[PATCH] add support for strnlen (PR 81384)

[Eric Gallager]

On 6/5/18, Martin Sebor <msebor@gmail.com> wrote:
> The attached patch adds basic support for handling strnlen
> as a built-in function.  It touches the strlen pass where
> it folds constant results of the function, and builtins.c
> to add simple support for expanding strnlen calls with known
> results.  It also changes calls.c to detect excessive bounds
> to the function and unsafe calls with arguments declared
> attribute nonstring.
>
> A side-effect of the strlen change I should call out is that
> strlen() calls to all zero-length arrays that aren't considered
> flexible array members (i.e., internal members or non-members)
> are folded into zero.  No warning is issued for such invalid
> uses of zero-length arrays but based on the responses to my
> question Re: aliasing between internal zero-length-arrays and
> other members(*) it sounds like one would be appropriate.
> I will see about adding one in a separate patch.
>
> Martin
>
> [*] https://gcc.gnu.org/ml/gcc/2018-06/msg00046.html
>

I see stuff in the patch mentioning the library version of strnlen;
have you tested on platforms both with and without strnlen in their
libcs? The gnulib documentation lists these platforms as having
missing or buggy strnlens:

This function is missing on some platforms: Mac OS X 10.5, FreeBSD
6.0, NetBSD 5.0, OpenBSD 3.8, AIX 4.3.2, HP-UX 11, IRIX 6.5, OSF/1
5.1, Solaris 10, mingw, Interix 3.5.
This function is buggy on some platforms: AIX 4.3.

https://www.gnu.org/software/gnulib/manual/html_node/strnlen.html