NAME

ld − link editor

SYNOPSIS

ld [ −sulxXrdnim ] [ −o name ] [ −t name ] [ −V num ] file ... 

DESCRIPTION

Ld combines several object programs into one; resolves external references; and searches libraries (as created by ar(1)). In the simplest case several object files are given, and ld combines them, producing an object module which can be either executed or 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 made executable if no errors occurred during the load and the −r flag was not specified. 

The argument routines are concatenated in the order specified.  The entry point of the output is the beginning of the first routine. 

If any argument is a library, it is searched exactly 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, the referenced routine must appear after the referencing routine in the library.  Thus the order of programs within libraries is important. 

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 respectively.  It is erroneous to define these symbols. 

Ld understands several flag arguments which are written preceded by a −.  Except for −l, they should appear before the file names. 

−s “Strip” the output, that is, remove the symbol table and relocation bits to save space (but impair the usefulness of the debugger).  This information can also be removed by strip(1). This option is turned off if there are any undefined symbols.

−u Take the following argument as a symbol and enter it as undefined in the symbol table.  This is useful for loading wholly from a library, since initially the symbol table is empty and an unresolved reference is needed to force the loading of the first routine. 

−l This option is an abbreviation for a library name.  −l alone stands for /lib/libc.a, which is the standard system library for C and assembly language programs.  −lx stands for /lib/libx.a, where x is a string.  If that does not exist, ld tries /usr/lib/libx.a A library is searched when its name is encountered, so the placement of a −l is significant. 

−x Do not preserve local (non-.globl) symbols in the output symbol table; only enter external symbols.  This option saves some space in the output file. 

−X Save local symbols except for those whose names begin with L.  This option is used by cc to discard internally generated labels while retaining symbols local to routines. 

−r Generate 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. 

−d Force definition of common storage even if the −r flag is present. 

−n Arrange that when the output file is executed, the text portion will be read-only and shared among all users executing the file.  This involves moving the data areas up to the first possible 4K word boundary following the end of the text.  On the VAX 11/780, this option is on by default; use −N to turn it off. 

−i When the output file is executed, the program text and data areas will live in separate address spaces.  The only difference between this option and −n is that here the data starts at location 0.  This option is meaningful only on the PDP-11; it does nothing on the VAX. 

−m The names of all files and archive members used to create the output file are written to the standard output. 

−o The name argument after −o is used as the name of the ld output file, instead of a.out. 

−t The name argument is taken to be a symbol name, and any references to or definitions of that symbol are listed, along with their types.  There can be up to 16 occurrences of −tname on the command line. 

−V The num argument is taken as a decimal version number identifying the a.out that is produced.  Num must be in the range 0−32767.  The version stamp is stored in the a.out header; see a.out(5).

FILES

/lib/lib?.a libraries

/usr/lib/lib?.a
more libraries

a.out output file

SEE ALSO

ar(1), as(1), cc(1), a.out(5). 

May 16, 1980