add test assembly file

asm/Makefile

@@ -0,0 +1,20 @@
+all: test.hex
+
+CC = riscv64-linux-gnu-gcc
+# CFLAGS = -march=rv32i -mabi=ilp32
+CFLAGS = -march=rv64i -mabi=lp64
+
+AS = riscv64-linux-gnu-as
+ASFLAGS = $(CFLAGS)
+
+LD = riscv64-linux-gnu-ld
+LDFLAGS = -T test.ld
+
+%.o: %.S
+	$(AS) $(ASFLAGS) $^ -o $@
+
+%.elf: %.o
+	$(LD) $(LDFLAGS) $^ -o $@
+
+test.hex: test.elf
+	riscv64-linux-gnu-objdump -s $^ | sed -n '/0000/,$$p' | cut -f3-6 -d ' ' | sed -e 's/ /\n/g' > $@