Re: NULL passed as an argument to memcmp() in parse_func.c

On Mon, Jun 22, 2015 at 2:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Piotr Stefaniak <postgres(at)piotr-stefaniak(dot)me> writes:
>> There are two places in parse_func.c where memcmp() conditionally gets a
>> NULL as its first argument, which invokes undefined behavior. I guess
>> gcc -O2 will make some assumptions based on memcpy's __nonnull attribute.
>
> If I recall that code correctly, the assumption was that if the third
> argument is zero then memcmp() must not fetch any bytes (not should not,
> but MUST not) and therefore it doesn't matter if we pass a NULL. Are
> you seeing any observable problem here, and if so what is it?

I dunno, this seems like playing with fire to me. A null-test would
be pretty cheap insurance.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company