A hid-nvidia-shield ftrace demo

ftrace-hid-nvidia-shield.sh

# Initial setup
sudo su -
mount -t tracefs nodev /sys/kernel/tracing
cat /sys/kernel/tracing/available_tracers

# Function tracer

echo function > /sys/kernel/tracing/current_tracer
echo 0 > /sys/kernel/tracing/tracing_on
echo > /sys/kernel/tracing/trace
echo 1 > /sys/kernel/tracing/tracing_on 
# Use fftest
echo 0 > /sys/kernel/tracing/tracing_on 
cat /sys/kernel/tracing/trace | less # We see a lot of junk we do not care about
echo > /sys/kernel/tracing/trace

# Lets start filtering our trace

cat /sys/kernel/tracing/available_filter_functions | less
cat /sys/kernel/tracing/set_ftrace_filter
echo '*:mod:hid_nvidia_shield' > /sys/kernel/tracing/set_ftrace_filter
cat /sys/kernel/tracing/set_ftrace_filter
echo 1 > /sys/kernel/tracing/tracing_on
# Use fftest
echo 0 > /sys/kernel/tracing/tracing_on
cat /sys/kernel/tracing/trace | less # Great we know some functions are called
# What about what they do

# Ok, lets try function graph tracer

echo > /sys/kernel/tracing/trace
echo function_graph > /sys/kernel/tracing/current_tracer
echo 1 > /sys/kernel/tracing/tracing_on
# Use fftest
echo 0 > /sys/kernel/tracing/tracing_on
cat /sys/kernel/tracing/trace | less

# Ok, that was not very useful. I got a callgraph without any of the calls that
# the hid_nvidia_shield function made
# Hmm, that sucks. Everything inside these filtered functions are missing

echo > /sys/kernel/tracing/trace
echo > /sys/kernel/tracing/set_ftrace_filter
cat /sys/kernel/tracing/set_ftrace_filter
echo 'thunderstrike*' > /sys/kernel/tracing/set_graph_function
echo 'shield*' >> /sys/kernel/tracing/set_graph_function
echo 1 > /sys/kernel/tracing/tracing_on
echo 0 > /sys/kernel/tracing/tracing_on
cat /sys/kernel/tracing/trace | less

echo '*:mod:hid_nvidia_shield' > /sys/kernel/tracing/set_graph_function # No-go, someone needs to implement set_graph_filter