Writing Front End for GDB

Question

I want to write a GUI based debugger wrapped over GDB. Because, I dont want the program to stop after watch points or break points. Instead, it should redirect the details like filename, line number, new value and stuffs to a file and continue execution.

I am pretty bad at scripting. So, I want some starting point to start developing front end for GDB. As far as I googled, this link http://ftp.gnu.org/old-gnu/Manuals/gdb-5.1.1/html_node/gdb_211.html is not much understandable for a beginner in this activity?

Hopefully, I will get help on development in C/C++.

Answer 1

For writing a GDB frontend, you indeed want to use the GDB/MI protocol but perhaps read this up-to-date copy instead of the older one you linked to.

Sample GDB/MI session

(Lightly edited version of this section from the GDB manual)

Launching GDB with the MI Command Interpreter

$ gdb -q --interpreter=mi2
=thread-group-added,id="i1"
(gdb)

File /bin/true

-file-exec-and-symbols /bin/true
^done
(gdb) 

Break main

-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x00000000004014c0",func="main",file="true.c",fullname="/usr/src/debug/coreutils-8.17/src/true.c",line="59",times="0",original-location="main"}
(gdb) 

Run and Breakpoint Hit

-exec-run
=thread-group-started,id="i1",pid="2275"
=thread-created,id="1",group-id="i1"
^running
*running,thread-id="all"
(gdb) 
=library-loaded,id="/lib64/ld-linux-x86-64.so.2",target-name="/lib64/ld-linux-x86-64.so.2",host-name="/lib64/ld-linux-x86-64.so.2",symbols-loaded="0",thread-group="i1"
=library-loaded,id="/lib64/libc.so.6",target-name="/lib64/libc.so.6",host-name="/lib64/libc.so.6",symbols-loaded="0",thread-group="i1"
=breakpoint-modified,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x00000000004014c0",func="main",file="true.c",fullname="/usr/src/debug/coreutils-8.17/src/true.c",line="59",times="1",original-location="main"}
*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame={addr="0x00000000004014c0",func="main",args=[{name="argc",value="1"},{name="argv",value="0x7fffffffde98"}],file="true.c",fullname="/usr/src/debug/coreutils-8.17/src/true.c",line="59"},thread-id="1",stopped-threads="all",core="1"
(gdb) 

Continue

-exec-continue
^running
*running,thread-id="1"
(gdb) 
=thread-exited,id="1",group-id="i1"
=thread-group-exited,id="i1",exit-code="0"
*stopped,reason="exited-normally"

Quitting GDB

(gdb) 
-gdb-exit
^exit

Existing GDB/MI Clients

There are several GDB/MI client implementations in C, C++, Java, Python. I'll list a few that I find easy to read:

• The inactive libmigdb project (sample program, public interfaces) -- The good news is that it's an attempt at creating a reusable C library. The bad news is that it's not well maintained, e.g. I think it's missing GDB non-stop mode and catchpoint commands support, features that your use case would likely need.
• python-gdb-mi -- Quite readable if you know Python
• The C++ GDB/MI client code in QtCreator -- Also quite readable though it's written as part of an abstraction layer to support multiple debugger engines.

You might want to also browse this list of GDB frontends.