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| <a name="Getting-the-Return-or-Frame-Address-of-a-Function"></a> |
| <h3 class="section">6.48 Getting the Return or Frame Address of a Function</h3> |
| |
| <p>These functions may be used to get information about the callers of a |
| function. |
| </p> |
| <dl> |
| <dt><a name="index-_005f_005fbuiltin_005freturn_005faddress"></a>Built-in Function: <em>void *</em> <strong>__builtin_return_address</strong> <em>(unsigned int <var>level</var>)</em></dt> |
| <dd><p>This function returns the return address of the current function, or of |
| one of its callers. The <var>level</var> argument is number of frames to |
| scan up the call stack. A value of <code>0</code> yields the return address |
| of the current function, a value of <code>1</code> yields the return address |
| of the caller of the current function, and so forth. When inlining |
| the expected behavior is that the function returns the address of |
| the function that is returned to. To work around this behavior use |
| the <code>noinline</code> function attribute. |
| </p> |
| <p>The <var>level</var> argument must be a constant integer. |
| </p> |
| <p>On some machines it may be impossible to determine the return address of |
| any function other than the current one; in such cases, or when the top |
| of the stack has been reached, this function returns <code>0</code> or a |
| random value. In addition, <code>__builtin_frame_address</code> may be used |
| to determine if the top of the stack has been reached. |
| </p> |
| <p>Additional post-processing of the returned value may be needed, see |
| <code>__builtin_extract_return_addr</code>. |
| </p> |
| <p>This function should only be used with a nonzero argument for debugging |
| purposes. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-_005f_005fbuiltin_005fextract_005freturn_005faddr"></a>Built-in Function: <em>void *</em> <strong>__builtin_extract_return_addr</strong> <em>(void *<var>addr</var>)</em></dt> |
| <dd><p>The address as returned by <code>__builtin_return_address</code> may have to be fed |
| through this function to get the actual encoded address. For example, on the |
| 31-bit S/390 platform the highest bit has to be masked out, or on SPARC |
| platforms an offset has to be added for the true next instruction to be |
| executed. |
| </p> |
| <p>If no fixup is needed, this function simply passes through <var>addr</var>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-_005f_005fbuiltin_005ffrob_005freturn_005faddress"></a>Built-in Function: <em>void *</em> <strong>__builtin_frob_return_address</strong> <em>(void *<var>addr</var>)</em></dt> |
| <dd><p>This function does the reverse of <code>__builtin_extract_return_addr</code>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-_005f_005fbuiltin_005fframe_005faddress"></a>Built-in Function: <em>void *</em> <strong>__builtin_frame_address</strong> <em>(unsigned int <var>level</var>)</em></dt> |
| <dd><p>This function is similar to <code>__builtin_return_address</code>, but it |
| returns the address of the function frame rather than the return address |
| of the function. Calling <code>__builtin_frame_address</code> with a value of |
| <code>0</code> yields the frame address of the current function, a value of |
| <code>1</code> yields the frame address of the caller of the current function, |
| and so forth. |
| </p> |
| <p>The frame is the area on the stack that holds local variables and saved |
| registers. The frame address is normally the address of the first word |
| pushed on to the stack by the function. However, the exact definition |
| depends upon the processor and the calling convention. If the processor |
| has a dedicated frame pointer register, and the function has a frame, |
| then <code>__builtin_frame_address</code> returns the value of the frame |
| pointer register. |
| </p> |
| <p>On some machines it may be impossible to determine the frame address of |
| any function other than the current one; in such cases, or when the top |
| of the stack has been reached, this function returns <code>0</code> if |
| the first frame pointer is properly initialized by the startup code. |
| </p> |
| <p>This function should only be used with a nonzero argument for debugging |
| purposes. |
| </p></dd></dl> |
| |
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