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ping-pong exercise

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This commit is contained in:
Robert Morris 2019-07-24 10:39:05 -04:00
parent 8f6865d1f1
commit b4f89bb529
1 changed files with 5 additions and 5 deletions
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10
kernel/trampoline.S
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@ -2,8 +2,8 @@
# code to switch between user and kernel space.
#
# this code is mapped at the same virtual address
# in user and kernel space so that it can switch
# page tables.
# in user and kernel space so that it continues
# to work when it switches page tables.
#
# kernel.ld causes trampout to be aligned
# to a page boundary.
@ -18,7 +18,7 @@ trampout:
# a0: p->tf in user page table
# a1: new value for satp, for user page table
# switch to user page table.
# switch to the user page table.
sfence.vma zero, zero
csrw satp, a1
@ -59,11 +59,11 @@ trampout:
ld t5, 272(a0)
ld t6, 280(a0)
# restore user a0, and save p->tf
# restore user a0, and save p->tf in sscratch
csrrw a0, sscratch, a0
# return to user mode and user pc.
# caller has set up sstatus and sepc.
# usertrapret() set up sstatus and sepc.
sret
.align 4