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

[Bruce Richardson <bruce.richardson@intel.com>]

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>
> 
> ---
> 
> v2: Change from a global disable to just disabling for x86/rte_memcpy.h
> ---
>  lib/librte_eal/x86/include/rte_memcpy.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/lib/librte_eal/x86/include/rte_memcpy.h b/lib/librte_eal/x86/include/rte_memcpy.h
> index ba44c4a32..283fb79ba 100644
> --- a/lib/librte_eal/x86/include/rte_memcpy.h
> +++ b/lib/librte_eal/x86/include/rte_memcpy.h
> @@ -23,4 +23,8 @@ extern "C" {
>  #endif
>  
> +#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 100000)
> +#pragma GCC diagnostic ignored "-Wstringop-overflow"
> +#endif
> +
>  /**
>   * Copy bytes from one location to another. The locations must not overlap.

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?