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<PRE>
_as_decimal = 57005;
</PRE>

<P>
<A NAME="IDX144"></A>
<A NAME="IDX145"></A>
A hexadecimal integer is <SAMP>`0x'</SAMP> or <SAMP>`0X'</SAMP> followed by one or
more hexadecimal digits chosen from <SAMP>`0123456789abcdefABCDEF'</SAMP>.

<PRE>
_as_hex = 0xdead;
</PRE>

<P>
<A NAME="IDX146"></A>
To write a negative integer, use
the prefix operator <SAMP>`-'</SAMP>; see section <A HREF="ld.html#SEC11">Operators</A>.

<PRE>
_as_neg = -57005;
</PRE>

<P>
<A NAME="IDX147"></A>
<A NAME="IDX148"></A>
<A NAME="IDX149"></A>
<A NAME="IDX150"></A>
<A NAME="IDX151"></A>
Additionally the suffixes <CODE>K</CODE> and <CODE>M</CODE> may be used to scale a
constant by 
respectively. For example, the following all refer to the same quantity:

</P>

<PRE>
        _fourk_1 = 4K;
        _fourk_2 = 4096;
        _fourk_3 = 0x1000;
</PRE>



<H3><A NAME="SEC9" HREF="ld_toc.html#TOC9">Symbol Names</A></H3>
<P>
<A NAME="IDX152"></A>
<A NAME="IDX153"></A>
<A NAME="IDX154"></A>
<A NAME="IDX155"></A>
Unless quoted, symbol names start with a letter, underscore, or point
and may include any letters, underscores, digits, points,
and hyphens.  Unquoted symbol names must not conflict with any
keywords.  You can specify a symbol which contains odd characters or has
the same name as a keyword, by surrounding the symbol name in double quotes:

<PRE>
        "SECTION" = 9;
        "with a space" = "also with a space" + 10;
</PRE>

<P>
Since symbols can contain many non-alphabetic characters, it is safest
to delimit symbols with spaces.  For example, <SAMP>`A-B'</SAMP> is one symbol,
whereas <SAMP>`A - B'</SAMP> is an expression involving subtraction.

</P>


<H3><A NAME="SEC10" HREF="ld_toc.html#TOC10">The Location Counter</A></H3>
<P>
<A NAME="IDX156"></A>
<A NAME="IDX157"></A>
<A NAME="IDX158"></A>
<A NAME="IDX159"></A>
The special linker variable <EM>dot</EM> <SAMP>`.'</SAMP> always contains the
current output location counter. Since the <CODE>.</CODE> always refers to
a location in an output section, it must always appear in an
expression within a <CODE>SECTIONS</CODE> command. The <CODE>.</CODE> symbol
may appear anywhere that an ordinary symbol is allowed in an
expression, but its assignments have a side effect. Assigning a value
to the <CODE>.</CODE> symbol will cause the location counter to be moved.
<A NAME="IDX160"></A>
This may be used to create holes in the output section.  The location
counter may never be moved backwards.

<PRE>
SECTIONS
{
  output :
  {
  file1(.text)
  . = . + 1000;
  file2(.text)
  . += 1000;
  file3(.text)
  } = 0x1234;
}
</PRE>

<P>
In the previous example, <CODE>file1</CODE> is located at the beginning of the
output section, then there is a 1000 byte gap.  Then <CODE>file2</CODE>
appears, also with a 1000 byte gap following before <CODE>file3</CODE> is
loaded.  The notation <SAMP>`= 0x1234'</SAMP> specifies what data to write in
the gaps (see section <A HREF="ld.html#SEC20">Optional Section Attributes</A>).

