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| <title>Debugging with GDB: Symbols In Python</title> |
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| <a name="Symbols-In-Python"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Symbol-Tables-In-Python.html#Symbol-Tables-In-Python" accesskey="n" rel="next">Symbol Tables In Python</a>, Previous: <a href="Blocks-In-Python.html#Blocks-In-Python" accesskey="p" rel="prev">Blocks In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="Python-representation-of-Symbols_002e"></a> |
| <h4 class="subsubsection">23.2.2.26 Python representation of Symbols.</h4> |
| |
| <a name="index-symbols-in-python"></a> |
| <a name="index-gdb_002eSymbol"></a> |
| |
| <p><small>GDB</small> represents every variable, function and type as an |
| entry in a symbol table. See <a href="Symbols.html#Symbols">Examining the Symbol Table</a>. |
| Similarly, Python represents these symbols in <small>GDB</small> with the |
| <code>gdb.Symbol</code> object. |
| </p> |
| <p>The following symbol-related functions are available in the <code>gdb</code> |
| module: |
| </p> |
| <a name="index-gdb_002elookup_005fsymbol"></a> |
| <dl> |
| <dt><a name="index-gdb_002elookup_005fsymbol-1"></a>Function: <strong>gdb.lookup_symbol</strong> <em>(name <span class="roman">[</span>, block <span class="roman">[</span>, domain<span class="roman">]]</span>)</em></dt> |
| <dd><p>This function searches for a symbol by name. The search scope can be |
| restricted to the parameters defined in the optional domain and block |
| arguments. |
| </p> |
| <p><var>name</var> is the name of the symbol. It must be a string. The |
| optional <var>block</var> argument restricts the search to symbols visible |
| in that <var>block</var>. The <var>block</var> argument must be a |
| <code>gdb.Block</code> object. If omitted, the block for the current frame |
| is used. The optional <var>domain</var> argument restricts |
| the search to the domain type. The <var>domain</var> argument must be a |
| domain constant defined in the <code>gdb</code> module and described later |
| in this chapter. |
| </p> |
| <p>The result is a tuple of two elements. |
| The first element is a <code>gdb.Symbol</code> object or <code>None</code> if the symbol |
| is not found. |
| If the symbol is found, the second element is <code>True</code> if the symbol |
| is a field of a method’s object (e.g., <code>this</code> in C<tt>++</tt>), |
| otherwise it is <code>False</code>. |
| If the symbol is not found, the second element is <code>False</code>. |
| </p></dd></dl> |
| |
| <a name="index-gdb_002elookup_005fglobal_005fsymbol"></a> |
| <dl> |
| <dt><a name="index-gdb_002elookup_005fglobal_005fsymbol-1"></a>Function: <strong>gdb.lookup_global_symbol</strong> <em>(name <span class="roman">[</span>, domain<span class="roman">]</span>)</em></dt> |
| <dd><p>This function searches for a global symbol by name. |
| The search scope can be restricted to by the domain argument. |
| </p> |
| <p><var>name</var> is the name of the symbol. It must be a string. |
| The optional <var>domain</var> argument restricts the search to the domain type. |
| The <var>domain</var> argument must be a domain constant defined in the <code>gdb</code> |
| module and described later in this chapter. |
| </p> |
| <p>The result is a <code>gdb.Symbol</code> object or <code>None</code> if the symbol |
| is not found. |
| </p></dd></dl> |
| |
| <p>A <code>gdb.Symbol</code> object has the following attributes: |
| </p> |
| <dl> |
| <dt><a name="index-Symbol_002etype"></a>Variable: <strong>Symbol.type</strong></dt> |
| <dd><p>The type of the symbol or <code>None</code> if no type is recorded. |
| This attribute is represented as a <code>gdb.Type</code> object. |
| See <a href="Types-In-Python.html#Types-In-Python">Types In Python</a>. This attribute is not writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002esymtab"></a>Variable: <strong>Symbol.symtab</strong></dt> |
| <dd><p>The symbol table in which the symbol appears. This attribute is |
| 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. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002eline"></a>Variable: <strong>Symbol.line</strong></dt> |
| <dd><p>The line number in the source code at which the symbol was defined. |
| This is an integer. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002ename"></a>Variable: <strong>Symbol.name</strong></dt> |
| <dd><p>The name of the symbol as a string. This attribute is not writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002elinkage_005fname"></a>Variable: <strong>Symbol.linkage_name</strong></dt> |
| <dd><p>The name of the symbol, as used by the linker (i.e., may be mangled). |
| This attribute is not writable. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002eprint_005fname"></a>Variable: <strong>Symbol.print_name</strong></dt> |
| <dd><p>The name of the symbol in a form suitable for output. This is either |
