linux-kernel - Re: [PATCH] kbuild: fix if_change and friends to consider argument order

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Date:	Fri, 6 May 2016 11:12:03 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	"Woodhouse, David" <david.woodhouse@...el.com>
Cc:	"linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
	"mmarek@...e.com" <mmarek@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dhowells@...hat.com" <dhowells@...hat.com>
Subject: Re: [PATCH] kbuild: fix if_change and friends to consider argument order

Hi David,


2016-05-05 17:08 GMT+09:00 Woodhouse, David <david.woodhouse@...el.com>:
> On Thu, 2016-05-05 at 16:45 +0900, Masahiro Yamada wrote:
>>
>> This commit fixes arg-check to compare two strings as a whole.
>> $(strip ...) is important because we want to ignore the difference
>> that comes from white-spaces.
>
> Do we?
>
> I can construct a hypothetical situation in which whitespace differs
> and we *do* want it to make a difference (for example I used to sign
> with a key called 'My Signing Key.pem' and now I've changed to use
> 'My  Signing  Key.pem'. (OK, it's a *stupid* example but still...)
>

Have you ever succeeded in passing such a string in Kbuild in the first place?

For example, I added the following line into init/Makefile

CFLAGS_main.o += -DHELLO_WORLD='"hello        world!"'


and

     printk("%s\n", HELLO_WORLD);

to start_kernel().



But, I got the console log

[     0.001639] hello world!




The root cause of this problem is the following line

_c_flags       = $(filter-out $(CFLAGS_REMOVE_$(basetarget).o), $(orig_c_flags))


$(filter-out  ) strips extra spaces, so Kbuild can not keep
white-spaces as they are.


Maybe, we can fix this problem.  (This is another problem, though)

Thank you for spotting this.



-- 
Best Regards
Masahiro Yamada