</P>
<P>
</P>


<H3><A NAME="SEC11" HREF="ld_toc.html#TOC11">Operators</A></H3>
<P>
<A NAME="IDX161"></A>
<A NAME="IDX162"></A>
<A NAME="IDX163"></A>
The linker recognizes  the standard C set of arithmetic operators, with
the standard bindings and precedence levels:
<table>
<tr><td colspan=4><hr></td></tr>
<tr><th><b>Precedence</b></th><th><b>Associativity</b></th><th><b>Operators</b><th><b>Notes</b></th></tr>
<tr><td colspan=4><hr></td></tr>
<tr><td>(highest)</td></tr>
<tr><td>1</td><td>left</td><td>!  -  ~</td><td>(1)</td></tr>
<tr><td>2</td><td>left</td><td>*  /  %</td></tr>
<tr><td>3</td><td>left</td><td>+  -</td></tr>
<tr><td>4</td><td>left</td><td>>>  &l;&lt;</td></tr>
<tr><td>5</td><td>left</td><td>==  !=  &gt;  &lt;  &lt;=  &gt;=</td></tr>
<tr><td>6</td><td>left</td><td>&amp;</td></tr>
<tr><td>7</td><td>left</td><td>|</td></tr>
<tr><td>8</td><td>left</td><td>&amp;&amp;</td></tr>
<tr><td>9</td><td>left</td><td>||</td></tr>
<tr><td>10</td><td>right</td><td>? :</td></tr>
<tr><td>11</td><td>right</td><td>&amp;=  +=  -=  *=  /=</td><td>       (2)</td></tr>
<tr><td>(lowest)</td></tr>
<tr><td colspan=4><hr></td></tr>
<tr><td>(1)</td><td colspan=3>Prefix operators.</td></tr>
<tr><td>(2)</td><td colspan=3>See section <A HREF="ld.html#SEC13">Assignment: Defining Symbols</A>.</td></tr>
<tr><td colspan=4><hr></td></tr>
</table>

</P>


<H3><A NAME="SEC12" HREF="ld_toc.html#TOC12">Evaluation</A></H3>

<P>
<A NAME="IDX164"></A>
<A NAME="IDX165"></A>
The linker uses "lazy evaluation" for expressions; it only calculates
an expression when absolutely necessary.  The linker needs the value of
the start address, and the lengths of memory regions, in order to do any
linking at all; these values are computed as soon as possible when the
linker reads in the command file.  However, other values (such as symbol
values) are not known or needed until after storage allocation.  Such
values are evaluated later, when other information (such as the sizes of
output sections) is available for use in the symbol assignment
expression.

</P>


<H3><A NAME="SEC13" HREF="ld_toc.html#TOC13">Assignment: Defining Symbols</A></H3>
<P>
<A NAME="IDX166"></A>
<A NAME="IDX167"></A>
<A NAME="IDX168"></A>
You may create global symbols, and assign values (addresses) to global
symbols, using any of the C assignment operators:

</P>
<DL COMPACT>

<DT><CODE><VAR>symbol</VAR>  = <VAR>expression</VAR> ;</CODE>
<DD>
<DT><CODE><VAR>symbol</VAR> &#38;= <VAR>expression</VAR> ;</CODE>
<DD>
<DT><CODE><VAR>symbol</VAR> += <VAR>expression</VAR> ;</CODE>
<DD>
<DT><CODE><VAR>symbol</VAR> -= <VAR>expression</VAR> ;</CODE>
<DD>
<DT><CODE><VAR>symbol</VAR> *= <VAR>expression</VAR> ;</CODE>
<DD>
<DT><CODE><VAR>symbol</VAR> /= <VAR>expression</VAR> ;</CODE>
<DD>
</DL>

<P>
Two things distinguish assignment from other operators in <CODE>ld</CODE>
expressions.

<UL>
<LI>

Assignment may only be used at the root of an expression;
<SAMP>`a=b+3;'</SAMP> is allowed, but <SAMP>`a+b=3;'</SAMP> is an error.

<A NAME="IDX169"></A>
<A NAME="IDX170"></A>
<LI>

You must place a trailing semicolon ("<KBD>;</KBD>") at the end of an
assignment statement.
</UL>

<P>
Assignment statements may appear:

<UL>
<LI>

as commands in their own right in an <CODE>ld</CODE> script; or
<LI>

as independent statements within a <CODE>SECTIONS</CODE> command; or
<LI>

as part of the contents of a section definition in a
<CODE>SECTIONS</CODE> command.
</UL>

<P>
The first two cases are equivalent in effect--both define a symbol with
an absolute address.  The last case defines a symbol whose address is
relative to a particular section (see section <A HREF="ld.html#SEC16">Specifying Output Sections</A>).

</P>
<P>
<A NAME="IDX171"></A>
<A NAME="IDX172"></A>
<A NAME="IDX173"></A>
When a linker expression is evaluated and assigned to a variable, it is
given either an absolute or a relocatable type. An absolute expression
type is one in which the symbol contains the value that it will have in
the output file; a relocatable expression type is one in which the
value is expressed as a fixed offset from the base of a section.

