Pie, Interrupts, Symmetric MultiProcessing

[GglLfr]

Summary

• Make the kernel compile with -fPIE
• Increased amount of stack pages (very important)
• Bootloader no longer controls higher-half addressing
• Virtual mapping is now done completely by the kernel, making the bootloader significantly leaner; see next point
• Kernel now has a "setup" phase: after jumping from bootloader, it enters setup_identity_mapped which maps the kernel ELF segments, boot info page, and stack pages into higher-half (starts at 0xffff_8000_0000_0000); then it enables virtual-mapping via cr3, and enters setup_virtual_mapped which sets logger up and physical page allocator; finally, it moves on to main
• BOOT_INFO is no longer a static, but a reference pass through rdi
• Symbol relocations is done twice; once in the bootloader for adjusting to physical addresses returned by UEFI, and once more in the kernel (relocates itself, Elf64_Rela information relayed by the bootloader) after higher-half mapping
• Virtual mapper is now accessible as a global static reference
• Added a global physical page allocator

To-do

• Unmap the identity virtual addresses
• Add a kernel "stack guard," i.e. an unmapped page as the bottom-most page in higher-half addressing to "catch" kernel stack overflows by page faulting
• The page allocator can't deallocate yet

[GglLfr]

Drafted, because I forgot that the framebuffer isn't mapped yet

[GglLfr]

Framebuffer is now mapped!