Fwd: Can GDB interact with serial ports on remote targets?

[Luis Machado]

Hi Brendan,

On 02/20/2015 12:27 PM, Brendan J wrote:
> I am using GDB to debug a remote target: I start GDB then type `target
> remote foo:1234`. I do I/O with the target via a serial port. So I
> have to have two terminals open: one with picocom (connected to
> something like /dev/ttyUSB0) and one with GDB (connected to OpenOCD
> via a socket). To be clear: the debug connection is *not over the
> serial port*, it's over a totally separate JTAG interface.
>
> As you know, when you debug a "normal" (i.e. not "remote") inferior in
> GDB, its stdin and stdout are multiplexed into GDB's TTY so that you
> can interact with it while it's running [1].
>
> Is it possible to achieve that for a remote target - that is: can GDB
> connect to the serial port itself so I can do I/O with the target from
> within the GDB session?
>
> If not, is this something that might be feasible? Maybe GDB could
> multiplex its I/O so that while the inferior is running it passes
> characters to/from an external tool like picocom? (As you can see I'm
> fairly ignorant about this whole issue at the moment).
>
> Thanks,
> Brendan
>
> PS: I'm using arm-none-eabi-gdb, in case that happens to be relevant.
>
> [1] https://sourceware.org/gdb/onlinedocs/gdb/Input_002fOutput.html
>
>

It sounds like what you want is semihosting support, an I/O operation 
that is initiated on the remote end, passing through the host and then 
back again to the remote end.

For example, the remote program needs to read a character. In this case 
the remote debug agent issues a vFile request with the right system 
call, GDB receives it, the user enters the character via GDB and then 
GDB sends the reply back to the target. The remote program then reads 
the character and continues executing.

You can check the documentation here:

https://sourceware.org/gdb/current/onlinedocs/gdb/File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension

Check this one as well:

https://sourceware.org/gdb/current/onlinedocs/gdb/Console-I_002fO.html#Console-I_002fO

This feature is only available on all-stop mode.

Luis