| <code>name</code> or <code>linkage_name</code>, depending on whether the user |
| asked <small>GDB</small> to display demangled or mangled names. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002eaddr_005fclass"></a>Variable: <strong>Symbol.addr_class</strong></dt> |
| <dd><p>The address class of the symbol. This classifies how to find the value |
| of a symbol. Each address class is a constant defined in the |
| <code>gdb</code> module and described later in this chapter. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002eneeds_005fframe"></a>Variable: <strong>Symbol.needs_frame</strong></dt> |
| <dd><p>This is <code>True</code> if evaluating this symbol’s value requires a frame |
| (see <a href="Frames-In-Python.html#Frames-In-Python">Frames In Python</a>) and <code>False</code> otherwise. Typically, |
| local variables will require a frame, but other symbols will not. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002eis_005fargument"></a>Variable: <strong>Symbol.is_argument</strong></dt> |
| <dd><p><code>True</code> if the symbol is an argument of a function. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002eis_005fconstant"></a>Variable: <strong>Symbol.is_constant</strong></dt> |
| <dd><p><code>True</code> if the symbol is a constant. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002eis_005ffunction"></a>Variable: <strong>Symbol.is_function</strong></dt> |
| <dd><p><code>True</code> if the symbol is a function or a method. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002eis_005fvariable"></a>Variable: <strong>Symbol.is_variable</strong></dt> |
| <dd><p><code>True</code> if the symbol is a variable. |
| </p></dd></dl> |
| |
| <p>A <code>gdb.Symbol</code> object has the following methods: |
| </p> |
| <dl> |
| <dt><a name="index-Symbol_002eis_005fvalid"></a>Function: <strong>Symbol.is_valid</strong> <em>()</em></dt> |
| <dd><p>Returns <code>True</code> if the <code>gdb.Symbol</code> object is valid, |
| <code>False</code> if not. A <code>gdb.Symbol</code> object can become invalid if |
| the symbol it refers to does not exist in <small>GDB</small> any longer. |
| All other <code>gdb.Symbol</code> methods will throw an exception if it is |
| invalid at the time the method is called. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-Symbol_002evalue"></a>Function: <strong>Symbol.value</strong> <em>(<span class="roman">[</span>frame<span class="roman">]</span>)</em></dt> |
| <dd><p>Compute the value of the symbol, as a <code>gdb.Value</code>. For |
| functions, this computes the address of the function, cast to the |
| appropriate type. If the symbol requires a frame in order to compute |
| its value, then <var>frame</var> must be given. If <var>frame</var> is not |
| given, or if <var>frame</var> is invalid, then this method will throw an |
| exception. |
| </p></dd></dl> |
| |
| <p>The available domain categories in <code>gdb.Symbol</code> are represented |
| as constants in the <code>gdb</code> module: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-SYMBOL_005fUNDEF_005fDOMAIN"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_UNDEF_DOMAIN</code> |
| <a name="index-gdb_002eSYMBOL_005fUNDEF_005fDOMAIN"></a> |
| </dt> |
| <dd><p>This is used when a domain has not been discovered or none of the |
| following domains apply. This usually indicates an error either |
| in the symbol information or in <small>GDB</small>’s handling of symbols. |
| </p> |
| <a name="index-SYMBOL_005fVAR_005fDOMAIN"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_VAR_DOMAIN</code> |
| <a name="index-gdb_002eSYMBOL_005fVAR_005fDOMAIN"></a> |
| </dt> |
| <dd><p>This domain contains variables, function names, typedef names and enum |
| type values. |
| </p> |
| <a name="index-SYMBOL_005fSTRUCT_005fDOMAIN"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_STRUCT_DOMAIN</code> |
| <a name="index-gdb_002eSYMBOL_005fSTRUCT_005fDOMAIN"></a> |
| </dt> |
| <dd><p>This domain holds struct, union and enum type names. |
| </p> |
| <a name="index-SYMBOL_005fLABEL_005fDOMAIN"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LABEL_DOMAIN</code> |
| <a name="index-gdb_002eSYMBOL_005fLABEL_005fDOMAIN"></a> |
| </dt> |
| <dd><p>This domain contains names of labels (for gotos). |
| </p> |
| <a name="index-SYMBOL_005fVARIABLES_005fDOMAIN"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_VARIABLES_DOMAIN</code> |
| <a name="index-gdb_002eSYMBOL_005fVARIABLES_005fDOMAIN"></a> |
| </dt> |
| <dd><p>This domain holds a subset of the <code>SYMBOLS_VAR_DOMAIN</code>; it |
| contains everything minus functions and types. |
| </p> |
| <a name="index-SYMBOL_005fFUNCTIONS_005fDOMAIN"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_FUNCTION_DOMAIN</code> |
| <a name="index-gdb_002eSYMBOL_005fFUNCTION_005fDOMAIN"></a> |
| </dt> |
| <dd><p>This domain contains all functions. |
| </p> |
