linux-kernel - Re: [PATCH] x86/process: Silence KASAN warnings in get

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Date:	Wed, 7 Oct 2015 12:11:05 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>
CC:	Andi Kleen <ak@...ux.intel.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	kasan-dev <kasan-dev@...glegroups.com>,
	Borislav Petkov <bp@...en8.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Wolfram Gloger <wmglo@...t.med.uni-muenchen.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86/process: Silence KASAN warnings in get_wchan()



On 10/07/2015 11:54 AM, Andrey Ryabinin wrote:
> On 10/06/2015 09:11 PM, Andy Lutomirski wrote:
>>
>> But what's wrong with the GCC attribute mechanism?  Surely GCC ought
>> to be able to generate the code, at least in the simple cases, and the
>> attribute already exists.  The attribute and READ_ONCE_NOCHECK seem
>> like the least messy in the C code.
> 
> The problem with 'no_sanitize_address' attribute is incompatibility with inlining. 
> GCC can't inline function with that attribute into function without it.
> And the contrary is also true - GCC can't inline function without attribute into function with such attribute.
> 
> Failure to inline always_inline function leads to build failure.
> And under CONFIG_OPTIMIZE=n 'inline' means 'always_inline'.
> 
> include/linux/compiler-gcc.h:
> 
> #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||		\
>     !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
> #define inline		inline		__attribute__((always_inline)) notrace
> 

Huh, 'inline' effectively means 'always_inline' on every arch, except x86.
This looks like a bug IMO.
Allowing gcc to uninline functions marked 'inline' could be beneficial for some arches/configs.

$ git grep ARCH_SUPPORTS_OPTIMIZED_INLINING
	arch/tile/Kconfig:config ARCH_SUPPORTS_OPTIMIZED_INLINING
	arch/x86/Kconfig:config ARCH_SUPPORTS_OPTIMIZED_INLINING
	include/linux/compiler-gcc.h:#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||           \

$ git grep OPTIMIZE_INLINING
	arch/x86/Kconfig.debug:config OPTIMIZE_INLINING
	arch/x86/configs/i386_defconfig:CONFIG_OPTIMIZE_INLINING=y
	arch/x86/configs/x86_64_defconfig:CONFIG_OPTIMIZE_INLINING=y
	arch/x86/entry/vdso/vdso32/vclock_gettime.c:#undef CONFIG_OPTIMIZE_INLINING
	include/linux/compiler-gcc.h:    !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
	kernel/configs/tiny.config:CONFIG_OPTIMIZE_INLINING=y
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