On Wed, Sep 18, 2013 at 07:07:46PM +0200, Lukas Slebodnik wrote:
On (12/09/13 16:55), Michal Židek wrote:
>On 09/12/2013 02:03 PM, Lukas Slebodnik wrote:
>>On (11/09/13 17:05), Michal Židek wrote:
>>>Patches 1-4 and 9:
>>>These patches use the SAFEALIGN macros where it is appropriate. I
>>>split them into several patches for easier review, so that client
>>>code changes are not mixed with the rest of the code and changes that
>>>are a little different than the rest have their own patch.
>>>
>>>Patches 5-6:
>>>Here I think it is not needed to use uint8_t* or char*. We cast the
>>>pointer anyway and there are no real alignment issues (the memory is
>>>aligned properly). I was thinking about suppressing the warnings with
>>>#pragma here, but in this particular situation it is IMO better to
>>>have just void*.
>>>
>>>Patches 7-8:
>>>These were all false positive warnings. It is possible to suppress
>>>them with additional casting but I found it less readable so I used
>>>#pragma.
>>>
>>>Patch 10:
>>>We had improperly aligned part of a buffer used in client code. Also
>>>some code blocks here must rely on fact that the buffer they get is
>>>aligned properly (they can do nothing about it if it isn't). In these
>>>cases it is better to silence the warnings, so that it does not make
>>>permanent noise during compilation.
>>>
>>>Thanks
>>>Michal
>>
>>You forgot to fix two warnings in tests.
>>
>> CC src/tests/cmocka/dyndns_tests-test_dyndns.o
>>src/tests/cmocka/test_dyndns.c:130:10: warning: cast from 'struct sockaddr
*' to
>> 'struct sockaddr_in *' increases required alignment from 2 to 4
[-Wcast-align]
>> ((struct sockaddr_in *) ifap->ifa_addr)->sin_family = AF_INET;
>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>src/tests/cmocka/test_dyndns.c:134:26: warning: cast from 'struct sockaddr
*' to
>> 'struct sockaddr_in *' increases required alignment from 2 to 4
[-Wcast-align]
>> &(((struct sockaddr_in *)
ifap->ifa_addr)->sin_addr)) != 1) {
>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>2 warnings generated.
>>
>>LS
>
>Thanks, new patches are attached.
>
>Michal
>
I tested some compilers and patches work fine with clang and gcc.
But there are also another compilers in the world :-)
ant they needn't understand "pragma GCC". This pragma is not standardized.
src/providers/dp_dyndns.c(145): warning #161: unrecognized #pragma
#pragma GCC diagnostic push
^
src/providers/dp_dyndns.c(146): warning #161: unrecognized #pragma
#pragma GCC diagnostic ignored "-Wcast-align"
^
src/providers/dp_dyndns.c(206): warning #161: unrecognized #pragma
#pragma GCC diagnostic pop
^
If you are 100% sure about alignment, you can define own macro.
Something like this:
#define ignore_align(var, dest_type) \
(dest_type *)((void*)(var))
And usage:
wrapper->refcount = ignore_align(wrapper->ptr + refcount_offset, int);
Does anybody have any better ideas?
Compiler specific #pragma should not be used. And I think in general
#pragma should be used with great care. Currently there is only one use
case in sssd in the memcache code to align some structs which make
sense.
Especially I think ingnoring a warning is not a good idea. If currently
no one has a good idea how to handle the sockaddr and in_addr structs in
a way which does not produce a warning I would prefer to keep the
warning around until someone has a good idea. Imo a comment in the code
that the warning can be ignored would be sufficient for the time being.
bye,
Sumit
LS
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