Re: [dpdk-dev] [PATCH] build: gcc 10 disable stringop-overflow warnings

[Kevin Traynor <ktraynor@redhat.com>]

On 07/04/2020 17:27, Kevin Traynor wrote:
> stringop-overflow warns when it sees a possible overflow
> in a string operation.
> 
> In the rte_memcpy functions different implementations are
> used depending on the size. stringop-overflow is raised for
> the paths 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.
> 
> Disable this warning at the top level as it is being raised on
> several components.
> 
> 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 */
>       |     ^~~
> 

As an alternative, we could remove these warnings for rte_memcpy.h(s)
only. WDYT?

diff --git a/lib/librte_eal/x86/include/rte_memcpy.h
b/lib/librte_eal/x86/include/rte_memcpy.h
index ba44c4a32..862e0c402 100644
--- a/lib/librte_eal/x86/include/rte_memcpy.h
+++ b/lib/librte_eal/x86/include/rte_memcpy.h
@@ -19,4 +19,6 @@
 #include <rte_config.h>

+#pragma GCC diagnostic ignored "-Wstringop-overflow"
+
 #ifdef __cplusplus
 extern "C" {

> Bugzilla ID: 394
> Bugzilla ID: 421
> 
> Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
> --->  config/meson.build           | 3 ++-
>  mk/toolchain/gcc/rte.vars.mk | 3 +++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/config/meson.build b/config/meson.build
> index 58421342b..476a667a9 100644
> --- a/config/meson.build
> +++ b/config/meson.build
> @@ -200,5 +200,6 @@ warning_flags = [
>  	'-Wno-address-of-packed-member',
>  	'-Wno-packed-not-aligned',
> -	'-Wno-missing-field-initializers'
> +	'-Wno-missing-field-initializers',
> +	'-Wno-stringop-overflow'
>  ]
>  if not dpdk_conf.get('RTE_ARCH_64')
> diff --git a/mk/toolchain/gcc/rte.vars.mk b/mk/toolchain/gcc/rte.vars.mk
> index f19305e49..fe4b8c705 100644
> --- a/mk/toolchain/gcc/rte.vars.mk
> +++ b/mk/toolchain/gcc/rte.vars.mk
> @@ -101,4 +101,7 @@ endif
>  WERROR_FLAGS += -Wno-address-of-packed-member
>  
> +# disable stringop-overflow warnings
> +WERROR_FLAGS += -Wno-stringop-overflow
> +
>  export CC AS AR LD OBJCOPY OBJDUMP STRIP READELF
>  export TOOLCHAIN_CFLAGS TOOLCHAIN_LDFLAGS TOOLCHAIN_ASFLAGS
>