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// Segments in proc->gdt
#define SEG_KCODE 1 // kernel code
#define SEG_KDATA 2 // kernel data+stack
#define SEG_UCODE 3
#define SEG_UDATA 4
#define SEG_TSS 5 // this process's task state
#define NSEGS 6
// Saved registers for kernel context switches.
// Don't need to save all the %fs etc. segment registers,
// because they are constant across kernel contexts.
// Save all the regular registers so we don't need to care
// which are caller save, but not the return register %eax.
// (Not saving %eax just simplifies the switching code.)
// The layout of context must match code in swtch.S.
struct context {
int eip;
int esp;
int ebx;
int ecx;
int edx;
int esi;
int edi;
int ebp;
// Per-process state
struct proc {
char *mem; // Start of process memory (kernel address)
uint sz; // Size of process memory (bytes)
char *kstack; // Bottom of kernel stack for this process
enum proc_state state; // Process state
int pid; // Process ID
struct proc *parent; // Parent 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
struct context context; // Switch here to run process
struct trapframe *tf; // Trap frame for current interrupt
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
// Per-CPU state
struct cpu {
uchar apicid; // Local APIC ID
struct proc *curproc; // Process currently running.
struct context context; // Switch here to enter scheduler
struct taskstate ts; // Used by x86 to find stack for interrupt
struct segdesc gdt[NSEGS]; // x86 global descriptor table
volatile uint booted; // Has the CPU started?
int ncli; // Depth of pushcli nesting.
int intena; // Were interrupts enabled before pushcli?
extern struct cpu cpus[NCPU];
extern int ncpu;
// "cp" is a short alias for curproc().
// It gets used enough to make this worthwhile.
#define cp curproc()