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Re: [Qemu-block] [Qemu-devel] [PATCH] block/vvfat: Fix compiler warning

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH] block/vvfat: Fix compiler warning with gcc 7
Date: Mon, 17 Jul 2017 10:22:37 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

On 07/17/2017 10:12 AM, Max Reitz wrote:
> gcc 7 complains that the sprintf() might write a null byte beyond the
> end of the tail buffer.  That is wrong, but we can silence it by making
> i unsigned (it can never be negative anyway, see the if condition right
> before).  For some reason, this allows gcc to suddenly accurately
> calculate the range of i so we can give the tail[] array the exact size
> it needs to have (which is 8 bytes) without gcc complaining.
> In addition, let us convert the sprintf() to snprintf(), because that is
> always nicer, and add an assertion about the range of the return value
> afterwards so we can see that "8 - len" will never be negative and thus
> "entry->name + MIN(j, 8 - len)" will never be out of bounds.
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block/vvfat.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Reviewed-by: Eric Blake <address@hidden>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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