</P>
<P>
The type of the expression is controlled by its position in the script
file.  A symbol assigned within a section definition is created relative
to the base of the section; a symbol assigned in any other place is
created as an absolute symbol. Since a symbol created within a
section definition is relative to the base of the section, it
will remain relocatable if relocatable output is requested.  A symbol
may be created with an absolute value even when assigned to within a
section definition by using the absolute assignment function
<CODE>ABSOLUTE</CODE>.  For example, to create an absolute symbol whose address
is the last byte of an output section named <CODE>.data</CODE>:

<PRE>
SECTIONS{ ...
  .data : 
    {
      *(.data)
      _edata = ABSOLUTE(.) ;
    } 
... }
</PRE>

<P>
The linker tries to put off the evaluation of an assignment until all
the terms in the source expression are known (see section <A HREF="ld.html#SEC12">Evaluation</A>).  For
instance, the sizes of sections cannot be known until after allocation,
so assignments dependent upon these are not performed until after
allocation. Some expressions, such as those depending upon the location
counter <EM>dot</EM>, <SAMP>`.'</SAMP> must be evaluated during allocation. If the
result of an expression is required, but the value is not available,
then an error results.  For example, a script like the following

<PRE>
SECTIONS { ...
  text 9+this_isnt_constant : 
    { ...
    }
... }
</PRE>

<P>
<A NAME="IDX174"></A>
will cause the error message "<CODE>Non constant expression for initial
address</CODE>".

</P>
<P>
<A NAME="IDX175"></A>
In some cases, it is desirable for a linker script to define a symbol
only if it is referenced, and only if it is not defined by any object
included in the link.  For example, traditional linkers defined the
symbol <SAMP>`etext'</SAMP>.  However, ANSI C requires that the user be able to
use <SAMP>`etext'</SAMP> as a function name without encountering an error.
The <CODE>PROVIDE</CODE> keyword may be used to define a symbol, such as
<SAMP>`etext'</SAMP>, only if it is referenced but not defined.  The syntax is
<CODE>PROVIDE(<VAR>symbol</VAR> = <VAR>expression</VAR>)</CODE>.

</P>


<H3><A NAME="SEC14" HREF="ld_toc.html#TOC14">Arithmetic Functions</A></H3>
<P>
<A NAME="IDX176"></A>
The command language includes a number of built-in
functions for use in link script expressions.
<DL COMPACT>

<DT><CODE>ABSOLUTE(<VAR>exp</VAR>)</CODE>
<DD>
<A NAME="IDX177"></A>
 <A NAME="IDX178"></A>
 
Return the absolute (non-relocatable, as opposed to non-negative) value
of the expression <VAR>exp</VAR>.  Primarily useful to assign an absolute
value to a symbol within a section definition, where symbol values are
normally section-relative.

<A NAME="IDX179"></A>
<A NAME="IDX180"></A>
<DT><CODE>ADDR(<VAR>section</VAR>)</CODE>
<DD>
Return the absolute address of the named <VAR>section</VAR>.  Your script must
previously have defined the location of that section. In the following
example, <CODE>symbol_1</CODE> and <CODE>symbol_2</CODE> are assigned identical
values:

<PRE>
SECTIONS{ ...
  .output1 :
    { 
    start_of_output_1 = ABSOLUTE(.);
    ...
    }
  .output :
    {
    symbol_1 = ADDR(.output1);
    symbol_2 = start_of_output_1;
    }
... }
</PRE>

<A NAME="IDX181"></A>
<A NAME="IDX182"></A>
<DT><CODE>ALIGN(<VAR>exp</VAR>)</CODE>
<DD>
Return the result of the current location counter (<CODE>.</CODE>) aligned to
the next <VAR>exp</VAR> boundary.  <VAR>exp</VAR> must be an expression whose
value is a power of two.  This is equivalent to 

<PRE>
(. + <VAR>exp</VAR> - 1) &#38; ~(<VAR>exp</VAR> - 1)
</PRE>

<CODE>ALIGN</CODE> doesn't change the value of the location counter--it just
does arithmetic on it.  As an example, to align the output <CODE>.data</CODE>
section to the next <CODE>0x2000</CODE> byte boundary after the preceding
section and to set a variable within the section to the next
<CODE>0x8000</CODE> boundary after the input sections:

<PRE>
SECTIONS{ ...
  .data ALIGN(0x2000): {
    *(.data)
    variable = ALIGN(0x8000);
  }
... }
</PRE>

The first use of <CODE>ALIGN</CODE> in this example specifies the location of
a section because it is used as the optional <VAR>start</VAR> attribute of a
section definition (see section <A HREF="ld.html#SEC20">Optional Section Attributes</A>).  The second use simply
defines the value of a variable.

The built-in <CODE>NEXT</CODE> is closely related to <CODE>ALIGN</CODE>.

<A NAME="IDX183"></A>
<A NAME="IDX184"></A>
<DT><CODE>DEFINED(<VAR>symbol</VAR>)</CODE>
<DD>