Question

i came across following shell script as part of makefile in u-boot.
what it does and how is it evaluated

cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
        > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)

it is called as

PLATFORM_RELFLAGS +=$(call cc-option,-mshort-load-bytes,\
            $(call cc-option,-malignment-traps,))

Answer 1

The code runs the if command. if takes one argument: A command to execute ($(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null > /dev/null 2>&1).

If the command succeeds, the then part is executed (echo "$(1)"). If the command fails, the else part is executed (echo "$(2)").

In your case, the compiler is started with some options which it might not support ($1 is -mshort-load-bytes).

Since $2 is empty, the result will either be the option (if the compiler supports it) or the empty string.