diff --git a/Makefile b/Makefile
index 1363245..f8cc863 100644
--- a/Makefile
+++ b/Makefile
@@ -135,7 +135,6 @@ UPROGS=\
 	$U/_wc\
 	$U/_zombie\
 	$U/_clear\
-	$U/_halt\
 
 fs.img: mkfs/mkfs README.md $(UPROGS)
 	mkfs/mkfs fs.img README.md $(UPROGS)
diff --git a/kernel/defs.h b/kernel/defs.h
index ecbcf26..a89c445 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -64,34 +64,10 @@ void ramdiskinit(void);
 void ramdiskintr(void);
 void ramdiskrw(struct buf *);
 
-/**
- * Kernel memory allocator
- *
- * Allocate one 4096-byte page of physical memory.
- * Returns a pointer that the kernel can use.
- * Returns 0 if the memory cannot be allocated.
- * See: kalloc.c
- */
+// kalloc.c
 void *kalloc(void);
-
-/**
- * Kernel memory allocator
- *
- * Free the page of physical memory pointed at by pa,
- * which normally should have been returned by a
- * call to kalloc().  (The exception is when
- * initializing the allocator; see kinit above.)
- * See: kalloc.c
- */
-void kfree(void *);
-
-/**
- * Initialize kernel memory allocator
- *
- * Called by main() on the way to the kernel's main loop.
- * See: kalloc.c
- */
-void kinit(void);
+void  kfree(void *);
+void  kinit(void);
 
 // log.c
 void initlog(int, struct superblock *);
diff --git a/kernel/kalloc.c b/kernel/kalloc.c
index b880933..a3de3d5 100644
--- a/kernel/kalloc.c
+++ b/kernel/kalloc.c
@@ -3,23 +3,21 @@
 // and pipe buffers. Allocates whole 4096-byte pages.
 
 #include "types.h"
+#include "param.h"
 #include "memlayout.h"
 #include "spinlock.h"
 #include "riscv.h"
 #include "defs.h"
 
-/** Free list of physical pages. */
 void freerange(void *pa_start, void *pa_end);
 
-/** first address after kernel. defined by kernel.ld. */
-extern char end[];
+extern char end[]; // first address after kernel.
+                   // defined by kernel.ld.
 
-/** A run is a node in the free list. */
 struct run {
   struct run *next;
 };
 
-/** Kernel memory allocator. */
 struct {
   struct spinlock lock;
   struct run     *freelist;
@@ -41,6 +39,10 @@ freerange(void *pa_start, void *pa_end)
     kfree(p);
 }
 
+// Free the page of physical memory pointed at by pa,
+// which normally should have been returned by a
+// call to kalloc().  (The exception is when
+// initializing the allocator; see kinit above.)
 void
 kfree(void *pa)
 {
@@ -60,6 +62,9 @@ kfree(void *pa)
   release(&kmem.lock);
 }
 
+// Allocate one 4096-byte page of physical memory.
+// Returns a pointer that the kernel can use.
+// Returns 0 if the memory cannot be allocated.
 void *
 kalloc(void)
 {
diff --git a/kernel/kernel.ld b/kernel/kernel.ld
index 2844edf..7ab21d8 100644
--- a/kernel/kernel.ld
+++ b/kernel/kernel.ld
@@ -15,25 +15,12 @@ SECTIONS
    * that reference the functions in your object file.
    */
   .text : {
-    /* Match any section that starts with .text. */
     *(.text .text.*)
-
-    /* Align the next section to a 4KB (page) boundary. */
     . = ALIGN(0x1000);
-
-    /* Put the trampoline code here. */
     _trampoline = .;
-
-    /* Match any section that starts with .trampsec. */
     *(trampsec)
-
-    /* Align the next section to a 4KB (page) boundary. */
     . = ALIGN(0x1000);
-
-    /* Assert that the trampoline code is exactly 4KB (page) in size. */
     ASSERT(. - _trampoline == 0x1000, "error: trampoline larger than one page");
-
-    /* Define symbol etext to be the current location. */
     PROVIDE(etext = .);
   }
 
@@ -42,7 +29,6 @@ SECTIONS
    * It is not unusual to find this data interleaved with the text section.
    */
   .rodata : {
-    /* Align on quadword boundary. */
     . = ALIGN(16);
     *(.srodata .srodata.*) /* do not need to distinguish this from .rodata */
     . = ALIGN(16);
@@ -73,6 +59,6 @@ SECTIONS
     *(.bss .bss.*)
   }
 
