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Re: command Ctrll-C

On Wednesday 05 November 2008 05:12:06, Michael Snyder wrote:
> wrote:
> > Hi,
> > 
> > During program execution thought GDB, the execution can be stopped by
> > command Ctrll-C
> > 
> > How it works internally in GDB source? Which function will be called after
> > user enters the command Ctrl-C ?
> > 
> > Thanks in Advance
> > Raja Saleru

> Have a look at "handle_sigint" and "async_request_quit"
> in gdb/event-top.c.

Nope, sorry, that's used when there's no execution.  It calls
quit(), doesn't interrupt the target at all.

If you're talking about native debugging, running a program
under GDB, not attached, then GDB "gives the terminal"
to the inferior (debuggee) (see target_terminal_inferior and friends)
whenever it is going to run it, so the ctrl-c hit while the inferior
is running is sent directly to the debuggee --- GDB is then informed
by ptrace that the inferior got a SIGINT (waitpid returns) (that is
the inferior sees the ctrl-c before gdb does in this case).

If talking about native debugging, attached to a program,
GDB installs a SIGINT handler that forwards the SIGINT to the inferior.
See set_sigint_trap/pass_signal in inflow.c/linux-nat.c for example.
If you go the to attachee's terminal and do a ctrl-c there, GDB will
be reported about a SIGINT just like the in native,non-attached case.

If talking about remote debugging, there are more steps involved depending
on the mode you're talking about, but, in the simplest and standard
mode (all-stop, sync), the idea is that GDB installs a SIGINT signal
handler that ends up passing an "out-of-band" interrupt "packet" to the
remote side (\\03).  Then, when seeing this packet, the remote stub interrupts
its inferior (e.g., sends it a SIGINT) and then informs GDB that the remote
was interrupted with a regular stop reply.  See remote_wait_as installing
remote_interrupt as SIGINT handler.  When ctrl-c is done on GDB, this
handler then calls through async_remote_interrupt -> remote_stop_as -> serial_write (\\03).

Pedro Alves

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