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| <h3 class="section">7.94 <code>.symver</code></h3> |
| |
| <p><a name="index-g_t_0040code_007bsymver_007d-directive-495"></a><a name="index-symbol-versioning-496"></a><a name="index-versions-of-symbols-497"></a>Use the <code>.symver</code> directive to bind symbols to specific version nodes |
| within a source file. This is only supported on ELF platforms, and is |
| typically used when assembling files to be linked into a shared library. |
| There are cases where it may make sense to use this in objects to be bound |
| into an application itself so as to override a versioned symbol from a |
| shared library. |
| |
| <p>For ELF targets, the <code>.symver</code> directive can be used like this: |
| <pre class="smallexample"> .symver <var>name</var>, <var>name2@nodename</var> |
| </pre> |
| <p>If the symbol <var>name</var> is defined within the file |
| being assembled, the <code>.symver</code> directive effectively creates a symbol |
| alias with the name <var>name2@nodename</var>, and in fact the main reason that we |
| just don't try and create a regular alias is that the <var>@</var> character isn't |
| permitted in symbol names. The <var>name2</var> part of the name is the actual name |
| of the symbol by which it will be externally referenced. The name <var>name</var> |
| itself is merely a name of convenience that is used so that it is possible to |
| have definitions for multiple versions of a function within a single source |
| file, and so that the compiler can unambiguously know which version of a |
| function is being mentioned. The <var>nodename</var> portion of the alias should be |
| the name of a node specified in the version script supplied to the linker when |
| building a shared library. If you are attempting to override a versioned |
| symbol from a shared library, then <var>nodename</var> should correspond to the |
| nodename of the symbol you are trying to override. |
| |
| <p>If the symbol <var>name</var> is not defined within the file being assembled, all |
| references to <var>name</var> will be changed to <var>name2@nodename</var>. If no |
| reference to <var>name</var> is made, <var>name2@nodename</var> will be removed from the |
| symbol table. |
| |
| <p>Another usage of the <code>.symver</code> directive is: |
| <pre class="smallexample"> .symver <var>name</var>, <var>name2@@nodename</var> |
| </pre> |
| <p>In this case, the symbol <var>name</var> must exist and be defined within |
| the file being assembled. It is similar to <var>name2@nodename</var>. The |
| difference is <var>name2@@nodename</var> will also be used to resolve |
| references to <var>name2</var> by the linker. |
| |
| <p>The third usage of the <code>.symver</code> directive is: |
| <pre class="smallexample"> .symver <var>name</var>, <var>name2@@@nodename</var> |
| </pre> |
| <p>When <var>name</var> is not defined within the |
| file being assembled, it is treated as <var>name2@nodename</var>. When |
| <var>name</var> is defined within the file being assembled, the symbol |
| name, <var>name</var>, will be changed to <var>name2@@nodename</var>. |
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