Re: [dpdk-dev] [PATCH v2] x86/eal: gcc 10 ignore stringop-overflow warnings

[Kevin Traynor <ktraynor@redhat.com>]

On 17/04/2020 11:13, Thomas Monjalon wrote:
> 17/04/2020 11:33, Bruce Richardson:
>> On Thu, Apr 16, 2020 at 07:45:49PM +0100, Kevin Traynor wrote:
>>> stringop-overflow warns when it sees a possible overflow
>>> in a string operation.
>>>
>>> In the rte_memcpy functions different branches are taken
>>> depending on the size. stringop-overflow is raised for the
>>> branches in the function where it sees the static size of the
>>> src could be overflowed.
>>>
>>> However, in reality a correct size argument and in some cases
>>> dynamic allocation would ensure that this does not happen.
>>>
>>> For example, in the case below for key, the correct path will be
>>> chosen in rte_memcpy_generic at runtime based on the size argument
>>> but as some paths in the function could lead to a cast to 32 bytes
>>> a warning is raised.
>>>
>>> In function ‘_mm256_storeu_si256’,
>>> inlined from ‘rte_memcpy_generic’
>>> at ../lib/librte_eal/common/include/arch/x86/rte_memcpy.h:315:2,
>>> inlined from ‘iavf_configure_rss_key’
>>> at ../lib/librte_eal/common/include/arch/x86/rte_memcpy.h:869:10:
>>>
>>> /usr/lib/gcc/x86_64-redhat-linux/10/include/avxintrin.h:928:8:
>>> warning: writing 32 bytes into a region of size 1 [-Wstringop-overflow=]
>>>   928 |   *__P = __A;
>>>       |   ~~~~~^~~~~
>>> In file included
>>> from ../drivers/net/iavf/../../common/iavf/iavf_prototype.h:10,
>>> from ../drivers/net/iavf/iavf.h:9,
>>> from ../drivers/net/iavf/iavf_vchnl.c:22:
>>>
>>> ../drivers/net/iavf/iavf_vchnl.c:
>>> In function ‘iavf_configure_rss_key’:
>>>
>>> ../drivers/net/iavf/../../common/iavf/virtchnl.h:508:5:
>>> note: at offset 0 to object ‘key’ with size 1 declared here
>>>   508 |  u8 key[1];         /* RSS hash key, packed bytes */
>>>       |     ^~~
>>>
>>> Ignore the stringop-overflow warnings for rte_memcpy.h functions.
>>>
>>> Bugzilla ID: 394
>>> Bugzilla ID: 421
>>>
>>> Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
> [...]
>>> --- a/lib/librte_eal/x86/include/rte_memcpy.h
>>> +++ b/lib/librte_eal/x86/include/rte_memcpy.h
>>> +#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 100000)
>>> +#pragma GCC diagnostic ignored "-Wstringop-overflow"
>>> +#endif
>>
>> Does this permanently need to be disabled for all compilation units
>> including rte_memcpy.h, or can it be used with a push/pop set of pragmas to
>> only disable for the required functions?
> 
> Even better, isn't there a solution in memcpy code?
> 
> 

There may be, it could do with fresh eyes - Bruce/Konstantin?

In the meantime I will send a v3 with push/pop so it is available as an
option.