mingw/info/gdb/Active-Targets.html

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  18 <h3 class="section">Active targets</h3>
  19
  20    <p>There are three classes of targets: processes, core files, and
  21 executable files.  GDB can work concurrently on up to three
  22 active targets, one in each class.  This allows you to (for example)
  23 start a process and inspect its activity without abandoning your work on
  24 a core file.
  25
  26    <p>For example, if you execute <code>gdb a.out</code>, then the executable file
  27 <code>a.out</code> is the only active target.  If you designate a core file as
  28 well--presumably from a prior run that crashed and coredumped--then
  29 GDB has two active targets and uses them in tandem, looking
  30 first in the corefile target, then in the executable file, to satisfy
  31 requests for memory addresses.  (Typically, these two classes of target
  32 are complementary, since core files contain only a program's
  33 read-write memory--variables and so on--plus machine status, while
  34 executable files contain only the program text and initialized data.)
  35
  36    <p>When you type <code>run</code>, your executable file becomes an active process
  37 target as well.  When a process target is active, all GDB
  38 commands requesting memory addresses refer to that target; addresses in
  39 an active core file or executable file target are obscured while the
  40 process target is active.
  41
  42    <p>Use the <code>core-file</code> and <code>exec-file</code> commands to select a new
  43 core file or executable target (see <a href="Files.html#Files">Commands to specify files</a>).  To specify as a target a process that is already running, use
  44 the <code>attach</code> command (see <a href="Attach.html#Attach">Debugging an already-running process</a>).
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