gdb: Interrupts
E.8 Interrupts
==============
In all-stop mode, when a program on the remote target is running, GDB
may attempt to interrupt it by sending a 'Ctrl-C', 'BREAK' or a 'BREAK'
followed by 'g', control of which is specified via GDB's
'interrupt-sequence'.
The precise meaning of 'BREAK' is defined by the transport mechanism
and may, in fact, be undefined. GDB does not currently define a 'BREAK'
mechanism for any of the network interfaces except for TCP, in which
case GDB sends the 'telnet' BREAK sequence.
'Ctrl-C', on the other hand, is defined and implemented for all
transport mechanisms. It is represented by sending the single byte
'0x03' without any of the usual packet overhead described in the
Overview section (
Overview). When a '0x03' byte is transmitted
as part of a packet, it is considered to be packet data and does _not_
represent an interrupt. E.g., an 'X' packet (X packet), used
for binary downloads, may include an unescaped '0x03' as part of its
packet.
'BREAK' followed by 'g' is also known as Magic SysRq g. When Linux
kernel receives this sequence from serial port, it stops execution and
connects to gdb.
In non-stop mode, because packet resumptions are asynchronous (
vCont packet), GDB is always free to send a remote command to the
remote stub, even when the target is running. For that reason, GDB
instead sends a regular packet (vCtrlC packet) with the usual
packet framing instead of the single byte '0x03'.
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 (Stop Reply Packets) to GDB 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.
Info Catalog
gdb: Host I/O Packets
gdb: Remote Protocol
gdb: Notification Packets