Question

As the title says, what are they and what’s the difference?

Some examples:

dmain:

void dmain(void* mbd, unsigned int magic)

kmain:

void kmain( void* mbd, unsigned int magic )

P.S. I found a similar post here but it was about wmain:

What is the difference between wmain and main?

Also _tmain:

What is the difference between _tmain() and main() in C++?

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They take the same arguments but is there a difference? And any links to some info this so I could learn is appreciated, google yielded weird results…

Also, is there an official sort of like ‘man’ pages of C?

Answer 1

You seem to be referring to this tutorial on OSDev.org.

If you’ll notice, this is not a standard C program with main() as its entry point. In fact, the page shows two entry points: one written in Assembler in a way for GRUB to find & load, and which sets up & loads the second, kmain(), which is written in C. The writers use the name kmain to mean “kernel main”; presumably dmain is the entry point for drivers & would stand for “driver main”.

C makes a distinction between “freestanding” and “hosted” implementations. Hosted is what you’re probably more familiar with; the standard C library is available, and all programs start at the main function.

OS kernels are (often) good examples of freestanding environments. The C library will likely not be available, for example (except for certain headers like stddef.h & stdarg.h; see the standard for details). Also, the entry point is not defined by the standard anymore. The OSDev.org tutorial is making a special point of that fact, by explicitly defining its entry point with a different name.

You could probably run the tutorial renaming kmain to main, but note that it’s still void main(void*, unsigned int), not int main(int, char**); in fact that sort of confusion is likely part of the reason the writers chose to use a different name. But is is just a convention they’ve selected, not anything standardized.