You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
64 lines
2.1 KiB
64 lines
2.1 KiB
3 years ago
|
.section trapsec
|
||
|
|
.globl trap_sec_start
|
||
|
|
trap_sec_start:
|
||
|
|
|
||
|
|
#include "util/load_store.S"
|
||
|
|
|
||
|
|
#
|
||
|
|
# When a trap (e.g., a syscall from User mode in this lab) happens and the computer
|
||
|
|
# enters the Supervisor mode, the computer will continue to execute the following
|
||
|
|
# function (smode_trap_vector) to actually handle the trap.
|
||
|
|
#
|
||
|
|
# NOTE: sscratch points to the trapframe of current process before entering
|
||
|
|
# smode_trap_vector. It is done by reture_to_user function (defined below) when
|
||
|
|
# scheduling a user-mode application to run.
|
||
|
|
#
|
||
|
|
.globl smode_trap_vector
|
||
|
|
.align 4
|
||
|
|
smode_trap_vector:
|
||
|
|
# swap a0 and sscratch, so that points a0 to the trapframe of current process
|
||
|
|
csrrw a0, sscratch, a0
|
||
|
|
|
||
|
|
# save the context (user registers) of current process in its trapframe.
|
||
|
|
addi t6, a0 , 0
|
||
|
|
|
||
|
|
# store_all_registers is a macro defined in util/load_store.S, it stores contents
|
||
|
|
# of all general purpose registers into a piece of memory started from [t6].
|
||
|
|
store_all_registers
|
||
|
|
|
||
|
|
# come back to save a0 register before entering trap handling in trapframe
|
||
|
|
# [t0]=[sscratch]
|
||
|
|
csrr t0, sscratch
|
||
|
|
sd t0, 72(a0)
|
||
|
|
|
||
|
|
# use the "user kernel" stack (whose pointer stored in p->trapframe->kernel_sp)
|
||
|
|
ld sp, 248(a0)
|
||
|
|
|
||
|
|
# load the address of smode_trap_handler() from p->trapframe->kernel_trap
|
||
|
|
ld t0, 256(a0)
|
||
|
|
|
||
|
|
# jump to smode_trap_handler() that is defined in kernel/trap.c
|
||
|
|
jr t0
|
||
|
|
|
||
|
|
#
|
||
|
|
# return from Supervisor mode to User mode, transition is made by using a trapframe,
|
||
|
|
# which stores the context of a user application.
|
||
|
|
# return_to_user() takes one parameter, i.e., the pointer (a0 register) pointing to a
|
||
|
|
# trapframe (defined in kernel/process.h) of the process.
|
||
|
|
#
|
||
|
|
.globl return_to_user
|
||
|
|
return_to_user:
|
||
|
|
# [sscratch]=[a0], save a0 in sscratch, so sscratch points to a trapframe now.
|
||
|
|
csrw sscratch, a0
|
||
|
|
|
||
|
|
# let [t6]=[a0]
|
||
|
|
addi t6, a0, 0
|
||
|
|
|
||
|
|
# restore_all_registers is a assembly macro defined in util/load_store.S.
|
||
|
|
# the macro restores all registers from trapframe started from [t6] to all general
|
||
|
|
# purpose registers, so as to resort the execution of a process.
|
||
|
|
restore_all_registers
|
||
|
|
|
||
|
|
# return to user mode and user pc.
|
||
|
|
sret
|