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Diffstat (limited to 'share/man/man5/link.5')
| -rw-r--r-- | share/man/man5/link.5 | 141 |
1 files changed, 90 insertions, 51 deletions
diff --git a/share/man/man5/link.5 b/share/man/man5/link.5 index 52c8343ebf9..7f0d6cf4524 100644 --- a/share/man/man5/link.5 +++ b/share/man/man5/link.5 @@ -1,3 +1,4 @@ +.\" $OpenBSD: link.5,v 1.6 1998/11/26 04:25:58 aaron Exp $ .\" $NetBSD: link.5,v 1.5 1996/01/09 00:14:32 pk Exp $ .\" .\" Copyright (c) 1993 Paul Kranenburg @@ -42,8 +43,10 @@ The include file declares several structures that are present in dynamically linked programs and libraries. The structures define the interface between several components of the -link-editor and loader mechanism. The layout of a number of these -structures within the binaries resembles the a.out format in many places +link editor and loader mechanism. The layout of a number of these +structures within the binaries resembles the +.Xr a.out 5 +format in many places as it serves such similar functions as symbol definitions (including the accompanying string table) and relocation records needed to resolve references to external entities. It also records a number of data structures @@ -56,7 +59,7 @@ The collection of data structures described here will be referred to as the .Em Run-time Relocation Section (RRS) and is embedded in the standard text and data segments of the dynamically linked program or shared object image as the existing -.Xr a.out +.Xr a.out 5 format offers no room for it elsewhere. .Pp Several utilities co-operate to ensure that the task of getting a program @@ -65,10 +68,12 @@ of system resources. The compiler emits PIC code from which shared libraries can be built by .Xr ld 1 . The compiler also includes size information of any initialized data items -through the .size assembler directive. PIC code differs from conventional code +through the +.Dq .size +assembler directive. PIC code differs from conventional code in that it accesses data variables through an indirection table, the Global Offset Table, by convention accessible by the reserved name -.Em _GLOBAL_OFFSET_TABLE_ . +.Dv _GLOBAL_OFFSET_TABLE_ . The exact mechanism used for this is machine dependent, usually a machine register is reserved for the purpose. The rational behind this construct is to generate code that is independent of the actual load address. Only @@ -83,16 +88,19 @@ image. Again, this is done to avoid run-time modifications to the text segment. The linker-editor allocates the Global Offset Table and Procedure Linkage Table when combining PIC object files into an image suitable for mapping into the process address space. It also collects all symbols that may be needed by the -run-time link-editor and stores these along with the image's text and data bits. +run-time link editor and stores these along with the image's text and data bits. Another reserved symbol, -.Em _DYNAMIC +.Dv _DYNAMIC is used to indicate the presence of the run-time linker structures. Whenever -_DYNAMIC is relocated to 0, there is no need to invoke the run-time -link-editor. If this symbol is non-zero, it points at a data structure from +.Dv _DYNAMIC +is relocated to 0, there is no need to invoke the run-time +link editor. If this symbol is non-zero, it points at a data structure from which the location of the necessary relocation and symbol information can be derived. This is most notably used by the start-up module, .Em crt0 . -The _DYNAMIC structure is conventionally located at the start of the data +The +.Dv _DYNAMIC +structure is conventionally located at the start of the data segment of the image to which it pertains. .Pp .Sh DATA STRUCTURES @@ -102,7 +110,9 @@ The text segments contain read-only data such as symbol descriptions and names, while the data segments contain the tables that need to be modified by during the relocation process. .Pp -The _DYNAMIC symbol references a +The +.Dv _DYNAMIC +symbol references a .Fa _dynamic structure: .Bd -literal -offset indent @@ -118,21 +128,25 @@ struct _dynamic { .Bl -tag -width d_version .It Fa d_version This field provides for different versions of the dynamic linking -implementation. The current version numbers understood by ld and ld.so are -.Em LD_VERSION_SUN (3), -which is used by the SunOS 4.x releases, and -.Em LD_VERSION_BSD (8), -which is currently in use by OpenBSD. +implementation. The current version numbers understood by ld and +.Xr ld.so +are LD_VERSION_SUN(3), +which is used by the SunOS 4.x releases, and LD_VERSION_BSD(8), +which is currently in use by +.Ox . .It Fa d_un Refers to a .Em d_version dependent data structure. .It Fa d_debug -this field provides debuggers with a hook to access symbol tables of shared -objects loaded as a result of the actions of the run-time link-editor. +This field provides debuggers with a hook to access symbol tables of shared +objects loaded as a result of the actions of the run-time link editor. .It Fa d_entry -this field is obsoleted by CRT interface version CRT_VERSION_BSD4, and is -replaced by the crt_ldentry in +This field is obsoleted by CRT interface version +.Li CRT_VERSION_BSD4 , +and is by the +.Fa crt_ldentry +in .Fa crt_ldso . .El .Pp @@ -169,8 +183,7 @@ for the benefit of debuggers that may use it to load a shared object's symbol table. .It Fa sdt_sods The start of a (linked) list of shared object descriptors needed by -.Em this -object. +this object. .It Fa sdt_paths Library search rules. A colon separated list of directories corresponding to the @@ -213,8 +226,8 @@ The size of the Procedure Linkage Table. .Pp A .Fa sod -structure descibes a shared object that is needed -to complete the link edit process of the object containing it. +structure describes a shared object that is needed +to complete the link-edit