[kbuild-all] Re: [linux-next:master 1430/3917] drivers/platform/surface/surface_aggregator_registry.c:398:25: warning: implicit conversion from 'int' to '__u8' (aka 'unsigned char') changes value from 65535 to 255

On 3/11/21 2:06 PM, kernel test robot wrote: > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master > head: 98546348153dee5f8ced572fd6c4690461d20f51 > commit: 797e78564634275ed4fe6b3f586c4b96eb1d86bc [1430/3917] platform/surface: aggregator_registry: Add base device hub > config: arm64-randconfig-r026-20210311 (attached as .config) > compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 574a9dabc63ba1e7a04c08d4bde2eacd61b44ce1) > reproduce (this is a W=1 build): > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > chmod +x ~/bin/make.cross > # install arm64 cross compiling tool for clang build > # apt-get install binutils-aarch64-linux-gnu > # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commi... > git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git > git fetch --no-tags linux-next master > git checkout 797e78564634275ed4fe6b3f586c4b96eb1d86bc > # save the attached .config to linux build tree > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm64 > > If you fix the issue, kindly add following tag as appropriate > Reported-by: kernel test robot <lkp(a)intel.com&gt; > > All warnings (new ones prefixed by >>): > > In file included from drivers/platform/surface/surface_aggregator_registry.c:12: > In file included from include/linux/acpi.h:35: > In file included from include/acpi/acpi_io.h:7: > In file included from arch/arm64/include/asm/acpi.h:12: > include/linux/efi.h:1093:34: warning: passing 1-byte aligned argument to 4-byte aligned parameter 2 of 'get_var' may result in an unaligned pointer access [-Walign-mismatch] > status = get_var(L"SecureBoot", &EFI_GLOBAL_VARIABLE_GUID, NULL, &size, > ^ > include/linux/efi.h:1101:24: warning: passing 1-byte aligned argument to 4-byte aligned parameter 2 of 'get_var' may result in an unaligned pointer access [-Walign-mismatch] > get_var(L"SetupMode", &EFI_GLOBAL_VARIABLE_GUID, NULL, &size, &setupmode); > ^ > >> drivers/platform/surface/surface_aggregator_registry.c:398:25: warning: implicit conversion from 'int' to '__u8' (aka 'unsigned char') changes value from 65535 to 255 [-Wconstant-conversion] > { SSAM_VDEV(HUB, 0x02, SSAM_ANY_IID, 0x00) }, > ~ ^~~~~~~~~~~~ This is a false positive: > include/linux/surface_aggregator/device.h:71:23: note: expanded from macro 'SSAM_ANY_IID' > #define SSAM_ANY_IID 0xffff > ^~~~~~ Here, clang complains that the input is SSAM_ANY_ID. That is a special value which has special considerations below. The SSAM_DEVICE() and thus SSAM_VDEV() macros are intended to only allow either __u8 or SSAM_ANY_ID as input in this place. > include/linux/surface_aggregator/device.h:126:63: note: expanded from macro 'SSAM_VDEV' > SSAM_DEVICE(SSAM_DOMAIN_VIRTUAL, SSAM_VIRTUAL_TC_##cat, tid, iid, fun) > ^~~ > include/linux/surface_aggregator/device.h:102:41: note: expanded from macro 'SSAM_DEVICE' > .instance = ((iid) != SSAM_ANY_IID) ? (iid) : 0, \ > ^~~ Here is the special handling for SSAM_ANY_ID. So there is an implicit conversion from iid, which may be __u8, to int (i.e. the type of SSAM_ANY_ID), but there is at no point any implicit conversion of SSAM_ANY_ID to __u8, as clang alleges.

Is there any way to silence this warning in particular without suppressing it (e.g. by explicit casting) when users of this macro _actually_ input any non-u8 and non-SSAM_ANY_ID value as iid, leading to an _actual_ implicit value-changing cast?