linux-kernel - Re: [PATCH v6 03/10] x86, mpx: add macro cpu_has

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Date:	Wed, 18 Jun 2014 07:35:17 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Borislav Petkov <bp@...en8.de>, Qiaowei Ren <qiaowei.ren@...el.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 03/10] x86, mpx: add macro cpu_has_mpx

On 06/18/2014 02:57 AM, Borislav Petkov wrote:
>> > @@ -339,6 +339,12 @@ extern const char * const x86_power_flags[32];
>> >  #define cpu_has_eager_fpu	boot_cpu_has(X86_FEATURE_EAGER_FPU)
>> >  #define cpu_has_topoext		boot_cpu_has(X86_FEATURE_TOPOEXT)
>> >  
>> > +#ifdef CONFIG_X86_INTEL_MPX
>> > +#define cpu_has_mpx boot_cpu_has(X86_FEATURE_MPX)
> I think we don't want those macros anymore because they're obfuscating
> the code. You should use static_cpu_has instead.

It looks like static_cpu_has() is the right thing to use instead of
boot_cpu_has().  But, this doesn't just obfuscate things.

We actually _want_ the compiler to cull code out when the config option
is off.  Things like do_bounds() will see code savings with _some_ kind
of #ifdef rather than using static_cpu_has().

So, we can either use the well worn, consistent with other features in
x86, cpu_has_$foo approach.  Or, we can roll our own macros.
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