Index: mod/kcore/syscall.fn.x86.lin.64.s
==================================================================
--- mod/kcore/syscall.fn.x86.lin.64.s
+++ mod/kcore/syscall.fn.x86.lin.64.s
@@ -33,10 +33,17 @@
 	; arg 0 = s64* result
 	; arg 1 = errno ptr
 	; arg 2 = syscall num
 	; arg 3 = valency
 	; arg 4 = args ptr
+
+	; we use two registers that are supposed
+	; to be callee-saved, so we need to
+	; push them to the stack and then pop
+	; them back off just before the fn rets.
+	push rbx
+	push r12
 
 	; store the locals in registers that
 	; are guaranteed not to be clobbered,
 	; saving us some cycles pushing to
 	; and popping back from the stack
@@ -84,14 +91,18 @@
 	; move our return values into place and
 	; return to the caller (which should
 	; always be k_platform_syscall, btw)
 	mov       [rbx], sys.reg.ret
 	mov qword [r12], 0 ; no error
-	ret
+	jmp .return
 
 	; an error was returned - we need to set
 	; the errno to its positive equivalent,
 	; and store -1 in the return variable
 	.error: neg sys.reg.ret
 	        mov qword [rbx], -1
 			mov       [r12], sys.reg.ret
-			ret
+			jmp .return
+
+	.return: pop r12
+	         pop rbx
+			 ret