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| <h4 class="subsection">6.56.18 SH Built-in Functions</h4> |
| |
| <p>The following built-in functions are supported on the SH1, SH2, SH3 and SH4 |
| families of processors: |
| |
| <div class="defun"> |
| — Built-in Function: void <b>__builtin_set_thread_pointer</b> (<var>void *ptr</var>)<var><a name="index-g_t_005f_005fbuiltin_005fset_005fthread_005fpointer-3449"></a></var><br> |
| <blockquote><p>Sets the ‘<samp><span class="samp">GBR</span></samp>’ register to the specified value <var>ptr</var>. This is usually |
| used by system code that manages threads and execution contexts. The compiler |
| normally does not generate code that modifies the contents of ‘<samp><span class="samp">GBR</span></samp>’ and |
| thus the value is preserved across function calls. Changing the ‘<samp><span class="samp">GBR</span></samp>’ |
| value in user code must be done with caution, since the compiler might use |
| ‘<samp><span class="samp">GBR</span></samp>’ in order to access thread local variables. |
| |
| </blockquote></div> |
| |
| <div class="defun"> |
| — Built-in Function: void * <b>__builtin_thread_pointer</b> (<var>void</var>)<var><a name="index-g_t_005f_005fbuiltin_005fthread_005fpointer-3450"></a></var><br> |
| <blockquote><p>Returns the value that is currently set in the ‘<samp><span class="samp">GBR</span></samp>’ register. |
| Memory loads and stores that use the thread pointer as a base address are |
| turned into ‘<samp><span class="samp">GBR</span></samp>’ based displacement loads and stores, if possible. |
| For example: |
| <pre class="smallexample"> struct my_tcb |
| { |
| int a, b, c, d, e; |
| }; |
| |
| int get_tcb_value (void) |
| { |
| // Generate ‘<samp><span class="samp">mov.l @(8,gbr),r0</span></samp>’ instruction |
| return ((my_tcb*)__builtin_thread_pointer ())->c; |
| } |
| |
| </pre> |
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