fixed it it now works :)

case.asm

@@ -1,10 +1,9 @@
 extern length_func
 
-
+global _case_func
 section .text
-	global tolower
 
-tolower:
+_case_func:
 	sub rsp, 8	;enter
 
 	mov r11, rdi

diff.asm

@@ -1,13 +1,20 @@
+global diff_func
 section .text
-	global diff_func
 
 diff_func:
 	sub rsp, 8	;enter
 
 	xor rcx, rcx	;we do this to clear garbage in rcx (i have had garbage in it before)
+
+	mov r8, rdi	;dupe them
+	mov r9, rsi
+	
 _loopwasp12bsharknado:
 ;loop tings
 
+	mov rdi, r8
+	mov rsi, r9
+
 	add rdi, rcx
 	add rsi, rcx
 

example.asm

@@ -1,11 +1,13 @@
 extern puts
 extern length_func
-extern tolower
+extern _case_func
 extern diff_func
 
 section .data
-	text db "rEEEeee!EEeeeEeEEeE!EEEEEeEEE$eeeEE)EEeEeEEeeeEeEEEEEeeeEeeEeeEeeeeeEeEeEeeE",0
+	text2 db 0,0
-	text2 db "reee",0
+	text db 0,0,0
+
+
 	stoer db "0",0
 	differ db "they differ",0
 	notdiffer db "they dont differ",0
@@ -16,13 +18,20 @@ main:
 	sub rsp, 8	;enter
 
 	mov rdi, text
-	call tolower
+	call _case_func
 
 	mov rdi, text
 	cld
 	call puts	;this is the puts way of printing a string
 
 
+	mov rdi, text2
+	cld
+	call puts
+
+
+
+
 	mov rdi, text2
 	call length_func
 

length.asm

@@ -1,7 +1,7 @@
+global length_func
 section .data
 	testasd dq 0
 section .text
-	global length_func
 
 length_func:
 	sub rsp, 8	;enter