linux-kernel - Re: [PATCH v2] ARM: vdso: Define vdso

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Message-ID: <87tw0ytbwr.fsf@mentor.com>
Date:   Wed, 23 Aug 2017 12:46:28 -0500
From:   Nathan Lynch <nathan_lynch@...tor.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Nicolas Pitre <nico@...xnic.net>,
        Mark Rutland <mark.rutland@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Will Deacon <will.deacon@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH v2] ARM: vdso: Define vdso_{start,end} as array

Arnd Bergmann <arnd@...db.de> writes:

> gcc-8 correctly points out that reading four bytes from a pointer to a
> 'char' variable is wrong
>
> arch/arm/kernel/vdso.c: In function 'vdso_init':
> arch/arm/kernel/vdso.c:200:6: error: '__builtin_memcmp_eq' reading 4 bytes from a region of size 1 [-Werror=stringop-overflow=]
>
> However, in this case the variable just stands for the beginning of the
> vdso and is not actually a 'char', so the code is doing what it is meant
> to do.
>
> This uses the same approach as arm64 and x86, declaring the addresses
> as char arrays.
>
> See also: dbbb08f500d6 ("arm64, vdso: Define vdso_{start,end} as array")
>
> Suggested-by: Mark Rutland <mark.rutland@....com>
> Suggested-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Nathan Lynch <nathan_lynch@...tor.com>

Thanks!