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Return 1 if <VAR>symbol</VAR> is in the linker global symbol table and is
defined, otherwise return 0.  You can use this function to provide default
values for symbols.  For example, the following command-file fragment shows how
to set a global symbol <CODE>begin</CODE> to the first location in the
<CODE>.text</CODE> section--but if a symbol called <CODE>begin</CODE> already
existed, its value is preserved:


<PRE>
SECTIONS{ ...
  .text : {
    begin = DEFINED(begin) ? begin : . ;
    ...
  }
... }
</PRE>

<A NAME="IDX185"></A>
<A NAME="IDX186"></A>
<DT><CODE>NEXT(<VAR>exp</VAR>)</CODE>
<DD>
Return the next unallocated address that is a multiple of <VAR>exp</VAR>.
This function is closely related to <CODE>ALIGN(<VAR>exp</VAR>)</CODE>; unless you
use the <CODE>MEMORY</CODE> command to define discontinuous memory for the
output file, the two functions are equivalent.

<A NAME="IDX187"></A>
<A NAME="IDX188"></A>
<DT><CODE>SIZEOF(<VAR>section</VAR>)</CODE>
<DD>
Return the size in bytes of the named <VAR>section</VAR>, if that section has
been allocated.  In the following example, <CODE>symbol_1</CODE> and
<CODE>symbol_2</CODE> are assigned identical values:

<PRE>
SECTIONS{ ...
  .output {
    .start = . ;
    ...
    .end = . ;
    }
  symbol_1 = .end - .start ;
  symbol_2 = SIZEOF(.output);
... }
</PRE>

<A NAME="IDX189"></A>
<A NAME="IDX190"></A>
<A NAME="IDX191"></A>
<DT><CODE>SIZEOF_HEADERS</CODE>
<DD>
<DT><CODE>sizeof_headers</CODE>
<DD>
Return the size in bytes of the output file's headers.  You can use this number
as the start address of the first section, if you choose, to facilitate
paging. 

</DL>



<H2><A NAME="SEC15" HREF="ld_toc.html#TOC15">Memory Layout</A></H2>
<P>
<A NAME="IDX192"></A>
<A NAME="IDX193"></A>
<A NAME="IDX194"></A>
<A NAME="IDX195"></A>
The linker's default configuration permits allocation of all available memory.
You can override this configuration by using the <CODE>MEMORY</CODE> command.  The
<CODE>MEMORY</CODE> command describes the location and size of blocks of
memory in the target.  By using it carefully, you can describe which
memory regions may be used by the linker, and which memory regions it
must avoid.  The linker does not shuffle sections to fit into the
available regions, but does move the requested sections into the correct
regions and issue errors when the regions become too full.  

</P>
<P>
A command file may contain at most one use of the <CODE>MEMORY</CODE>
command; however, you can define as many blocks of memory within it as
you wish.  The syntax is:
        

<PRE>
MEMORY 
  {
    <VAR>name</VAR> (<VAR>attr</VAR>) : ORIGIN = <VAR>origin</VAR>, LENGTH = <VAR>len</VAR>
    ...
  }
</PRE>

<DL COMPACT>

<DT><CODE><VAR>name</VAR></CODE>
<DD>
<A NAME="IDX196"></A>
 
is a name used internally by the linker to refer to the region. Any
symbol name may be used.  The region names are stored in a separate
name space, and will not conflict with symbols, file names or section
names.  Use distinct names to specify multiple regions.

<A NAME="IDX197"></A>
<DT><CODE>(<VAR>attr</VAR>)</CODE>
<DD>
is an optional list of attributes, permitted for compatibility with the
AT&#38;T linker but not used by <CODE>ld</CODE> beyond checking that the
attribute list is valid.  Valid attribute lists must be made up of the
characters "<CODE>LIRWX</CODE>".  If you omit the attribute list, you may
omit the parentheses around it as well.

<A NAME="IDX198"></A>
<A NAME="IDX199"></A>
<A NAME="IDX200"></A>
<DT><CODE><VAR>origin</VAR></CODE>
<DD>
is the start address of the region in physical memory.  It is
an expression that must evaluate to a constant before
memory allocation is performed. The keyword <CODE>ORIGIN</CODE> may be
abbreviated to <CODE>org</CODE> or <CODE>o</CODE> (but not, for example, <SAMP>`ORG'</SAMP>).

