ld(1) — VAX
Name
ld − link editor
Syntax
ld [option...] file...
Description
The ld command combines several object programs into one, resolves external references, and searches libraries. In the simplest case, several object files are given, and ld combines them, producing an object module which can either be executed or can become the input for a further ld run. (In the latter case, the −r option must be given to preserve the relocation bits.) The output of ld is left on a.out. This file is only made executable if no errors occurred during the load.
The argument routines are linked together in the order specified. The entry point of the output is the beginning of the first routine, unless the −e option is specified.
If the argument is a library, it is searched only once at the point it is encountered in the argument list. Only those routines defining an unresolved external reference are loaded. If a routine from a library references another routine in the library, and the library has not been processed by ranlib(,), the referenced routine must appear after the referencing routine in the library. Thus, the order of programs within libraries is important. The first member of a library should be a file named __.SYMDEF, which is a dictionary for the library that is produced by ranlib(.). The dictionary is searched repeatedly to satisfy as many references as possible.
The symbols _etext, _edata and _end (etext, edata and end in C) are reserved and, if referred to, are set to the first location above the program, the first location above initialized data, and the first location above all data, in that order. It is an error to define these symbols.
Options
The ld command has several options. Except for the −l option, they should appear before the file names.
−A Specifies incremental loading. Linking is done so that the resulting object may be read into an already executing program. The next argument is the name of a file whose symbol table is used to define additional symbols. Only newly linked material is entered into the text and data portions of a.out, but the new symbol table reflects every symbol defined before and after the incremental load. This argument must appear before any other object file in the argument list.
The −T option may be used as well, and is taken to mean that the newly linked segment commences at the corresponding address (which must be a multiple of 1024). The default value is the old value of _end.
−D Takes the next argument as a hexadecimal number and pads the data segment with zero bytes to the indicated length.
−d Forces definition of common storage even if the −r flag is present.
−e Takes the next argument as the name of the entry point of the loaded program; location 0 is the default.
−Ldir Adds dir to the list of directories that are searched for libraries. Directories specified with −L are searched before the standard directories.
−lx Abbreviates the library name libx.a, where x is a string. The ld command searches for libraries first in any directories specified with −L options, then in the standard directories /lib, /usr/lib, and /usr/local/lib. A library is searched when its name is encountered, so the placement of a −l is significant.
−H Takes the next argument as a decimal integer, adds it to the end of text, and causes the data section to start at a higher address.
−M Produces a primitive load map, listing the names of the files that are loaded.
−N Indicates a portion of text to not make read-only or sharable. (Use magic number 0407.)
−n Arranges (by giving the output file a 0410 magic number) that the text portion is read-only and shared among all users executing the file when the output file is executed. This involves moving the data areas up to the first possible 1024 byte boundary following the end of the text.
−o Takes the name argument after −o as the name of the ld output file, instead of a.out.
−r Generates relocation bits in the output file so that it can be the subject of another ld run. This flag also prevents final definitions from being given to common symbols and suppresses the undefined symbol diagnostics.
−S Strips the output by removing all symbols except locals and globals.
−s Removes the symbol table and relocation bits to save space (this impairs the usefulness of the debuggers). This information can also be removed by strip(.).
−T Takes the next argument as a hexadecimal number which sets the text segment origin. The default origin is 0.
−t(trace) Prints the name of each file as it is processed.
−u Takes the next argument as a symbol and enters it as undefined in the symbol table. This is useful for loading from a library, since initially the symbol table is empty and an unresolved reference is needed to force the loading of the first routine.
−X Saves local symbols except for those whose names begin with a capital L. This option is used by cc() to discard internally-generated labels while retaining symbols local to routines.
−x Discards local (non-global) symbols in the output symbol table; only enters external symbols. This option saves some space in the output file.
−Yenvironment
Adjusts the magic number in the output file so that the program runs in the specified environment . The parameter can be POSIX, SYSTEM_FIVE, or BSD . The parameter sets the program’s execution environment to conform with one of the three standards. If it is present, this parameter overrides the PROG_ENV environment variable. If no environment is given, SYSTEM_FIVE is assumed. If neither this parameter nor the PROG_ENV variable is present, −YBSD is assumed.
−ysym Indicates each file in which sym appears, its type, and whether the file defines or references it. Many such options may be given to trace many symbols. It is usually necessary to begin sym with an underscore (_), because external C, FORTRAN and Pascal variables begin with underscores.
−z Arranges for the process to be loaded on demand from the resulting executable file (413 format) rather than preloaded. This is the default. It results in a 1024 byte header on the output file followed by a text and data segment whose size is a multiple of 1024 bytes (being padded out with nulls in the file if necessary). With this format the first few BSS segment symbols may, from the output of size(,), appear to reside in the data segment. This avoids wasting the space which results from the roundup of the data segment size.
Restrictions
There is no way to force data to be page aligned. The ld command pads the images which are to be demand loaded from the file system to the next page boundary.
When linking code contains GFLOAT instructions, the GFLOAT versions of libc and/or the math library must be used rather than the normal DFLOAT versions. Link to these by using −lcg and/or −lmg.
The compiler and the linker ld() cannot detect the use of mixed double floating point types, and your program may produce erroneous results.
Files
/lib/lib*.a libraries.
/usr/lib/lib*.a libraries
/usr/local/lib/lib*.a libraries
a.out output file