--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/kalloc.c	Fri May 26 23:11:05 2017 +0900
@@ -0,0 +1,111 @@
+// Physical memory allocator, intended to allocate
+// memory for user processes, kernel stacks, page table pages,
+// and pipe buffers. Allocates 4096-byte pages.
+
+#include "types.h"
+#include "defs.h"
+#include "param.h"
+#include "memlayout.h"
+#include "mmu.h"
+#include "spinlock.h"
+#include "arm.h"
+
+void freerange(void *vstart, void *vend);
+extern char end[]; // first address after kernel loaded from ELF file
+
+struct run {
+    struct run *next;
+};
+
+static struct {
+    struct spinlock lock;
+    int use_lock;
+    struct run *freelist;
+} kmem;
+
+void kmem_init (void)
+{
+    initlock(&kmem.lock, "kmem");
+    kmem.use_lock = 0;
+}
+
+// Initialization happens in two phases.
+// 1. main() calls kinit1() while still using entrypgdir to place just
+// the pages mapped by entrypgdir on free list.
+// 2. main() calls kinit2() with the rest of the physical pages
+// after installing a full page table that maps them on all cores.
+void kinit1(void *vstart, void *vend)
+{
+    freerange(vstart, vend);
+}
+
+void kinit2(void *vstart, void *vend)
+{
+    freerange(vstart, vend);
+    kmem.use_lock = 1;
+}
+
+void freerange(void *vstart, void *vend)
+{
+    char *p;
+
+    p = (char*)align_up (vstart, PTE_SZ);
+
+    for(; p + PTE_SZ <= (char*)vend; p += PTE_SZ) {
+        kfree(p);
+    }
+}
+
+//PAGEBREAK: 21
+// Free the page of physical memory pointed at by v,
+// which normally should have been returned by a
+// call to kalloc().  (The exception is when
+// initializing the allocator; see kinit above.)
+void kfree(char *v)
+{
+    struct run *r;
+
+    if((uint)v % PTE_SZ || v < end || v2p(v) >= PHYSTOP) {
+        cprintf("kfree(0x%x)\n", v);
+        panic("kfree");
+    }
+
+    // Fill with junk to catch dangling refs.
+    //memset(v, 0x00, PG_SIZE);
+
+    if(kmem.use_lock) {
+        acquire(&kmem.lock);
+    }
+
+    r = (struct run*)v;
+    r->next = kmem.freelist;
+    kmem.freelist = r;
+
+    if(kmem.use_lock) {
+        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.
+char* kalloc(void)
+{
+    struct run *r;
+
+    if(kmem.use_lock) {
+        acquire(&kmem.lock);
+    }
+
+    r = kmem.freelist;
+
+    if(r) {
+        kmem.freelist = r->next;
+    }
+
+    if(kmem.use_lock) {
+        release(&kmem.lock);
+    }
+
+    return (char*)r;
+}