-  /* Define symbol end as current location, note that this is not aligned, see vm.c */
+  /* PROVIDE, see vm.c */
   PROVIDE(end = .);
 }
diff --git a/kernel/proc.c b/kernel/proc.c
index ccccf79..58a3160 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -650,8 +650,9 @@ either_copyin(void *dst, int user_src, u64 src, u64 len)
 void
 procdump(void)
 {
-  static char *states[] = { [UNUSED] = "unused",   [USED] = "used",      [SLEEPING] = "sleep ",
-                            [RUNNABLE] = "runble", [RUNNING] = "run   ", [ZOMBIE] = "zombie" };
+  static char *states[] = {
+    [UNUSED] "unused", [USED] "used", [SLEEPING] "sleep ", [RUNNABLE] "runble", [RUNNING] "run   ", [ZOMBIE] "zombie"
+  };
   struct proc *p;
   char        *state;
 
diff --git a/kernel/syscall.c b/kernel/syscall.c
index a027276..075fb36 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -102,7 +102,6 @@ extern u64 sys_link(void);
 extern u64 sys_mkdir(void);
 extern u64 sys_close(void);
 extern u64 sys_trace(void);
-extern u64 sys_halt(void);
 
 // An array mapping syscall numbers from syscall.h
 // to the function that handles the system call.
@@ -112,7 +111,7 @@ static u64 (*syscalls[])(void) = {
   [SYS_chdir] = sys_chdir, [SYS_dup] = sys_dup,       [SYS_getpid] = sys_getpid, [SYS_sbrk] = sys_sbrk,
   [SYS_sleep] = sys_sleep, [SYS_uptime] = sys_uptime, [SYS_open] = sys_open,     [SYS_write] = sys_write,
   [SYS_mknod] = sys_mknod, [SYS_unlink] = sys_unlink, [SYS_link] = sys_link,     [SYS_mkdir] = sys_mkdir,
-  [SYS_close] = sys_close, [SYS_trace] = sys_trace,   [SYS_halt] = sys_halt,
+  [SYS_close] = sys_close, [SYS_trace] = sys_trace,
 };
 
 void
diff --git a/kernel/syscall.h b/kernel/syscall.h
index 0162584..dfc9645 100644
--- a/kernel/syscall.h
+++ b/kernel/syscall.h
@@ -23,4 +23,3 @@
 #define SYS_mkdir  20
 #define SYS_close  21
 #define SYS_trace  22
-#define SYS_halt   23
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index ba0aeb9..5645c72 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -96,9 +96,3 @@ sys_trace(void)
   /* TODO: Implement sys_trace */
   return 0;
 }
-
-void
-sys_halt(void)
-{
-  /* TODO: Implement sys_halt */
-}
diff --git a/kernel/trap.c b/kernel/trap.c
index 3db4558..359fe39 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -1,4 +1,5 @@
 #include "types.h"
+#include "param.h"
 #include "memlayout.h"
 #include "riscv.h"
 #include "spinlock.h"
diff --git a/user/halt.c b/user/halt.c
deleted file mode 100644
index ab73dd3..0000000
--- a/user/halt.c
+++ /dev/null
@@ -1,9 +0,0 @@
-#include "user.h"
-
-/** Stops the machine */
-int
-main(int argc, char *argv[])
-{
-  halt();
-  return 0;
-}
diff --git a/user/user.h b/user/user.h
index ed10ca8..1e56f3d 100644
--- a/user/user.h
+++ b/user/user.h
@@ -74,9 +74,6 @@ int uptime(void);
 /** trace */
 int trace(int);
 
-/** halt */
-void halt(void);
-
 /**
  * Library functions (ulib.c)
  */
diff --git a/user/usys.pl b/user/usys.pl
index cdaec02..9c97b05 100755
--- a/user/usys.pl
+++ b/user/usys.pl
@@ -14,7 +14,7 @@ sub entry {
     print " ecall\n";
     print " ret\n";
 }
-
+	
 entry("fork");
 entry("exit");
 entry("wait");
@@ -37,4 +37,3 @@ entry("sbrk");
 entry("sleep");
 entry("uptime");
 entry("trace");
-entry("halt");