basic alloc

input/baseline/alloc.asm

@@ -0,0 +1,88 @@
+global alloc, free
+
+; metadata
+; +0: size
+; +8: next
+; +16 data
+
+section .bss
+    free_list:		resq 1		; head of free list
+    alloc_list:		resq 1		; head of allocation list
+
+section .text
+alloc:
+	add rdi, 16					; add space for metadata
+	mov rax, [free_list]		; load head of free list
+	xor r8, r8					; last block
+.loop:
+	test rax, rax				; end of list?
+	jz .new_block				; yes? allocate new block
+	cmp [rax], rdi				; does object fit in block and have space for metadata?
+	jge .found_block			; yes? use this block
+	mov r8, rax
+	mov rax, [rax + 8]			; load next free block
+	jb .loop					; no? go to next block
+.found_block:
+	sub qword [rax], rdi		; reduce the available size of the block
+	cmp qword [rax], 0			; no space left in block?
+	jg .done_remove_free_block	; no? do not remove block from free list
+	mov rsi, [rax + 8]			; yes? remove block from free list
+	test r8, r8					; is current head of list?
+	jz .remove_free_head		; yes? remove head
+	mov [r8 + 8], rsi			; set prev.next to this.next
+	jmp .done_remove_free_block
+.remove_free_head
+	mov [free_list], rsi
+.done_remove_free_block:
+	mov rsi, [rax]				; load size of block excluding the newly allocated object
+	lea rax, [rax + rsi + 16]	; address of allocated block
+	sub rdi, 16
+	mov [rax], rdi				; save size
+	mov rsi, [alloc_list]		; load head of allocated blocks
+	mov [rax + 8], rsi			; move head to be next item after this block
+	mov [alloc_list], rax		; set new head to this block
+	lea rax, [rax + 16]			; skip metadata for return value
+	ret
+.new_block:
+	push rdi
+	push r8
+	mov rdi, 4096				; page size
+	call sys_mmap				; allocate a page
+	mov qword [rax], 4080		; set size of block to block size - metadata
+	mov rsi, [free_list]
+	mov qword [rax + 8], rsi	; move head to be the next item after this block
+	mov [free_list], rax		; set new head to this block
+	pop r8
+	pop rdi
+	jmp .found_block
+
+free:
+	ret
+
+sys_mmap:
+	mov rax, 9
+	mov rsi, rdi
+	mov rdi, 0
+	mov rdx, 3
+	mov r10, 34
+	mov r8, -1
+	mov r9, 0
+	syscall
+	cmp rax, -1
+	je .error
+	ret
+.error:
+	mov rax, 60
+	mov rdi, 1
+	syscall
+
+sys_munmap:
+	mov rax, 11
+	syscall
+	cmp rax, -1
+	je .error
+	ret
+.error:
+	mov rax, 60
+	mov rdi, 1
+	syscall