[PATCH 5/5] ntoskrnl.exe: Make user shared data pointers volatile (GCC 11).

[Rémi Bernon]

On 9/27/21 6:33 PM, Zebediah Figura wrote:
> On 9/27/21 3:58 AM, Rémi Bernon wrote:
>> So that GCC 11 stops warning about reading from a 0-size memory region.
>>
>> Signed-off-by: Rémi Bernon <rbernon at codeweavers.com>
>> ---
>>   dlls/ntoskrnl.exe/instr.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/dlls/ntoskrnl.exe/instr.c b/dlls/ntoskrnl.exe/instr.c
>> index f197570db0c..fbcd376dbc1 100644
>> --- a/dlls/ntoskrnl.exe/instr.c
>> +++ b/dlls/ntoskrnl.exe/instr.c
>> @@ -498,8 +498,8 @@ WINE_DEFAULT_DEBUG_CHANNEL(int);
>>   #define SIB_BASE( sib, rex )    (((sib) & 7) | (((rex) & REX_B) ? 8 
>> : 0))
>>   /* keep in sync with dlls/ntdll/thread.c:thread_init */
>> -static const BYTE *wine_user_shared_data = (BYTE *)0x7ffe0000;
>> -static const BYTE *user_shared_data      = (BYTE *)0xfffff78000000000;
>> +static const BYTE *volatile wine_user_shared_data = (BYTE *)0x7ffe0000;
>> +static const BYTE *volatile user_shared_data      = (BYTE 
>> *)0xfffff78000000000;
>>   static inline DWORD64 *get_int_reg( CONTEXT *context, int index )
>>   {
>>
> 
> This looks wrong. It should presumably be "const volatile BYTE *" 
> (actually: "const volatile BYTE *const"), but I'm guessing that doesn't 
> actually fix the warning. Granted, there's an open GCC bug for this [1], 
> and marking the variable volatile is suggested as a workaround...
> 
> Perhaps at least we should mark that we're working around a GCC bug in 
> the code, since otherwise it looks like "volatile" is in the wrong place.
> 
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578
> 

No, the contents of the memory don't need to be volatile, the pointer 
does. This way GCC cannot assume its fixed value (the warning triggers 
when accessing non-NULL pointers).
-- 
Rémi Bernon <rbernon at codeweavers.com>