# 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>>.

#### 30.5.2. ARM UDF instruction

Guaranteed undefined! Therefore raise illegal instruction signal. Used by GCC `__builtin_trap` apparently: https://stackoverflow.com/questions/16081618/programmatically-cause-undefined-instruction-exception

- userland/arch/arm/udf.S

- userland/arch/aarch64/udf.S

Why GNU GAS 2.29 does not have a mnemonic for it in A64 because it is very recent: shows in ARMv8 architecture reference manual db but not `ca`.