wisejohn
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buildtool


			
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<a name="Section"></a>
<div class="header">
<p>
Next: <a href="Set.html#Set" accesskey="n" rel="next">Set</a>, Previous: <a href="Scl.html#Scl" accesskey="p" rel="prev">Scl</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="g_t_002esection-name"></a>
<h3 class="section">7.84 <code>.section <var>name</var></code></h3>

<a name="index-named-section"></a>
<p>Use the <code>.section</code> directive to assemble the following code into a section
named <var>name</var>.
</p>
<p>This directive is only supported for targets that actually support arbitrarily
named sections; on <code>a.out</code> targets, for example, it is not accepted, even
with a standard <code>a.out</code> section name.
</p>
<a name="COFF-Version"></a>
<h4 class="subheading">COFF Version</h4>

<a name="index-section-directive-_0028COFF-version_0029"></a>
<p>For COFF targets, the <code>.section</code> directive is used in one of the following
ways:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var>[, &quot;<var>flags</var>&quot;]
.section <var>name</var>[, <var>subsection</var>]
</pre></div>

<p>If the optional argument is quoted, it is taken as flags to use for the
section.  Each flag is a single character.  The following flags are recognized:
</p>
<dl compact="compact">
<dt><code>b</code></dt>
<dd><p>bss section (uninitialized data)
</p></dd>
<dt><code>n</code></dt>
<dd><p>section is not loaded
</p></dd>
<dt><code>w</code></dt>
<dd><p>writable section
</p></dd>
<dt><code>d</code></dt>
<dd><p>data section
</p></dd>
<dt><code>e</code></dt>
<dd><p>exclude section from linking
</p></dd>
<dt><code>r</code></dt>
<dd><p>read-only section
</p></dd>
<dt><code>x</code></dt>
<dd><p>executable section
</p></dd>
<dt><code>s</code></dt>
<dd><p>shared section (meaningful for PE targets)
</p></dd>
<dt><code>a</code></dt>
<dd><p>ignored.  (For compatibility with the ELF version)
</p></dd>
<dt><code>y</code></dt>
<dd><p>section is not readable (meaningful for PE targets)
</p></dd>
<dt><code>0-9</code></dt>
<dd><p>single-digit power-of-two section alignment (GNU extension)
</p></dd>
</dl>

<p>If no flags are specified, the default flags depend upon the section name.  If
the section name is not recognized, the default will be for the section to be
loaded and writable.  Note the <code>n</code> and <code>w</code> flags remove attributes
from the section, rather than adding them, so if they are used on their own it
will be as if no flags had been specified at all.
</p>
<p>If the optional argument to the <code>.section</code> directive is not quoted, it is
taken as a subsection number (see <a href="Sub_002dSections.html#Sub_002dSections">Sub-Sections</a>).
</p>
<a name="ELF-Version"></a>
<h4 class="subheading">ELF Version</h4>

<a name="index-Section-Stack-3"></a>
<p>This is one of the ELF section stack manipulation directives.  The others are
<code>.subsection</code> (see <a href="SubSection.html#SubSection">SubSection</a>), <code>.pushsection</code>
(see <a href="PushSection.html#PushSection">PushSection</a>), <code>.popsection</code> (see <a href="PopSection.html#PopSection">PopSection</a>), and
<code>.previous</code> (see <a href="Previous.html#Previous">Previous</a>).
</p>
<a name="index-section-directive-_0028ELF-version_0029"></a>
<p>For ELF targets, the <code>.section</code> directive is used like this:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var> [, &quot;<var>flags</var>&quot;[, @<var>type</var>[,<var>flag_specific_arguments</var>]]]
</pre></div>

<a name="Section-Name-Substitutions"></a><a name="index-_002d_002dsectname_002dsubst"></a>
<a name="index-section-name-substitution"></a>
<p>If the &lsquo;<samp>--sectname-subst</samp>&rsquo; command-line option is provided, the <var>name</var>
argument may contain a substitution sequence. Only <code>%S</code> is supported
at the moment, and substitutes the current section name. For example:
</p>
<div class="smallexample">
<pre class="smallexample">.macro exception_code
.section %S.exception
[exception code here]
.previous
.endm

.text
[code]
exception_code
[...]

