Re: [PATCH v2] C, ObjC: Add -Wunterminated-string-initialization

[David Malcolm <dmalcolm@redhat.com>]

On Fri, 2023-03-24 at 14:39 +0100, Alejandro Colomar via Gcc-patches
wrote:
> Warn about the following:
> 
>     char  s[3] = "foo";
> 
> Initializing a char array with a string literal of the same length as
> the size of the array is usually a mistake.  Rarely is the case where
> one wants to create a non-terminated character sequence from a string
> literal.
> 
> In some cases, for writing faster code, one may want to use arrays
> instead of pointers, since that removes the need for storing an array
> of
> pointers apart from the strings themselves.
> 
>     char  *log_levels[]   = { "info", "warning", "err" };
> vs.
>     char  log_levels[][7] = { "info", "warning", "err" };
> 
> This forces the programmer to specify a size, which might change if a
> new entry is later added.  Having no way to enforce null termination
> is
> very dangerous, however, so it is useful to have a warning for this,
> so
> that the compiler can make sure that the programmer didn't make any
> mistakes.  This warning catches the bug above, so that the programmer
> will be able to fix it and write:
> 
>     char  log_levels[][8] = { "info", "warning", "err" };
> 
> This warning already existed as part of -Wc++-compat, but this patch
> allows enabling it separately.  It is also included in -Wextra, since
> it may not always be desired (when unterminated character sequences
> are
> wanted), but it's likely to be desired in most cases.
> 
> Link:
> <https://lists.gnu.org/archive/html/groff/2022-11/msg00059.html>
> Link:
> <https://lists.gnu.org/archive/html/groff/2022-11/msg00063.html>
> Link:
> <https://inbox.sourceware.org/gcc/36da94eb-1cac-5ae8-7fea-ec66160cf41
> 3@gmail.com/T/>
> Acked-by: Doug McIlroy <douglas.mcilroy@dartmouth.edu>
> Cc: "G. Branden Robinson" <g.branden.robinson@gmail.com>
> Cc: Ralph Corderoy <ralph@inputplus.co.uk>
> Cc: Dave Kemper <saint.snit@gmail.com>
> Cc: Larry McVoy <lm@mcvoy.com>
> Cc: Andrew Pinski <pinskia@gmail.com>
> Cc: Jonathan Wakely <jwakely.gcc@gmail.com>
> Cc: Andrew Clayton <andrew@digital-domain.net>
> Cc: Martin Uecker <muecker@gwdg.de>
> Signed-off-by: Alejandro Colomar <alx@kernel.org>
> ---
> 
> Hi,

Hi Alex, thanks for the patch.

> 
> I sent v1 to the wrong list.  This time I've made sure to write to
> gcc-patches@.

Note that right now we're deep in bug-fixing/stabilization for GCC 13
(and trunk is still tracking that effort), so your patch might be more
suitable for GCC 14.

> 
> v2 adds some draft of a test, as suggested by Martin.  However, I
> don't
> know yet how to write those, so the test is just a draft.  But I did
> test the feature, by compiling GCC and compiling some small program
> with
> it.

Unfortunately the answer to the question "how do I run just one
testcase in GCC's testsuite" is rather non-trivial; FWIW I've written
up some notes on working with the GCC testsuite here:
https://gcc-newbies-guide.readthedocs.io/en/latest/working-with-the-testsuite.html

Hope this is helpful
Dave


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