112 lines
2.5 KiB
C
112 lines
2.5 KiB
C
#include "types.h"
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#include "param.h"
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#include "memlayout.h"
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#include "riscv.h"
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#include "proc.h"
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#include "spinlock.h"
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#include "defs.h"
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struct spinlock tickslock;
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uint ticks;
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extern char trampstart[], trampvec[];
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void kerneltrap();
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void
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trapinit(void)
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{
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int i;
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// send interrupts and exceptions to kerneltrap().
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w_stvec((uint64)kerneltrap);
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initlock(&tickslock, "time");
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}
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//
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// handle an interrupt, exception, or system call from user space.
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// called from trampoline.S
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//
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void
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usertrap(void)
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{
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if((r_sstatus() & SSTATUS_SPP) != 0)
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panic("usertrap: not from user mode");
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// send interrupts and exceptions to kerneltrap(),
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// since we're now in the kernel.
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w_stvec((uint64)kerneltrap);
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struct proc *p = myproc();
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// save user program counter.
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p->tf->epc = r_sepc();
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if(r_scause() == 8){
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// system call
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// sepc points to the ecall instruction,
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// but we want to return to the next instruction.
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p->tf->epc += 4;
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syscall();
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} else {
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printf("usertrap(): unexpected scause 0x%x pid=%d\n", r_scause(), p->pid);
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panic("usertrap");
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}
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usertrapret();
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}
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//
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// return to user space
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//
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void
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usertrapret(void)
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{
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struct proc *p = myproc();
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// XXX turn off interrupts, since we're switching
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// now from kerneltrap() to usertrap().
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// send interrupts and exceptions to trampoline.S
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w_stvec(TRAMPOLINE + (trampvec - trampstart));
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// set up values that trampoline.S will need when
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// the process next re-enters the kernel.
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p->tf->kernel_satp = r_satp();
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p->tf->kernel_sp = (uint64)p->kstack + PGSIZE;
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p->tf->kernel_trap = (uint64)usertrap;
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// set up the registers that trampoline.S's sret will use
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// to get to user space.
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// set S Previous Privilege mode to User.
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unsigned long x = r_sstatus();
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x &= ~SSTATUS_SPP; // clear SPP to 0 for user mode
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w_sstatus(x);
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// set S Exception Program Counter to the saved user pc.
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w_sepc(p->tf->epc);
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// tell trampline.S the user page table to switch to.
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uint64 satp = MAKE_SATP(p->pagetable);
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// jump to trampoline.S at the top of memory, which
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// switches to the user page table, restores user registers,
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// and switches to user mode with sret.
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((void (*)(uint64,uint64))TRAMPOLINE)(TRAMPOLINE - PGSIZE, satp);
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}
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// interrupts and exceptions from kernel code go here,
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// on whatever the current kernel stack is.
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// must be 4-byte aligned to fit in stvec.
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void __attribute__ ((aligned (4)))
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kerneltrap()
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{
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if((r_sstatus() & SSTATUS_SPP) == 0)
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panic("kerneltrap: not from supervisor mode");
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panic("kerneltrap");
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}
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