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<DT><CODE>-traditional-format</CODE>
<DD>
For some targets, the output of <CODE>ld</CODE> is different in some ways from
the output of some existing linker.  This switch requests <CODE>ld</CODE> to
use the traditional format instead.

<A NAME="IDX102"></A>
For example, on SunOS, <CODE>ld</CODE> combines duplicate entries in the
symbol string table.  This can reduce the size of an output file with
full debugging information by over 30 percent.  Unfortunately, the SunOS
<CODE>dbx</CODE> program can not read the resulting program (<CODE>gdb</CODE> has no
trouble).  The <SAMP>`-traditional-format'</SAMP> switch tells <CODE>ld</CODE> to not
combine duplicate entries.

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<DT><CODE>-u <VAR>symbol</VAR></CODE>
<DD>
Force <VAR>symbol</VAR> to be entered in the output file as an undefined symbol.
Doing this may, for example, trigger linking of additional modules from
standard libraries.  <SAMP>`-u'</SAMP> may be repeated with different option
arguments to enter additional undefined symbols.

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<DT><CODE>-Ur</CODE>
<DD>
For anything other than C++ programs, this option is equivalent to
<SAMP>`-r'</SAMP>: it generates relocatable output--i.e., an output file that can in
turn serve as input to <CODE>ld</CODE>.  When linking C++ programs, <SAMP>`-Ur'</SAMP>
<EM>does</EM> resolve references to constructors, unlike <SAMP>`-r'</SAMP>.
It does not work to use <SAMP>`-Ur'</SAMP> on files that were themselves linked
with <SAMP>`-Ur'</SAMP>; once the constructor table has been built, it cannot
be added to.  Use <SAMP>`-Ur'</SAMP> only for the last partial link, and
<SAMP>`-r'</SAMP> for the others.

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<DT><CODE>--verbose</CODE>
<DD>
Display the version number for <CODE>ld</CODE> and list the linker emulations
supported.  Display which input files can and cannot be opened.

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<DT><CODE>-v</CODE>
<DD>
<DT><CODE>-V</CODE>
<DD>
Display the version number for <CODE>ld</CODE>.  The <CODE>-V</CODE> option also
lists the supported emulations.

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<DT><CODE>-version</CODE>
<DD>
Display the version number for <CODE>ld</CODE> and exit.

<A NAME="IDX113"></A>
<A NAME="IDX114"></A>
<A NAME="IDX115"></A>
<DT><CODE>-warn-common</CODE>
<DD>
Warn when a common symbol is combined with another common symbol or with
a symbol definition.  Unix linkers allow this somewhat sloppy practice,
but linkers on some other operating systems do not.  This option allows
you to find potential problems from combining global symbols.
Unfortunately, some C libraries use this practice, so you may get some
warnings about symbols in the libraries as well as in your programs.

There are three kinds of global symbols, illustrated here by C examples:

<DL COMPACT>

<DT><SAMP>`int i = 1;'</SAMP>
<DD>
A definition, which goes in the initialized data section of the output
file.

<DT><SAMP>`extern int i;'</SAMP>
<DD>
An undefined reference, which does not allocate space.
There must be either a definition or a common symbol for the
variable somewhere.

<DT><SAMP>`int i;'</SAMP>
<DD>
A common symbol.  If there are only (one or more) common symbols for a
variable, it goes in the uninitialized data area of the output file.
The linker merges multiple common symbols for the same variable into a
single symbol.  If they are of different sizes, it picks the largest
size.  The linker turns a common symbol into a declaration, if there is
a definition of the same variable.
</DL>

The <SAMP>`-warn-common'</SAMP> option can produce five kinds of warnings.  Each
warning consists of a pair of lines: the first describes the symbol just
encountered, and the second describes the previous symbol encountered
with the same name.  One or both of the two symbols will be a common
symbol.


<OL>
<LI>

Turning a common symbol into a reference, because there is already a
definition for the symbol.

