Since testing modules for GRUB by compile/reboot/test/boot/… is time consuming, frustrating – simply not very efficient, there was an utility shipped with the sources called grub-emu that (like the name states) emulates the grub console. But: it was/is not a perfect emulation (stm), no modules are loaded/loadable so every module must be hand-coded-added to the built and… it does not build (like descibed here).
The playground – world:
And thats is okay cause there is another great tool: grub_mkrescue – an image builder that creates floppy/cdrom-images with… grub on it. (and it supports the preloading of modules) Sample:
Gives a GRUB inside qemu with hello.mod already loaded. Fine. Put the lines into the Makefile of the module currently developed (maybe as run-target) and testing becomes a lot easier…
The playground – garden:
Assume you have checked out the (latest) sources of grub2, and now you stay into the source-dir grub-1.98. Your new module (for the firsttime a copy/paste/change of hello/hello.c) goes to grub-1.98/simplemod.
Building a module could be done two ways: the slower one by adding a probate entry in conf/common.mk (simple copy/paste an entry for a given module like hello) – results in building everything again, and again when calling make clean/make… or the good, fast and due to the handcrafted standalone-Makefile ugly one.
No more filling phrases… here is the makefile (to be placed in grub-1.98/simplemod/Makefile):
Okay, on the first time you must create the surrounding grub2-ecosystem (grub-1.98/configure;make;make install). But after that you only need to compile your new module. That is efficient.