Debugging Linux Kernel using ftrace Part4 - Tracing a specific Process

With ftrace, we can trace kernel calls only related to a specific process by echoing pid in the set_ftrace_pid file.

Steps to trace kernel calls of a particular PID:

1. Disable tracing by echoing "nop" to "current_tracer" file
$ echo "nop" > current_tracer

$ cat current_tracer 

nop

2. Echo the pid of the process which you want to trace in "set_ftrace_pid" file. 2588 is the pid of "gnome-terminal"

$ echo "2588" > set_ftrace_pid

$ cat set_ftrace_pid 

2588

3. Enable either "function" or "function_tracer" by echoing into "current_tracer" file

$ echo "function_graph" > current_tracer 

4. You can now "cat trace" to see what all kernel functions are being executed by the gnome-terminal.

You can also find out what all kernel function calls being executed by the running bash 

$ echo "$$" > set_ftrace_pid

The "$$" will convert into the PID of the bash in which all the commands we are executing.