k0iry/xv6-jos-i386-lab

All Labs implementation of 6.828 2018 OS course of MIT.

Hi there 👋

xv6-jos-i386-lab's Issues

dereference a null pointer

make virtual address 0 isn’t mapped for user programs

exploit the kernel

if we delete check: if(ph.vaddr + ph.memsz < ph.vaddr) in exec.c, how can we exploit the kernel by loading code directly into the kernel space?

why breakpoint exception generates a general protection?

Optimize code for disk interrupt driver

Currently I handle the disk operation totally in kernel mode, is it possible to let user space do the handlings?

We passed quite a lot parameters in system calls, can we minimize the work for our code?

use STAB for printing out names

in syscall.c, a name table would not be needed

sysenter spinlock

because when we enter the kernel space from user mode, we use spin lock to only let one at a time trap into the kernel. So we add code here in trap.c

if ((tf->tf_cs & 3) == 3) {
    lock_kernel();
    .....

But with sysenter fast system call, we also need to do the similar stuff, adding the lock, but it seems a bit tricky here. Need to find a way to add something like below in file trapentry.S:

.text
.globl sysenter_handler
.type sysenter_handler, @function
.align 2
# bypass trap to reach syscall directly
sysenter_handler:
call spin_lock(&kernel_lock)
pushl %edi
pushl %ebx
pushl %ecx
pushl %edx
pushl %eax
# only support 4 syscall arguments
call syscall
# movl $0x174, %ecx
# movl $0, %edx
# movl $(GD_UT), %eax	/* no need, because of continuity, GD_UT will be found by adding 16(0x10) to GD_KT */
# wrmsr
movl %esi, %edx
movl %ebp, %ecx
call spin_unlock(&kernel_lock)
sysexit

support interpreter like #!

For example, if exec is called to run myprog arg1 and myprog’s first line is #!/interp, then exec runs /interp with command line /interp myprog arg1. Implement support for this convention in xv6.

support super pages by enable PTE_PS for appropriate processors like pentium

1. How to use PTE_PS flag to enable larger page size (4 MB) ?

Maybe need to use qemu-system-x86_64 processor, could go back and have a try, now I just add show memory mapping function

write end address should use %p to format

xv6-jos-i386-lab/0001-homework-syscall-part1.patch

Line 282 in 9ad90a1

+ cprintf("pipe read end here: %p, write end here: %d\n", fd, fd + 1);

Modify xv6 so that the pages for the kernel are shared among processes, which reduces memory consumption.

tidy up trap handler code, remove similar code

Challenge! You probably have a lot of very similar code right now, between the lists of TRAPHANDLER in trapentry.S and their installations in trap.c. Clean this up. Change the macros in trapentry.S to automatically generate a table for trap.c to use. Note that you can switch between laying down code and data in the assembler by using the directives .text and .data.

implement fine-grained locking in JOS

drop the big kernel lock, implement these locks:

• page free list lock for memory allocation and deallocation
• scheduler lock for running processes on SMP
• console lock for printing messages
• ipc lock for inter-process communication

save & restore caller-saved registers for signal handler

mainly for CPU alarm handler, see: https://pdos.csail.mit.edu/6.828/2018/homework/xv6-alarm.html

optional challenges.