Re: Why the asprintf patch is still breaking the buildfarm

Noah Misch <noah@leadboat.com> writes:
> On Tue, Oct 22, 2013 at 11:00:42AM -0400, Tom Lane wrote:
>> Yeah.  As a separate matter, it might be useful to revise stringinfo.c
>> and the asprintf code so that *if* the returned value is larger than the
>> given buffer size, we use it as a guide to resizing, avoiding the possible
>> need to loop multiple times to make the buffer large enough.  And we could
>> also improve our own implementation of snprintf to follow the C99 spec.
>> 
>> The point here is that we still need to cope with pre-C99 implementations
>> that might return -1 or the given buffer size on overflow.  The NetBSD
>> implementation doesn't do that, which is reasonable in their context, but
>> not workable for us.

> I would vote for choosing the standard we want vsnprintf() to follow (probably
> C99) and substituting a conforming implementation wherever "configure" detects
> that libc does not conform.  We'll be shipping some replacement vsnprintf() in
> any case; we may as well use it to insulate the rest of our code from
> less-preferred variants.

The problem is that we can't tell whether vsnprintf is standard-conforming
without a run-time test.  That's bad for cross-compiled builds, and it's
pretty hazardous even for normal cases, since conceivably an executable
built on one machine could be used on another one with different run-time
behavior.  I'd be willing to take those risks if we got a significant
benefit from it, but in this case I don't see much advantage to be had.
The code in stringinfo/psprintf wouldn't get very much simpler if we
assumed C99 behavior, and we've pretty well isolated the number of places
that care to those.  (I see a couple places in pg_dump that could be
modified to use psprintf instead of direct vsnprintf calls; will go fix.)
        regards, tom lane