Building gdb frontend

Building gdb frontend

[Johannes Bauer]

Hi list,

I'm having a strange issue with gdb. Currently I'm building a frontend
for gdb to augment its features easily. It uses Python and forks a gdb
subprocess that it communicates over stdin/stdout.

This all works nice and well, but sometimes it locks up. The frontend
always waits to see a terminated line and then the prompt "(gdb) ". So
for example, if I send "p" without arguments, usually the response will
be (calling read with a 1024 bytes buffer):

b'The history is empty.'
b'\n'
b'(gdb) '

At which I know gdb is ready to receive another command. However,
sometimes the order of these messages is messed up and reception happens
like this:

b'The history is empty.'
b'(gdb) '
b'\n'

So that my frontend waits for the prompt (because it sees "The history
is empty.(gdb) " as one line).

When I change the reading buffer to minimum size 1, the results become
even more unpredictable:

b'('
b'The history is empty.\n'
b'g'
b'd'
b'b'
b')'
b' '

i.e. "(The history is empty.\n" and "gdb) ", which also leads to a lockup.

There seems to be some kind of concurrency/buffering issue here. Is
there a way to solve this? Is there a preferred way to talk to gdb in a
"machine-readable" friendly way so I know exactly when gdb is ready to
receive commands again?

Best regards,
Johannes

Re: Building gdb frontend

[Pedro Alves]

On 09/07/2012 11:36 AM, Johannes Bauer wrote:
> Is there a preferred way to talk to gdb in a
> "machine-readable" friendly way so I know exactly when gdb is ready to
> receive commands again?

See "The gdb/mi Interface" in the manual.

-- 
Pedro Alves

Re: Building gdb frontend

[Johannes Bauer]

On 07.09.2012 12:45, Pedro Alves wrote:
> On 09/07/2012 11:36 AM, Johannes Bauer wrote:
>> Is there a preferred way to talk to gdb in a
>> "machine-readable" friendly way so I know exactly when gdb is ready to
>> receive commands again?
> 
> See "The gdb/mi Interface" in the manual.

Aaaahhhh! This is *beautiful*. Even better than what I hoped for. This
will work out nicely, a first test shows that it works perfectly.

Thank you very much,
Best regards,
Johannes

Re: Building gdb frontend

[Andrew Burgess]

On 07/09/2012 11:36 AM, Johannes Bauer wrote:

> I'm having a strange issue with gdb. Currently I'm building a frontend
> for gdb to augment its features easily. It uses Python and forks a gdb
> subprocess that it communicates over stdin/stdout.

You may already be aware of this, forgive me if I'm telling you 
something you already know...

gdb has python scripting support built in, see,
   http://sourceware.org/gdb/current/onlinedocs/gdb/Python.html#Python

so you /might/ be able to achieve the augmentation you are aiming for by 
writing python scripts that are loaded into gdb.

Cheers,
Andrew