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

[Thomas Monjalon <thomas@monjalon.net>]

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?