// 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 scheduler;   // 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];

//PAGEBREAK: 17

// per-process data for the early 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.
// trampoline.S saves user registers, then restores kernel_sp and
// kernel_satp.
// includes callee-saved 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;
  /*   8 */ uint64 kernel_sp;
  /*  16 */ uint64 kernel_trap; // usertrap()
  /*  24 */ uint64 epc; // saved user program counter
  /*  32 */ uint64 hartid;
  /*  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 };

// Per-process state
struct proc {
  struct spinlock lock;
  char *kstack;                // Bottom of kernel stack for this process
  uint64 sz;                   // Size of process memory (bytes)
  pagetable_t pagetable;       // Page table
  enum procstate state;        // Process state
  int pid;                     // Process ID
  struct proc *parent;         // Parent process
  struct trapframe *tf;        // data page for trampoline.S
  struct context context;      // swtch() here to run process
  void *chan;                  // If non-zero, sleeping on chan
  int killed;                  // If non-zero, have been killed
  struct file *ofile[NOFILE];  // Open files
  struct inode *cwd;           // Current directory
  char name[16];               // Process name (debugging)
};

// Process memory is laid out contiguously, low addresses first:
//   text
//   original data and bss
//   fixed-size stack
//   expandable heap