Re: serious compiler warnings in mingw64 build of master

[Eli Zaretskii <eliz@gnu.org>]

> From: Stephen Leake <stephen_leake@stephe-leake.org>
> Date: Sat, 14 Aug 2021 10:18:56 -0700
> 
> I just updated emacs/master (to
> bf55b5ac17cd5a40ad5ff2e25af7e050602180bb), and it's giving these
> compiler warnings:
> 
>    CC       process.o
> In file included from process.c:33:
> process.c: In function 'Fmake_process':
> lisp.h:1561:31: warning: null pointer dereference [-Wnull-dereference]
>  1561 |   return XSTRING (string)->u.s.data;
>       |          ~~~~~~~~~~~~~~~~~~~~~^~~~~
> 
> This is from line 1990 in process.c:
> 	  new_argv[i] = SSDATA (XCAR (tem));
> 
> I have not tried to figure out a fix.

Neither did I.

>    CC       w32.o
> w32.c: In function '_sys_read_ahead':
> w32.c:8858:10: warning: 'rc' may be used uninitialized in this function [-Wmaybe-uninitialized]
>  8858 |   if (rc == sizeof (char))
>       |       ~~~^~~~~~~~~~~~~~~~
> 
> The preceding if/elsif block has no final 'else', so rc may not be set.

This is bogus: the compiler isn't smart enough to understand that the
3 possible flag bits are the only ones that can happen: a descriptor
is either for a pipe, or a serial connection, or a socket, because
_sys_read_ahead is only ever used for reading process output.  I added
an initialization to pacify the compiler.

> I've been getting mysterious crashes when mail spawns a process to get
> more mail, so I'm hoping these are the root cause of that.

Unlikely, because this code hasn't changed in eons.