Re: New warnings on emacs-26 branch with gcc 8.2.0

[Andy Moreton <andrewjmoreton@gmail.com>]

On Sat 18 Aug 2018, Eli Zaretskii wrote:

>> From: Bruno Haible <bruno@clisp.org>
>> Date: Sat, 18 Aug 2018 18:09:27 +0200
>> Cc: Paul Eggert <eggert@cs.ucla.edu>, Andy Moreton <andrewjmoreton@gmail.com>,
>> 	emacs-devel@gnu.org
>> 
>> So, there are 4 options:
>>   1) Use static reference to Windows API functions.
>>   2) Use '#pragma GCC diagnostic ignored "-Wcast-function-type"'
>>   3) Remove -Wcast-function-type from the compiler options.
>>   4) Live with the warning.
>> 
>> I'm opposed to 1), since it removes either features or portability.
>> 
>> I could do 2), but it does not feel like the right thing, to silence
>> a compiler warning when the user has explicitly requested a warning.
>> 
>> So, please choose among 3) and 4).
>
> There's also this additional option:
>
>   5) Cast through (void *).  Like this:
>
>       GetSystemTimePreciseAsFileTimeFunc =
>         (GetSystemTimePreciseAsFileTimeFuncType) (void (*) (void)) GetProcAddress (kernel32, "GetSystemTimePreciseAsFileTime");

This is the sensible option. GetProcAddress returns FARPROC, so there is
no way of performing this cast correctly without some sort of type
mismatch.

The additional (void (*) (void)) cast deliberately suppresses the warning
in this case, which still allowing use of the warning to catch abuse of
function pointer types in other parts of the program.

    AndyM