDATA2MSB +for big-endian architectures. +.Pp +ELF objects are also associated with an API version number. +This version number determines the layout of the individual components +of an ELF file and the semantics associated with these. +.Ss Data Representation And Translation +The +.Xr ELF 3 +library distinguishes between +.Dq native +representations of ELF data structures and their +.Dq file +representations. +.Pp +An application would work with ELF data in its +.Dq native +representation, i.e., using the native byteorder and alignment mandated +by the processor the application is running on. +The +.Dq file +representation of the same data could use a different byte ordering +and follow different constraints on object alignment than these native +constraints. +.Pp +Accordingly, the +.Xr ELF 3 +library offers translation facilities +.Xr ( elf32_xlatetof 3 , +.Xr elf32_xlatetom 3 , +.Xr elf64_xlatetof 3 +and +.Xr elf64_xlatetom 3 ) +to and from these representations. +It also provides higher-level APIs +.Xr ( gelf_xlatetof 3 , +.Xr gelf_xlatetom 3 ) +that retrieve and store data from the ELF object in a class-agnostic +manner. +.Ss Library Working Version +Conceptually, there are three version numbers associated with an +application using the ELF library to manipulate ELF objects: +.Bl -bullet -compact -offset indent +.It +The ELF version that the application was compiled against. +This version determines the ABI expected by the application. +.It +The ELF version of the ELF object being manipulated by the +application through the ELF library. +.It +The ELF version (or set of versions) supported by the ELF library itself. +.El +.Pp +In order to facilitate working with ELF objects of differing versions, +the ELF library requires the application to call the +.Fn elf_version +function before invoking many of its operations, in order to inform +the library of the application's desired working version. +.Pp +In the current implementation, all three versions have to be +.Dv EV_CURRENT . +.Ss Namespace use +The ELF library uses the following prefixes: +.Bl -tag -width "ELF_F_*" +.It Dv elf_ +Used for class-independent functions. +.It Dv elf32_ +Used for functions working with 32 bit ELF objects. +.It Dv elf64_ +Used for functions working with 64 bit ELF objects. +.It Dv Elf_ +Used for class-independent data types. +.It Dv ELF_C_ +Used for command values used in a few functions. +These symbols are defined as members of the +.Vt Elf_Cmd +enumeration. +.It Dv ELF_E_ +Used for error numbers. +.It Dv ELF_F_ +Used for flags. +.It Dv ELF_K_ +These constants define the kind of file associated with an ELF +descriptor. +See +.Xr elf_kind 3 . +The symbols are defined by the +.Vt Elf_Kind +enumeration. +.It Dv ELF_T_ +These values are defined by the +.Vt Elf_Type +enumeration, and denote the types of ELF data structures +that can be present in an ELF object. +.El +.Pp +In addition, the library uses symbols with prefixes +.Dv _ELF +and +.Dv _libelf +for its internal use. +.Ss Descriptors +Applications communicate with the library using descriptors. +These are: +.Bl -tag -width ".Vt Elf_Data" +.It Vt Elf +An +.Vt Elf +descriptor represents an ELF object or an +.Xr ar 1 +archive. +It is allocated using one of the +.Fn elf_begin +or +.Fn elf_memory +functions. +An +.Vt Elf +descriptor can be used to read and write data to an ELF file. +An +.Vt Elf +descriptor can be associated with zero or more +.Vt Elf_Scn +section descriptors. +.Pp +Given an ELF descriptor, the application may retrieve the ELF +object's class-dependent +.Dq "Executable Header" +structures using the +.Fn elf32_getehdr +or +.Fn elf64_getehdr +functions. +A new Ehdr structure may be allocated using the +.Fn elf64_newehdr +or +.Fn elf64_newehdr +functions. +.Pp +The +.Dq "Program Header Table" +associated with an ELF descriptor may be allocated using the +.Fn elf32_getphdr +or +.Fn