From 8d541ce498be46142d09a41ceea4d790301f1a98 Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Sat, 16 Mar 2019 10:46:01 +0000
Subject: [PATCH] PoC for heap

---
 heap.asm | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 main.asm | 11 ++++++++---
 2 files changed, 63 insertions(+), 3 deletions(-)
 create mode 100644 heap.asm

diff --git a/heap.asm b/heap.asm
new file mode 100644
index 0000000..9035b6a
--- /dev/null
+++ b/heap.asm
@@ -0,0 +1,55 @@
+verbose_malloc:
+  call malloc
+  push si ; both backup and input value for kprintf
+  mov si,.fmt
+  call kprintf
+  pop si
+  ret
+.fmt:
+  db "malloc %X", 0
+
+; Allocates memory on the kernel heap
+; Strategy: smallest fit
+; in	cx	size in bytes
+; out	si	pointer
+;
+; Header:
+;	word	ptr to next item (this implies its size)
+;	byte	00 = free, FF = in use
+malloc:
+  push ax
+  mov si,heap
+  jmp .check
+.next:
+  mov si,[si]
+.check:
+  mov ax,[si]
+  test ax,0xFFFF
+  jz .append ; we are on last entry
+  cmp byte [si+2],0x00
+  jne .next ; entry is in use
+  sub ax,cx
+  je .reuse ; entry has exact length
+  jc .next ; entry too short
+  jmp .next ; we'd have to split
+.reuse: ; exact length
+  mov byte [si+2],0xFF
+  add si, 0x03
+  pop ax
+  ret
+.append: ; append to last item
+  mov ax, si
+  add ax, 3
+  add ax, cx
+  mov word [si], ax
+  mov byte [si+2], 0xFF
+  push si
+  mov word si,[si]
+  mov byte [si],0x0000
+  pop si
+  add si, 0x03
+  pop ax
+  ret
+
+; Deallocates memory on the kernel heap
+free:
diff --git a/main.asm b/main.asm
index 7c865f6..4af2c0b 100644
--- a/main.asm
+++ b/main.asm
@@ -48,12 +48,17 @@ main:
 
   call ivt_set
 
-  int 0x2E
-  cmp ax,0x55AA
-  int 0x2E
+  mov cx, 0x0010
+  call verbose_malloc
+  call verbose_malloc
+  call verbose_malloc
 
   ret
 
 %include "intr.asm"
 %include "debug.asm"
 %include "kprintf.asm"
+%include "heap.asm"
+
+heap:
+  dw 0