Re: Unable to cross build for Windows

[Eli Zaretskii]

> From: Martin Dorey <Martin.Dorey@hitachivantara.com>
> CC: "bug-make@gnu.org" <bug-make@gnu.org>
> Date: Fri, 9 Jun 2023 06:32:28 +0000
> msip_labels:
> 
> #include <stdint.h>
> 
> intptr_t _get_osfhandle(int);
> typedef void* HANDLE;
> 
> HANDLE fn() {
>   return (HANDLE)_get_osfhandle(0);
> }
> martind@sirius:~/tmp/svensson-2023-06-08$ gcc -c -Wbad-function-cast make.c
> make.c: In function ‘fn’:
> make.c:7:10: warning: cast from function call of type ‘intptr_t {aka long 
> int}’ to non-matching type ‘void *’ [-Wbad-function-cast]
>    return (HANDLE)_get_osfhandle(0);
>           ^
> martind@sirius:~/tmp/svensson-2023-06-08$ 
> 
> That's gcc-6.3, but it's much the same in every version I tested from gcc-4.4 
> to gcc-10.  A random version's man page, 
> https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Warning-Options.html, explains 
> the flag as to:
> 
> > Warn when a function call is cast to a non-matching type. For example, warn 
> > if a call to a function returning an integer type is cast to a pointer type.
> 
> I fear they mean exactly what they say there.  So, while you might call it a 
> mistake, I don't think it's an accident.  
> https://stackoverflow.com/a/35308713/18096 has some explanation of why it 
> might sometimes be useful... and how it could be sidestepped by a change to 
> Gnu Make, like our new friend wished for.

Yes, it sounds like -Wbad-function-cast will always emit a warning in
such cases, and one cannot use it with the likes of _get_osfhandle,
which _require_ such casts.

You can, of course, work around it; the following compiles without a
warning:

#include <stdint.h>

intptr_t _get_osfhandle(int);
typedef void* HANDLE;

HANDLE fn() {
  intptr_t handle = _get_osfhandle(0);
  return (HANDLE)handle;
}