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| <h3 class="section">4.7 Parameters</h3> |
| |
| <p>Formal parameters to a function are represented by a stab (or sometimes |
| two; see below) for each parameter. The stabs are in the order in which |
| the debugger should print the parameters (i.e., the order in which the |
| parameters are declared in the source file). The exact form of the stab |
| depends on how the parameter is being passed. |
| |
| <p><a name="index-N_005fPSYM-44"></a><a name="index-C_005fPSYM-45"></a>Parameters passed on the stack use the symbol descriptor ‘<samp><span class="samp">p</span></samp>’ and |
| the <code>N_PSYM</code> symbol type (or <code>C_PSYM</code> for XCOFF). The value |
| of the symbol is an offset used to locate the parameter on the stack; |
| its exact meaning is machine-dependent, but on most machines it is an |
| offset from the frame pointer. |
| |
| <p>As a simple example, the code: |
| |
| <pre class="example"> main (argc, argv) |
| int argc; |
| char **argv; |
| </pre> |
| <p>produces the stabs: |
| |
| <pre class="example"> .stabs "main:F1",36,0,0,_main # <span class="roman">36 is N_FUN</span> |
| .stabs "argc:p1",160,0,0,68 # <span class="roman">160 is N_PSYM</span> |
| .stabs "argv:p20=*21=*2",160,0,0,72 |
| </pre> |
| <p>The type definition of <code>argv</code> is interesting because it contains |
| several type definitions. Type 21 is pointer to type 2 (char) and |
| <code>argv</code> (type 20) is pointer to type 21. |
| |
| <!-- FIXME: figure out what these mean and describe them coherently. --> |
| <p>The following symbol descriptors are also said to go with <code>N_PSYM</code>. |
| The value of the symbol is said to be an offset from the argument |
| pointer (I'm not sure whether this is true or not). |
| |
| <pre class="example"> pP (<<??>>) |
| pF Fortran function parameter |
| X (function result variable) |
| </pre> |
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