.section .init
[init code]
exception_code
[...]
</pre></div>

<p>The two <code>exception_code</code> invocations above would create the
<code>.text.exception</code> and <code>.init.exception</code> sections respectively.
This is useful e.g. to discriminate between ancillary sections that are
tied to setup code to be discarded after use from ancillary sections that
need to stay resident without having to define multiple <code>exception_code</code>
macros just for that purpose.
</p>
<p>The optional <var>flags</var> argument is a quoted string which may contain any
combination of the following characters:
</p>
<dl compact="compact">
<dt><code>a</code></dt>
<dd><p>section is allocatable
</p></dd>
<dt><code>d</code></dt>
<dd><p>section is a GNU_MBIND section
</p></dd>
<dt><code>e</code></dt>
<dd><p>section is excluded from executable and shared library.
</p></dd>
<dt><code>o</code></dt>
<dd><p>section references a symbol defined in another section (the linked-to
section) in the same file.
</p></dd>
<dt><code>w</code></dt>
<dd><p>section is writable
</p></dd>
<dt><code>x</code></dt>
<dd><p>section is executable
</p></dd>
<dt><code>M</code></dt>
<dd><p>section is mergeable
</p></dd>
<dt><code>S</code></dt>
<dd><p>section contains zero terminated strings
</p></dd>
<dt><code>G</code></dt>
<dd><p>section is a member of a section group
</p></dd>
<dt><code>T</code></dt>
<dd><p>section is used for thread-local-storage
</p></dd>
<dt><code>?</code></dt>
<dd><p>section is a member of the previously-current section&rsquo;s group, if any
</p></dd>
<dt><code>R</code></dt>
<dd><p>retained section (apply SHF_GNU_RETAIN to prevent linker garbage
collection, GNU ELF extension)
</p></dd>
<dt><code><code>&lt;number&gt;</code></code></dt>
<dd><p>a numeric value indicating the bits to be set in the ELF section header&rsquo;s flags
field.  Note - if one or more of the alphabetic characters described above is
also included in the flags field, their bit values will be ORed into the
resulting value.
</p></dd>
<dt><code><code>&lt;target specific&gt;</code></code></dt>
<dd><p>some targets extend this list with their own flag characters
</p></dd>
</dl>

<p>Note - once a section&rsquo;s flags have been set they cannot be changed.  There are
a few exceptions to this rule however.  Processor and application specific
flags can be added to an already defined section.  The <code>.interp</code>,
<code>.strtab</code> and <code>.symtab</code> sections can have the allocate flag
(<code>a</code>) set after they are initially defined, and the <code>.note-GNU-stack</code>
section may have the executable (<code>x</code>) flag added.  Also note that the
<code>.attach_to_group</code> directive can be used to add a section to a group even
if the section was not originally declared to be part of that group.
</p>
<p>The optional <var>type</var> argument may contain one of the following constants:
</p>
<dl compact="compact">
<dt><code>@progbits</code></dt>
<dd><p>section contains data
</p></dd>
<dt><code>@nobits</code></dt>
<dd><p>section does not contain data (i.e., section only occupies space)
</p></dd>
<dt><code>@note</code></dt>
<dd><p>section contains data which is used by things other than the program
</p></dd>
<dt><code>@init_array</code></dt>
<dd><p>section contains an array of pointers to init functions
</p></dd>
<dt><code>@fini_array</code></dt>
<dd><p>section contains an array of pointers to finish functions
</p></dd>
<dt><code>@preinit_array</code></dt>
<dd><p>section contains an array of pointers to pre-init functions
</p></dd>
<dt><code>@<code>&lt;number&gt;</code></code></dt>
<dd><p>a numeric value to be set as the ELF section header&rsquo;s type field.
</p></dd>
<dt><code>@<code>&lt;target specific&gt;</code></code></dt>
<dd><p>some targets extend this list with their own types
</p></dd>
</dl>

<p>Many targets only support the first three section types.  The type may be
enclosed in double quotes if necessary.
</p>
<p>Note on targets where the <code>@</code> character is the start of a comment (eg
ARM) then another character is used instead.  For example the ARM port uses the
<code>%</code> character.
</p>
<p>Note - some sections, eg <code>.text</code> and <code>.data</code> are considered to be
special and have fixed types.  Any attempt to declare them with a different
type will generate an error from the assembler.
</p>
<p>If <var>flags</var> contains the <code>M</code> symbol then the <var>type</var> argument must
be specified as well as an extra argument&mdash;<var>entsize</var>&mdash;like this:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var> , &quot;<var>flags</var>&quot;M, @<var>type</var>, <var>entsize</var>
</pre></div>

<p>Sections with the <code>M</code> flag but not <code>S</code> flag must contain fixed size
constants, each <var>entsize</var> octets long. Sections with both <code>M</code> and
<code>S</code> must contain zero terminated strings where each character is
<var>entsize</var> bytes long. The linker may remove duplicates within sections with
the same name, same entity size and same flags.  <var>entsize</var> must be an
absolute expression.  For sections with both <code>M</code> and <code>S</code>, a string
which is a suffix of a larger string is considered a duplicate.  Thus
<code>&quot;def&quot;</code> will be merged with <code>&quot;abcdef&quot;</code>;  A reference to the first
<code>&quot;def&quot;</code> will be changed to a reference to <code>&quot;abcdef&quot;+3</code>.
</p>
<p>If <var>flags</var> contains the <code>o</code> flag, then the <var>type</var> argument
must be present along with an additional field like this:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var>,&quot;<var>flags</var>&quot;o,@<var>type</var>,<var>SymbolName</var>|<var>SectionIndex</var>
</pre></div>

