Linked by Hadrien Grasland on Fri 28th Jan 2011 20:37 UTC
OSNews, Generic OSes It's recently been a year since I started working on my pet OS project, and I often end up looking backwards at what I have done, wondering what made things difficult in the beginning. One of my conclusions is that while there's a lot of documentation on OS development from a technical point of view, more should be written about the project management aspect of it. Namely, how to go from a blurry "I want to code an OS" vision to either a precise vision of what you want to achieve, or the decision to stop following this path before you hit a wall. This article series aims at putting those interested in hobby OS development on the right track, while keeping this aspect of things in mind.
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RE[4]: Machine language or C
by Alfman on Sat 29th Jan 2011 20:22 UTC in reply to "RE[3]: Machine language or C"
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The majority should definitely be coded in a high level language.

In the days of DOS TSRs, we wrote in assembly because the code had to be small and efficient.

Even to this day it's often easy to beat a compiler's output simply because it is restrained by a fixed calling convention. In x86 assembly language, I am free to stuff values where I please. A variable can be stuffed into segment registers, a function returning boolean can use the "zero flag". This eliminates the need to do "cmp" in the calling function.

In my own assembly, I can keep variables intact across function calls without touching the stack. To my knowledge, all C compilers use unoptimized calling conventions by design so that separately compiled object files link correctly.

Of course above I'm assuming that function call overhead is significant, YMMV.

However, all this optimization aside, looking back on TSRs I wrote, it takes a long time to familiarize oneself with code paths again. This is true of HLL too, but even more so with assembly. It is crucial to comment everything in assembly, and it is equally crucial that the comments be accurate.

Low level assembly is just not suitable for code that is meant to developed over time by many people. Besides, it's not portable, and cannot benefit from new architectures with a simple recompile.

Off the top of my head, the bootloader and protected mode task management are the only things which really require any significant assembly language.

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