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64 lines
2.1 KiB
64 lines
2.1 KiB
2 years ago
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.section trapsec
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.globl trap_sec_start
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trap_sec_start:
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#include "util/load_store.S"
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#
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# When a trap (e.g., a syscall from User mode in this lab) happens and the computer
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# enters the Supervisor mode, the computer will continue to execute the following
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# function (smode_trap_vector) to actually handle the trap.
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#
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# NOTE: sscratch points to the trapframe of current process before entering
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# smode_trap_vector. It is done by reture_to_user function (defined below) when
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# scheduling a user-mode application to run.
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#
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.globl smode_trap_vector
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.align 4
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smode_trap_vector:
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# swap a0 and sscratch, so that points a0 to the trapframe of current process
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csrrw a0, sscratch, a0
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# save the context (user registers) of current process in its trapframe.
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addi t6, a0 , 0
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# store_all_registers is a macro defined in util/load_store.S, it stores contents
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# of all general purpose registers into a piece of memory started from [t6].
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store_all_registers
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# come back to save a0 register before entering trap handling in trapframe
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# [t0]=[sscratch]
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csrr t0, sscratch
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sd t0, 72(a0)
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# use the "user kernel" stack (whose pointer stored in p->trapframe->kernel_sp)
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ld sp, 248(a0)
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# load the address of smode_trap_handler() from p->trapframe->kernel_trap
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ld t0, 256(a0)
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# jump to smode_trap_handler() that is defined in kernel/trap.c
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jr t0
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#
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# return from Supervisor mode to User mode, transition is made by using a trapframe,
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# which stores the context of a user application.
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# return_to_user() takes one parameter, i.e., the pointer (a0 register) pointing to a
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# trapframe (defined in kernel/process.h) of the process.
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#
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.globl return_to_user
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return_to_user:
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# [sscratch]=[a0], save a0 in sscratch, so sscratch points to a trapframe now.
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csrw sscratch, a0
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# let [t6]=[a0]
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addi t6, a0, 0
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# restore_all_registers is a assembly macro defined in util/load_store.S.
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# the macro restores all registers from trapframe started from [t6] to all general
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# purpose registers, so as to resort the execution of a process.
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restore_all_registers
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# return to user mode and user pc.
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sret
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