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

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Jun 22, 2015 at 2:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> 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.

A null test would be a pretty cheap way of masking a bug in that logic,
if we ever introduced one; to wit, that it would cause a call with
argtypes==NULL to match anything.

Possibly saner is

if (nargs == 0 ||
memcmp(argtypes, best_candidate->args, nargs * sizeof(Oid)) == 0)
break;

I remain unconvinced that this is necessary, though. It looks a *whole*
lot like the guards we have against old Solaris' bsearch-of-zero-entries
bug. I maintain that what glibc has done is exactly to introduce a bug
for the zero-entries case, and that Piotr ought to complain to them
about it. At the very least, if you commit this please annotate it
as working around a memcmp bug.

regards, tom lane