using gdb to debug a interactive program that reads input from stdin

Question

I'm writing a client/server program in C.

My client has a thread reading input from stdin, it's just a while(1) loop to read input from stdin. Whenever it reads a line, it deliver it to another thread that handles message parsing and framing.

As I enter gdb, the command line is occupied by gdb prompt and I can no longer input lines into stdin.

Is there a way to do it? (I don't want to redirect stdin to an input file because I've tried this method and it didn't work)

caf · Accepted Answer · 2017-02-03 02:04:32Z

10

Run your program in one terminal and attach to it from gdb in another terminal.

To attach to a running program, find the process ID (PID) of the program you want to attach to, then execute gdb <executable> <PID>.

edited Feb 3, 2017 at 2:04

caf

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answered Feb 3, 2017 at 1:17

Jonathon Reinhart

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3 Comments

zanyman Over a year ago

how to attach a process to gdb?

PazO Over a year ago

What if I want to debug program startup?

Ömer GÜZEL Over a year ago

@zanyman that command will attach directly your process. It required root permission in my try.

throws_exceptions_at_you · Accepted Answer · 2021-05-09 08:33:36Z

2

As an addition to Jonathan Reinhart's answer, here is a oneliner to attach to a running program by name:

gdb -p $(pgrep <executable-name>)

answered May 9, 2021 at 8:33

throws_exceptions_at_you

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2 Comments

Jonathon Reinhart Over a year ago

This works if there is only one running instance of <executable-name>.

throws_exceptions_at_you Over a year ago

One of these does the job: gdb -p $(pgrep <executable-name> | select); gdb -p $(pgrep <executable-name> | peco); gdb -p $(pgrep <executable-name> | fzf );

Polarimetric · Accepted Answer · 2022-11-14 18:23:02Z

1

As a clarification you don't need the executable name if you do know the process id of the program. This will allow you to attach a program directly.

gdb -p PID

answered Nov 14, 2022 at 18:23

Polarimetric

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3 Comments

Jonathon Reinhart Over a year ago

This will work, but I don't think GDB will know where to find the executable in order to access the symbols and debug info.

Polarimetric Over a year ago

In principle if the executable is built with debug symbols or say RelWithDebInfo modern gdb is able to attach the executable corresponding to the PID specified.

Jonathon Reinhart Over a year ago

Oh it probably uses /proc/$PID/exe.

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