Re: [PATCH cb/pedantic-build-for-developers] lazyload.h: fix warnings about mismatching function pointer types

On Wed, Sep 22, 2021 at 12:56 PM Johannes Sixt [off-list ref] wrote:

Here, GCC warns about every use of the INIT_PROC_ADDR macro, for example:

In file included from compat/mingw.c:8:
compat/mingw.c: In function 'mingw_strftime':
compat/win32/lazyload.h:38:12: warning: assignment to
   'size_t (*)(char *, size_t,  const char *, const struct tm *)'
   {aka 'long long unsigned int (*)(char *, long long unsigned int,
      const char *, const struct tm *)'} from incompatible pointer type
   'FARPROC' {aka 'long long int (*)()'} [-Wincompatible-pointer-types]
   38 |  (function = get_proc_addr(&proc_addr_##function))
      |            ^
compat/mingw.c:1014:6: note: in expansion of macro 'INIT_PROC_ADDR'
 1014 |  if (INIT_PROC_ADDR(strftime))
      |      ^~~~~~~~~~~~~~

did you have CFLAGS adding -Wincompatible-pointer-types explicitly?

This is the reason why the code that got merged to master had -Wno
for this case.

(message wrapper for convenience). Insert a cast to keep the compiler
happy. A cast is fine in these cases because they are generic function
pointer values that have been looked up in a DLL.

I have a more complete "fix" which I got stuck testing GGG[1]; you are likely
going to also hit -Wcast-function-type otherwise.

Signed-off-by: Johannes Sixt <redacted>
---
 How can this have worked ever without a warning?

POSIX have a specific exception that allows (void *) for this, it is incorrect
though in platforms where pointers to code and data might be different
(ex DOS with its segmented model)

Carlo

[1] https://github.com/git/git/pull/1094