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From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <philmd@redhat.com>
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Date: Tue, 18 Dec 2018 17:55:27 +0100
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Subject: Re: [Qemu-devel] [PATCH v2 0/3] Fix strncpy() warnings for GCC8 new
 -Wstringop-truncation
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To: "Michael S. Tsirkin" <mst@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, Ben Pye <ben@curlybracket.co.uk>, Stefan Weil <sw@weilnetz.de>, Howard Spoelstra <hsp.cat7@gmail.com>, Jeff Cody <jcody@redhat.com>, =?UTF-8?Q?C=c3=a9dric_Le_Goater?= <clg@kaod.org>, Thomas Huth <thuth@redhat.com>, Liu Yuan <namei.unix@gmail.com>, Igor Mammedov <imammedo@redhat.com>, Max Reitz <mreitz@redhat.com>, Kevin Wolf <kwolf@redhat.com>, Eric Blake <eblake@redhat.com>, =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= <marcandre.lureau@redhat.com>, David Hildenbrand <david@redhat.com>, David Gibson <david@gibson.dropbear.id.au>, Markus Armbruster <armbru@redhat.com>, qemu-block@nongnu.org, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= <berrange@redhat.com>, 1803872@bugs.launchpad.net, Juan Quintela <quintela@redhat.com>

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.