Subject: Re: [PATCH v5 2/6] x86/kasan, mm: introduce generic
 kasan_populate_zero_shadow()
To: Catalin Marinas <catalin.marinas@arm.com>
References: <1439259499-13913-1-git-send-email-ryabinin.a.a@gmail.com>
 <1439259499-13913-3-git-send-email-ryabinin.a.a@gmail.com>
 <20150811154117.GH23307@e104818-lin.cambridge.arm.com>
Cc: Will Deacon <will.deacon@arm.com>, linux-arm-kernel@lists.infradead.org,
        Yury <yury.norov@gmail.com>, Alexey Klimov <klimov.linux@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>, linux-mm@kvack.org,
        Linus Walleij <linus.walleij@linaro.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, David Keitel <dkeitel@codeaurora.org>,
        Alexander Potapenko <glider@google.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        Dmitry Vyukov <dvyukov@google.com>
From: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Message-ID: <55CA2332.7040206@gmail.com>
Date: Tue, 11 Aug 2015 19:30:42 +0300
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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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