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<title>Symbols In Python - Debugging with GDB</title>
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<a name="Symbols-In-Python"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Symbol-Tables-In-Python.html#Symbol-Tables-In-Python">Symbol Tables In Python</a>,
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Previous: <a rel="previous" accesskey="p" href="Blocks-In-Python.html#Blocks-In-Python">Blocks In Python</a>,
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Up: <a rel="up" accesskey="u" href="Python-API.html#Python-API">Python API</a>
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<h5 class="subsubsection">23.2.2.27 Python representation of Symbols</h5>
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<p><a name="index-symbols-in-python-2299"></a><a name="index-gdb_002eSymbol-2300"></a>
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<span class="sc">gdb</span> represents every variable, function and type as an
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entry in a symbol table. See <a href="Symbols.html#Symbols">Examining the Symbol Table</a>.
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Similarly, Python represents these symbols in <span class="sc">gdb</span> with the
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<code>gdb.Symbol</code> object.
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<p>The following symbol-related functions are available in the <code>gdb</code>
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module:
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<p><a name="index-gdb_002elookup_005fsymbol-2301"></a>
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<div class="defun">
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— Function: <b>gdb.lookup_symbol</b> (<var>name </var><span class="roman">[</span><var>, block </var><span class="roman">[</span><var>, domain</var><span class="roman">]]</span>)<var><a name="index-gdb_002elookup_005fsymbol-2302"></a></var><br>
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<blockquote><p>This function searches for a symbol by name. The search scope can be
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restricted to the parameters defined in the optional domain and block
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arguments.
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<p><var>name</var> is the name of the symbol. It must be a string. The
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optional <var>block</var> argument restricts the search to symbols visible
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in that <var>block</var>. The <var>block</var> argument must be a
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<code>gdb.Block</code> object. If omitted, the block for the current frame
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is used. The optional <var>domain</var> argument restricts
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the search to the domain type. The <var>domain</var> argument must be a
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domain constant defined in the <code>gdb</code> module and described later
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in this chapter.
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<p>The result is a tuple of two elements.
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The first element is a <code>gdb.Symbol</code> object or <code>None</code> if the symbol
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is not found.
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If the symbol is found, the second element is <code>True</code> if the symbol
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is a field of a method's object (e.g., <code>this</code> in C<tt>++</tt>),
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otherwise it is <code>False</code>.
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If the symbol is not found, the second element is <code>False</code>.
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</p></blockquote></div>
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<p><a name="index-gdb_002elookup_005fglobal_005fsymbol-2303"></a>
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<div class="defun">
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— Function: <b>gdb.lookup_global_symbol</b> (<var>name </var><span class="roman">[</span><var>, domain</var><span class="roman">]</span>)<var><a name="index-gdb_002elookup_005fglobal_005fsymbol-2304"></a></var><br>
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<blockquote><p>This function searches for a global symbol by name.
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The search scope can be restricted to by the domain argument.
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<p><var>name</var> is the name of the symbol. It must be a string.
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The optional <var>domain</var> argument restricts the search to the domain type.
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The <var>domain</var> argument must be a domain constant defined in the <code>gdb</code>
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module and described later in this chapter.
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<p>The result is a <code>gdb.Symbol</code> object or <code>None</code> if the symbol
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is not found.
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</p></blockquote></div>
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<p>A <code>gdb.Symbol</code> object has the following attributes:
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<div class="defun">
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— Variable: <b>Symbol.type</b><var><a name="index-Symbol_002etype-2305"></a></var><br>
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<blockquote><p>The type of the symbol or <code>None</code> if no type is recorded.
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This attribute is represented as a <code>gdb.Type</code> object.
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See <a href="Types-In-Python.html#Types-In-Python">Types In Python</a>. This attribute is not writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.symtab</b><var><a name="index-Symbol_002esymtab-2306"></a></var><br>
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<blockquote><p>The symbol table in which the symbol appears. This attribute is
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represented as a <code>gdb.Symtab</code> object. See <a href="Symbol-Tables-In-Python.html#Symbol-Tables-In-Python">Symbol Tables In Python</a>. This attribute is not writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.line</b><var><a name="index-Symbol_002eline-2307"></a></var><br>
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<blockquote><p>The line number in the source code at which the symbol was defined.
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This is an integer.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.name</b><var><a name="index-Symbol_002ename-2308"></a></var><br>
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<blockquote><p>The name of the symbol as a string. This attribute is not writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.linkage_name</b><var><a name="index-Symbol_002elinkage_005fname-2309"></a></var><br>
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<blockquote><p>The name of the symbol, as used by the linker (i.e., may be mangled).
