142 lines
3.5 KiB
ArmAsm
142 lines
3.5 KiB
ArmAsm
#
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# code to switch between user and kernel space.
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#
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# this code is mapped at the same virtual address
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# (TRAMPOLINE) in user and kernel space so that
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# it continues to work when it switches page tables.
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#
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# kernel.ld causes this to be aligned
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# to a page boundary.
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#
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.section trampsec
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.globl trampoline
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trampoline:
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.align 4
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.globl uservec
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uservec:
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#
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# trap.c sets stvec to point here, so
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# traps from user space start here,
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# in supervisor mode, but with a
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# user page table.
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#
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# sscratch points to where the process's p->tf is
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# mapped into user space, at TRAPFRAME.
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#
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# swap a0 and sscratch
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# so that a0 is TRAPFRAME
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csrrw a0, sscratch, a0
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# save the user registers in TRAPFRAME
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sd ra, 40(a0)
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sd sp, 48(a0)
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sd gp, 56(a0)
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sd tp, 64(a0)
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sd t0, 72(a0)
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sd t1, 80(a0)
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sd t2, 88(a0)
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sd s0, 96(a0)
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sd s1, 104(a0)
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sd a1, 120(a0)
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sd a2, 128(a0)
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sd a3, 136(a0)
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sd a4, 144(a0)
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sd a5, 152(a0)
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sd a6, 160(a0)
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sd a7, 168(a0)
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sd s2, 176(a0)
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sd s3, 184(a0)
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sd s4, 192(a0)
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sd s5, 200(a0)
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sd s6, 208(a0)
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sd s7, 216(a0)
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sd s8, 224(a0)
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sd s9, 232(a0)
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sd s10, 240(a0)
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sd s11, 248(a0)
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sd t3, 256(a0)
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sd t4, 264(a0)
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sd t5, 272(a0)
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sd t6, 280(a0)
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# save the user a0 in p->tf->a0
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csrr t0, sscratch
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sd t0, 112(a0)
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# restore kernel stack pointer from p->tf->kernel_sp
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ld sp, 8(a0)
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# make tp hold the current hartid, from p->tf->kernel_hartid
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ld tp, 32(a0)
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# load the address of usertrap(), p->tf->kernel_trap
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ld t0, 16(a0)
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# restore kernel page table from p->tf->kernel_satp
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ld t1, 0(a0)
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csrw satp, t1
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sfence.vma zero, zero
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# a0 is no longer valid, since the kernel page
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# table does not specially map p->tf.
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# jump to usertrap(), which does not return
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jr t0
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.globl userret
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userret:
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# userret(TRAPFRAME, pagetable)
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# switch from kernel to user.
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# usertrapret() calls here.
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# a0: TRAPFRAME, in user page table.
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# a1: user page table, for satp.
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# switch to the user page table.
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csrw satp, a1
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sfence.vma zero, zero
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# put the saved user a0 in sscratch, so we
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# can swap it with our a0 (TRAPFRAME) in the last step.
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ld t0, 112(a0)
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csrw sscratch, t0
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# restore all but a0 from TRAPFRAME
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ld ra, 40(a0)
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ld sp, 48(a0)
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ld gp, 56(a0)
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ld tp, 64(a0)
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ld t0, 72(a0)
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ld t1, 80(a0)
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ld t2, 88(a0)
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ld s0, 96(a0)
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ld s1, 104(a0)
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ld a1, 120(a0)
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ld a2, 128(a0)
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ld a3, 136(a0)
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ld a4, 144(a0)
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ld a5, 152(a0)
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ld a6, 160(a0)
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ld a7, 168(a0)
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ld s2, 176(a0)
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ld s3, 184(a0)
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ld s4, 192(a0)
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ld s5, 200(a0)
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ld s6, 208(a0)
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ld s7, 216(a0)
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ld s8, 224(a0)
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ld s9, 232(a0)
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ld s10, 240(a0)
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ld s11, 248(a0)
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ld t3, 256(a0)
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ld t4, 264(a0)
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ld t5, 272(a0)
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ld t6, 280(a0)
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# restore user a0, and save TRAPFRAME in sscratch
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csrrw a0, sscratch, a0
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# return to user mode and user pc.
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# usertrapret() set up sstatus and sepc.
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sret
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