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Re: [Qemu-block] [PATCH v2 0/3] Fix strncpy() warnings for GCC8 new -Wst

From: Philippe Mathieu-Daudé
Subject: Re: [Qemu-block] [PATCH v2 0/3] Fix strncpy() warnings for GCC8 new -Wstringop-truncation
Date: Tue, 18 Dec 2018 17:55:27 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1

On 12/18/18 3:54 PM, Michael S. Tsirkin wrote:
> On Tue, Dec 18, 2018 at 03:45:08PM +0100, Paolo Bonzini wrote:
>> On 18/12/18 15:31, Michael S. Tsirkin wrote:
>>> Do you happen to know why does it build fine with
>>> Gcc 8.2.1?
>>> Reading the GCC manual it seems that
>>> there is a "nostring" attribute that means
>>> "might not be 0 terminated".
>>> I think we should switch to that which fixes the warning
>>> but also warns if someone tries to misuse these
>>> as C-strings.
>>> Seems to be a better option, does it not?
>> Using strpadcpy is clever and self-documenting, though.  We have it
>> already, so why not use it.
>> Paolo
> The advantage of nonstring is that it will catch attempts to
> use these fields with functions that expect a 0 terminated string.
> strpadcpy will instead just silence the warning.

migration/global_state.c:109:15: error: 'strlen' argument 1 declared
attribute 'nonstring' [-Werror=stringop-overflow=]
     s->size = strlen((char *)s->runstate) + 1;

GCC won... It is true this strlen() is buggy, indeed s->runstate might
be not NUL-terminated.

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