Re: [PATCH] fix format security

Bruno Haible <[email protected]> writes:

> Paul Eggert wrote:
>> > It is a bit unfortunate that this warning comes up almost monthly
>> 
>> Perhaps we should add something like the following to
>> gnulib/lib/gettext.h, once we have a Clang bug report number?
>> Although drastic, this would save us time and we'd still get static
>> checking when compiling with GCC, except for printf calls in
>> clang-only code (which should be rare).
>> 
>> /* Pacify clang false alarm
>>     <https://github.com/llvm/llvm-project/issues/987654321>.  */
>> #ifdef __clang__
>> # pragma clang diagnostic ignored "-Wformat-security"
>> #endif
>
> Nice idea. But I still [1] think that it is too drastic. Some people
> might be really upset.

Yes, it is probably a bit excessive. The warning is generally helpful
outside of this specific instance.

I was preparing a bug report for Clang, and think I found out how to fix
the issue.  See the following program:

    $ cat example.c 
    #include <stdio.h>
    #include <stdlib.h>
    #ifdef ENABLE_NLS
    # include <libintl.h>
    #else
    __attribute__ ((__always_inline__, __gnu_inline__,
                    __format_arg__ (1)))
    extern inline char const *
    gettext (const char *msgid)
    {
      return msgid;
    }
    #endif
    #define _(msgid) gettext (msgid)
    int
    main (void)
    {
      /* No warning.  */
      printf (_("Hello, %s!\n"), "world");
      /* Warning.  */
      printf (_("Hello, world!\n"));
      return EXIT_SUCCESS;
    }
    $ clang -Wformat-security example.c

So, adding "__format_arg__ (1)" in this instance will silence it.

If that sounds okay, I'll figure out what version of GCC and Clang added
them and submit a patch.

Collin