The main functions of head.s: reload each data segment register, reset the interrupt descriptor table, reset the global descriptor table, set the paging processing mechanism (a page directory table and 4 page tables), push the main function on the stack, and execute the head After finishing, pop up main and go to main function.
Reload register
Set interrupt description table
Set up the global description table
Call main function
Set page directory and page table
Empty 5 pages of memory
Set values for 4 items of the page directory
Assign a value to each item of the 4-page table: including the corresponding physical address and identification
Store the base address of the page directory in register cr3
End of head.s , run the main program
