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| <h3 class="section">E.8 Interrupts</h3> |
| |
| <p><a name="index-interrupts-_0028remote-protocol_0029-3589"></a><a name="interrupting-remote-targets"></a>In all-stop mode, when a program on the remote target is running, |
| <span class="sc">gdb</span> may attempt to interrupt it by sending a ‘<samp><span class="samp">Ctrl-C</span></samp>’, |
| <code>BREAK</code> or a <code>BREAK</code> followed by <code>g</code>, control of which |
| is specified via <span class="sc">gdb</span>'s ‘<samp><span class="samp">interrupt-sequence</span></samp>’. |
| |
| <p>The precise meaning of <code>BREAK</code> is defined by the transport |
| mechanism and may, in fact, be undefined. <span class="sc">gdb</span> does not |
| currently define a <code>BREAK</code> mechanism for any of the network |
| interfaces except for TCP, in which case <span class="sc">gdb</span> sends the |
| <code>telnet</code> BREAK sequence. |
| |
| <p>‘<samp><span class="samp">Ctrl-C</span></samp>’, on the other hand, is defined and implemented for all |
| transport mechanisms. It is represented by sending the single byte |
| <code>0x03</code> without any of the usual packet overhead described in |
| the Overview section (see <a href="Overview.html#Overview">Overview</a>). When a <code>0x03</code> byte is |
| transmitted as part of a packet, it is considered to be packet data |
| and does <em>not</em> represent an interrupt. E.g., an ‘<samp><span class="samp">X</span></samp>’ packet |
| (see <a href="X-packet.html#X-packet">X packet</a>), used for binary downloads, may include an unescaped |
| <code>0x03</code> as part of its packet. |
| |
| <p><code>BREAK</code> followed by <code>g</code> is also known as Magic SysRq g. |
| When Linux kernel receives this sequence from serial port, |
| it stops execution and connects to gdb. |
| |
| <p>In non-stop mode, because packet resumptions are asynchronous |
| (see <a href="vCont-packet.html#vCont-packet">vCont packet</a>), <span class="sc">gdb</span> is always free to send a remote |
| command to the remote stub, even when the target is running. For that |
| reason, <span class="sc">gdb</span> instead sends a regular packet (see <a href="vCtrlC-packet.html#vCtrlC-packet">vCtrlC packet</a>) with the usual packet framing instead of the single byte |
| <code>0x03</code>. |
| |
| <p>Stubs are not required to recognize these interrupt mechanisms and the |
| precise meaning associated with receipt of the interrupt is |
| implementation defined. If the target supports debugging of multiple |
| threads and/or processes, it should attempt to interrupt all |
| currently-executing threads and processes. |
| If the stub is successful at interrupting the |
| running program, it should send one of the stop |
| reply packets (see <a href="Stop-Reply-Packets.html#Stop-Reply-Packets">Stop Reply Packets</a>) to <span class="sc">gdb</span> as a result |
| of successfully stopping the program in all-stop mode, and a stop reply |
| for each stopped thread in non-stop mode. |
| Interrupts received while the |
| program is stopped are queued and the program will be interrupted when |
| it is resumed next time. |
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