elf64_getphdr +functions. +A new program header table may be allocated or an existing table +resized using the +.Fn elf32_newphdr +or +.Fn elf64_newphdr +functions. +.Pp +The +.Vt Elf +structure is opaque and has no members visible to the +application. +.It Vt Elf_Data +An +.Vt Elf_Data +data structure describes an individual chunk of a ELF file as +represented in memory. +It has the following application-visible members: +.Bl -tag -width ".Vt unsigned int d_version" -compact +.It Vt "uint64_t d_align" +The in-file alignment of the data buffer within its containing ELF section. +This value must be non-zero and a power of two. +.It Vt "void *d_buf" +A pointer to data in memory. +.It Vt "uint64_t d_off" +The offset within the containing section where this descriptor's data +would be placed. +This field will be computed by the library unless the application +requests full control of the ELF object's layout. +.It Vt "uint64_t d_size" +The number of bytes of data in this descriptor. +.It Vt "Elf_Type d_type" +The ELF type (see below) of the data in this descriptor. +.It Vt "unsigned int d_version" +The operating version for the data in this buffer. +.El +.Pp +.Vt Elf_Data +descriptors are usually associated with +.Vt Elf_Scn +descriptors. +Existing data descriptors associated with an ELF section may be +structures are retrieved using the +.Fn elf_getdata +and +.Fn elf_rawdata +functions. +The +.Fn elf_newdata +function may be used to attach new data descriptors to an ELF section. +.It Vt Elf_Scn +.Vt Elf_Scn +descriptors represent a section in an ELF object. +.Pp +They are retrieved using the +.Fn elf_getscn +function. +An application may iterate through the existing sections of an ELF +object using the +.Fn elf_nextscn +function. +New sections may be allocated using the +.Fn elf_newscn +function. +.Pp +The +.Vt Elf_Scn +descriptor is opaque and contains no application modifiable fields. +.El +.Ss Supported Elf Types +The following ELF datatypes are supported by the library. +.Pp +.Bl -tag -width ".Dv ELF_T_SYMINFO" -compact +.It Dv ELF_T_ADDR +Machine addresses. +.It Dv ELF_T_BYTE +Byte data. +The library will not attempt to translate byte data. +.It Dv ELF_T_CAP +Software and hardware capability records. +.It Dv ELF_T_DYN +Records used in a section of type +.Dv SHT_DYNAMIC . +.It Dv ELF_T_EHDR +ELF executable header. +.It Dv ELF_T_GNUHASH +GNU-style hash tables. +.It Dv ELF_T_HALF +16-bit unsigned words. +.It Dv ELF_T_LWORD +64 bit unsigned words. +.It Dv ELF_T_MOVE +ELF Move records. +.\".It Dv ELF_T_MOVEP +.\" As yet unsupported. +.It Dv ELF_T_NOTE +ELF Note structures. +.It Dv ELF_T_OFF +File offsets. +.It Dv ELF_T_PHDR +ELF program header table entries. +.It Dv ELF_T_REL +ELF relocation entries. +.It Dv ELF_T_RELA +ELF relocation entries with addends. +.It Dv ELF_T_SHDR +ELF section header entries. +.It Dv ELF_T_SWORD +Signed 32-bit words. +.It Dv ELF_T_SXWORD +Signed 64-bit words. +.It Dv ELF_T_SYMINFO +ELF symbol information. +.It Dv ELF_T_SYM +ELF symbol table entries. +.It Dv ELF_T_VDEF +Symbol version definition records. +.It Dv ELF_T_VNEED +Symbol version requirement records. +.It Dv ELF_T_WORD +Unsigned 32-bit words. +.It Dv ELF_T_XWORD +Unsigned 64-bit words. +.El +.Pp +The symbol +.Dv ELF_T_NUM +denotes the number of Elf types known to the library. +.Pp +The following table shows the mapping between ELF section types +defined in +.Xr elf 5 +and the types supported by the library. +.Bl -column ".Dv SHT_PREINIT_ARRAY" ".Dv ELF_T_SYMINFO" +.It Em Section Type Ta Em "Library Type" Ta Em Description +.It Dv SHT_DYNAMIC Ta Dv ELF_T_DYN Ta Xo +.Sq .dynamic +section entries. +.Xc +.It Dv SHT_DYNSYM Ta Dv ELF_T_SYM Ta Symbols for dynamic linking. +.It Dv SHT_FINI_ARRAY Ta Dv ELF_T_ADDR Ta Termination function pointers. +.It Dv SHT_GNU_HASH Ta Dv ELF_T_GNUHASH Ta GNU hash sections. +.It Dv SHT_GNU_LIBLIST Ta Dv ELF_T_WORD Ta List of