kernel: user safe strlen

src/arch/x86_64/Makefile

@@ -1,4 +1,4 @@
-objects := $(patsubst %.c,%.o,$(wildcard *.c)) israsm.o context.o syscall.o sched.o
+objects := $(patsubst %.c,%.o,$(wildcard *.c)) israsm.o context.o syscall.o sched.o ustringasm.o
 subdirs=boot
 OBJPATH=$(OBJDIR)/arch/${TARGET}/
 export
@@ -27,3 +27,8 @@ sched.o: sched.asm
 	nasm -f elf64 -o $@ $<
 	mkdir -p $(OBJPATH)
 	cp $@ $(OBJPATH)/$@
+
+ustringasm.o: ustring.asm
+	nasm -f elf64 -o $@ $<
+	mkdir -p $(OBJPATH)
+	cp $@ $(OBJPATH)/$@

src/arch/x86_64/ustring.asm

@@ -0,0 +1,19 @@
+section .text:
+
+global arch_u_strlen
+global arch_u_strlen_cont
+
+arch_u_strlen:
+    xor rcx, rcx
+   .loop:
+        cmp byte [rdi],0
+        je .done
+        inc rcx
+        inc rdi
+    .done:
+    mov [rsi], rcx
+    xor rax, rax
+    ret
+arch_u_strlen_cont:
+    mov rax, 1
+    ret