Ping: [PATCH v5] C, ObjC: Add -Wunterminated-string-initialization

[Alejandro Colomar <alx@kernel.org>]

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Hi,

Gentle ping here.

Thanks,
Alex

On Sun, Oct 01, 2023 at 06:24:00PM +0200, Alejandro Colomar 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.
> 
> Since Wc++-compat now includes this warning, the test has to be modified
> to expect the text of the new warning too, in <gcc.dg/Wcxx-compat-14.c>.
> 
> 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-ec66160cf413@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>
> Cc: David Malcolm <dmalcolm@redhat.com>
> Signed-off-by: Alejandro Colomar <alx@kernel.org>
> ---
> 
> v5:
> 
> -  Fix existing C++-compat tests.  [reported by <ci_notify@linaro.org>]
> 
> 
>  gcc/c-family/c.opt                                         | 4 ++++
>  gcc/c/c-typeck.cc                                          | 6 +++---
>  gcc/testsuite/gcc.dg/Wcxx-compat-14.c                      | 2 +-
>  gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c | 6 ++++++
>  4 files changed, 14 insertions(+), 4 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c
> 
> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> index 44b9c862c14..e8f6b836836 100644
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -1407,6 +1407,10 @@ Wunsuffixed-float-constants
>  C ObjC Var(warn_unsuffixed_float_constants) Warning
>  Warn about unsuffixed float constants.
>  
> +Wunterminated-string-initialization
> +C ObjC Var(warn_unterminated_string_initialization) Warning LangEnabledBy(C ObjC,Wextra || Wc++-compat)
> +Warn about character arrays initialized as unterminated character sequences by a string literal.
> +
>  Wunused
>  C ObjC C++ ObjC++ LangEnabledBy(C ObjC C++ ObjC++,Wall)
>  ; documented in common.opt
> diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
> index e55e887da14..7df9de819ed 100644
> --- a/gcc/c/c-typeck.cc
> +++ b/gcc/c/c-typeck.cc
> @@ -8399,11 +8399,11 @@ digest_init (location_t init_loc, tree type, tree init, tree origtype,
>  		pedwarn_init (init_loc, 0,
>  			      ("initializer-string for array of %qT "
>  			       "is too long"), typ1);
> -	      else if (warn_cxx_compat
> +	      else if (warn_unterminated_string_initialization
>  		       && compare_tree_int (TYPE_SIZE_UNIT (type), len) < 0)
> -		warning_at (init_loc, OPT_Wc___compat,
> +		warning_at (init_loc, OPT_Wunterminated_string_initialization,
>  			    ("initializer-string for array of %qT "
> -			     "is too long for C++"), typ1);
> +			     "is too long"), typ1);
>  	      if (compare_tree_int (TYPE_SIZE_UNIT (type), len) < 0)
>  		{
>  		  unsigned HOST_WIDE_INT size
> diff --git a/gcc/testsuite/gcc.dg/Wcxx-compat-14.c b/gcc/testsuite/gcc.dg/Wcxx-compat-14.c
> index 23783711be6..6df0ee197cc 100644
> --- a/gcc/testsuite/gcc.dg/Wcxx-compat-14.c
> +++ b/gcc/testsuite/gcc.dg/Wcxx-compat-14.c
> @@ -2,5 +2,5 @@
>  /* { dg-options "-Wc++-compat" } */
>  
>  char a1[] = "a";
> -char a2[1] = "a";	/* { dg-warning "C\[+\]\[+\]" } */
> +char a2[1] = "a";	/* { dg-warning "initializer-string for array of 'char' is too long" } */
>  char a3[2] = "a";
> diff --git a/gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c b/gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c
> new file mode 100644
> index 00000000000..13d5dbc6640
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c
> @@ -0,0 +1,6 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Wunterminated-string-initialization" } */
> +
> +char a1[] = "a";
> +char a2[1] = "a";	/* { dg-warning "initializer-string for array of 'char' is too long" } */
> +char a3[2] = "a";
> -- 
> 2.40.1
> 

-- 
<https://www.alejandro-colomar.es/>

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