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traps.s
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# void trap_init(void);
.func trap_init
.globl trap_init
trap_init:
# initialize trap functionality
# save `trap_vector` address to `mtvec` by `t0`
lui t0, %hi(trap_vector) # load upper 20 bits
addi t0, t0, %lo(trap_vector) # load lower 12 bits
csrw mtvec, t0
ret
.endfunc
.macro store_regs base
sw ra, 0(\base)
sw sp, 4(\base)
sw gp, 8(\base)
sw tp, 12(\base)
sw t0, 16(\base)
sw t1, 20(\base)
sw t2, 24(\base)
sw s0, 28(\base)
sw s1, 32(\base)
sw a0, 36(\base)
sw a1, 40(\base)
sw a2, 44(\base)
sw a3, 48(\base)
sw a4, 52(\base)
sw a5, 56(\base)
sw a6, 60(\base)
sw a7, 64(\base)
sw s2, 68(\base)
sw s3, 72(\base)
sw s4, 76(\base)
sw s5, 80(\base)
sw s6, 84(\base)
sw s7, 88(\base)
sw s8, 92(\base)
sw s9, 96(\base)
sw s10, 100(\base)
sw s11, 104(\base)
sw t3, 108(\base)
sw t4, 112(\base)
sw t5, 116(\base)
sw t6, 120(\base)
.endm
.macro load_regs base
lw ra, 0(\base)
lw sp, 4(\base)
lw gp, 8(\base)
lw tp, 12(\base)
lw t0, 16(\base)
lw t1, 20(\base)
lw t2, 24(\base)
lw s0, 28(\base)
lw s1, 32(\base)
lw a0, 36(\base)
lw a1, 40(\base)
lw a2, 44(\base)
lw a3, 48(\base)
lw a4, 52(\base)
lw a5, 56(\base)
lw a6, 60(\base)
lw a7, 64(\base)
lw s2, 68(\base)
lw s3, 72(\base)
lw s4, 76(\base)
lw s5, 80(\base)
lw s6, 84(\base)
lw s7, 88(\base)
lw s8, 92(\base)
lw s9, 96(\base)
lw s10, 100(\base)
lw s11, 104(\base)
lw t3, 108(\base)
lw t4, 112(\base)
lw t5, 116(\base)
lw t6, 120(\base)
.endm
.func trap_vector
.globl trap_vector
.align 4
trap_vector:
# save context
# mscratch is a pointer holds the address of contexts
csrrw t6, mscratch, t6
# save the registers.
store_regs t6
mv a2, t6
mv t5, t6
csrr t6, mscratch
sw t6, 120(t5)
# save a copy of mepc
csrr a0, mepc
sw a0, 124(t5)
# restore the context pointer
csrw mscratch, t5
# call trap_handler
csrr a1, mcause
call trap_handler
# in case that return address was changed
csrw mepc, a0
# restore context
csrr t6, mscratch
load_regs t6
mret
.endfunc
.end