Hi Paolo, On Mon, Jun 25, 2018 at 06:05:01PM +0200, Paolo Bonzini wrote: > On 19/06/2018 21:25, Matthias Kaehlcke wrote: > > update_permission_bitmask() negates u8 bitmask values and assigns them > > to variables of type u8. Since the MSB is set in the bitmask values the > > compiler expands the negated values to int, which then is assigned to > > an u8 variable. Cast the negated value back to u8. > > > > This fixes several warnings like this when building with clang: > > > > arch/x86/kvm/mmu.c:4266:39: error: implicit conversion from 'int' to 'u8' > > (aka 'unsigned char') changes value from -205 to 51 [-Werror, > > -Wconstant-conversion] > > u8 wf = (pfec & PFERR_WRITE_MASK) ? ~w : 0; > > ~~ ^~ > > > > (gcc also raises a warning (see https://godbolt.org/g/6JWfWk), however it > > doesn't seem to be universally enabled) > > > > Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > > --- > > Changes in v2: > > - negate the bitmask at initialization and rename variables to not_X > > The patch is not that bad, but I'd like to get confirmation that other > maintainers are applying fixes like this. Honestly I'm not really > impressed by most new clang warnings, these days. Some other instances of the warning that have been addressed are: commit 644d87dccdc69cf79834a72ed0c889580d6af32a Author: Stefan Agner <stefan@xxxxxxxx> Date: Thu Apr 5 16:25:38 2018 -0700 mm/memblock.c: cast constant ULLONG_MAX to phys_addr_t commit e2a5dca753d1cdc3212519023ed8a13e13f5495b Author: Borislav Petkov <bp@xxxxxxx> Date: Thu Nov 23 10:19:51 2017 +0100 x86/umip: Fix insn_get_code_seg_params()'s return value commit dae1a432ab1fe79ae53129ededeaece35a2dc14d Author: Nick Desaulniers <nick.desaulniers@xxxxxxxxx> Date: Sat Jun 24 22:50:12 2017 -0700 Input: mousedev - fix implicit conversion warning commit d1600401faad4bc186bfdb291d8af644465e20bd Author: Matthias Kaehlcke <mka@xxxxxxxxxxxx> Date: Fri Mar 31 18:00:04 2017 -0700 ALSA: hda/ca0132: Limit values for chip addresses to 32-bit commit a45463cbf3f9dcdae683033c256f50bded513d6a Author: Arnd Bergmann <arnd@xxxxxxxx> Date: Wed Feb 1 18:01:17 2017 +0100 workqueue: avoid clang warning Thanks Matthias
