ld.1

MinGW+MSYS必备的开发工具链

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.\" ========================================================================
.\"
.IX Title "LD 1"
.TH LD 1 "2006-08-25" "binutils-2.17.50" "GNU Development Tools"
.SH "NAME"
ld \- The GNU linker
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
ld [\fBoptions\fR] \fIobjfile\fR ...
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBld\fR combines a number of object and archive files, relocates
their data and ties up symbol references. Usually the last step in
compiling a program is to run \fBld\fR.
.PP
\&\fBld\fR accepts Linker Command Language files written in
a superset of \s-1AT&T\s0's Link Editor Command Language syntax,
to provide explicit and total control over the linking process.
.PP
This man page does not describe the command language; see the
\&\fBld\fR entry in \f(CW\*(C`info\*(C'\fR for full details on the command
language and on other aspects of the \s-1GNU\s0 linker.
.PP
This version of \fBld\fR uses the general purpose \s-1BFD\s0 libraries
to operate on object files. This allows \fBld\fR to read, combine, and
write object files in many different formats\-\-\-for example, \s-1COFF\s0 or
\&\f(CW\*(C`a.out\*(C'\fR.  Different formats may be linked together to produce any
available kind of object file.  
.PP
Aside from its flexibility, the \s-1GNU\s0 linker is more helpful than other
linkers in providing diagnostic information.  Many linkers abandon
execution immediately upon encountering an error; whenever possible,
\&\fBld\fR continues executing, allowing you to identify other errors
(or, in some cases, to get an output file in spite of the error).
.PP
The \s-1GNU\s0 linker \fBld\fR is meant to cover a broad range of situations,
and to be as compatible as possible with other linkers.  As a result,
you have many choices to control its behavior.
.SH "OPTIONS"
.IX Header "OPTIONS"
The linker supports a plethora of command-line options, but in actual
practice few of them are used in any particular context.
For instance, a frequent use of \fBld\fR is to link standard Unix
object files on a standard, supported Unix system.  On such a system, to
link a file \f(CW\*(C`hello.o\*(C'\fR:
.PP
.Vb 1
\&        ld -o <output> /lib/crt0.o hello.o -lc
.Ve
.PP
This tells \fBld\fR to produce a file called \fIoutput\fR as the
result of linking the file \f(CW\*(C`/lib/crt0.o\*(C'\fR with \f(CW\*(C`hello.o\*(C'\fR and
the library \f(CW\*(C`libc.a\*(C'\fR, which will come from the standard search
directories.  (See the discussion of the \fB\-l\fR option below.)
.PP
Some of the command-line options to \fBld\fR may be specified at any
point in the command line.  However, options which refer to files, such
as \fB\-l\fR or \fB\-T\fR, cause the file to be read at the point at
which the option appears in the command line, relative to the object
files and other file options.  Repeating non-file options with a
different argument will either have no further effect, or override prior
occurrences (those further to the left on the command line) of that
option.  Options which may be meaningfully specified more than once are
noted in the descriptions below.
.PP
Non-option arguments are object files or archives which are to be linked
together.  They may follow, precede, or be mixed in with command-line
options, except that an object file argument may not be placed between
an option and its argument.
.PP
Usually the linker is invoked with at least one object file, but you can
specify other forms of binary input files using \fB\-l\fR, \fB\-R\fR,
and the script command language.  If \fIno\fR binary input files at all
are specified, the linker does not produce any output, and issues the
message \fBNo input files\fR.
.PP
If the linker cannot recognize the format of an object file, it will
assume that it is a linker script.  A script specified in this way
augments the main linker script used for the link (either the default
linker script or the one specified by using \fB\-T\fR).  This feature
permits the linker to link against a file which appears to be an object
or an archive, but actually merely defines some symbol values, or uses
\&\f(CW\*(C`INPUT\*(C'\fR or \f(CW\*(C`GROUP\*(C'\fR to load other objects.  Note that
specifying a script in this way merely augments the main linker script;
use the \fB\-T\fR option to replace the default linker script entirely.
.PP
For options whose names are a single letter,
option arguments must either follow the option letter without intervening
whitespace, or be given as separate arguments immediately following the
option that requires them.
