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| <a name="g_t_002esection-name"></a> |
| <h3 class="section">7.99 <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>[, "<var>flags</var>"] |
| .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> [, "<var>flags</var>"[, @<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 ‘<samp>--sectname-subst</samp>’ 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 anciliary sections that are |
| tied to setup code to be discarded after use from anciliary 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>e</code></dt> |
| <dd><p>section is excluded from executable and shared library. |
| </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’s group, if any |
| </p></dd> |
| </dl> |
| |
| <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> |
| </dl> |
| |
| <p>Many targets only support the first three section types. |
| </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>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—<var>entsize</var>—like this: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">.section <var>name</var> , "<var>flags</var>"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>"def"</code> will be merged with <code>"abcdef"</code>; A reference to the first |
| <code>"def"</code> will be changed to a reference to <code>"abcdef"+3</code>. |
| </p> |
| <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> , "<var>flags</var>"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> , "<var>flags</var>"MG, @<var>type</var>, <var>entsize</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’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>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 "<var>name</var>"[, <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> |
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