[Bug c++/64867] split warning for passing non-POD to varargs function from -Wconditionally-supported into new warning flag, -Wnon-pod-varargs

["dcb314 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64867

David Binderman <dcb314 at hotmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dcb314 at hotmail dot com

--- Comment #30 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to Trass3r from comment #27)
> This should really be enabled by -Wall or -Wextra as it generates code that
> may easily crash or corrupt something.

+1.

Clang errors, intel warns and for gcc you have to enable the somewhat
obscure flag -Wconditionally-supported to see anything at all.

gcc looks to be a trailer on this issue. It's not about standards conformance,
its about making it easy for users to find bugs.

Source code I used is:

struct S
{
        S();
        S( const S &);
        ~S();

        char * p;
};

void f( int, ...);

void g()
{
        S s1;

        f( 3, s1);
};

$ /home/dcb/llvm/results/bin/clang++   sep3f.cc
sep3f.cc:19:8: error: cannot pass object of non-trivial type 'S' through
variadic function; call will abort at runtime [-Wnon-pod-varargs]
        f( 3, s1);
              ^
1 error generated.

$ /home/dcb34/intel/oneapi/compiler/2021.3.0/linux/bin/intel64/icpc  sep3f.cc
sep3f.cc(19): warning #1595: a class type that is not trivially copyable passed
through ellipsis
        f( 3, s1);
              ^

$ /home/dcb/gcc/results/bin/g++ -c -g -O2 -Wall -Wextra  sep3f.cc
$ /home/dcb/gcc/results/bin/g++ -c -g -O2 -Wall -Wextra
-Wconditionally-supported sep3f.cc
sep3f.cc: In function ‘void g()’:
sep3f.cc:19:10: warning: passing objects of non-trivially-copyable type ‘struct
S’ through ‘...’ is conditionally supported [-Wconditionally-supported]
   19 |         f( 3, s1);
      |         ~^~~~~~~~


I'll add flag -Wconditionally-supported to a build of Fedora and see
what happens.