linux-kernel - Re: [PATCH v2] x86/asm/entry/64: Minor cleanup of conditional compilation

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Message-ID: <55EBD714.30509@zytor.com>
Date:	Sat, 5 Sep 2015 23:03:00 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Nikolay Borisov <nikolay.b.borisov@...il.com>, mingo@...nel.org
Cc:	dvlasenk@...hat.com, luto@...capital.net,
	linux-kernel@...r.kernel.org, bp@...e.de
Subject: Re: [PATCH v2] x86/asm/entry/64: Minor cleanup of conditional
 compilation

On 09/05/15 13:53, Nikolay Borisov wrote:
> The entry_SYSCALL_64_fastpath was checking the value of __SYSCALL_MASK,
> which in turn was being set in arch/x86/include/asm/unistd.h depending on
> whether CONFIG_X86_X32_ABI was set or not. This made the intention a bit
> cryptic.

On the contrary: that instruction can be omitted if and only if the 
value of the mask is all 1's; it doesn't matter how the mask is set.  So 
you just turned a local constraint into a global constraint.  This is 
both unnecessarily confusing and opens the risk for bugs later.

If you feel the need, you could submit a patch to add a comment, but 
this version is:

Nacked-by: H. Peter Anvin <hpa@...or.com>

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