Обсуждение: Re: Refactor: allow pg_strncoll(), etc., to accept -1 length for NUL-terminated cstrings.

Hi,

On 2024-08-22 11:00:54 -0700, Jeff Davis wrote:
> Like ICU, allow -1 length to mean that the input string is NUL-
> terminated for pg_strncoll(), pg_strnxfrm(), and pg_strnxfrm_prefix().
> 
> This simplifies the API and code a bit.

I don't really like this.  I was hacking on a patch that uses compiler
annotations to tell the compiler what range of memory a function access. The
compiler then can use that knowledge to give you both compile-time warnings
and, more importantly, it makes ubsan much more accurate. It'll e.g. often be
able to warn you if a function accesses more memory than its annotation would
suggest, even if the memory is part of a larger memory allocation (something
asan, valgrind etc can't warn about, yet are often the most security critical
issues).  I found a bunch of issues that way already.

But the annotations can't work if the access size is sometimes is -1.

I also don't find this very convincing code-wise. You end up with lots of
branches for -1. You have to support cases where one of the arguments is
specifies as -1 and the other one with a real length, even though that's
presumably a non-existing case.

It seems reasonable to want the more efficient path for zero terminated
strings with libc, but it seems like if we want that, we should add add a
collate_method->strcoll, rather than have a strncoll that's not actually
strncoll but strcoll.

Greetings,

Andres Freund

On Fri, 2026-05-01 at 12:40 -0400, Andres Freund wrote:
> Hi,
>
> On 2024-08-22 11:00:54 -0700, Jeff Davis wrote:
> > Like ICU, allow -1 length to mean that the input string is NUL-
> > terminated for pg_strncoll(), pg_strnxfrm(), and
> > pg_strnxfrm_prefix().
> >
> > This simplifies the API and code a bit.
>
> I don't really like this.

Agreed. I did this to match up with the ICU API a bit better, but if
it's interfering with useful tools, then the special cases aren't worth
it.

Patch attached. It causes a bit of churn, so one disadvantage is that
it will complicate future backports in this area.

Regards,
    Jeff Davis