Thanks mx3,
I use the entry.s and scanled.c only with the below commands,
arm-elf-gcc -fno-builtin -O2 -Ilib -nostdinc -c entry.s
arm-elf-gcc -fno-builtin -O1 -Ilib -c scanled.c
arm-elf-gcc -fno-builtin -O2 -Ilib -nostdlib -Wl,-N,-Ttext,1900 -o scanled.exec entry.o scanled.o -lgcc
arm-elf-objcopy -O binary scanled.exec scanled.bin
decrypt20d.exe scanled.bin scanled.fir