text: 
  // Saved registers for kernel context switches.
  struct context {
    uint64 ra;
    uint64 sp;
  
    // callee-saved
    uint64 s0;
    uint64 s1;
    uint64 s2;
    uint64 s3;
    uint64 s4;
    uint64 s5;
    uint64 s6;
    uint64 s7;
    uint64 s8;
    uint64 s9;
    uint64 s10;
    uint64 s11;
  };
  
  // Per-CPU state.
  struct cpu {
    struct proc *proc;          // The process running on this cpu, or null.
    struct context context;     // swtch() here to enter scheduler().
    int noff;                   // Depth of push_off() nesting.
    int intena;                 // Were interrupts enabled before push_off()?
  };
  
  extern struct cpu cpus[NCPU];
  
  // per-process data for the trap handling code in trampoline.S.
  // sits in a page by itself just under the trampoline page in the
  // user page table. not specially mapped in the kernel page table.
  // the sscratch register points here.
  // uservec in trampoline.S saves user registers in the trapframe,
  // then initializes registers from the trapframe's
  // kernel_sp, kernel_hartid, kernel_satp, and jumps to kernel_trap.
  // usertrapret() and userret in trampoline.S set up
  // the trapframe's kernel_*, restore user registers from the
  // trapframe, switch to the user page table, and enter user space.
  // the trapframe includes callee-saved user registers like s0-s11 because the
  // return-to-user path via usertrapret() doesn't return through
  // the entire kernel call stack.
  struct trapframe {
    /*   0 */ uint64 kernel_satp;   // kernel page table
    /*   8 */ uint64 kernel_sp;     // top of process's kernel stack
    /*  16 */ uint64 kernel_trap;   // usertrap()
    /*  24 */ uint64 epc;           // saved user program counter
    /*  32 */ uint64 kernel_hartid; // saved kernel tp
    /*  40 */ uint64 ra;
    /*  48 */ uint64 sp;
    /*  56 */ uint64 gp;
    /*  64 */ uint64 tp;
    /*  72 */ uint64 t0;
    /*  80 */ uint64 t1;
    /*  88 */ uint64 t2;
    /*  96 */ uint64 s0;
    /* 104 */ uint64 s1;
    /* 112 */ uint64 a0;
    /* 120 */ uint64 a1;
    /* 128 */ uint64 a2;
    /* 136 */ uint64 a3;
    /* 144 */ uint64 a4;
    /* 152 */ uint64 a5;
    /* 160 */ uint64 a6;
    /* 168 */ uint64 a7;
    /* 176 */ uint64 s2;
    /* 184 */ uint64 s3;
    /* 192 */ uint64 s4;
    /* 200 */ uint64 s5;
    /* 208 */ uint64 s6;
    /* 216 */ uint64 s7;
    /* 224 */ uint64 s8;
    /* 232 */ uint64 s9;
    /* 240 */ uint64 s10;
    /* 248 */ uint64 s11;
    /* 256 */ uint64 t3;
    /* 264 */ uint64 t4;
    /* 272 */ uint64 t5;
    /* 280 */ uint64 t6;
  };
  
  enum procstate { UNUSED, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
  
  // CMT:proc结构体是进程控制块的一部分,PCB中还有user结构
  // Per-process state
  struct proc {
    // 这个是啥？为什么要有个Lock?
    struct spinlock lock;
  
    // p->lock must be held when using these:
    enum procstate state;        // Process state
    struct proc *parent;         // Parent process
    void *chan;                  // If non-zero, sleeping on chan
    int killed;                  // If non-zero, have been killed
    int xstate;                  // Exit status to be returned to parent's wait
    int pid;                     // Process ID
  
    // these are private to the process, so p->lock need not be held.
    uint64 kstack;               // Virtual address of kernel stack
    uint64 sz;                   // Size of process memory (bytes)
    pagetable_t pagetable;       // User page table
    struct trapframe *trapframe; // data page for trampoline.S // 映射进程到内核
    struct context context;      // swtch() here to run process
    struct file *ofile[NOFILE];  // Open files
    struct inode *cwd;           // Current directory
    char name[16];               // Process name (debugging)
  };
  