> -----Original Message-----
> From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> Sent: Friday, April 20, 2018 11:57 AM
> To: linux-rdma@xxxxxxxxxxxxxxx
> Cc: Steve Wise <swise@xxxxxxxxxxxxxxxxxxxxx>
> Subject: [PATCH rdma-core] Check for broken strict aliasing
>
> At least the gcc 4.4 that comes with Centos6 does not support this
> properly and throws bogus warnings.
>
> Globally disable strict aliasing for safety on these compilers.
>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> ---
> CMakeLists.txt | 10 ++++++++++
> buildlib/RDMA_EnableCStd.cmake | 28 ++++++++++++++++++++++++++++
> 2 files changed, 38 insertions(+)
>
> Here is the patch you wanted Steve.. It works for you?
Thanks Jason! Is there a git repo I can pull this from? I'll test it out.
>
> diff --git a/CMakeLists.txt b/CMakeLists.txt
> index 859d7e85d0c274..99202a7548fbdb 100644
> --- a/CMakeLists.txt
> +++ b/CMakeLists.txt
> @@ -276,6 +276,13 @@ CHECK_C_SOURCE_COMPILES("
> RDMA_DoFixup("${HAVE_GLIBC_UAPI_COMPAT}" "linux/in.h")
> RDMA_DoFixup("${HAVE_GLIBC_UAPI_COMPAT}" "linux/in6.h")
>
> +# The compiler has working -fstrict-aliasing support, old gcc's do not.
If
> +# broken then globally disable strict aliasing.
> +RDMA_Check_Aliasing(HAVE_WORKING_STRICT_ALIASING)
> +if (NOT HAVE_WORKING_STRICT_ALIASING)
> + set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS}
> ${NO_STRICT_ALIASING_FLAGS}")
> +endif()
> +
> # Check if off_t is 64 bits, eg large file support is enabled
> CHECK_C_SOURCE_COMPILES("
> #include <sys/types.h>
> @@ -557,6 +564,9 @@ endif()
> if (NOT HAVE_STATIC_ASSERT)
> message(STATUS " C11 static_assert NOT available (old compiler)")
> endif()
> +if (NOT HAVE_WORKING_STRICT_ALIASING)
> + message(STATUS " Compiler cannot do strict aliasing")
> +endif()
> if (NOT HAVE_VALGRIND_MEMCHECK)
> message(STATUS " Valgrind memcheck.h NOT enabled")
> endif()
> diff --git a/buildlib/RDMA_EnableCStd.cmake
> b/buildlib/RDMA_EnableCStd.cmake
> index c2e170929b7dde..dc448726c03cc8 100644
> --- a/buildlib/RDMA_EnableCStd.cmake
> +++ b/buildlib/RDMA_EnableCStd.cmake
> @@ -57,3 +57,31 @@ function(RDMA_EnableCStd)
> set(CMAKE_C_STANDARD 11 PARENT_SCOPE)
> endif()
> endfunction()
> +
> +function(RDMA_Check_Aliasing TO_VAR)
> + SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O2")
> + CHECK_C_SOURCE_COMPILES("
> +struct in6_addr {unsigned int u6_addr32[4];};
> +struct iphdr {unsigned int daddr;};
> +union ibv_gid {unsigned char raw[16];};
> +
> +static void map_ipv4_addr_to_ipv6(struct in6_addr *ipv6) {ipv6-
> >u6_addr32[0] = 0;}
> +static int set_ah_attr_by_ipv4(struct iphdr *ip4h)
> +{
> + union ibv_gid sgid = {};
> + map_ipv4_addr_to_ipv6((struct in6_addr *)&sgid);
> + return 0;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + struct in6_addr a;
> + struct iphdr h = {};
> + map_ipv4_addr_to_ipv6(&a);
> + return set_ah_attr_by_ipv4(&h);
> +}"
> + HAVE_WORKING_STRICT_ALIASING
> + FAIL_REGEX "warning")
> +
> + set(${TO_VAR} "${HAVE_WORKING_STRICT_ALIASING}" PARENT_SCOPE)
> +endfunction()
> --
> 2.17.0
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