linux-kernel - Re: [PATCH v4 2/3] mac80211: Prevent build failure with CONFIG

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Date:	Thu, 3 Dec 2015 22:18:05 +0300
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Johannes Berg <johannes@...solutions.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-wireless@...r.kernel.org,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Jonathan Corbet <corbet@....net>,
	Michal Marek <mmarek@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Yury Gribov <y.gribov@...sung.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Kostya Serebryany <kcc@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	"open list:KERNEL BUILD + fi..." <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] mac80211: Prevent build failure with CONFIG_UBSAN=y

2015-12-03 20:05 GMT+03:00 Johannes Berg <johannes@...solutions.net>:
> On Thu, 2015-12-03 at 18:50 +0300, Andrey Ryabinin wrote:
>> With upcoming CONFIG_UBSAN the following BUILD_BUG_ON in
>> net/mac80211/debugfs.c starts to trigger:
>>       BUILD_BUG_ON(hw_flag_names[NUM_IEEE80211_HW_FLAGS] != (void
>> *)0x1);
>>
>> It seems, that compiler instrumentation causes some code
>> deoptimizations.
>> Because of that GCC is not being able to resolve condition in
>> BUILD_BUG_ON()
>> at compile time.
>>
>> We could make size of hw_flag_names array unspecified and replace the
>> condition in BUILD_BUG_ON() with following:
>>       ARRAY_SIZE(hw_flag_names) != NUM_IEEE80211_HW_FLAGS
>>
>> That will have the same effect as before (adding new flag without
>> updating
>> array will trigger build failure) except it doesn't fail with
>> CONFIG_UBSAN.
>> As a bonus this patch slightly decreases size of hw_flag_names array.
>>
> Seems fine, would you want to take it through some other tree together
> with UBSAN, or do you expect that to still take long enough to allow
> this to trickle through our trees?
>

I expect that Andrew will take it with UBSAN for 4.5
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