[grahamedgecombe]

It's worth pointing out there are a few bugs in James Molloy's tutorial [1], and some of the things he does in them aren't exactly best practices - for example, a few I remember are:

- Disabling interrupts and paging (which also has the side effect of flushing the TLB) to copy memory around by physical address. This could be done without disabling them by mapping all of physical memory into virtual memory instead (possible in 64-bit mode, but in 32-bit there isn't enough room when your PC has a similar amount of RAM to virtual memory space, in which case you could map smaller parts of it as needed).

- Moving the stack around to get around the fact that GRUB doesn't set ESP to some well-defined value (instead of defining the stack yourself, which would be much more robust) and then attempting to rewrite the base pointers to fix it. For example, his code can't tell the difference between integers that just happen to have a value in the range of the pointers and a pointer, and will happily rewrite both. Also as ESP isn't defined by the Multiboot standard you could be using any location at all as the stack (such as some memory address that doesn't exist, or your kernel's code itself, or some memory-mapped area for a piece of hardware, etc.) All of which will mean things go wrong. It's better to just set ESP yourself before you enter C - see another of my comments on this submission here [3].

There's actually a newer and much better version of JamesM's tutorials on GitHub, but I believe they aren't quite finished [2].

[1]: http://wiki.osdev.org/James_Molloy%27s_Known_Bugs [2]: https://github.com/jmolloy/JMTK [3]: https://news.ycombinator.com/item?id=7590753

[AdrianoKF]

Oh, didn't know there was a follow-up to his original tutorial - I'll have a look at your resources when I get back from work!