proc.h

// Per-CPU state
struct cpu {
  uchar id;
  uchar apicid;              // Local APIC ID
  struct context *scheduler; // swtch() here to enter scheduler
  volatile uint started;     // Has the CPU started?
  int ncli;                  // Depth of pushcli nesting.
  int intena;                // Were interrupts enabled before pushcli?
  void *local;               // CPU-local storage; see seginit()
};

extern struct cpu cpus[NCPU];
extern int ncpu;

// Per-CPU variables, holding pointers to the
// current cpu and to the current process.
// The asm suffix tells gcc to use "%gs:(-16)" to refer to cpu
// and "%gs:(-8)" to refer to proc.  seginit sets up the
// %gs segment register so that %gs refers to the memory
// holding those two variables in the local cpu's struct cpu.
// This is similar to how thread-local variables are implemented
// in thread libraries such as Linux pthreads.
extern __thread struct cpu *cpu;
extern __thread struct proc *proc;

//PAGEBREAK: 17
// Saved registers for kernel context switches.
// Don't need to save all the segment registers (%cs, etc),
// because they are constant across kernel contexts.
// Don't need to save %rax, %rcx, etc., because the
// x86 convention is that the caller has saved them.
// Contexts are stored at the bottom of the stack they
// describe; the stack pointer is the address of the context.
// The layout of the context matches the layout of the stack in swtch.S
// at the "Switch stacks" comment. Switch doesn't save rip explicitly,
// but it is on the stack and allocproc() manipulates it.
struct context {
  addr_t r15;
  addr_t r14;
  addr_t r13;
  addr_t r12;
  addr_t rbx;
  addr_t rbp;
  addr_t rip;
};

enum procstate { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };

// Per-process state
struct proc {
  addr_t sz;                   // Size of process memory (bytes)
  pde_t* pgdir;                // Page table
  char *kstack;                // Bottom of kernel stack for this process
  enum procstate state;        // Process state
  int pid;                     // Process ID
  struct proc *parent;         // Parent process
  struct trapframe *tf;        // Trap frame for current syscall
  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