linux-kernel - Re: [GIT PULL] x86/build change for v3.6

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Message-ID: <20120725201511.GA888@merkur.ravnborg.org>
Date:	Wed, 25 Jul 2012 22:15:11 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86/build change for v3.6

> 
> No, the reason for the odd looking diff is that lots of lines in 
> arch/x86/Makefile have 8-space tabs for histerical reasons but 
> new code (such as this one) has proper tabs.

Use of tabs for indent in a Makefile is just asking for trouble.
Consider following simple Makefile:

$ cat Makefile
bar:
#bla bla
        foo = war

love:
	@echo make love, not $(foo)



If you execute:
    $make love
    make love, not war

But if you replace the 8 spaces in front of the assignment
with a tab then suddenly the output looks like this:
    $make love
    make love, not

This is not as expected....
In this silly example it is maybe obvious but I have lost hours tracking
down bugs due to this.
You add a new target and suddenly someting unrelated breaks.

What happens is that make consider the assignment a command due to the leading
tab - and because is follows a target (or other commands).

I hope this makes it clear why many makefiles in the kernel uses tabs for indent.

	Sam
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