xref: /csrg-svn/old/ld/ld.1 (revision 44955)

.\" Copyright (c) 1980, 1990 The Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"     @(#)ld.1	6.4 (Berkeley) 07/24/90
.\"
.Dd
.Dt LD 1
.Os BSD 4
.Sh NAME
.Nm ld
.Nd link editor
.Sh SYNOPSIS
.Nm ld
.Op  option
\&...
.Ar file ...
.Sh DESCRIPTION
.Nm Ld
combines several
object programs into one, resolves external
references, and searches libraries.
In the simplest case several object
.Ar files
are given, and
.Nm ld
combines them, producing
an object module which can be either executed or
become the input for a further
.Nm ld
run.
(In the latter case, the
.Fl r
option must be given
to preserve the relocation bits.)
The output of
.Nm ld
is left on
.Pa a.out  .
This file is made executable
only if no errors occurred during the load.
.Pp
The argument routines are concatenated in the order
specified.  The entry point of the output is the
beginning of the first routine (unless the
.Fl e
option is specified).
.Pp
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,
and the library has not been processed by
.Xr ranlib  1  ,
the referenced routine must appear after the
referencing routine in the library.
Thus the order of programs within libraries
may be important.
The first member of a library
should be a file named `\_\^\_.SYMDEF',
which is understood to be a dictionary for the library as produced by
.Xr ranlib  1  ;
the dictionary is searched iteratively to satisfy as many references as
possible.
.Pp
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.
.Pp
.Nm Ld
understands several options.
Except for
.Fl l  ,
they should appear before the file names.
.Tw Ds
.Tp Fl A
This option specifies incremental loading, i.e.
linking is to be done in a manner 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 will be
taken as a basis on which to define additional symbols.
Only newly linked material will be entered into the text and
data portions of
.Xr a.out ,
but the new symbol table will reflect
every symbol defined before and after the incremental load.
This argument must appear before any other object file in the argument list.
The
.Fl T
option may be used as well, and will be taken to mean that the
newly linked segment will commence at the corresponding address
(which must be a multiple of 1024).
The default value is the old value of _end.
.Tp Fl D
Take the next argument as a hexadecimal number and pad the data segment
with zero bytes to the indicated length.
.Tp Fl d
Force definition of common storage
even if the
.Fl r
flag is present.
.Tp Fl e
The following argument is taken to be the
name of the entry point of the loaded
program; location 0 is the default.
.Tc Fl L
.Ar dir
.Cx
Add
.Ar dir
to the list of directories in which libraries are searched for.
Directories specified with
.Fl L
are searched before the standard directories.
.Tc Fl l
.Ar x
.Cx
This
option is an abbreviation for the library name
.Sq Pa libx.a,
where
.Ar x
is a string.
.Nm Ld
searches for libraries first in any directories
specified with
.Fl L
options, then in the standard directories
.Pa /lib ,
.Pa /usr/lib ,
and
.Pa /usr/local/lib .
A library is searched when its name is encountered,
so the placement of a
.Fl l
is significant.
.Tp Fl M
produce a primitive load map, listing the names of the files
which will be loaded.
.Tp Fl N
Do not make the text portion read only or sharable.  (Use "magic number" 0407.)
.Tp Fl n
Arrange (by giving the output file a 0410 "magic number") 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 1024 byte boundary following the
end of the text.
.Tp Fl o
The
.Ar name
argument after
.Fl o
is used as the name of the
.Nm ld
output file, instead of
.Pa a.out  .
.Tp Fl r
Generate relocation bits in the output file
so that it can be the subject of another
.Nm ld
run.
This flag also prevents final definitions from being
given to common symbols,
and suppresses the `undefined symbol' diagnostics.
.Tp Fl S
`Strip' the output by removing all symbols except locals and globals.
.Tp Fl s
`Strip' the output, that is, remove the symbol table
and relocation bits to save space (but impair the
usefulness of the debuggers).
This information can also be removed by
.Xr strip  1  .
.Tp Fl T
The next argument is a hexadecimal number which sets the text segment origin.
The default origin is 0.
.Tp Fl t
("trace")  Print the name of each file as it is processed.
.Tp Fl 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.
.Tp Fl X
Save local symbols
except for those whose names begin with `L'.
This option is used by
.Xr cc  1
to discard internally-generated labels while
retaining symbols local to routines.
.Tp Fl 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.
.Tc Fl y
.Ar sym
.Cx
Indicate each file in which
.Ar 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
.Ar sym
with an `_', as external C, FORTRAN and Pascal variables begin
with underscores.)
.Tp Fl z
Arrange for the process to be loaded on
demand from the resulting executable file (413 format)
rather than preloaded.
This is the default.
Results in a 1024 byte header on the output file followed by
a text and data segment each of which have size 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 actually appear
(from the output of
.Xr size  1  )
to live in the data segment;
this to avoid wasting the space resulting from data segment size roundup.
.Tp
.Sh FILES
.Dw /usr/local/lib/lib*.a
.Di L
.Dp Pa /usr/lib/lib*.a
libraries
.Dp Pa /usr/local/lib/lib*.a
more libraries
.Dp Pa a.out
output file
.Dp
.Sh SEE ALSO
.Xr as 1 ,
.Xr ar 1 ,
.Xr cc 1 ,
.Xr ranlib 1
.Sh HISTORY
.Nm Ld
appeared in Version 6 AT&T Unix.
.Sh BUGS
There is no way to force data to be page aligned.
.Nm Ld
pads images which are to be demand loaded from
the file system to the next
page boundary to avoid a bug in the system.