libraries to be pre-linked. +.It Dv SHT_GNU_verdef Ta Dv ELF_T_VDEF Ta Symbol version definitions. +.It Dv SHT_GNU_verneed Ta Dv ELF_T_VNEED Ta Symbol versioning requirements. +.It Dv SHT_GNU_versym Ta Dv ELF_T_HALF Ta Version symbols. +.It Dv SHT_GROUP Ta Dv ELF_T_WORD Ta Section group marker. +.It Dv SHT_HASH Ta Dv ELF_T_HASH Ta Symbol hashes. +.It Dv SHT_INIT_ARRAY Ta Dv ELF_T_ADDR Ta Initialization function pointers. +.It Dv SHT_NOBITS Ta Dv ELF_T_BYTE Ta Xo +Empty sections. +See +.Xr elf 5 . +.Xc +.It Dv SHT_NOTE Ta Dv ELF_T_NOTE Ta ELF note records. +.It Dv SHT_PREINIT_ARRAY Ta Dv ELF_T_ADDR Ta Pre-initialization function pointers. +.It Dv SHT_PROGBITS Ta Dv ELF_T_BYTE Ta Machine code. +.It Dv SHT_REL Ta Dv ELF_T_REL Ta ELF relocation records. +.It Dv SHT_RELA Ta Dv ELF_T_RELA Ta Relocation records with addends. +.It Dv SHT_STRTAB Ta Dv ELF_T_BYTE Ta String tables. +.It Dv SHT_SYMTAB Ta Dv ELF_T_SYM Ta Symbol tables. +.It Dv SHT_SYMTAB_SHNDX Ta Dv ELF_T_WORD Ta Used with extended section numbering. +.It Dv SHT_SUNW_dof Ta Dv ELF_T_BYTE Ta Xo +Used by +.Xr dtrace 1 . +.Xc +.It Dv SHT_SUNW_move Ta Dv ELF_T_MOVE Ta ELF move records. +.It Dv SHT_SUNW_syminfo Ta Dv ELF_T_SYMINFO Ta Additional symbol flags. +.It Dv SHT_SUNW_verdef Ta Dv ELF_T_VDEF Ta Xo +Same as +.Dv SHT_GNU_verdef . +.Xc +.It Dv SHT_SUNW_verneed Ta Dv ELF_T_VNEED Ta Xo +Same as +.Dv SHT_GNU_verneed . +.Xc +.It Dv SHT_SUNW_versym Ta Dv ELF_T_HALF Ta Xo +Same as +.Dv SHT_GNU_versym . +.Xc +.El +.Pp +Section types in the range +.Dv [ SHT_LOOS , +.Dv SHT_HIUSER ] +are otherwise considered to be of type +.Dv ELF_T_BYTE . +.Ss Functional Grouping +This section contains a brief overview of the available functionality +in the ELF library. +Each function listed here is described further in its own manual page. +.Bl -tag -width indent +.It "Archive Access" +.Bl -tag -compact -width indent +.It Fn elf_getarsym +Retrieve the archive symbol table. +.It Fn elf_getarhdr +Retrieve the archive header for an object. +.It Fn elf_getbase +Retrieve the offset of a member inside an archive. +.It Fn elf_next +Iterate through an +.Xr ar 1 +archive. +.It Fn elf_rand +Random access inside an +.Xr ar 1 +archive. +.El +.It "Data Structures" +.Bl -tag -compact -width indent +.It Fn elf_getdata +Retrieve translated data for an ELF section. +.It Fn elf_getscn +Retrieve the section descriptor for a named section. +.It Fn elf_ndxscn +Retrieve the index for a section. +.It Fn elf_newdata +Add a new +.Vt Elf_Data +descriptor to an ELF section. +.It Fn elf_newscn +Add a new section descriptor to an ELF descriptor. +.It Fn elf_nextscn +Iterate through the sections in an ELF object. +.It Fn elf_rawdata +Retrieve untranslated data for an ELF section. +.It Fn elf_rawfile +Return a pointer to the untranslated file contents for an ELF object. +.It Fn elf32_getehdr , Fn elf64_getehdr +Retrieve the Executable Header in an ELF object. +.It Fn elf32_getphdr , Fn elf64_getphdr +Retrieve the Program Header Table in an ELF object. +.It Fn elf32_getshdr , Fn elf64_getshdr +Retrieve the ELF section header associated with an +.Vt Elf_Scn +descriptor. +.It Fn elf32_newehdr , Fn elf64_newehdr +Allocate an Executable Header in an ELF object. +.It Fn elf32_newphdr , Fn elf64_newphdr +Allocate or resize the Program Header Table in an ELF object. +.El +.It "Data Translation" +.Bl -tag -compact -width indent +.It Fn elf32_xlatetof , Fn elf64_xlatetof +Translate an ELF data structure from its native representation to its +file representation. +.It Fn elf32_xlatetom , Fn elf64_xlatetom +Translate an ELF data structure from its file representation to a +native representation. +.El +.It "Error Reporting" +.Bl -tag -compact -width indent +.It Fn elf_errno +Retrieve the current error. +.It Fn elf_errmsg +Retrieve a human readable description of the current error. +.El +.It "Initialization" +.Bl -tag -compact -width indent +.It Fn elf_begin +Opens an +.Xr ar 1 +archive or ELF object given a file descriptor. +.It Fn elf_end +Close an ELF descriptor and release all its resources. +.It Fn elf_memory +Opens an +.Xr ar 1 +archive or ELF object present in a memory arena. +.It Fn elf_version +Sets the operating version. +.El +.It "IO Control" +.Bl -tag -width ".Fn elf_setshstrndx" -compact +.It Fn elf_cntl +Manage the association between and ELF descriptor and its underlying file. +.It Fn elf_flagdata +Mark an +.Vt Elf_Data +descriptor as dirty. +.It Fn elf_flagehdr +Mark the ELF Executable Header in an ELF descriptor as dirty. +.It Fn elf_flagphdr +Mark the ELF Program Header Table in an ELF descriptor as dirty. +.It Fn elf_flagscn +Mark an +.Vt Elf_Scn +descriptor as dirty. +.It Fn elf_flagshdr +Mark an ELF Section Header as dirty. +.It Fn elf_setshstrndx +Set the index of the section name string table for the ELF object. +.It Fn elf_update +Recompute ELF object layout and optionally write the modified object +back to the underlying file. +.El +.It "Queries" +.Bl -tag -width ".Fn elf_getshstrndx" -compact +.It Fn elf32_checksum , Fn elf64_checkum +Compute checksum of an ELF object. +.It Fn elf_getident +Retrieve the identification bytes for an ELF object. +.It Fn elf_getphdrnum +Retrieve the number of program headers in an ELF object. +.It Fn elf_getshdrnum +Retrieve the number of sections in an ELF object. +.It Fn elf_getshdrstrndx +Retrieve the section index of the section name string table in +an ELF object. +.It Fn elf_hash +Compute the ELF hash value of a string. +.It Fn elf_kind +Query the kind of object associated with an ELF descriptor. +.It Fn elf32_fsize , Fn elf64_fsize +Return the size of the file representation of an ELF type. +.El +.El +.Ss Controlling ELF Object Layout +In the usual mode of operation, library will compute section +offsets and alignments based on the contents of an ELF descriptor's +sections without need for further intervention by the +application. +.Pp +However, if the application wishes to take complete charge of the +layout of the ELF file, it may set the +.Dv ELF_F_LAYOUT +flag on an ELF descriptor using +.Xr elf_flagelf 3 , +following which the library will use the data offsets and alignments +specified by the application when laying out the file. +Application control of file layout is described further in the +.Xr elf_update 3 +manual page. +.Pp +Gaps in between sections will be filled with the fill character +set by function +.Fn elf_fill . +.Ss Error Handling +In case an error is encountered, these library functions set an +internal error number and signal the presence of the error by +returning an special return value. +The application can check the +current error number by calling +.Xr elf_errno 3 . +A human readable description of the recorded error is available by +calling +.Xr elf_errmsg 3 . +.Ss Memory Management Rules +The library keeps track of all +.Vt Elf_Scn +and +.Vt Elf_Data +descriptors associated with an ELF descriptor and recovers them +when the descriptor is closed using +.Xr elf_end 3 . +Thus the application must not call +.Xr free 3 +on data structures allocated by the ELF library. +.Pp +Conversely the library will not +free data that it has not allocated. +As an example, an application may call +.Xr elf_newdata 3 +to allocate a new +.Vt Elf_Data +descriptor and can set the +.Va d_off +member of the descriptor to point to a region of memory allocated +using +.Xr malloc 3 . +It is the applications responsibility to free this arena, though the +library will reclaim the space used by the +.Vt Elf_Data +descriptor itself. +.Sh SEE ALSO +.Xr gelf 3 , +.Xr ar 5 , +.Xr elf 5 +.Sh HISTORY +The original ELF(3) API was developed for Unix System V. +The current implementation of the ELF(3) API appeared in +.Fx 7.0 . +.Sh AUTHORS +The ELF library was written by +.An Joseph Koshy Aq Mt jkoshy@FreeBSD.org . |