linux-kernel - Re: [PATCH v2 2/2] x86: Support compiling out human-friendly processor feature names

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Date:	Sun, 23 Feb 2014 13:55:52 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <bp@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Feng Tang <feng.tang@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Jacob Shin <jacob.shin@....com>,
	Jan Beulich <JBeulich@...e.com>,
	Jussi Kivilinna <jussi.kivilinna@....fi>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Rob Landley <rob@...dley.net>,
	Seiji Aguchi <seiji.aguchi@....com>,
	Stephane Eranian <eranian@...gle.com>,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 2/2] x86: Support compiling out human-friendly
 processor feature names

On Sun, Feb 23, 2014 at 01:44:20PM -0800, H. Peter Anvin wrote:
> On 02/23/2014 01:32 PM, Josh Triplett wrote:
> > 
> > Because, in order to un-break the build, v3 wraps an ifdef around that
> > dependency, to prevent building cpustr.h.  Otherwise, the rule for
> > cpustr.h tries and fails to build mkcpustr.
> > 
> 
> Why did it fail to build mkcpustr?  It would seem that mkcpustr is or at
> least ought to be completely agnostic to any of these options.
> 
> The extra build machinery here seems completely pointless.
> 
> I agree that the #ifdef isn't a big deal, but all this extra machinery
> really indicates something is odd.
> 
> Oh, and of course, looking at the v2 patchset, the problem is the ifdef
> around the mkcapflags shell script which really shouldn't be necessary.
>  We may have to add a rule to force capflags.c to be built even if
> capflags.o is not requested, but that is fine.
> 
> That will cut down on the Makefile hacks considerably, and will avoid
> this problem completely.

Why have the build system waste time building several things that won't
be used?  It seems like the Makefiles are exactly where we *should* have
the ifdef machinery, rather than in source.  I'd happily add another
ifdef in the Makefile rule that builds cpustr.h, to generate a stub
cpustr.h header, and then remove one more ifdef in the source.

- Josh Triplett
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