[v1] migration: Silence compiler warning in global_state_store_running()

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

Posted by Thomas Huth 3 years, 7 months ago

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));
 }
 
 bool global_state_received(void)
-- 
2.18.2

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

Posted by Eric Blake 3 years, 7 months ago

On 9/16/20 12:19 PM, 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;

Do we still need the cast to char*?

>       assert(strlen(state) < sizeof(global_state.runstate));
> -    strncpy((char *)global_state.runstate,
> -           state, sizeof(global_state.runstate));
> +    strncpy(dest, state, sizeof(global_state.runstate));
>   }
>   

Otherwise,
Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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

Posted by Thomas Huth 3 years, 7 months ago

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?

 Thomas

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

Posted by Paolo Bonzini 3 years, 7 months ago

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

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

Posted by Thomas Huth 3 years, 7 months ago

On 17/09/2020 09.18, Paolo Bonzini wrote:
> 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.

I think the trick with QEMU_NONSTRING should work fine in all cases
where we have a real array, see e.g. buf[] in find_vdi_name() in
block/sheepdog.c. It just does not seem to work in case you have a char*
pointer instead of an array...

 Thomas