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This attribute is not writable.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.print_name</b><var><a name="index-Symbol_002eprint_005fname-2310"></a></var><br>
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<blockquote><p>The name of the symbol in a form suitable for output. This is either
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<code>name</code> or <code>linkage_name</code>, depending on whether the user
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asked <span class="sc">gdb</span> to display demangled or mangled names.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.addr_class</b><var><a name="index-Symbol_002eaddr_005fclass-2311"></a></var><br>
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<blockquote><p>The address class of the symbol. This classifies how to find the value
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of a symbol. Each address class is a constant defined in the
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<code>gdb</code> module and described later in this chapter.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.needs_frame</b><var><a name="index-Symbol_002eneeds_005fframe-2312"></a></var><br>
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<blockquote><p>This is <code>True</code> if evaluating this symbol's value requires a frame
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(see <a href="Frames-In-Python.html#Frames-In-Python">Frames In Python</a>) and <code>False</code> otherwise. Typically,
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local variables will require a frame, but other symbols will not.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.is_argument</b><var><a name="index-Symbol_002eis_005fargument-2313"></a></var><br>
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<blockquote><p><code>True</code> if the symbol is an argument of a function.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.is_constant</b><var><a name="index-Symbol_002eis_005fconstant-2314"></a></var><br>
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<blockquote><p><code>True</code> if the symbol is a constant.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.is_function</b><var><a name="index-Symbol_002eis_005ffunction-2315"></a></var><br>
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<blockquote><p><code>True</code> if the symbol is a function or a method.
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</p></blockquote></div>
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<div class="defun">
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— Variable: <b>Symbol.is_variable</b><var><a name="index-Symbol_002eis_005fvariable-2316"></a></var><br>
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<blockquote><p><code>True</code> if the symbol is a variable.
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</p></blockquote></div>
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<p>A <code>gdb.Symbol</code> object has the following methods:
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<div class="defun">
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— Function: <b>Symbol.is_valid</b> ()<var><a name="index-Symbol_002eis_005fvalid-2317"></a></var><br>
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<blockquote><p>Returns <code>True</code> if the <code>gdb.Symbol</code> object is valid,
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<code>False</code> if not. A <code>gdb.Symbol</code> object can become invalid if
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the symbol it refers to does not exist in <span class="sc">gdb</span> any longer.
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All other <code>gdb.Symbol</code> methods will throw an exception if it is
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invalid at the time the method is called.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Symbol.value</b> (<span class="roman">[</span><var>frame</var><span class="roman">]</span>)<var><a name="index-Symbol_002evalue-2318"></a></var><br>
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<blockquote><p>Compute the value of the symbol, as a <code>gdb.Value</code>. For
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functions, this computes the address of the function, cast to the
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appropriate type. If the symbol requires a frame in order to compute
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its value, then <var>frame</var> must be given. If <var>frame</var> is not
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given, or if <var>frame</var> is invalid, then this method will throw an
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exception.
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</p></blockquote></div>
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<p>The available domain categories in <code>gdb.Symbol</code> are represented
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as constants in the <code>gdb</code> module:
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<a name="index-SYMBOL_005fUNDEF_005fDOMAIN-2319"></a>
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<dl><dt><code>gdb.SYMBOL_UNDEF_DOMAIN</code><a name="index-gdb_002eSYMBOL_005fUNDEF_005fDOMAIN-2320"></a><dd>This is used when a domain has not been discovered or none of the
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following domains apply. This usually indicates an error either
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in the symbol information or in <span class="sc">gdb</span>'s handling of symbols.
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<p><a name="index-SYMBOL_005fVAR_005fDOMAIN-2321"></a><br><dt><code>gdb.SYMBOL_VAR_DOMAIN</code><a name="index-gdb_002eSYMBOL_005fVAR_005fDOMAIN-2322"></a><dd>This domain contains variables, function names, typedef names and enum
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type values.
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<p><a name="index-SYMBOL_005fSTRUCT_005fDOMAIN-2323"></a><br><dt><code>gdb.SYMBOL_STRUCT_DOMAIN</code><a name="index-gdb_002eSYMBOL_005fSTRUCT_005fDOMAIN-2324"></a><dd>This domain holds struct, union and enum type names.
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<p><a name="index-SYMBOL_005fLABEL_005fDOMAIN-2325"></a><br><dt><code>gdb.SYMBOL_LABEL_DOMAIN</code><a name="index-gdb_002eSYMBOL_005fLABEL_005fDOMAIN-2326"></a><dd>This domain contains names of labels (for gotos).
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<p><a name="index-SYMBOL_005fMODULE_005fDOMAIN-2327"></a><br><dt><code>gdb.SYMBOL_MODULE_DOMAIN</code><a name="index-gdb_002eSYMBOL_005fMODULE_005fDOMAIN-2328"></a><dd>This domain contains names of Fortran module types.
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<p><a name="index-SYMBOL_005fCOMMON_005fBLOCK_005fDOMAIN-2329"></a><br><dt><code>gdb.SYMBOL_COMMON_BLOCK_DOMAIN</code><a name="index-gdb_002eSYMBOL_005fCOMMON_005fBLOCK_005fDOMAIN-2330"></a><dd>This domain contains names of Fortran common blocks.
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</dl>
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<p>The available address class categories in <code>gdb.Symbol</code> are represented
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as constants in the <code>gdb</code> module:
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<a name="index-SYMBOL_005fLOC_005fUNDEF-2331"></a>
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<dl><dt><code>gdb.SYMBOL_LOC_UNDEF</code><a name="index-gdb_002eSYMBOL_005fLOC_005fUNDEF-2332"></a><dd>If this is returned by address class, it indicates an error either in
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the symbol information or in <span class="sc">gdb</span>'s handling of symbols.
