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| <h3 class="section">4.9 Debugging Multiple Inferiors and Programs</h3> |
| |
| <p><span class="sc">gdb</span> lets you run and debug multiple programs in a single |
| session. In addition, <span class="sc">gdb</span> 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-137"></a><span class="sc">gdb</span> represents the state of each program execution with an |
| object called an <dfn>inferior</dfn>. 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>To find out what inferiors exist at any moment, use <code>info inferiors</code><!-- /@w -->: |
| |
| |
| <a name="index-info-inferiors-138"></a> |
| <dl><dt><code>info inferiors</code><dd>Print a list of all inferiors currently being managed by <span class="sc">gdb</span>. |
| |
| <p><span class="sc">gdb</span> displays for each inferior (in this order): |
| |
| <ol type=1 start=1> |
| <li>the inferior number assigned by <span class="sc">gdb</span> |
| |
| <li>the target system's inferior identifier |
| |
| <li>the name of the executable the inferior is running. |
| |
| </ol> |
| |
| <p class="noindent">An asterisk ‘<samp><span class="samp">*</span></samp>’ preceding the <span class="sc">gdb</span> inferior number |
| indicates the current inferior. |
| |
| <p>For example, |
| </dl> |
| <!-- end table here to get a little more width for example --> |
| |
| <pre class="smallexample"> (gdb) info inferiors |
| Num Description Executable |
| 2 process 2307 hello |
| * 1 process 3401 goodbye |
| </pre> |
| <p>To switch focus between inferiors, use the <code>inferior</code> command: |
| |
| |
| <a name="index-inferior-_0040var_007binfno_007d-139"></a> |
| <dl><dt><code>inferior </code><var>infno</var><dd>Make inferior number <var>infno</var> the current inferior. The argument |
| <var>infno</var> is the inferior number assigned by <span class="sc">gdb</span>, as shown |
| in the first field of the ‘<samp><span class="samp">info inferiors</span></samp>’ display. |
| </dl> |
| |
| <p>You can get multiple executables into a debugging session via the |
| <code>add-inferior</code> and <code>clone-inferior</code><!-- /@w --> commands. On some |
| systems <span class="sc">gdb</span> 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>remove-inferior</code><!-- /@w --> command. |
| |
| |
| <a name="index-add_002dinferior-140"></a> |
| <dl><dt><code>add-inferior [ -copies </code><var>n</var><code> ] [ -exec </code><var>executable</var><code> ]</code><dd>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-141"></a><br><dt><code>clone-inferior [ -copies </code><var>n</var><code> ] [ </code><var>infno</var><code> ]</code><dd>Adds <var>n</var> inferiors ready to execute the same program as inferior |
| <var>infno</var>. <var>n</var> defaults to 1. <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. |
| |
| <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> |
| <p>You can now simply switch focus to inferior 2 and run it. |
| |
| <p><a name="index-remove_002dinferior-142"></a><br><dt><code>remove-inferior </code><var>infno</var><dd>Removes the inferior <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. |
| |
| </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 inferior</code><!-- /@w --> command: |
| |
| |
| <a name="index-detach-inferior-_0040var_007binfno_007d-143"></a> |
| <dl><dt><code>detach inferior </code><var>infno</var><dd>Detach from the inferior identified by <span class="sc">gdb</span> inferior number |
| <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><span class="samp"><null></span></samp>’. |
| |
| <p><a name="index-kill-inferior-_0040var_007binfno_007d-144"></a><br><dt><code>kill inferior </code><var>infno</var><dd>Kill the inferior identified by <span class="sc">gdb</span> inferior number |
| <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><span class="samp"><null></span></samp>’. |
| </dl> |
| |
| <p>After the successful completion of a command such as <code>detach</code>, |
| <code>detach inferior</code>, <code>kill</code> or <code>kill inferior</code>, or after |
| a normal process exit, the inferior is still valid and listed with |
| <code>info inferiors</code>, ready to be restarted. |
| |
| <p>To be notified when inferiors are started or exit under <span class="sc">gdb</span>'s |
| control use <code>set print inferior-events</code><!-- /@w -->: |
| |
| |
| <a name="index-set-print-inferior_002devents-145"></a> |
| <a name="index-print-messages-on-inferior-start-and-exit-146"></a> |
| <dl><dt><code>set print inferior-events</code><dt><code>set print inferior-events on</code><dt><code>set print inferior-events off</code><dd>The <code>set print inferior-events</code> command allows you to enable or |
| disable printing of messages when <span class="sc">gdb</span> 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-147"></a><br><dt><code>show print inferior-events</code><dd>Show whether messages will be printed when <span class="sc">gdb</span> detects that |
| inferiors have started, exited or have been detached. |
| </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>Occasionaly, when debugging <span class="sc">gdb</span> 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 program-spaces</code><!-- /@w --> command. |
| |
| |
| <a name="index-maint-info-program_002dspaces-148"></a> |
| <dl><dt><code>maint info program-spaces</code><dd>Print a list of all program spaces currently being managed by |
| <span class="sc">gdb</span>. |
| |
| <p><span class="sc">gdb</span> displays for each program space (in this order): |
| |
| <ol type=1 start=1> |
| <li>the program space number assigned by <span class="sc">gdb</span> |
| |
| <li>the name of the executable loaded into the program space, with e.g., |
| the <code>file</code> command. |
| |
| </ol> |
| |
| <p class="noindent">An asterisk ‘<samp><span class="samp">*</span></samp>’ preceding the <span class="sc">gdb</span> program space number |
| indicates the current program space. |
| |
| <p>In addition, below each program space line, <span class="sc">gdb</span> prints extra |
| information that isn't suitable to display in tabular form. For |
| example, the list of inferiors bound to the program space. |
| |
| <pre class="smallexample"> (gdb) maint info program-spaces |
| Id Executable |
| 2 goodbye |
| Bound inferiors: ID 1 (process 21561) |
| * 1 hello |
| </pre> |
| <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, |
| |
| <pre class="smallexample"> (gdb) maint info program-spaces |
| Id Executable |
| * 1 vfork-test |
| Bound inferiors: ID 2 (process 18050), ID 1 (process 18045) |
| </pre> |
| <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. |
| </dl> |
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