[PATCH] dlls/windows.globalization: don't allocate a partial structure

[Eric Pouech]

Le 23/03/2022 à 11:15, Rémi Bernon a écrit :
> On 3/23/22 08:19, Eric Pouech wrote:
>> GCC 11 complains about accessing struct hstring_vector (-Warray-bounds)
>> when the allocation is made for a 0-sized vector
>>
>> so ensure that we always allocate a memory block to fit a whole
>> structure
>>
>> Signed-off-by: Eric Pouech <eric.pouech at gmail.com>
>>
>> ---
>>   dlls/windows.globalization/main.c |    6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/dlls/windows.globalization/main.c 
>> b/dlls/windows.globalization/main.c
>> index 3e5a59bde14..363e0150af1 100644
>> --- a/dlls/windows.globalization/main.c
>> +++ b/dlls/windows.globalization/main.c
>> @@ -213,8 +213,10 @@ static const struct IVectorView_HSTRINGVtbl 
>> hstring_vector_vtbl =
>>   static HRESULT hstring_vector_create(HSTRING *values, SIZE_T count, 
>> IVectorView_HSTRING **out)
>>   {
>>       struct hstring_vector *impl;
>> -
>> -    if (!(impl = malloc(offsetof(struct hstring_vector, 
>> values[count])))) return E_OUTOFMEMORY;
>> +    /* always allocate at least the full structure to avoid GCC11 
>> warnings */
>> +    if (!(impl = malloc(max(offsetof(struct hstring_vector, 
>> values[count]),
>> +                            sizeof(struct hstring_vector)))))
>> +        return E_OUTOFMEMORY;
>>       impl->ref = 1;
>>         impl->IVectorView_HSTRING_iface.lpVtbl = &hstring_vector_vtbl;
>>
>>
>
> IMHO GCC should fix its warning instead, we do that in many places and 
> I think it's completely valid.

Hi Rémi

see 
https://www.winehq.org/pipermail/wine-devel/2022-February/thread.html#207795 
for a previous discussion on a similar issue (and the final decision of 
over-allocating)

to my understanding, accessing through a pointer of type mytype* a 
memory block which storage is strictly smaller to sizeo(mytype) is 
clearly undefined behavior (I'm not stating that it does in fact 
generate wrong results)

(even if the accessed field is inside the allocated memory size)

in this precise case, defining the structure with 0 length array would 
be another option, yet non portable

and for the record, gcc12 (even if non yet released) generates a few 
more warnings about this subject on wine code (and I'm not even talking 
of mingw port of gcc12)

A+

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