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<p><a name="index-SYMBOL_005fLOC_005fCONST-2333"></a><br><dt><code>gdb.SYMBOL_LOC_CONST</code><a name="index-gdb_002eSYMBOL_005fLOC_005fCONST-2334"></a><dd>Value is constant int.
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<p><a name="index-SYMBOL_005fLOC_005fSTATIC-2335"></a><br><dt><code>gdb.SYMBOL_LOC_STATIC</code><a name="index-gdb_002eSYMBOL_005fLOC_005fSTATIC-2336"></a><dd>Value is at a fixed address.
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<p><a name="index-SYMBOL_005fLOC_005fREGISTER-2337"></a><br><dt><code>gdb.SYMBOL_LOC_REGISTER</code><a name="index-gdb_002eSYMBOL_005fLOC_005fREGISTER-2338"></a><dd>Value is in a register.
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<p><a name="index-SYMBOL_005fLOC_005fARG-2339"></a><br><dt><code>gdb.SYMBOL_LOC_ARG</code><a name="index-gdb_002eSYMBOL_005fLOC_005fARG-2340"></a><dd>Value is an argument. This value is at the offset stored within the
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symbol inside the frame's argument list.
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<p><a name="index-SYMBOL_005fLOC_005fREF_005fARG-2341"></a><br><dt><code>gdb.SYMBOL_LOC_REF_ARG</code><a name="index-gdb_002eSYMBOL_005fLOC_005fREF_005fARG-2342"></a><dd>Value address is stored in the frame's argument list. Just like
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<code>LOC_ARG</code> except that the value's address is stored at the
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offset, not the value itself.
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<p><a name="index-SYMBOL_005fLOC_005fREGPARM_005fADDR-2343"></a><br><dt><code>gdb.SYMBOL_LOC_REGPARM_ADDR</code><a name="index-gdb_002eSYMBOL_005fLOC_005fREGPARM_005fADDR-2344"></a><dd>Value is a specified register. Just like <code>LOC_REGISTER</code> except
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the register holds the address of the argument instead of the argument
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itself.
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<p><a name="index-SYMBOL_005fLOC_005fLOCAL-2345"></a><br><dt><code>gdb.SYMBOL_LOC_LOCAL</code><a name="index-gdb_002eSYMBOL_005fLOC_005fLOCAL-2346"></a><dd>Value is a local variable.
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<p><a name="index-SYMBOL_005fLOC_005fTYPEDEF-2347"></a><br><dt><code>gdb.SYMBOL_LOC_TYPEDEF</code><a name="index-gdb_002eSYMBOL_005fLOC_005fTYPEDEF-2348"></a><dd>Value not used. Symbols in the domain <code>SYMBOL_STRUCT_DOMAIN</code> all
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have this class.
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<p><a name="index-SYMBOL_005fLOC_005fBLOCK-2349"></a><br><dt><code>gdb.SYMBOL_LOC_BLOCK</code><a name="index-gdb_002eSYMBOL_005fLOC_005fBLOCK-2350"></a><dd>Value is a block.
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<p><a name="index-SYMBOL_005fLOC_005fCONST_005fBYTES-2351"></a><br><dt><code>gdb.SYMBOL_LOC_CONST_BYTES</code><a name="index-gdb_002eSYMBOL_005fLOC_005fCONST_005fBYTES-2352"></a><dd>Value is a byte-sequence.
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<p><a name="index-SYMBOL_005fLOC_005fUNRESOLVED-2353"></a><br><dt><code>gdb.SYMBOL_LOC_UNRESOLVED</code><a name="index-gdb_002eSYMBOL_005fLOC_005fUNRESOLVED-2354"></a><dd>Value is at a fixed address, but the address of the variable has to be
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determined from the minimal symbol table whenever the variable is
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referenced.
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<p><a name="index-SYMBOL_005fLOC_005fOPTIMIZED_005fOUT-2355"></a><br><dt><code>gdb.SYMBOL_LOC_OPTIMIZED_OUT</code><a name="index-gdb_002eSYMBOL_005fLOC_005fOPTIMIZED_005fOUT-2356"></a><dd>The value does not actually exist in the program.
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<p><a name="index-SYMBOL_005fLOC_005fCOMPUTED-2357"></a><br><dt><code>gdb.SYMBOL_LOC_COMPUTED</code><a name="index-gdb_002eSYMBOL_005fLOC_005fCOMPUTED-2358"></a><dd>The value's address is a computed location.
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<p><a name="index-SYMBOL_005fLOC_005fCOMPUTED-2359"></a><br><dt><code>gdb.SYMBOL_LOC_COMPUTED</code><a name="index-gdb_002eSYMBOL_005fLOC_005fCOMPUTED-2360"></a><dd>The value's address is a symbol. This is only used for Fortran common
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blocks.
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</dl>
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</body></html>
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