<PRE>
<VAR>file</VAR>(<VAR>section</VAR>): warning: common of `<VAR>symbol</VAR>'
   overridden by definition
<VAR>file</VAR>(<VAR>section</VAR>): warning: defined here
</PRE>

<LI>

Turning a common symbol into a reference, because a later definition for
the symbol is encountered.  This is the same as the previous case,
except that the symbols are encountered in a different order.

<PRE>
<VAR>file</VAR>(<VAR>section</VAR>): warning: definition of `<VAR>symbol</VAR>'
   overriding common
<VAR>file</VAR>(<VAR>section</VAR>): warning: common is here
</PRE>

<LI>

Merging a common symbol with a previous same-sized common symbol.

<PRE>
<VAR>file</VAR>(<VAR>section</VAR>): warning: multiple common
   of `<VAR>symbol</VAR>'
<VAR>file</VAR>(<VAR>section</VAR>): warning: previous common is here
</PRE>

<LI>

Merging a common symbol with a previous larger common symbol.

<PRE>
<VAR>file</VAR>(<VAR>section</VAR>): warning: common of `<VAR>symbol</VAR>'
   overridden by larger common
<VAR>file</VAR>(<VAR>section</VAR>): warning: larger common is here
</PRE>

<LI>

Merging a common symbol with a previous smaller common symbol.  This is
the same as the previous case, except that the symbols are
encountered in a different order.

<PRE>
<VAR>file</VAR>(<VAR>section</VAR>): warning: common of `<VAR>symbol</VAR>'
   overriding smaller common
<VAR>file</VAR>(<VAR>section</VAR>): warning: smaller common is here
</PRE>

</OL>

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<DT><CODE>-warn-constructors</CODE>
<DD>
Warn if any global constructors are used.  This is only useful for a few
object file formats.  For formats like COFF or ELF, the linker can not
detect the use of global constructors.

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<A NAME="IDX118"></A>
<A NAME="IDX119"></A>
<DT><CODE>-warn-once</CODE>
<DD>
Only warn once for each undefined symbol, rather than once per module
which refers to it.

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<A NAME="IDX121"></A>
For each archive mentioned on the command line, include every object
file in the archive in the link, rather than searching the archive for
the required object files.  This is normally used to turn an archive
file into a shared library, forcing every object to be included in the
resulting shared library.

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<A NAME="IDX123"></A>
<A NAME="IDX124"></A>
<DT><CODE>-X</CODE>
<DD>
Delete all temporary local symbols.  For most targets, this is all local
symbols whose names begin with <SAMP>`L'</SAMP>.

<A NAME="IDX125"></A>
<A NAME="IDX126"></A>
<DT><CODE>-x</CODE>
<DD>
Delete all local symbols.

<A NAME="IDX127"></A>
<A NAME="IDX128"></A>
<DT><CODE>-y <VAR>symbol</VAR></CODE>
<DD>
Print the name of each linked file in which <VAR>symbol</VAR> appears.  This
option may be given any number of times.  On many systems it is necessary
to prepend an underscore.

This option is useful when you have an undefined symbol in your link but
don't know where the reference is coming from.

<A NAME="IDX129"></A>
<A NAME="IDX130"></A>
<DT><CODE>-( <VAR>archives</VAR> -)</CODE>
<DD>
<DT><CODE>--start-group <VAR>archives</VAR> --end-group</CODE>
<DD>
The <VAR>archives</VAR> should be a list of archive files.  They may be
either explicit file names, or <SAMP>`-l'</SAMP> options.

The specified archives are searched repeatedly until no new undefined
references are created.  Normally, an archive is searched only once in
the order that it is specified on the command line.  If a symbol in that
archive is needed to resolve an undefined symbol referred to by an
object in an archive that appears later on the command line, the linker
would not be able to resolve that reference.  By grouping the archives,
they all be searched repeatedly until all possible references are
resolved.

Using this option has a significant performance cost.  It is best to use
it only when there are unavoidable circular references between two or
more archives.
</DL>



<H2><A NAME="SEC4" HREF="ld_toc.html#TOC4">Environment Variables</A></H2>

<P>
You can change the behavior of <CODE>ld</CODE> with the environment
variable <CODE>GNUTARGET</CODE>.  

