From mboxrd@z Thu Jan  1 00:00:00 1970
From: wbin00@gmail.com (Bin Wang)
Date: Fri, 18 Jan 2013 10:42:51 +0800
Subject: When does Makefile init the variables like KBUILD_OUTPUT
In-Reply-To: <50F76155.3000506@gmail.com>
References: <50F76155.3000506@gmail.com>
Message-ID: <50F8B6AB.4030709@gmail.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On 2013/01/17/ 10:26, Bin Wang wrote:
> Hi, all
>
> The kernel Makefile init the variables like KBUILD_OUTPUT outside any 
> target's make process. But when I try to output the KBUILD_OUTPUT in 
> the target's make process, for example, the target "help", I find it 
> is not defined. I want to know when will it init? Thanks a lot

However, when I just write a Makefile with this:

|ifeq ("$(origin O)", "command line")
   KBUILD_OUTPUT := $(O)
endif

help:
     @echo 'KBUILD_OUTPUT: ${KBUILD_OUTPUT}'
|

Then I run|make O=../build help|, I will see|KBUILD_OUTPUT: ../build|.

Is there anything special in kernel's Makefile?