<A NAME="IDX201"></A>
<A NAME="IDX202"></A>
<A NAME="IDX203"></A>
<DT><CODE><VAR>len</VAR></CODE>
<DD>
is the size in bytes of the region (an expression).
The keyword <CODE>LENGTH</CODE> may be abbreviated to <CODE>len</CODE> or <CODE>l</CODE>.
</DL>

<P>
For example, to specify that memory has two regions available for
allocation--one starting at 0 for 256 kilobytes, and the other
starting at <CODE>0x40000000</CODE> for four megabytes:

</P>

<PRE>
MEMORY 
  {
  rom : ORIGIN = 0, LENGTH = 256K
  ram : org = 0x40000000, l = 4M
  }
</PRE>

<P>
Once you have defined a region of memory named <VAR>mem</VAR>, you can direct
specific output sections there by using a command ending in
<SAMP>`&#62;<VAR>mem</VAR>'</SAMP> within the <CODE>SECTIONS</CODE> command (see section <A HREF="ld.html#SEC20">Optional Section Attributes</A>).  If the combined output sections directed to a region are too
big for the region, the linker will issue an error message.

</P>


<H2><A NAME="SEC16" HREF="ld_toc.html#TOC16">Specifying Output Sections</A></H2>

<P>
<A NAME="IDX204"></A>
The <CODE>SECTIONS</CODE> command controls exactly where input sections are
placed into output sections, their order in the output file, and to
which output sections they are allocated.

</P>
<P>
You may use at most one <CODE>SECTIONS</CODE> command in a script file,
but you can have as many statements within it as you wish.  Statements
within the <CODE>SECTIONS</CODE> command can do one of three things:

</P>

<UL>
<LI>

define the entry point;

<LI>

assign a value to a symbol;

<LI>

describe the placement of a named output section, and which input
sections go into it.
</UL>

<P>
You can also use the first two operations--defining the entry point and
defining symbols--outside the <CODE>SECTIONS</CODE> command: see section <A HREF="ld.html#SEC22">The Entry Point</A>, and see section <A HREF="ld.html#SEC13">Assignment: Defining Symbols</A>.  They are permitted here as well for
your convenience in reading the script, so that symbols and the entry
point can be defined at meaningful points in your output-file layout.

</P>
<P>
If you do not use a <CODE>SECTIONS</CODE> command, the linker places each input
section into an identically named output section in the order that the
sections are first encountered in the input files.  If all input sections
are present in the first file, for example, the order of sections in the
output file will match the order in the first input file.

</P>



<H3><A NAME="SEC17" HREF="ld_toc.html#TOC17">Section Definitions</A></H3>
<P>
<A NAME="IDX205"></A>
The most frequently used statement in the <CODE>SECTIONS</CODE> command is
the <EM>section definition</EM>, which specifies the
properties of an output section: its location, alignment, contents,
fill pattern, and target memory region.  Most of
these specifications are optional; the simplest form of a section
definition is

<PRE>
SECTIONS { ...
  <VAR>secname</VAR> : {
    <VAR>contents</VAR>
  }
... }
</PRE>

<P>
<A NAME="IDX206"></A>
<VAR>secname</VAR> is the name of the output section, and <VAR>contents</VAR> a
specification of what goes there--for example, a list of input files or
sections of input files (see section <A HREF="ld.html#SEC18">Section Placement</A>).  As you might
assume, the whitespace shown is optional.  You do need the colon
<SAMP>`:'</SAMP> and the braces <SAMP>`{}'</SAMP>, however.

</P>
<P>
<VAR>secname</VAR> must meet the constraints of your output format.  In
formats which only support a limited number of sections, such as
<CODE>a.out</CODE>, the name must be one of the names supported by the format
(<CODE>a.out</CODE>, for example, allows only <CODE>.text</CODE>, <CODE>.data</CODE> or
<CODE>.bss</CODE>). If the output format supports any number of sections, but
with numbers and not names (as is the case for Oasys), the name should be
supplied as a quoted numeric string.  A section name may consist of any
sequence of characters, but any name which does not conform to the standard
<CODE>ld</CODE> symbol name syntax must be quoted.
See section <A HREF="ld.html#SEC9">Symbol Names</A>.

</P>
<P>
The linker will not create output sections which do not have any
contents.  This is for convenience when referring to input sections that
may or may not exist.  For example,

<PRE>
.foo { *(.foo) }
</PRE>

<P>
will only create a <SAMP>`.foo'</SAMP> section in the output file if there is a
<SAMP>`.foo'</SAMP> section in at least one input file.

