Re: [PATCH] migration: Silence compiler warning in global_state_store_running()

[Paolo Bonzini <pbonzini@redhat.com>]

On 17/09/20 08:30, Thomas Huth wrote:
> On 16/09/2020 19.19, Thomas Huth wrote:
>> GCC 9.3.0 on Ubuntu complains:
>>
>> In file included from /usr/include/string.h:495,
>>                  from /home/travis/build/huth/qemu/include/qemu/osdep.h:87,
>>                  from ../migration/global_state.c:13:
>> In function ‘strncpy’,
>>     inlined from ‘global_state_store_running’ at ../migration/global_state.c:47:5:
>> /usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ specified bound 100 equals destination size [-Werror=stringop-truncation]
>>   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
>>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> ... but we apparently really want to do the strncpy here. Silence the
>> warning with QEMU_NONSTRING.
>>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>  migration/global_state.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/migration/global_state.c b/migration/global_state.c
>> index 25311479a4..f1355d7d97 100644
>> --- a/migration/global_state.c
>> +++ b/migration/global_state.c
>> @@ -43,9 +43,9 @@ int global_state_store(void)
>>  void global_state_store_running(void)
>>  {
>>      const char *state = RunState_str(RUN_STATE_RUNNING);
>> +    QEMU_NONSTRING char *dest = (char *)global_state.runstate;
>>      assert(strlen(state) < sizeof(global_state.runstate));
>> -    strncpy((char *)global_state.runstate,
>> -           state, sizeof(global_state.runstate));
>> +    strncpy(dest, state, sizeof(global_state.runstate));
>>  }
> 
> Darn, I was sending too fast here, sorry, but seems like this does *not*
> fix the issue with GCC 9.3:
> 
>  https://travis-ci.com/github/huth/qemu/jobs/385871010#L2930
> 
> ... so maybe we should simply switch to strpadcpy() instead?

Yes, and probably do so everywhere that strncpy is used.

Paolo