diff --git a/Makefile b/Makefile
index 706a415..d53f989 100644
--- a/Makefile
+++ b/Makefile
@@ -120,7 +120,7 @@ GLOBALSRC := $(addprefix $(GLOBALDIR)/, $(addsuffix .s, \
             ))
 
 SBSRC := $(addprefix $(SBDIR)/, $(addsuffix .s, \
-			string_builder\
+			string_builder sb_append \
             ))
 
 # Collect all sources and objects
diff --git a/langc b/langc
index 38f77c9..9797382 100755
Binary files a/langc and b/langc differ
diff --git a/lib/core.a b/lib/core.a
index e3ad679..012caf9 100644
Binary files a/lib/core.a and b/lib/core.a differ
diff --git a/src/core/string_builder/sappend.s b/src/core/string_builder/sb_append.s
similarity index 71%
rename from src/core/string_builder/sappend.s
rename to src/core/string_builder/sb_append.s
index cb91dd8..e18582c 100644
--- a/src/core/string_builder/sappend.s
+++ b/src/core/string_builder/sb_append.s
@@ -2,15 +2,17 @@
 
 section .text
     extern strlen
-    extern strcpy
+    extern memcpy
     extern malloc
     extern err_malloc
 
 %define SB [rbp - 16]
-%define SB_LEN [rbp - 4]
-%define SB_CAP [rbp - 8]
+%define SB_LEN dword [rbp - 4]
+%define SB_CAP dword [rbp - 8]
 %define APPENDIX [rbp - 24]
+%define APP_LEN dword [rbp - 28]
 
+global sb_append
 sb_append:      ; (rdi: *sb, rsi: char*)
     push rbp
     mov rbp, rsp
@@ -26,26 +28,28 @@ sb_append:      ; (rdi: *sb, rsi: char*)
 
     ; get sb len
     mov eax, dword [rdi + STR_LEN]
-    mov dword SB_LEN, eax
+    mov SB_LEN, eax
 
     mov eax, dword [rdi + STR_CAP]
-    mov dword SB_CAP, eax
+    mov SB_CAP, eax
 
     push rdi
     mov rdi, rsi
     call strlen
 
-    add rax, SB_LEN
-    cmp rax, SB_CAP
+    mov APP_LEN, eax
+
+    add eax, SB_LEN
+    cmp eax, SB_CAP
     jl .copy_string
 
-    mov r9, SB_CAP
+    mov r9d, SB_CAP
     ; new string will be to large for current cap, need to realloc
 .get_new_len:
     imul r9, 2
     cmp r9, rax
     jl .get_new_len
-    mov SB_CAP, r9
+    mov SB_CAP, r9d
     push r9
     push rax
     mov rdi, r9
@@ -55,11 +59,12 @@ sb_append:      ; (rdi: *sb, rsi: char*)
     mov rdi, rax
     mov rsi, SB
     mov rsi, [rsi + STR_DATA]
-    call strcpy
+    mov edx, SB_LEN
+    call memcpy
     pop rax
     mov rsi, SB
     pop r9
-    mov [SB + STR_CAP], r9
+    mov [rsi + STR_CAP], r9
 
 .copy_string:
     pop rdi
@@ -67,9 +72,10 @@ sb_append:      ; (rdi: *sb, rsi: char*)
     mov dword [r9 + STR_LEN], eax
     mov rdi, [r9 + STR_DATA]
     mov eax, dword [rbp - 4]
-    lea rdi, [rdi + eax]
-    mov rsi, [rbp - 24]
-    call strcpy
+    lea rdi, [rdi + rax]
+    mov rsi, APPENDIX
+    mov edx, APP_LEN
+    call memcpy
 
 .done:
     mov rsp, rbp
diff --git a/src/core/string_builder/string_builder.s b/src/core/string_builder/string_builder.s
index b731e3d..c6990e5 100644
--- a/src/core/string_builder/string_builder.s
+++ b/src/core/string_builder/string_builder.s
@@ -10,7 +10,6 @@ section .text
 global sb_new
 sb_new:     ; rax: str*(rdi: char* || NULL, rsi: *hidden_copy_ptr)
     push rbx
-    push rdi
     push rsi
 
     mov rbx, STRING_INIT_CAP
@@ -31,7 +30,6 @@ sb_new:     ; rax: str*(rdi: char* || NULL, rsi: *hidden_copy_ptr)
     cmp r9, rbx
     jg .calc_init_len
 
-
 .alloc_string:
     push rdi
     mov rdi, rbx
@@ -46,9 +44,10 @@ sb_new:     ; rax: str*(rdi: char* || NULL, rsi: *hidden_copy_ptr)
     mov [rsi + STR_DATA], rax
     test r9, r9
     jz .done
+    push rdi
     mov rdi, rax
-    mov rdx, r9
     pop rsi
+    mov rdx, r9
     call memcpy
 
 .done:
diff --git a/src/start.s b/src/start.s
index 3cc3294..b4ffb71 100644
--- a/src/start.s
+++ b/src/start.s
@@ -1,5 +1,8 @@
+%include "./src/core/string_builder/sb.s"
+
 section .data
     usage:  db "Usage: ./debug <file>.lang", 0xa, 0
+    example_data: db "Do you know Ligma?"
 
 section .text
     global _start
@@ -14,6 +17,7 @@ section .text
     extern putchar
     extern vec_pop
     extern sb_new
+    extern sb_append
 
 print_usage:
     mov rdi, usage
@@ -25,9 +29,17 @@ _start:
     mov rbp, rsp
     sub rsp, 16
     mov rdi, usage
-    lea rsi, [rsp - 16]
+    lea rsi, [rbp - 16]
     call sb_new
 
+    mov rdi, [rbp - 16 + STR_DATA]
+    call putstr
+    lea rdi, [rbp - 16]
+    mov rsi, example_data
+    call sb_append
+    mov rdi, [rbp - 16 + STR_DATA]
+    call putstr
+
 ;    pop rdi
 ;    cmp rdi, 2
 ;    jne err_args
@@ -44,9 +56,9 @@ _start:
 ;    mov rdi, rax
 ;    call lex
 ;
-;    mov rsp, rbp
-;    pop rbp
-;
+   mov rsp, rbp
+   pop rbp
+
 done:
-;    xor rdi, rdi
-;    call exit
+   xor rdi, rdi
+   call exit