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| <a name="Inferiors-and-Programs"></a> |
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| <a name="Debugging-Multiple-Inferiors-and-Programs"></a> |
| <h3 class="section">4.9 Debugging Multiple Inferiors and Programs</h3> |
| |
| <p><small>GDB</small> lets you run and debug multiple programs in a single |
| session. In addition, <small>GDB</small> on some systems may let you run |
| several programs simultaneously (otherwise you have to exit from one |
| before starting another). In the most general case, you can have |
| multiple threads of execution in each of multiple processes, launched |
| from multiple executables. |
| </p> |
| <a name="index-inferior"></a> |
| <p><small>GDB</small> represents the state of each program execution with an |
| object called an <em>inferior</em>. An inferior typically corresponds to |
| a process, but is more general and applies also to targets that do not |
| have processes. Inferiors may be created before a process runs, and |
| may be retained after a process exits. Inferiors have unique |
| identifiers that are different from process ids. Usually each |
| inferior will also have its own distinct address space, although some |
| embedded targets may have several inferiors running in different parts |
| of a single address space. Each inferior may in turn have multiple |
| threads running in it. |
| </p> |
| <p>To find out what inferiors exist at any moment, use <code>info inferiors</code><!-- /@w -->: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-info-inferiors"></a> |
| </dd> |
| <dt><code>info inferiors</code></dt> |
| <dd><p>Print a list of all inferiors currently being managed by <small>GDB</small>. |
| </p> |
| <p><small>GDB</small> displays for each inferior (in this order): |
| </p> |
| <ol> |
| <li> the inferior number assigned by <small>GDB</small> |
| |
| </li><li> the target system’s inferior identifier |
| |
| </li><li> the name of the executable the inferior is running. |
| |
| </li></ol> |
| |
| <p>An asterisk ‘<samp>*</samp>’ preceding the <small>GDB</small> inferior number |
| indicates the current inferior. |
| </p> |
| <p>For example, |
| </p></dd> |
| </dl> |
| |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) info inferiors |
| Num Description Executable |
| 2 process 2307 hello |
| * 1 process 3401 goodbye |
| </pre></div> |
| |
| <p>To switch focus between inferiors, use the <code>inferior</code> command: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-inferior-infno"></a> |
| </dd> |
| <dt><code>inferior <var>infno</var></code></dt> |
| <dd><p>Make inferior number <var>infno</var> the current inferior. The argument |
| <var>infno</var> is the inferior number assigned by <small>GDB</small>, as shown |
| in the first field of the ‘<samp>info inferiors</samp>’ display. |
| </p></dd> |
| </dl> |
| |
| |
| <p>You can get multiple executables into a debugging session via the |
| <code>add-inferior</code> and <code><span class="nolinebreak">clone-inferior</span></code><!-- /@w --> commands. On some |
| systems <small>GDB</small> can add inferiors to the debug session |
| automatically by following calls to <code>fork</code> and <code>exec</code>. To |
| remove inferiors from the debugging session use the |
| <code><span class="nolinebreak">remove-inferiors</span></code><!-- /@w --> command. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-add_002dinferior"></a> |
| </dd> |
| <dt><code>add-inferior [ -copies <var>n</var> ] [ -exec <var>executable</var> ]</code></dt> |
| <dd><p>Adds <var>n</var> inferiors to be run using <var>executable</var> as the |
| executable; <var>n</var> defaults to 1. If no executable is specified, |
| the inferiors begins empty, with no program. You can still assign or |
| change the program assigned to the inferior at any time by using the |
| <code>file</code> command with the executable name as its argument. |
| </p> |
| <a name="index-clone_002dinferior"></a> |
| </dd> |
| <dt><code>clone-inferior [ -copies <var>n</var> ] [ <var>infno</var> ]</code></dt> |
| <dd><p>Adds <var>n</var> inferiors ready to execute the same program as inferior |
| <var>infno</var>; <var>n</var> defaults to 1, and <var>infno</var> defaults to the |
| number of the current inferior. This is a convenient command when you |
| want to run another instance of the inferior you are debugging. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) info inferiors |
| Num Description Executable |
| * 1 process 29964 helloworld |
| (gdb) clone-inferior |
| Added inferior 2. |
| 1 inferiors added. |
| (gdb) info inferiors |
| Num Description Executable |
| 2 <null> helloworld |
| * 1 process 29964 helloworld |
| </pre></div> |
| |
| <p>You can now simply switch focus to inferior 2 and run it. |
| </p> |
| <a name="index-remove_002dinferiors"></a> |
| </dd> |
| <dt><code>remove-inferiors <var>infno</var>…</code></dt> |
| <dd><p>Removes the inferior or inferiors <var>infno</var>…. It is not |
| possible to remove an inferior that is running with this command. For |
| those, use the <code>kill</code> or <code>detach</code> command first. |