| <a name="index-SYMBOL_005fTYPES_005fDOMAIN"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_TYPES_DOMAIN</code> |
| <a name="index-gdb_002eSYMBOL_005fTYPES_005fDOMAIN"></a> |
| </dt> |
| <dd><p>This domain contains all types. |
| </p></dd> |
| </dl> |
| |
| <p>The available address class categories in <code>gdb.Symbol</code> are represented |
| as constants in the <code>gdb</code> module: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-SYMBOL_005fLOC_005fUNDEF"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_UNDEF</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fUNDEF"></a> |
| </dt> |
| <dd><p>If this is returned by address class, it indicates an error either in |
| the symbol information or in <small>GDB</small>’s handling of symbols. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fCONST"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_CONST</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fCONST"></a> |
| </dt> |
| <dd><p>Value is constant int. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fSTATIC"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_STATIC</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fSTATIC"></a> |
| </dt> |
| <dd><p>Value is at a fixed address. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fREGISTER"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_REGISTER</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fREGISTER"></a> |
| </dt> |
| <dd><p>Value is in a register. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fARG"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_ARG</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fARG"></a> |
| </dt> |
| <dd><p>Value is an argument. This value is at the offset stored within the |
| symbol inside the frame’s argument list. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fREF_005fARG"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_REF_ARG</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fREF_005fARG"></a> |
| </dt> |
| <dd><p>Value address is stored in the frame’s argument list. Just like |
| <code>LOC_ARG</code> except that the value’s address is stored at the |
| offset, not the value itself. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fREGPARM_005fADDR"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_REGPARM_ADDR</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fREGPARM_005fADDR"></a> |
| </dt> |
| <dd><p>Value is a specified register. Just like <code>LOC_REGISTER</code> except |
| the register holds the address of the argument instead of the argument |
| itself. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fLOCAL"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_LOCAL</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fLOCAL"></a> |
| </dt> |
| <dd><p>Value is a local variable. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fTYPEDEF"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_TYPEDEF</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fTYPEDEF"></a> |
| </dt> |
| <dd><p>Value not used. Symbols in the domain <code>SYMBOL_STRUCT_DOMAIN</code> all |
| have this class. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fBLOCK"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_BLOCK</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fBLOCK"></a> |
| </dt> |
| <dd><p>Value is a block. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fCONST_005fBYTES"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_CONST_BYTES</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fCONST_005fBYTES"></a> |
| </dt> |
| <dd><p>Value is a byte-sequence. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fUNRESOLVED"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_UNRESOLVED</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fUNRESOLVED"></a> |
| </dt> |
| <dd><p>Value is at a fixed address, but the address of the variable has to be |
| determined from the minimal symbol table whenever the variable is |
| referenced. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fOPTIMIZED_005fOUT"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_OPTIMIZED_OUT</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fOPTIMIZED_005fOUT"></a> |
| </dt> |
| <dd><p>The value does not actually exist in the program. |
| </p> |
| <a name="index-SYMBOL_005fLOC_005fCOMPUTED"></a> |
| </dd> |
| <dt><code>gdb.SYMBOL_LOC_COMPUTED</code> |
| <a name="index-gdb_002eSYMBOL_005fLOC_005fCOMPUTED"></a> |
| </dt> |
| <dd><p>The value’s address is a computed location. |
| </p></dd> |
| </dl> |
| |
| <hr> |
| <div class="header"> |
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| Next: <a href="Symbol-Tables-In-Python.html#Symbol-Tables-In-Python" accesskey="n" rel="next">Symbol Tables In Python</a>, Previous: <a href="Blocks-In-Python.html#Blocks-In-Python" accesskey="p" rel="prev">Blocks In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
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