This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Obscure crashes due to gcc 4.9 -O2 => -fisolate-erroneous-paths-dereference
- From: Andrew Haley <aph at redhat dot com>
- To: Florian Weimer <fweimer at redhat dot com>, Sandra Loosemore <sandra at codesourcery dot com>, Jakub Jelinek <jakub at redhat dot com>
- Cc: Jeff Prothero <jprother at altera dot com>, gcc at gcc dot gnu dot org
- Date: Fri, 20 Feb 2015 12:11:20 +0000
- Subject: Re: Obscure crashes due to gcc 4.9 -O2 => -fisolate-erroneous-paths-dereference
- Authentication-results: sourceware.org; auth=none
- References: <pdf61azt48b dot fsf at sj-interactive3 dot altera dot com> <20150218192943 dot GR1746 at tucnak dot redhat dot com> <54E64DFF dot 8030100 at codesourcery dot com> <54E71534 dot 8070805 at redhat dot com>
On 02/20/2015 11:06 AM, Florian Weimer wrote:
> On 02/19/2015 09:56 PM, Sandra Loosemore wrote:
>> Hmmmm, Passing the additional option in user code would be one thing,
>> but what about library code? E.g., using memcpy (either explicitly or
>> implicitly for a structure copy)?
>
> The memcpy problem isn't restricted to embedded architectures.
>
> size_t size;
> const unsigned char *source;
> std::vector<char> vec;
> â
> vec.resize(size);
> memcpy(vec.data(), source, size);
>
> std::vector<T>::data() can return a null pointer if the vector is empty,
> which means that this code is invalid for empty inputs.
Sure, but if that's a bug then it's a bug in the definition of
memcpy(), not in the definition of the properties of a null pointer.
If the size is zero then it really shouldn't matter if the destination
address is null.
Andrew.