process of the object containing it. A list of such objects .Po chained through @@ -223,7 +236,9 @@ chained through is pointed at by the .Fa sdt_sods -in the section_dispatch_table structure. +in the +.Fa section_dispatch_table +structure. .Bd -literal -offset indent struct sod { long sod_name; @@ -241,7 +256,9 @@ The offset in the text segment of a string describing this link object. .It Fa sod_library If set, .Fa sod_name -specifies a library that is to be searched for by ld.so. The path name +specifies a library that is to be searched for by +.Xr ld.so . +The path name is obtained by searching a set of directories .Po see also @@ -258,8 +275,8 @@ Specifies the major version number of the shared object to load. Specifies the preferred minor version number of the shared object to load. .El .Pp -The run-time link-editor maintains a list of structures called -.Em link maps +The run-time link editor maintains a list of structures called +.Dq link maps to keep track of all shared objects loaded into a process's address space. These structures are only used at run-time and do not occur within the text or data segment of an executable or shared library. @@ -296,7 +313,7 @@ Pointer to this object's .Fa _dynamic structure. .It Fa som_spd -Hook for attaching private data maintained by the run-time link-editor. +Hook for attaching private data maintained by the run-time link editor. .El .Pp Symbol description with size. This is simply an @@ -324,10 +341,8 @@ struct nzlist { .Ed .Bl -tag -width nz_size .It Fa nlist -.Po -see -.Xr nlist 5 -.Pc . +See +.Xr nlist 3 . .It Fa nz_size The size of the data represented by this symbol. .El @@ -357,6 +372,7 @@ field). In case of collisions, this field is the offset of the next entry in this hash table bucket. It is zero for the last bucket element. .El +.Pp The .Fa rt_symbol structure is used to keep track of run-time allocated commons @@ -380,9 +396,11 @@ struct rt_symbol { .It Fa rt_sp The symbol description. .It Fa rt_next -Virtual address of next rt_symbol. +Virtual address of next +.Fa rt_symbol . .It Fa rt_link -Next in hash bucket. Used by internally by ld.so. +Next in hash bucket. Used by internally by +.Xr ld.so . .It Fa rt_srcaddr Location of the source of initialized data within a shared object. .It Fa rt_smp @@ -394,9 +412,10 @@ The .Fa so_debug structure is used by debuggers to gain knowledge of any shared objects that have been loaded in the process's address space as a result of run-time -link-editing. Since the run-time link-editor runs as a part of process +link-editing. Since the run-time link editor runs as a part of process initialization, a debugger that wishes to access symbols from shared objects -can only do so after the link-editor has been called from crt0. +can only do so after the link editor has been called from +.Em crt0 . A dynamically linked binary contains a .Fa so_debug structure which can be located by means of the @@ -426,8 +445,9 @@ Set by the run-time linker whenever it adds symbols by loading shared objects. The address where a breakpoint will be set by the run-time linker to divert control to the debugger. This address is determined by the start-up module, -.Em crt0.o, -to be some convenient place before the call to _main. +.Em crt0.o , +to be some convenient place before the call to +.Fa _main . .It Fa dd_bpt_shadow Contains the original instruction that was at .Fa dd_bpt_addr . @@ -440,7 +460,9 @@ may be interested in. .Pp The .Em ld_entry -structure defines a set of service routines within ld.so. See +structure defines a set of service routines within +.Xr ld.so . +See .Xr dlfcn 3 for more information. .Bd -literal -offset indent @@ -455,7 +477,10 @@ struct ld_entry { The .Fa crt_ldso -structure defines the interface between ld.so and the start-up code in crt0. +structure defines the interface between +.Xr ld.so +and the start-up code in +.Em crt0 . .Bd -literal -offset indent struct crt_ldso { int crt_ba; @@ -475,13 +500,21 @@ struct crt_ldso { .Ed .Bl -tag -width crt_dzfd .It Fa crt_ba -The virtual address at which ld.so was loaded by crt0. +The virtual address at which +.Xr ld.so +was loaded by +.Em crt0 . .It Fa crt_dzfd On SunOS systems, this field contains an open file descriptor to -.Dq /dev/zero -used to get demand paged zeroed pages. On OpenBSD systems it contains -1. +.Pa /dev/zero +used to get demand paged zeroed pages. On +.Ox +systems it contains -1. .It Fa crt_ldfd -Contains an open file descriptor that was used by crt0 to load ld.so. +Contains an open file descriptor that was used by +.Em crt0 +to load +.Xr ld.so . .It Fa crt_dp A pointer to main's .Fa _dynamic @@ -492,11 +525,15 @@ A pointer to the environment strings. The address at which a breakpoint will be placed by the run-time linker if the main program is run by a debugger. See -.Fa so_debug +.Fa so_debug . .It Fa crt_prog -The name of the main program as determined by crt0 (CRT_VERSION_BSD3 only). +The name of the main program as determined by +.Em crt0 +(CRT_VERSION_BSD3 only). .It Fa crt_ldso -The path of the run-time linker as mapped by crt0 (CRT_VERSION_BSD4 only). +The path of the run-time linker as mapped by +.Em crt0 +(CRT_VERSION_BSD4 only). .It Fa crt_ldentry The .Xr dlfcn 3 @@ -508,11 +545,13 @@ The and .Fa hints_bucket structures define the layout of the library hints, normally found in -.Dq /var/run/ld.so.hints, -which is used by ld.so to quickly locate the shared object images in the +.Pa /var/run/ld.so.hints , +which is used by +.Xr ld.so +to quickly locate the shared object images in the filesystem. The organization of the hints file is not unlike that of an -.Dq a.out +.Xr a.out 5 object file, in that it contains a header determining the offset and size of a table of fixed sized hash buckets and a common string pool. .Bd -literal -offset indent |