a few core -> CPU

get rid of PDF generating support

kernel/entry.S

@@ -2,7 +2,7 @@
         # there seem to be provided by qemu, as if it
         # were a ROM. the code at 0x1000 jumps to
         # 0x8000000, the _start function here,
-        # in machine mode.
+        # in machine mode. each CPU starts here.
 .section .data
 .globl stack0
 .section .text
@@ -11,8 +11,9 @@
 .globl _entry
 _entry:
 	# set up a stack for C.
-        # stack0 is declared in start,
-        # with 4096 bytes per CPU.
+        # stack0 is declared in start.c,
+        # with a 4096-byte stack per CPU.
+        # sp = stack0 + (hartid * 4096)
         la sp, stack0
         li a0, 1024*4
 	csrr a1, mhartid

kernel/proc.c

@@ -46,7 +46,7 @@ cpuid()
   return id;
 }
 
-// Return this core's cpu struct.
+// Return this CPU's cpu struct.
 // Interrupts must be disabled.
 struct cpu*
 mycpu(void) {

kernel/spinlock.c

@@ -52,7 +52,7 @@ release(struct spinlock *lk)
 
   // Tell the C compiler and the CPU to not move loads or stores
   // past this point, to ensure that all the stores in the critical
-  // section are visible to other cores before the lock is released.
+  // section are visible to other CPUs before the lock is released.
   // On RISC-V, this turns into a fence instruction.
   __sync_synchronize();