mingw/info/gdb/Hooks.html

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  12 Node:<a name="Hooks">Hooks</a>,
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  18
  19 <h3 class="section">User-defined command hooks</h3>
  20
  21    <p>You may define <dfn>hooks</dfn>, which are a special kind of user-defined
  22 command.  Whenever you run the command <code>foo</code>, if the user-defined
  23 command <code>hook-foo</code> exists, it is executed (with no arguments)
  24 before that command.
  25
  26    <p>A hook may also be defined which is run after the command you executed.
  27 Whenever you run the command <code>foo</code>, if the user-defined command
  28 <code>hookpost-foo</code> exists, it is executed (with no arguments) after
  29 that command.  Post-execution hooks may exist simultaneously with
  30 pre-execution hooks, for the same command.
  31
  32    <p>It is valid for a hook to call the command which it hooks.  If this
  33 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
  34
  35    <p>In addition, a pseudo-command, <code>stop</code> exists.  Defining
  36 (<code>hook-stop</code>) makes the associated commands execute every time
  37 execution stops in your program: before breakpoint commands are run,
  38 displays are printed, or the stack frame is printed.
  39
  40    <p>For example, to ignore <code>SIGALRM</code> signals while
  41 single-stepping, but treat them normally during normal execution,
  42 you could define:
  43
  44 <pre class="example">     define hook-stop
  45      handle SIGALRM nopass
  46      end
  47
  48      define hook-run
  49      handle SIGALRM pass
  50      end
  51
  52      define hook-continue
  53      handle SIGLARM pass
  54      end
  55      </pre>
  56
  57    <p>As a further example, to hook at the begining and end of the <code>echo</code>
  58 command, and to add extra text to the beginning and end of the message,
  59 you could define:
  60
  61 <pre class="example">     define hook-echo
  62      echo &lt;&lt;&lt;---
  63      end
  64
  65      define hookpost-echo
  66      echo ---&gt;&gt;&gt;\n
  67      end
  68
  69      (gdb) echo Hello World
  70      &lt;&lt;&lt;---Hello World---&gt;&gt;&gt;
  71      (gdb)
  72
  73      </pre>
  74
  75    <p>You can define a hook for any single-word command in GDB, but
  76 not for command aliases; you should define a hook for the basic command
  77 name, e.g.  <code>backtrace</code> rather than <code>bt</code>.
  78 If an error occurs during the execution of your hook, execution of
  79 GDB commands stops and GDB issues a prompt
  80 (before the command that you actually typed had a chance to run).
  81
  82    <p>If you try to define a hook which does not match any known command, you
  83 get a warning from the <code>define</code> command.
  84
  85    </body></html>
  86