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| <title>Debugging with GDB: Specify Location</title> |
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| <a name="Specify-Location"></a> |
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| <a name="Specifying-a-Location"></a> |
| <h3 class="section">9.2 Specifying a Location</h3> |
| <a name="index-specifying-location"></a> |
| <a name="index-linespec"></a> |
| |
| <p>Several <small>GDB</small> commands accept arguments that specify a location |
| of your program’s code. Since <small>GDB</small> is a source-level |
| debugger, a location usually specifies some line in the source code; |
| for that reason, locations are also known as <em>linespecs</em>. |
| </p> |
| <p>Here are all the different ways of specifying a code location that |
| <small>GDB</small> understands: |
| </p> |
| <dl compact="compact"> |
| <dt><code><var>linenum</var></code></dt> |
| <dd><p>Specifies the line number <var>linenum</var> of the current source file. |
| </p> |
| </dd> |
| <dt><code>-<var>offset</var></code></dt> |
| <dt><code>+<var>offset</var></code></dt> |
| <dd><p>Specifies the line <var>offset</var> lines before or after the <em>current |
| line</em>. For the <code>list</code> command, the current line is the last one |
| printed; for the breakpoint commands, this is the line at which |
| execution stopped in the currently selected <em>stack frame</em> |
| (see <a href="Frames.html#Frames">Frames</a>, for a description of stack frames.) When |
| used as the second of the two linespecs in a <code>list</code> command, |
| this specifies the line <var>offset</var> lines up or down from the first |
| linespec. |
| </p> |
| </dd> |
| <dt><code><var>filename</var>:<var>linenum</var></code></dt> |
| <dd><p>Specifies the line <var>linenum</var> in the source file <var>filename</var>. |
| If <var>filename</var> is a relative file name, then it will match any |
| source file name with the same trailing components. For example, if |
| <var>filename</var> is ‘<samp>gcc/expr.c</samp>’, then it will match source file |
| name of <samp>/build/trunk/gcc/expr.c</samp>, but not |
| <samp>/build/trunk/libcpp/expr.c</samp> or <samp>/build/trunk/gcc/x-expr.c</samp>. |
| </p> |
| </dd> |
| <dt><code><var>function</var></code></dt> |
| <dd><p>Specifies the line that begins the body of the function <var>function</var>. |
| For example, in C, this is the line with the open brace. |
| </p> |
| </dd> |
| <dt><code><var>function</var>:<var>label</var></code></dt> |
| <dd><p>Specifies the line where <var>label</var> appears in <var>function</var>. |
| </p> |
| </dd> |
| <dt><code><var>filename</var>:<var>function</var></code></dt> |
| <dd><p>Specifies the line that begins the body of the function <var>function</var> |
| in the file <var>filename</var>. You only need the file name with a |
| function name to avoid ambiguity when there are identically named |
| functions in different source files. |
| </p> |
| </dd> |
| <dt><code><var>label</var></code></dt> |
| <dd><p>Specifies the line at which the label named <var>label</var> appears. |
| <small>GDB</small> searches for the label in the function corresponding to |
| the currently selected stack frame. If there is no current selected |
| stack frame (for instance, if the inferior is not running), then |
| <small>GDB</small> will not search for a label. |
| </p> |
| </dd> |
| <dt><code>*<var>address</var></code></dt> |
| <dd><p>Specifies the program address <var>address</var>. For line-oriented |
| commands, such as <code>list</code> and <code>edit</code>, this specifies a source |
| line that contains <var>address</var>. For <code>break</code> and other |
| breakpoint oriented commands, this can be used to set breakpoints in |
| parts of your program which do not have debugging information or |
| source files. |
| </p> |
| <p>Here <var>address</var> may be any expression valid in the current working |
| language (see <a href="Languages.html#Languages">working language</a>) that specifies a code |
| address. In addition, as a convenience, <small>GDB</small> extends the |
| semantics of expressions used in locations to cover the situations |
| that frequently happen during debugging. Here are the various forms |
| of <var>address</var>: |
| </p> |
| <dl compact="compact"> |
| <dt><code><var>expression</var></code></dt> |
| <dd><p>Any expression valid in the current working language. |
| </p> |
| </dd> |
| <dt><code><var>funcaddr</var></code></dt> |
| <dd><p>An address of a function or procedure derived from its name. In C, |
| C<tt>++</tt>, Java, Objective-C, Fortran, minimal, and assembly, this is |
| simply the function’s name <var>function</var> (and actually a special case |
| of a valid expression). In Pascal and Modula-2, this is |
| <code>&<var>function</var></code>. In Ada, this is <code><var>function</var>'Address</code> |
| (although the Pascal form also works). |
| </p> |
| <p>This form specifies the address of the function’s first instruction, |
| before the stack frame and arguments have been set up. |
| </p> |
| </dd> |
| <dt><code>'<var>filename</var>':<var>funcaddr</var></code></dt> |
| <dd><p>Like <var>funcaddr</var> above, but also specifies the name of the source |
| file explicitly. This is useful if the name of the function does not |
| specify the function unambiguously, e.g., if there are several |
| functions with identical names in different source files. |
| </p></dd> |
| </dl> |
| |
| <a name="index-breakpoint-at-static-probe-point"></a> |
| </dd> |
| <dt><code>-pstap|-probe-stap <span class="roman">[</span><var>objfile</var>:<span class="roman">[</span><var>provider</var>:<span class="roman">]</span><span class="roman">]</span><var>name</var></code></dt> |
| <dd><p>The <small>GNU</small>/Linux tool <code>SystemTap</code> provides a way for |
| applications to embed static probes. See <a href="Static-Probe-Points.html#Static-Probe-Points">Static Probe Points</a>, for more |
| information on finding and using static probes. This form of linespec |
| specifies the location of such a static probe. |
| </p> |
| <p>If <var>objfile</var> is given, only probes coming from that shared library |
| or executable matching <var>objfile</var> as a regular expression are considered. |
| If <var>provider</var> is given, then only probes from that provider are considered. |
| If several probes match the spec, <small>GDB</small> will insert a breakpoint at |
| each one of those probes. |
| </p> |
| </dd> |
| </dl> |
| |
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