</P>
<P>
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<A NAME="IDX132"></A>
<CODE>GNUTARGET</CODE> determines the input-file object format if you don't
use <SAMP>`-b'</SAMP> (or its synonym <SAMP>`-format'</SAMP>).  Its value should be one
of the BFD names for an input format (see section <A HREF="ld.html#SEC26">BFD</A>).  If there is no
<CODE>GNUTARGET</CODE> in the environment, <CODE>ld</CODE> uses the natural format
of the target. If <CODE>GNUTARGET</CODE> is set to <CODE>default</CODE> then BFD attempts to discover the
input format by examining binary input files; this method often
succeeds, but there are potential ambiguities, since there is no method
of ensuring that the magic number used to specify object-file formats is
unique.  However, the configuration procedure for BFD on each system
places the conventional format for that system first in the search-list,
so ambiguities are resolved in favor of convention.

</P>


<H1><A NAME="SEC5" HREF="ld_toc.html#TOC5">Command Language</A></H1>

<P>
<A NAME="IDX133"></A>
The command language provides explicit control over the link process,
allowing complete specification of the mapping between the linker's
input files and its output.  It controls:

<UL>
<LI>

input files 
<LI>

file formats
<LI>

output file layout
<LI>

addresses of sections
<LI>

placement of common blocks
</UL>

<P>
You may supply a command file (also known as a link script) to the
linker either explicitly through the <SAMP>`-T'</SAMP> option, or implicitly as
an ordinary file. If the linker opens a file which it cannot recognize
as a supported object or archive format, it reports an error.

</P>



<H2><A NAME="SEC6" HREF="ld_toc.html#TOC6">Linker Scripts</A></H2>
<P>
The <CODE>ld</CODE> command language is a collection of statements; some are
simple keywords setting a particular option, some are used to select and
group input files or name output files; and two statement
types have a fundamental and pervasive impact on the linking process.

</P>
<P>
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<A NAME="IDX135"></A>
<A NAME="IDX136"></A>
<A NAME="IDX137"></A>
The most fundamental command of the <CODE>ld</CODE> command language is the
<CODE>SECTIONS</CODE> command (see section <A HREF="ld.html#SEC16">Specifying Output Sections</A>).  Every meaningful command
script must have a <CODE>SECTIONS</CODE> command: it specifies a
"picture" of the output file's layout, in varying degrees of detail.
No other command is required in all cases.

</P>
<P>
The <CODE>MEMORY</CODE> command complements <CODE>SECTIONS</CODE> by describing the
available memory in the target architecture.  This command is optional;
if you don't use a <CODE>MEMORY</CODE> command, <CODE>ld</CODE> assumes sufficient
memory is available in a contiguous block for all output.
See section <A HREF="ld.html#SEC15">Memory Layout</A>.

</P>
<P>
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You may include comments in linker scripts just as in C: delimited
by <SAMP>`/*'</SAMP> and <SAMP>`*/'</SAMP>.  As in C, comments are syntactically
equivalent to whitespace.

</P>


<H2><A NAME="SEC7" HREF="ld_toc.html#TOC7">Expressions</A></H2>
<P>
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Many useful commands involve arithmetic expressions.  The syntax for
expressions in the command language is identical to that of C
expressions, with the following features:

<UL>
<LI>

All expressions evaluated as integers and
are of "long" or "unsigned long" type.
<LI>

All constants are integers.
<LI>

All of the C arithmetic operators are provided.
<LI>

You may reference, define, and create global variables.
<LI>

You may call special purpose built-in functions.
</UL>



<H3><A NAME="SEC8" HREF="ld_toc.html#TOC8">Integers</A></H3>
<P>
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<A NAME="IDX142"></A>
An octal integer is <SAMP>`0'</SAMP> followed by zero or more of the octal
digits (<SAMP>`01234567'</SAMP>).

<PRE>
_as_octal = 0157255;
</PRE>

<P>
<A NAME="IDX143"></A>
A decimal integer starts with a non-zero digit followed by zero or
more digits (<SAMP>`0123456789'</SAMP>).