</P>


<H3><A NAME="SEC18" HREF="ld_toc.html#TOC18">Section Placement</A></H3>

<P>
<A NAME="IDX207"></A>
In a section definition, you can specify the contents of an output
section by listing particular input files, by listing particular
input-file sections, or by a combination of the two.  You can also place
arbitrary data in the section, and define symbols relative to the
beginning of the section.

</P>
<P>
The <VAR>contents</VAR> of a section definition may include any of the
following kinds of statement.  You can include as many of these as you
like in a single section definition, separated from one another by
whitespace. 

</P>
<DL COMPACT>

<DT><CODE><VAR>filename</VAR></CODE>
<DD>
<A NAME="IDX208"></A>
 <A NAME="IDX209"></A>
 <A NAME="IDX210"></A>
 
You may simply name a particular input file to be placed in the current
output section; <EM>all</EM> sections from that file are placed in the
current section definition.  If the file name has already been mentioned
in another section definition, with an explicit section name list, then
only those sections which have not yet been allocated are used.

To specify a list of particular files by name:

<PRE>
.data : { afile.o bfile.o cfile.o }
</PRE>

The example also illustrates that multiple statements can be included in
the contents of a section definition, since each file name is a separate
statement. 

<A NAME="IDX211"></A>
<A NAME="IDX212"></A>
<DT><CODE><VAR>filename</VAR>( <VAR>section</VAR> )</CODE>
<DD>
<DT><CODE><VAR>filename</VAR>( <VAR>section</VAR>, <VAR>section</VAR>, ... )</CODE>
<DD>
<DT><CODE><VAR>filename</VAR>( <VAR>section</VAR> <VAR>section</VAR> ... )</CODE>
<DD>
You can name one or more sections from your input files, for
insertion in the current output section.  If you wish to specify a list
of input-file sections inside the parentheses, you may separate the
section names by either commas or whitespace.

<A NAME="IDX213"></A>
<A NAME="IDX214"></A>
<DT><CODE>* (<VAR>section</VAR>)</CODE>
<DD>
<DT><CODE>* (<VAR>section</VAR>, <VAR>section</VAR>, ...)</CODE>
<DD>
<DT><CODE>* (<VAR>section</VAR> <VAR>section</VAR> ...)</CODE>
<DD>
Instead of explicitly naming particular input files in a link control
script, you can refer to <EM>all</EM> files from the <CODE>ld</CODE> command
line: use <SAMP>`*'</SAMP> instead of a particular file name before the
parenthesized input-file section list.  

If you have already explicitly included some files by name, <SAMP>`*'</SAMP>
refers to all <EM>remaining</EM> files--those whose places in the output
file have not yet been defined.

For example, to copy sections <CODE>1</CODE> through <CODE>4</CODE> from an Oasys file
into the <CODE>.text</CODE> section of an <CODE>a.out</CODE> file, and sections <CODE>13</CODE>
and <CODE>14</CODE> into the <CODE>.data</CODE> section:

<PRE>
SECTIONS {
  .text :{
    *("1" "2" "3" "4")
  }
  
  .data :{
    *("13" "14")
  }
}
</PRE>

<A NAME="IDX215"></A>
<SAMP>`[ <VAR>section</VAR> ... ]'</SAMP> used to be accepted as an alternate way
to specify named sections from all unallocated input files.  Because
some operating systems (VMS) allow brackets in file names, that notation
is no longer supported.

<A NAME="IDX216"></A>
<A NAME="IDX217"></A>
<A NAME="IDX218"></A>
<DT><CODE><VAR>filename</VAR><CODE>( COMMON )</CODE></CODE>
<DD>
<DT><CODE>*( COMMON )</CODE>
<DD>
Specify where in your output file to place uninitialized data
with this notation.  <CODE>*(COMMON)</CODE> by itself refers to all
uninitialized data from all input files (so far as it is not yet
allocated); <VAR>filename</VAR><CODE>(COMMON)</CODE> refers to uninitialized data
from a particular file.  Both are special cases of the general
mechanisms for specifying where to place input-file sections:
<CODE>ld</CODE> permits you to refer to uninitialized data as if it
were in an input-file section named <CODE>COMMON</CODE>, regardless of the
input file's format.
</DL>

<P>
For example, the following command script arranges the output file into
three consecutive sections, named <CODE>.text</CODE>, <CODE>.data</CODE>, and
<CODE>.bss</CODE>, taking the input for each from the correspondingly named
sectio