Re: [PATCH v4 2/3] Linux: Implement a useful version of _startup_fatal

[Florian Weimer <fweimer@redhat.com>]

* Andreas Schwab:

> On Mai 05 2022, Florian Weimer via Libc-alpha wrote:
>
>> +/* Avoid a run-time invocation of strlen.  */
>> +#define _startup_fatal(message)                                         \
>> +  do                                                                    \
>> +    {                                                                   \
>> +      size_t __message_length = __builtin_strlen (message);             \
>> +      if (! __builtin_constant_p (__message_length))                    \
>> +        {                                                               \
>> +          extern void _startup_fatal_not_constant (void);               \
>> +          _startup_fatal_not_constant ();                               \
>> +        }                                                               \
>
> I think that could use _Static_assert.

It only works for simple cases, not for arguments that require constant
progagation:

libc-tls.c: In function ‘__libc_setup_tls’:
../sysdeps/unix/sysv/linux/startup.h:29:23: error: expression in static assertion is not constant
   29 |       _Static_assert (__builtin_constant_p (__message_length),          \
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thanks,
Florian