# Linux Kernel Module Cheat
The perfect emulation setup to study and develop the <<linux-kernel>> v5.9.2, kernel modules, <<qemu-buildroot-setup,QEMU>>, <<gem5-buildroot-setup,gem5>> and x86_64, ARMv7 and ARMv8 <<userland-assembly,userland>> and <<baremetal-setup,baremetal>> assembly, <<c,ANSI C>>, <<cpp,C++>> and <<posix,POSIX>>. <<gdb>> and <<kgdb>> just work. Powered by <<about-the-qemu-buildroot-setup,Buildroot>> and <<about-the-baremetal-setup,crosstool-NG>>. Highly automated. Thoroughly documented. Automated <<test-this-repo,tests>>.

##### 24.8.1.3. m5 fail

End the simulation with a failure exit event:

    m5 fail 1

Sane Python scripts would use that as the exit status of gem5, which would be useful for testing purposes, but `fs.py` at 200281b08ca21f0d2678e23063f088960d3c0819 just prints an error message:

    Simulated exit code not 0! Exit code is 1

and exits with status 0.

We then parse that string ourselves in run and exit with the correct status…​

TODO: it used to be like that, but it actually got changed to just print the message. Why? https://gem5-review.googlesource.com/c/public/gem5/+/4880

`m5 fail` is just a superset of `m5 exit`, which is just:

    m5 fail 0

as can be seen from the source: https://github.com/gem5/gem5/blob/50a57c0376c02c912a978c4443dd58caebe0f173/src/sim/pseudo_inst.cc#L303