how can I access makefile variable in xv6?

Question

Now I am trying to access makefile variable in my user program in xv6. In other linux system, it can be easily achieved by doing that

1. in makefile, define gcc -D MYVARIABLE=1 ...
2. in my linux user program, by defining #include <stdio.h>, I can access MYVARIABLE.

but in xv6, there is no <stdio.h>. so I can't access MYVARIABLE.

How can I do for access MYVARIABLE??

Answer 1

Guessing you use this repo: https://github.com/mit-pdos/xv6-public, you can define MYVARIABLE in CFLAGS declaration, near line 83.

CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer
CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
# Your macro here
CFLAGS += -DMYVARIABLE=1

In that makefile, there is no %.o: %.c rule: implicit rules are used:

n.o is made automatically from n.c with a command of the form $(CC) -c $(CPPFLAGS) $(CFLAGS)