Re: [PATCH] softmmu/physmem: Hint notifier is not NULL in as_translate_for_iotlb()

[Philippe Mathieu-Daudé]

On 1/17/21 5:47 PM, Peter Maydell wrote:
> On Sun, 17 Jan 2021 at 16:07, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>>
>> When using GCC 10.2 configured with --extra-cflags=-Os, we get:
>>
>>   softmmu/physmem.c: In function ‘address_space_translate_for_iotlb’:
>>   softmmu/physmem.c:643:26: error: ‘notifier’ may be used uninitialized in 
>> this function [-Werror=maybe-uninitialized]
>>     643 |         notifier->active = true;
>>         |                          ^
>>   softmmu/physmem.c:608:23: note: ‘notifier’ was declared here
>>     608 |     TCGIOMMUNotifier *notifier;
>>         |                       ^~~~~~~~
>>
>> Insert assertions as hint to the compiler that 'notifier' can
>> not be NULL there.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>> Yet another hole in our CI.
>> ---
>>  softmmu/physmem.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
>> index 6301f4f0a5c..65602ed548e 100644
>> --- a/softmmu/physmem.c
>> +++ b/softmmu/physmem.c
>> @@ -605,7 +605,7 @@ static void tcg_register_iommu_notifier(CPUState *cpu,
>>       * when the IOMMU tells us the mappings we've cached have changed.
>>       */
>>      MemoryRegion *mr = MEMORY_REGION(iommu_mr);
>> -    TCGIOMMUNotifier *notifier;
>> +    TCGIOMMUNotifier *notifier = NULL;
>>      int i;
>>
>>      for (i = 0; i < cpu->iommu_notifiers->len; i++) {
>> @@ -638,6 +638,7 @@ static void tcg_register_iommu_notifier(CPUState *cpu,
>>          memory_region_register_iommu_notifier(notifier->mr, &notifier->n,
>>                                                &error_fatal);
>>      }
>> +    assert(notifier != NULL);
>>
>>      if (!notifier->active) {
>>          notifier->active = true;
> 
> Is the assert() necessary to prevent the compiler complaining?
> Usually we don't bother if it's about to be dereferenced anyway.

Yes you are right, the assert() is not necessary. Simply initializing
the value silents the error.

Regards,

Phil.