ld.1

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 1 代码 · 共 301 行

.\" SCCSID: @(#)ld.1	3.1	11/23/87
.TH ld 1 VAX
.SH Name
ld \- link editor
.SH Syntax
.B ld
[\|\fIoption...\fR\|] \fIfile...\fR
.SH Description
.NXR "ld command"
.NXR "object file" "combining"
.NXS "link editor (general)" "ld command"
.NXAM "ld command" "ar file"
.NXAM "ld command" "a.out file"
.NXA "ld command" "strip command"
.NXA "ld command" "ranlib command"
.NXA "cc compiler" "ld command"
The
.PN ld
command combines several
object programs into one, resolves external
references, and searches libraries.
In the simplest case, several object
.I files
are given, and
.PN ld
combines them, producing
an object module which can either be executed or
can become the input for a further
.PN ld
run.
(In the latter case, the
.B \-r
option must be given
to preserve the relocation bits.)
The output of
.PN ld
is left on a.out.
This file is only made executable
if no errors occurred during the load.
.PP
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 \fB\-e\fP 
option is specified.
.PP
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
.MS ranlib 1 ,
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
.MS ranlib 1 .
The dictionary is searched repeatedly 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, in that order.
It is an error to define these symbols.
.SH Options
.NXR "ld command" "options"
The 
.PN ld
command has several options.
Except for the
.BR \-l 
option,
they should appear before the file names.
.TP 10
.B \-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.
.IP
The
.B \-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.
.TP
.B \-D
Takes the next argument as a hexadecimal number and pads the data segment
with zero bytes to the indicated length.
.TP 
.B  \-d
Forces definition of common storage
even if the
.B \-r
flag is present.
.TP
.B \-e
Takes the next argument as the
name of the entry point of the loaded
program; location 0 is the default.
.TP
.BI \-L dir
Adds
.I dir
to the list of directories that are searched for libraries.
Directories specified with 
.B \-L
are searched before the standard directories.
.TP 
.BI \-l x
Abbreviates the library name
.RI lib x \&.a,
where
.I x
is a string.
The
.PN ld
command searches for libraries first in any directories
specified with
.B \-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
.B \-l
is significant.
.TP
.B \-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.
.TP
.B \-M
Produces a primitive load map, listing the names of the files
that are loaded.
.TP
.B \-N
Indicates a portion of text to not make read-only or sharable.
(Use magic number 0407.)
.TP 
.B  \-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.
.TP 
.B  \-o
Takes the 
.I name
argument after
.B \-o
as the name of the
.PN ld
output file, instead of a.out.
.TP 
.B \-r
Generates relocation bits in the output file
so that it can be the subject of another
.PN ld
run.
This flag also prevents final definitions from being
given to common symbols
and suppresses the undefined symbol diagnostics.
.TP
.B \-S
Strips the output by removing all symbols except locals and globals.
.TP 
.B  \-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
.MS strip 1 .
.TP
.B \-T
Takes the next argument as a hexadecimal
number which sets the text segment origin.
The default origin is 0.
.TP
.BR \-t (trace)
Prints the name of each file as it is processed.
.TP 
.B  \-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.
.TP 
.B  \-X
Saves local symbols
except for those whose names begin with a capital L.
This option is used by 
.MS cc 1 
to discard internally-generated labels while
retaining symbols local to routines.
.TP 
.B  \-x
Discards local
(non-global) symbols in the output symbol table; only enters
external symbols.
This option saves some space in the output file.
.TP
.BI \-Y environment
Adjusts the magic number in the output file so that the program runs in 
the specified
.I environment .
The parameter can be
.B POSIX,
.B SYSTEM_FIVE, or
.B 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
.I environment
is given,
.B SYSTEM_FIVE
is assumed.  If neither this parameter nor the PROG_ENV variable is
present,
.B \-YBSD
is assumed.
.TP
\fB\-y\fIsym\fR
Indicates each file in which
.I 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
.I sym
with an underscore (_), because external C, FORTRAN and
Pascal variables begin with underscores.
.TP
.B \-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 
.MS size 1 ,
appear to reside in the data segment.
This avoids wasting the space which results from 
the roundup of the data segment size.
.SH Restrictions
.NXR "ld command" "restricted"
There is no way to force data to be page aligned.
The
.PN ld
command pads the images which are to be demand loaded from
the file system to the next
page boundary.  
.PP
When linking code contains GFLOAT instructions,
the GFLOAT versions of 
.I libc
and/or the math library must be used rather than the normal DFLOAT 
versions.  Link to these by using
.I \-lcg
and/or
.I \-lmg. 
.PP
The compiler and the linker 
.MS ld 1
cannot detect the use of mixed double floating point 
types, and your program may produce 
erroneous results. 				
.SH Files
.TP 20
/lib/lib*.a	
libraries.
.TP
/usr/lib/lib*.a 
libraries
.TP
/usr/local/lib/lib*.a  
libraries
.TP
a.out	
output file
.SH See Also
ar(1), as(1), cc(1), ranlib(1)