c: do not warn about truncating NUL char when initializing nonstring arrays [PR117178]

When initializing a nonstring char array when compiled with
-Wunterminated-string-initialization the warning trips even when
truncating the trailing NUL character from the string constant.  Only
warn about this when running under -Wc++-compat since under C++ we should
not initialize nonstrings from C strings.

This patch separates the -Wunterminated-string-initialization and
-Wc++-compat warnings, they are now independent option, the former implied
by -Wextra, the latter not implied by anything.  If -Wc++-compat is in effect,
it takes precedence over -Wunterminated-string-initialization and warns regardless
of nonstring attribute, otherwise if -Wunterminated-string-initialization is
enabled, it warns only if there isn't nonstring attribute.
In all cases, the warnings and also pedwarn_init for even larger sizes now
provide details on the lengths.

2025-03-07  Kees Cook  <kees@kernel.org>
	    Jakub Jelinek  <jakub@redhat.com>

	PR c/117178
gcc/
	* doc/invoke.texi (Wunterminated-string-initialization): Document
	the new interaction between this warning and -Wc++-compat and that
	initialization of decls with nonstring attribute aren't warned about.
gcc/c-family/
	* c.opt (Wunterminated-string-initialization): Don't depend on
	-Wc++-compat.
gcc/c/
	* c-typeck.cc (digest_init): Add DECL argument.  Adjust wording of
	pedwarn_init for too long strings and provide details on the lengths,
	for string literals where just the trailing NULL doesn't fit warn for
	warn_cxx_compat with OPT_Wc___compat, wording which mentions "for C++"
	and provides details on lengths, otherwise for
	warn_unterminated_string_initialization adjust the warning, provide
	details on lengths and don't warn if get_attr_nonstring_decl (decl).
	(build_c_cast, store_init_value, output_init_element): Adjust
	digest_init callers.
gcc/testsuite/
	* gcc.dg/Wunterminated-string-initialization.c: Add additional test
	coverage.
	* gcc.dg/Wcxx-compat-14.c: Check in dg-warning for "for C++" part of
	the diagnostics.
	* gcc.dg/Wcxx-compat-23.c: New test.
	* gcc.dg/Wcxx-compat-24.c: New test.

Signed-off-by: Kees Cook <kees@kernel.org>

0 files changed, 0 insertions, 0 deletions