unix - Homebrew UNIX operating system

Age	Commit message (Collapse)	Author
2018-07-30	Added a new subroutine invlpg() to asm.s which simply checks the current	Jake Mannens
	CPU is not an i386 before executing the invlpg instruction with the provided address. This will once again make the kernel compatible with the i386 processor as executing the invlpg instruction without these checks would have resulted in an invalid opcode exception.
2018-07-11	Implemented a basic scheduler using an array of task structures in which	Jake Mannens
	each structure has a TSS inside, as well as several descriptor entries in the GDT pointing to each task's TSS. Task switching is performed in hardware by means of far jumping to the new task's TSS descriptor in the GDT. Task states are saved manually by copying the saved state from the interrupt handler's stack, back into the task's TSS. Added the function save_state() to sched.c which can be called from assembly to copy the state information of the suspended task from the current stack, to it's respective task structure. NOTE: this assumes that the pointer cstate has been set ahead of time to point to the state information on the stack, and that the pointer ctask has not yet been modified. Added the function reschedule() which is currently called from the timer's tick handler. Currently, this function merely alternates between the two tasks created in sched_init(), but in future, will be expanded to decided independently which task will run next. The function userspace_init() was renamed to the more appropriate sched_init(). Moved most of the code from the original userspace_init() to the new function create_proc() which sets up a virtual address space and state information, copies the specified binary into the new address space, then returns a pointer to the newly created tasks entry in the task table. Defined the type pid_t in unistd.h as a 16-bit unsigned integer. Added two new debugging system calls for checking which task is currently active. The getpid() system calls returns the caller's PID whilst the getpdir() call returns the physical location of the caller's page directory (the value of CR3). The getpdir() call can be used as a fallback to determine which task is actually running if the information in ctask or the getpid() call is faulty. Added two new subroutines; set_tss() and clear_tss() (whose prototypes are defined in asm/system.h) for managing the task-state descriptor entries in the GDT. set_tss() initializes a TSS descriptor and sets it's base pointer to the supplied TSS pointer whilst clear_tss() simply marks a TSS descriptor as 'not present' without clearing it.
2018-07-07	Added '-g' flag for GCC to all makefiles to ensure debugging information	Jake Mannens
	is produced. This may change later. Added the new directory 'lib' to the source tree which build lib.a, an archive containing common library routines for both the kernel and userspace code to use. Added the file string.c to the lib directory (as well as the appropriate headers in /include) which provides some basic functions from the standard C string library. Added a physical memory manager which is now located in memory.c. This memory manager tracks free pages from 1MB-8MB with a simple table and allocates memory in blocks of 4KB pages. Multiple pages can be allocated in which they are returned as a linked list. Added a 'page window' in memory.c which allows the temporary mapping of a single page at a time into the current address space. Moved all paging routines that were previously located in page.s over to memory.c where they have been re-implemented as a mixture of C and inline assembly. Moved the primative userspace routines from usrspace.s over to the new sched.c. The only remaining routine, usrcall is now located in asm.s as 'switch_to' which takes two arguments, pointers to the task structure and task state structure of the new task which is being switched to. Pages for userspace are now allocated dynamically. The user binary is loaded in at 1GB upwards. The user stack is located at the end of the 4GB address space with the lower 1GB being reserved for the kernel. Updated the link.ld file for the userspace binary to include the new starting address 0x40000000 (1GB). Renamed the symbols for the user binary blob to make them shorter.