.PP
For options whose names are multiple letters, either one dash or two can
precede the option name; for example, \fB\-trace\-symbol\fR and
\&\fB\-\-trace\-symbol\fR are equivalent.  Note\-\-\-there is one exception to
this rule.  Multiple letter options that start with a lower case 'o' can
only be preceded by two dashes.  This is to reduce confusion with the
\&\fB\-o\fR option.  So for example \fB\-omagic\fR sets the output file
name to \fBmagic\fR whereas \fB\-\-omagic\fR sets the \s-1NMAGIC\s0 flag on the
output.
.PP
Arguments to multiple-letter options must either be separated from the
option name by an equals sign, or be given as separate arguments
immediately following the option that requires them.  For example,
\&\fB\-\-trace\-symbol foo\fR and \fB\-\-trace\-symbol=foo\fR are equivalent.
Unique abbreviations of the names of multiple-letter options are
accepted.
.PP
Note\-\-\-if the linker is being invoked indirectly, via a compiler driver
(e.g. \fBgcc\fR) then all the linker command line options should be
prefixed by \fB\-Wl,\fR (or whatever is appropriate for the particular
compiler driver) like this:
.PP
.Vb 1
\&          gcc -Wl,--startgroup foo.o bar.o -Wl,--endgroup
.Ve
.PP
This is important, because otherwise the compiler driver program may
silently drop the linker options, resulting in a bad link.
.PP
Here is a table of the generic command line switches accepted by the \s-1GNU\s0
linker:
.IP "\fB@\fR\fIfile\fR" 4
.IX Item "@file"
Read command-line options from \fIfile\fR.  The options read are
inserted in place of the original @\fIfile\fR option.  If \fIfile\fR
does not exist, or cannot be read, then the option will be treated
literally, and not removed.  
.Sp
Options in \fIfile\fR are separated by whitespace.  A whitespace
character may be included in an option by surrounding the entire
option in either single or double quotes.  Any character (including a
backslash) may be included by prefixing the character to be included
with a backslash.  The \fIfile\fR may itself contain additional
@\fIfile\fR options; any such options will be processed recursively.
.IP "\fB\-a\fR\fIkeyword\fR" 4
.IX Item "-akeyword"
This option is supported for \s-1HP/UX\s0 compatibility.  The \fIkeyword\fR
argument must be one of the strings \fBarchive\fR, \fBshared\fR, or
\&\fBdefault\fR.  \fB\-aarchive\fR is functionally equivalent to
\&\fB\-Bstatic\fR, and the other two keywords are functionally equivalent
to \fB\-Bdynamic\fR.  This option may be used any number of times.
.IP "\fB\-A\fR\fIarchitecture\fR" 4
.IX Item "-Aarchitecture"
.PD 0
.IP "\fB\-\-architecture=\fR\fIarchitecture\fR" 4
.IX Item "--architecture=architecture"
.PD
In the current release of \fBld\fR, this option is useful only for the
Intel 960 family of architectures.  In that \fBld\fR configuration, the
\&\fIarchitecture\fR argument identifies the particular architecture in
the 960 family, enabling some safeguards and modifying the
archive-library search path.  
.Sp
Future releases of \fBld\fR may support similar functionality for
other architecture families.
.IP "\fB\-b\fR \fIinput-format\fR" 4
.IX Item "-b input-format"
.PD 0
.IP "\fB\-\-format=\fR\fIinput-format\fR" 4
.IX Item "--format=input-format"
.PD
\&\fBld\fR may be configured to support more than one kind of object
file.  If your \fBld\fR is configured this way, you can use the
\&\fB\-b\fR option to specify the binary format for input object files
that follow this option on the command line.  Even when \fBld\fR is
configured to support alternative object formats, you don't usually need
to specify this, as \fBld\fR should be configured to expect as a
default input format the most usual format on each machine.
\&\fIinput-format\fR is a text string, the name of a particular format
supported by the \s-1BFD\s0 libraries.  (You can list the available binary
formats with \fBobjdump \-i\fR.)
.Sp
You may want to use this option if you are linking files with an unusual
binary format.  You can also use \fB\-b\fR to switch formats explicitly (when
linking object files of different formats), by including
\&\fB\-b\fR \fIinput-format\fR before each group of object files in a
particular format.
.Sp
The default format is taken from the environment variable