I'm just wondering how common this is, to "prototype" your operating system in userspace before actually writing it for real? What I mean is, to implement most of the basic functions of your kernel as a set of userspace programs/libraries to run under another operating system prior to writing your standalone kernel.
I've thought of a few advantages of this:
- It allows one to thouroughly test and find and correct flaws in their design prior to spending time writing it for real
- It allows one to focus on one's design without worrying about operating system stuff like hardware drivers
- It allows one to finalise the specifics of their design, such as the exact layout of data structures, without worrying about trying to write that in kernel space at the same time
- It means that when one comes to write one's kernel for real, one already has a set of algorithms for working with their data structures that can be ported over to the kernel
Currently I'm working on a set of routines to work with the object references in my operating system, and then I'll implement my object data structures and thoroughly test them. I'm doing all of this in C, and then when I come to write the kernel I'll port it over to assembler and replace C library functions (like "malloc", "strcmp", etc.) with those appropriate for my kernel. So when I write the kernel, I won't still be trying to work out the details of the operating system's actual design. The only things that I won't be able to test is loading stuff from disk (that will involve buffering data from disk and keeping track of which buffers are in use by which processes - a fairly complex thing which I probably won't implment for a LONG time) and the execution of code designed to run under the operating system.
Regards,
onlyonemac
. I am using windows built in messaging to simulate my kernel messaging and writing my graphics driver as a standalone application, which then gets interfaced via a .dll file (user mode library) that knows how to call into the graphics driver. This way, I can have multiple apps link to the .dll which then creates the connection to my "graphics driver" so I can test multi-tasking out in the driver. It is a simple LFB driver for now (software rendering), so I just use SFML to grab a texture, update it manually and render it to screen. I see no reason not test my code before putting it live, unless it is something that isn't allowed under another OS. I even testing most of my VMM/PMM code out in windows, wrote a malloc implementation, etc before putting it into my OS. Of course, it's hard to do certain aspects which are easier to just fire up bochs and test, like my page fault handler. I *could* probably simulated this under windows as well, but it was easier to just do it and test in bochs. Once it works in bochs, I like to boot on some live hardware for a sanity check. I am not that far along, so take my methods with a grain of salt.
