test: store curproc at top of stack

I don't actually think this is worthwhile, but I figured
I would check it in before reverting it, so that it can
be in the revision history.

Pros:
  * curproc doesn't need to turn on/off interrupts
  * scheduler doesn't have to edit curproc anymore

Cons:
  * it's ugly
  * all the stack computation is more complicated.
  * it doesn't actually simplify anything but curproc,
    and even curproc is harder to follow.

1 files changed, 7 insertions, 10 deletions

diff --git a/proc.c b/proc.c
index e139c39..d937258 100644
--- a/proc.c
+++ b/proc.c
@@ -75,7 +75,7 @@ setupsegs(struct proc *p)
   c = &cpus[cpu()];
   c->ts.ss0 = SEG_PROCSTACK << 3;
   if(p)
-    c->ts.esp0 = (uint)(p->kstack + KSTACKSIZE);
+    c->ts.esp0 = (uint)(p->kstack + KSTACKTOP);
   else
     c->ts.esp0 = 0xffffffff;
 
@@ -118,7 +118,8 @@ copyproc(struct proc *p)
     np->state = UNUSED;
     return 0;
   }
-  np->tf = (struct trapframe*)(np->kstack + KSTACKSIZE) - 1;
+  *(void**)(np->kstack + KSTACKTOP) = np;
+  np->tf = (struct trapframe*)(np->kstack + KSTACKTOP) - 1;
 
   if(p){  // Copy process state from p.
     np->parent = p;
@@ -187,12 +188,10 @@ userinit(void)
 struct proc*
 curproc(void)
 {
-  struct proc *p;
+  uint esp;
 
-  pushcli();
-  p = cpus[cpu()].curproc;
-  popcli();
-  return p;
+  asm volatile("movl %%esp, %0" : "=a" (esp));
+  return *(struct proc**)((esp & ~(KSTACKSIZE-1)) + KSTACKTOP);
 }
 
 //PAGEBREAK: 42
@@ -223,14 +222,12 @@ scheduler(void)
       // Switch to chosen process.  It is the process's job
       // to release proc_table_lock and then reacquire it
       // before jumping back to us.
-      c->curproc = p;
       setupsegs(p);
       p->state = RUNNING;
       swtch(&c->context, &p->context);
 
       // Process is done running for now.
       // It should have changed its p->state before coming back.
-      c->curproc = 0;
       setupsegs(0);
     }
 
@@ -239,7 +236,7 @@ scheduler(void)
 }
 
 // Enter scheduler.  Must already hold proc_table_lock
-// and have changed curproc[cpu()]->state.
+// and have changed cp->state.
 void
 sched(void)
 {