Linux Kernel Module Cheat

24.6.3. gem5 checkpoint restore and run a different script

You want to automate running several tests from a single pristine post-boot state.

The problem is that boot takes forever, and after the checkpoint, the memory and disk states are fixed, so you can’t for example:

hack up an existing rc script, since the disk is fixed
inject new kernel boot command line options, since those have already been put into memory by the bootloader

There is however a few loopholes, m5 readfile being the simplest, as it reads whatever is present on the host.

So we can do it like:

# Boot, checkpoint and exit.
printf 'echo "setup run";m5 exit' > "$(./getvar gem5_readfile_file)"
./run --emulator gem5 --eval 'm5 checkpoint;m5 readfile > /tmp/gem5.sh && sh /tmp/gem5.sh'

# Restore and run the first benchmark.
printf 'echo "first benchmark";m5 exit' > "$(./getvar gem5_readfile_file)"
./run --emulator gem5 --gem5-restore 1

# Restore and run the second benchmark.
printf 'echo "second benchmark";m5 exit' > "$(./getvar gem5_readfile_file)"
./run --emulator gem5 --gem5-restore 1

# If something weird happened, create an interactive shell to examine the system.
printf 'sh' > "$(./getvar gem5_readfile_file)"
./run --emulator gem5 --gem5-restore 1

Since this is such a common setup, we provide the following helpers for this operation:

./run --gem5-readfile is a convenient way to set the m5 readfile file contents from a string in the command line, e.g.:

# Boot, checkpoint and exit.
./run --emulator gem5 --eval './gem5.sh' --gem5-readfile 'echo "setup run"'

# Restore and run the first benchmark.
./run --emulator gem5 --gem5-restore 1 --gem5-readfile 'echo "first benchmark"'

# Restore and run the second benchmark.
./run --emulator gem5 --gem5-restore 1 --gem5-readfile 'echo "second benchmark"'

rootfs_overlay/lkmc/gem5.sh. This script is analogous to gem5’s in-tree hack_back_ckpt.rcS, but with less noise.

Usage:

# Boot, checkpoint and exit.
./run --emulator gem5 --eval './gem5.sh' --gem5-readfile 'echo "setup run"'

# Restore and run the first benchmark.
./run --emulator gem5 --gem5-restore 1 --gem5-readfile 'echo "first benchmark"'

# Restore and run the second benchmark.
./run --emulator gem5 --gem5-restore 1 --gem5-readfile 'echo "second benchmark"'

Their usage is also exemplified at gem5 run benchmark.

If you forgot to use an appropriate --eval for your boot and the simulation is already running, rootfs_overlay/lkmc/gem5.sh can be used directly from an interactive guest shell.

First we reset the readfile to something that runs quickly:

printf 'echo "first benchmark"' > "$(./getvar gem5_readfile_file)"

and then in the guest, take a checkpoint and exit with:

./gem5.sh

Now the guest is in a state where readfile will be executed automatically without interactive intervention:

./run --emulator gem5 --gem5-restore 1 --gem5-readfile 'echo "first benchmark"'
./run --emulator gem5 --gem5-restore 1 --gem5-readfile 'echo "second benchmark"'

Other loophole possibilities to execute different benchmarks non-interactively include:

9P
Secondary disk
expect as mentioned at: https://stackoverflow.com/questions/7013137/automating-telnet-session-using-bash-scripts
```
#!/usr/bin/expect
spawn telnet localhost 3456
expect "# $"
send "pwd\r"
send "ls /\r"
send "m5 exit\r"
expect eof
```
This is ugly however as it is not deterministic.

https://www.mail-archive.com/gem5-users@gem5.org/msg15233.html