Use a cross compiler for OS

[shakram02]

Hello, I"m very grateful that I found your book, it has lots of information laid nicely, I followed it to the end (I hope it gets complete one day!) and completed the missing information online without much trouble.

I just want to note that I guess GCC won't be friendly with the OS binary as it inserts calls to some of its functions (I don't remember the exact name of the function) like .text.***_ax or something like that which get the OS code into an undefined state. (I followed the code with gdb)

Guys on the osdev wiki mandated that we have a cross compiler build specifically for our target, when I did that and compiled the OS and retraced the code it worked as expected and contained to extra call.

Thank you so much for your efforts writing the book, I appreciate them

[tuhdo]

I'm glad you enjoy the book! I'm happy to hear it.

For cross compilers, indeed it is recommended that way. However, to reduce the complexity of already complex learning project, I decided to use a native compiler since code generated is x86 anyway. The code sections like .text.***_ax are filtered by a linker script. That is, you use a linker script and objcopy utility to discard unused code sections and assemble object files into a final binary image however you want. You can also tell gcc to not generate PIE (Position-independent Executable) code to strip more code sections for a simpler binary output. I always want to include more advance exercises on linker script and manual crafting of binary image, but haven't found the time to do so.

[shakram02]

I couldn't actually get it working with the linker script, the first issue was that I had to flip the order on PHDRS command (code comes first then headers), as it gave me an error that PHDR segment not covered by LOAD segment I knew that it wasn't correct to just flip the entries

after that I had a problem that I couldn't get physical and virtual memory addresses and the offset to be correct (even when I used the recipe in the book), I just kep trying in other ways until I got things barely working (I got shifted debug symbols at the very end)

I couldn't solve that problem, but in my opinion building a cross-compiler on Linux wasn't that complicated, to be honest, I was just scared of stepping into doing it just because it seemed complex, but using the steps ok OSDev made things easier, I just needed to modify the Makefiles after that (which was a bit tricky for me)

I also felt that linker scripts aren't documents and I couldn't really search about what's wrong when anything happened (I just kept randomly trying until things work), so that why I suggest that maybe using a cross compiler is a better option

but surely I'm not saying that was annoying, I'm grateful that those problems got me into the cross compiler thing, thanks 🙏