<p>The <var>SymbolName</var> field specifies the symbol name which the section
references.  Alternatively a numeric <var>SectionIndex</var> can be provided.  This
is not generally a good idea as section indicies are rarely known at assembly
time, but the facility is provided for testing purposes.  An index of zero is
allowed.  It indicates that the linked-to section has already been discarded.
</p>
<p>Note: If both the <var>M</var> and <var>o</var> flags are present, then the fields
for the Merge flag should come first, like this:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var>,&quot;<var>flags</var>&quot;Mo,@<var>type</var>,<var>entsize</var>,<var>SymbolName</var>
</pre></div>

<p>If <var>flags</var> contains the <code>G</code> symbol then the <var>type</var> argument must
be present along with an additional field like this:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var> , &quot;<var>flags</var>&quot;G, @<var>type</var>, <var>GroupName</var>[, <var>linkage</var>]
</pre></div>

<p>The <var>GroupName</var> field specifies the name of the section group to which this
particular section belongs.  The optional linkage field can contain:
</p>
<dl compact="compact">
<dt><code>comdat</code></dt>
<dd><p>indicates that only one copy of this section should be retained
</p></dd>
<dt><code>.gnu.linkonce</code></dt>
<dd><p>an alias for comdat
</p></dd>
</dl>

<p>Note: if both the <var>M</var> and <var>G</var> flags are present then the fields for
the Merge flag should come first, like this:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var> , &quot;<var>flags</var>&quot;MG, @<var>type</var>, <var>entsize</var>, <var>GroupName</var>[, <var>linkage</var>]
</pre></div>

<p>If both <code>o</code> flag and <code>G</code> flag are present, then the
<var>SymbolName</var> field for <code>o</code> comes first, like this:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var>,&quot;<var>flags</var>&quot;oG,@<var>type</var>,<var>SymbolName</var>,<var>GroupName</var>[,<var>linkage</var>]
</pre></div>

<p>If <var>flags</var> contains the <code>?</code> symbol then it may not also contain the
<code>G</code> symbol and the <var>GroupName</var> or <var>linkage</var> fields should not be
present.  Instead, <code>?</code> says to consider the section that&rsquo;s current before
this directive.  If that section used <code>G</code>, then the new section will use
<code>G</code> with those same <var>GroupName</var> and <var>linkage</var> fields implicitly.
If not, then the <code>?</code> symbol has no effect.
</p>
<p>The optional <var>unique,<code>&lt;number&gt;</code></var> argument must come last.  It
assigns <var><code>&lt;number&gt;</code></var> as a unique section ID to distinguish
different sections with the same section name like these:
</p>
<div class="smallexample">
<pre class="smallexample">.section <var>name</var>,&quot;<var>flags</var>&quot;,@<var>type</var>,<var>unique,<code>&lt;number&gt;</code></var>
.section <var>name</var>,&quot;<var>flags</var>&quot;G,@<var>type</var>,<var>GroupName</var>,[<var>linkage</var>],<var>unique,<code>&lt;number&gt;</code></var>
.section <var>name</var>,&quot;<var>flags</var>&quot;MG,@<var>type</var>,<var>entsize</var>,<var>GroupName</var>[,<var>linkage</var>],<var>unique,<code>&lt;number&gt;</code></var>
</pre></div>

<p>The valid values of <var><code>&lt;number&gt;</code></var> are between 0 and 4294967295.
</p>
<p>If no flags are specified, the default flags depend upon the section name.  If
the section name is not recognized, the default will be for the section to have
none of the above flags: it will not be allocated in memory, nor writable, nor
executable.  The section will contain data.
</p>
<p>For ELF targets, the assembler supports another type of <code>.section</code>
directive for compatibility with the Solaris assembler:
</p>
<div class="smallexample">
<pre class="smallexample">.section &quot;<var>name</var>&quot;[, <var>flags</var>...]
</pre></div>

<p>Note that the section name is quoted.  There may be a sequence of comma
separated flags:
</p>
<dl compact="compact">
<dt><code>#alloc</code></dt>
<dd><p>section is allocatable
</p></dd>
<dt><code>#write</code></dt>
<dd><p>section is writable
</p></dd>
<dt><code>#execinstr</code></dt>
<dd><p>section is executable
</p></dd>
<dt><code>#exclude</code></dt>
<dd><p>section is excluded from executable and shared library.
</p></dd>
<dt><code>#tls</code></dt>
<dd><p>section is used for thread local storage
</p></dd>
</dl>

<p>This directive replaces the current section and subsection.  See the
contents of the gas testsuite directory <code>gas/testsuite/gas/elf</code> for
some examples of how this directive and the other section stack directives
work.
</p>
<hr>
<div class="header">
<p>
Next: <a href="Set.html#Set" accesskey="n" rel="next">Set</a>, Previous: <a href="Scl.html#Scl" accesskey="p" rel="prev">Scl</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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