linux-kernel - Re: [PATCH v5 2/6] x86/kasan, mm: introduce generic kasan_populate_zero

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Date:	Tue, 11 Aug 2015 19:30:42 +0300
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, Yury <yury.norov@...il.com>,
	Alexey Klimov <klimov.linux@...il.com>,
	Arnd Bergmann <arnd@...db.de>, linux-mm@...ck.org,
	Linus Walleij <linus.walleij@...aro.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	David Keitel <dkeitel@...eaurora.org>,
	Alexander Potapenko <glider@...gle.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 2/6] x86/kasan, mm: introduce generic
 kasan_populate_zero_shadow()



On 08/11/2015 06:41 PM, Catalin Marinas wrote:
> On Tue, Aug 11, 2015 at 05:18:15AM +0300, Andrey Ryabinin wrote:
>> --- /dev/null
>> +++ b/mm/kasan/kasan_init.c
> [...]
>> +#if CONFIG_PGTABLE_LEVELS > 3
>> +pud_t kasan_zero_pud[PTRS_PER_PUD] __page_aligned_bss;
>> +#endif
>> +#if CONFIG_PGTABLE_LEVELS > 2
>> +pmd_t kasan_zero_pmd[PTRS_PER_PMD] __page_aligned_bss;
>> +#endif
>> +pte_t kasan_zero_pte[PTRS_PER_PTE] __page_aligned_bss;
> 
> Is there any problem if you don't add the #ifs here? Wouldn't the linker
> remove them if they are not used?
> 

AFAIK such optimization is possible if we build with -fdata-sections flag and
use --gc-sections flag in linker, but we don't do this.
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