95 lines
4.5 KiB
HTML
95 lines
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HTML
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<title>Jumping - Debugging with GDB</title>
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<a name="Jumping"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Signaling.html#Signaling">Signaling</a>,
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Previous: <a rel="previous" accesskey="p" href="Assignment.html#Assignment">Assignment</a>,
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Up: <a rel="up" accesskey="u" href="Altering.html#Altering">Altering</a>
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</div>
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<h3 class="section">17.2 Continuing at a Different Address</h3>
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<p>Ordinarily, when you continue your program, you do so at the place where
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it stopped, with the <code>continue</code> command. You can instead continue at
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an address of your own choosing, with the following commands:
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<a name="index-jump-1168"></a>
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<a name="index-j-_0040r_007b_0028_0040code_007bjump_007d_0029_007d-1169"></a>
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<dl><dt><code>jump </code><var>location</var><dt><code>j </code><var>location</var><dd>Resume execution at <var>location</var>. Execution stops again immediately
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if there is a breakpoint there. See <a href="Specify-Location.html#Specify-Location">Specify Location</a>, for a description
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of the different forms of <var>location</var>. It is common
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practice to use the <code>tbreak</code> command in conjunction with
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<code>jump</code>. See <a href="Set-Breaks.html#Set-Breaks">Setting Breakpoints</a>.
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<p>The <code>jump</code> command does not change the current stack frame, or
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the stack pointer, or the contents of any memory location or any
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register other than the program counter. If <var>location</var> is in
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a different function from the one currently executing, the results may
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be bizarre if the two functions expect different patterns of arguments or
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of local variables. For this reason, the <code>jump</code> command requests
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confirmation if the specified line is not in the function currently
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executing. However, even bizarre results are predictable if you are
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well acquainted with the machine-language code of your program.
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</dl>
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<p>On many systems, you can get much the same effect as the <code>jump</code>
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command by storing a new value into the register <code>$pc</code>. The
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difference is that this does not start your program running; it only
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changes the address of where it <em>will</em> run when you continue. For
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example,
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<pre class="smallexample"> set $pc = 0x485
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</pre>
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<p class="noindent">makes the next <code>continue</code> command or stepping command execute at
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address <code>0x485</code>, rather than at the address where your program stopped.
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See <a href="Continuing-and-Stepping.html#Continuing-and-Stepping">Continuing and Stepping</a>.
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<p>The most common occasion to use the <code>jump</code> command is to back
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up—perhaps with more breakpoints set—over a portion of a program
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that has already executed, in order to examine its execution in more
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detail.
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