GDB MI output vs. stdout

Question

I am using GDBs machine interface (mi) to write some simple tracers/loggers.

Now I ran into the problem of telling apart GDB output from text the target-program itself wrote to stdout.

If I look into the documentation here: https://ftp.gnu.org/old-gnu/Manuals/gdb/html_chapter/gdb_22.html

it says

target-stream-output is the output produced by the target program. All the target output is prefixed by `@'.

This is not what I observe, however. Consider this example session of running ls like so:

gdb -i mi ls
start

which gives this output:

...
...
~"[Thread debugging using libthread_db enabled]\n"
file1.jpg  file2.jpg  file3.jpg  dir1  dir2   <---(!!!)
~"[Inferior 1 (process 22233) exited normally]\n"
=thread-exited,id="1",group-id="i1"
=thread-group-exited,id="i1",exit-code="0"
*stopped,reason="exited-normally"
(gdb) 

As you can see, the output of the ls command was just randomly dumped into the console. Great.

How can I parse this?

Thanks!

gdb version is 8.1

Answer 1

According to this documentation page you can redirect your program stdout where-ever you want by using run>out_file_name . This will not solve the parsing problem, but should avoid it. Using other tty then gdb's is also described there.

In addition there is a simpler way to do it, with output redirection (see the first line of gdb output below). I checked it with simple program that prints to different strings to stderr and stdout :

#include <stdio.h>

int main(int argc, char ** argv)
{
    printf ("\ntest\n");
    fprintf (stderr, "stderr\n");
    return 0;
}

and here is my small debugging session results:

(gdb) set args 1>/home/ubuntu/out.txt 2> /home/ubuntu/err.txt
(gdb) b main
Breakpoint 1 at 0x4005b5: file ./gt.c, line 5.
(gdb) run
Starting program: /home/ubuntu/unittest/gt 1>/home/ubuntu/out.txt 2> /home/ubuntu/err.txt

Breakpoint 1, main (argc=1, argv=0x7fffffffe1f8) at ./gt.c:5
5       printf ("\ntest\n");
(gdb) c
Continuing.
[Inferior 1 (process 8659) exited normally]
(gdb) shell cat /home/ubuntu/out.txt

test
(gdb) shell cat /home/ubuntu/err.txt
stderr
(gdb)