| </p> |
| </dd> |
| </dl> |
| |
| <p>To quit debugging one of the running inferiors that is not the current |
| inferior, you can either detach from it by using the <code>detach inferior</code><!-- /@w --> command (allowing it to run independently), or kill it |
| using the <code>kill inferiors</code><!-- /@w --> command: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-detach-inferiors-infno_2026"></a> |
| </dd> |
| <dt><code>detach inferior <var>infno</var>…</code></dt> |
| <dd><p>Detach from the inferior or inferiors identified by <small>GDB</small> |
| inferior number(s) <var>infno</var>…. Note that the inferior’s entry |
| still stays on the list of inferiors shown by <code>info inferiors</code>, |
| but its Description will show ‘<samp><null></samp>’. |
| </p> |
| <a name="index-kill-inferiors-infno_2026"></a> |
| </dd> |
| <dt><code>kill inferiors <var>infno</var>…</code></dt> |
| <dd><p>Kill the inferior or inferiors identified by <small>GDB</small> inferior |
| number(s) <var>infno</var>…. Note that the inferior’s entry still |
| stays on the list of inferiors shown by <code>info inferiors</code>, but its |
| Description will show ‘<samp><null></samp>’. |
| </p></dd> |
| </dl> |
| |
| <p>After the successful completion of a command such as <code>detach</code>, |
| <code>detach inferiors</code>, <code>kill</code> or <code>kill inferiors</code>, or after |
| a normal process exit, the inferior is still valid and listed with |
| <code>info inferiors</code>, ready to be restarted. |
| </p> |
| |
| <p>To be notified when inferiors are started or exit under <small>GDB</small>’s |
| control use <code>set print <span class="nolinebreak">inferior-events</span></code><!-- /@w -->: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-set-print-inferior_002devents"></a> |
| <a name="index-print-messages-on-inferior-start-and-exit"></a> |
| </dd> |
| <dt><code>set print inferior-events</code></dt> |
| <dt><code>set print inferior-events on</code></dt> |
| <dt><code>set print inferior-events off</code></dt> |
| <dd><p>The <code>set print inferior-events</code> command allows you to enable or |
| disable printing of messages when <small>GDB</small> notices that new |
| inferiors have started or that inferiors have exited or have been |
| detached. By default, these messages will not be printed. |
| </p> |
| <a name="index-show-print-inferior_002devents"></a> |
| </dd> |
| <dt><code>show print inferior-events</code></dt> |
| <dd><p>Show whether messages will be printed when <small>GDB</small> detects that |
| inferiors have started, exited or have been detached. |
| </p></dd> |
| </dl> |
| |
| <p>Many commands will work the same with multiple programs as with a |
| single program: e.g., <code>print myglobal</code> will simply display the |
| value of <code>myglobal</code> in the current inferior. |
| </p> |
| |
| <p>Occasionaly, when debugging <small>GDB</small> itself, it may be useful to |
| get more info about the relationship of inferiors, programs, address |
| spaces in a debug session. You can do that with the <code>maint info <span class="nolinebreak">program-spaces</span></code><!-- /@w --> command. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-maint-info-program_002dspaces"></a> |
| </dd> |
| <dt><code>maint info program-spaces</code></dt> |
| <dd><p>Print a list of all program spaces currently being managed by |
| <small>GDB</small>. |
| </p> |
| <p><small>GDB</small> displays for each program space (in this order): |
| </p> |
| <ol> |
| <li> the program space number assigned by <small>GDB</small> |
| |
| </li><li> the name of the executable loaded into the program space, with e.g., |
| the <code>file</code> command. |
| |
| </li></ol> |
| |
| <p>An asterisk ‘<samp>*</samp>’ preceding the <small>GDB</small> program space number |
| indicates the current program space. |
| </p> |
| <p>In addition, below each program space line, <small>GDB</small> prints extra |
| information that isn’t suitable to display in tabular form. For |
| example, the list of inferiors bound to the program space. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) maint info program-spaces |
| Id Executable |
| 2 goodbye |
| Bound inferiors: ID 1 (process 21561) |
| * 1 hello |
| </pre></div> |
| |
| <p>Here we can see that no inferior is running the program <code>hello</code>, |
| while <code>process 21561</code> is running the program <code>goodbye</code>. On |
| some targets, it is possible that multiple inferiors are bound to the |
| same program space. The most common example is that of debugging both |
| the parent and child processes of a <code>vfork</code> call. For example, |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) maint info program-spaces |
| Id Executable |
| * 1 vfork-test |
| Bound inferiors: ID 2 (process 18050), ID 1 (process 18045) |
| </pre></div> |
| |
| <p>Here, both inferior 2 and inferior 1 are running in the same program |
| space as a result of inferior 1 having executed a <code>vfork</code> call. |
| </p></dd> |
| </dl> |
| |
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