An Intro to Kernel Development - MMU - Part 10

In the previous blog we have added the implementation for kmalloc. In this part, I have debugged all the bugs in my kmalloc implementation to make it work seemlessly. I have added all the new helpers for kmalloc and called it in my kmain, i got an error, that is not related to kmalloc, i have an "Kernel Inited" print message in top of my kmain, and that didn't get printed, so i knew i haven't reached my code, and my existing code just decided to stop working, only thing have changed i have added some new code, i uncomment all my new code, boom, everything works, that's all had and from there i had to bash my head for hour to figure out that because my .text section was not aligned, and as i have added new code, it was overflowing that section to overwrite stuff, which messed by the entire structure. Bug: .text : { *(.text*); } .rodata : { *(.rodata*) } Fixed: .text : { *(.text*); } . = ALIGN(4096); .rodata : { *(.rodata*) } I have Learned that because my setup fully written by me, i have to make sure i add things that fexible, if not i will be debugging random errors like this in future. I have streamed the entire debugging session on YouTube. You just wrote a value into the memory, instruction didnt throw any faults, but you dont see the value in the memory, what do you think is going wrong here? This is what i had me stuck for 3 hours, i ripped by MMU code into peices add fixed all of stuff, still i couldn't fix the bug. - VA => PA page table entry exist - 0xffff01f40000 = 0x000001f40000 (i confirmed this manually in gdb, that it exist) - Write instruction works fine - I dont have an cache enabled in my setup I had lot of minor bugs that i fixed as i read my code again and again, but nothing solved the core issue. I was hopeless looking in qemu logs, that when i saw a error message "pflash_write: Unimplemented flash cmd sequence (offset 0000000002ee0000, wcycle 0x0 cmd 0x0 value 0x66)" so i was starting my physical pages from 0x000000000000, but qemu maps ram from the location we give in command-line, which is 0x80000000 in my case. so i was never writing into RAM I fixed it by make my pages tables start from within 0x80000000, boom, everything worked. well, atleast i am happy i figured this finally after lot of bashing, you can watch then entire session on youtube.