Re: Warnings in mingw64 build on emacs-28 branch

[Andy Moreton]

On Sun 07 Nov 2021, Eli Zaretskii wrote:

>> From: Andy Moreton <andrewjmoreton@gmail.com>
>> Date: Sun, 07 Nov 2021 14:46:51 +0000
>> 
>> 1) In w32.h, "prepare_standard_handles" and "reset_standard_handles"
>> have "HANDLE handles[4]" argument, but the handle array has 3 elements
>> in the definitions and callers.
>
> I hope I fixed this now.

Yes, thanks.

>> 2) This warning has been present for a long time, and seems to be
>> confusion over the flexible array handling.
>
> I'm not sure what this is about.  We use memcpy to copy from a Lisp
> vector's contents in gazillion other places, and I understand they
> don't cause any warnings?  How is this place different?

No idea. I think this may have been discussed previously, but I cannot
find it in the mail archives. xvector_contents_addr in lisp.h mentions
gcc bug 95072 (filed by Paul Eggert with a similar code example).

Should this be using xvector_contents or vcopy to placate this warning ?

>> 3) This warning is new with gcc 11.
>> 
>> C:/emacs/git/emacs/emacs-28/src/w32heap.c: In function 'getrlimit':
>> C:/emacs/git/emacs/emacs-28/src/w32heap.c:853:14: warning: 'm' may be used 
>> uninitialized [-Wmaybe-uninitialized]
>>   853 |         if (!VirtualQuery ((LPCVOID) &m, &m, sizeof m))
>>       |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> In file included from 
>> C:/msys64/mingw64/x86_64-w64-mingw32/include/winbase.h:25,
>>                  from 
>> C:/msys64/mingw64/x86_64-w64-mingw32/include/windows.h:70,
>>                  from C:/emacs/git/emacs/emacs-28/src/w32common.h:24,
>>                  from C:/emacs/git/emacs/emacs-28/src/w32heap.c:54:
>> C:/msys64/mingw64/x86_64-w64-mingw32/include/memoryapi.h:45:28: note: by 
>> argument 1 of type 'LPCVOID' {aka 'const void *'} to 'VirtualQuery' declared 
>> here
>>    45 |   WINBASEAPI SIZE_T WINAPI VirtualQuery (LPCVOID lpAddress, 
>> PMEMORY_BASIC_INFORMATION lpBuffer, SIZE_T dwLength);
>>       |                            ^~~~~~~~~~~~
>> C:/emacs/git/emacs/emacs-28/src/w32heap.c:844:34: note: 'm' declared here
>>   844 |         MEMORY_BASIC_INFORMATION m;
>>       |                                  ^
>
> That's a compiler bug, I think.  I see nothing wrong in the call.

Indeed, although passing "&m" as PMEMORY_BASIC_INFORMATION and as LPCVOID
introduces aliasing.

    AndyM