On Fri, Jul 12, 2019 at 11:12 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > clang finds a contruct suspicious that converts an unsigned > character to a signed integer and back, causing an overflow: > > arch/x86/kvm/mmu.c:4605:39: 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; > ~~ ^~ > arch/x86/kvm/mmu.c:4607:38: error: implicit conversion from 'int' to 'u8' (aka 'unsigned char') changes value from -241 to 15 [-Werror,-Wconstant-conversion] > u8 uf = (pfec & PFERR_USER_MASK) ? ~u : 0; > ~~ ^~ > arch/x86/kvm/mmu.c:4609:39: error: implicit conversion from 'int' to 'u8' (aka 'unsigned char') changes value from -171 to 85 [-Werror,-Wconstant-conversion] > u8 ff = (pfec & PFERR_FETCH_MASK) ? ~x : 0; > ~~ ^~ > > Add an explicit cast to tell clang that everything works as > intended here. > Feel free to add: Link: https://github.com/ClangBuiltLinux/linux/issues/95 ( See also patch proposal of Matthias Kaehlcke ) I had a different "simpler" approach to not see this anymore :-). ( See attached 2 patches ) - Sedat - > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > --- > arch/x86/kvm/mmu.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 17ece7b994b1..aea7f969ecb8 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -4602,11 +4602,11 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu, > */ > > /* Faults from writes to non-writable pages */ > - u8 wf = (pfec & PFERR_WRITE_MASK) ? ~w : 0; > + u8 wf = (pfec & PFERR_WRITE_MASK) ? (u8)~w : 0; > /* Faults from user mode accesses to supervisor pages */ > - u8 uf = (pfec & PFERR_USER_MASK) ? ~u : 0; > + u8 uf = (pfec & PFERR_USER_MASK) ? (u8)~u : 0; > /* Faults from fetches of non-executable pages*/ > - u8 ff = (pfec & PFERR_FETCH_MASK) ? ~x : 0; > + u8 ff = (pfec & PFERR_FETCH_MASK) ? (u8)~x : 0; > /* Faults from kernel mode fetches of user pages */ > u8 smepf = 0; > /* Faults from kernel mode accesses of user pages */ > -- > 2.20.0 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20190712091239.716978-2-arnd%40arndb.de.
From bfc32d7f6c8d5bd7766e4292e25a184743a4b3b1 Mon Sep 17 00:00:00 2001 From: Sedat Dilek <sedat.dilek@credativ.de> Date: Tue, 19 Mar 2019 08:56:02 +0100 Subject: [PATCH] kbuild: Enable -Wconstant-conversion warning for "make W=3" --- scripts/Makefile.extrawarn | 1 + 1 file changed, 1 insertion(+) diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 768306add591..eb831a8c6a20 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -47,6 +47,7 @@ warning-2 += $(call cc-option, -Wunused-macros) warning-3 := -Wbad-function-cast warning-3 += -Wcast-qual warning-3 += -Wconversion +warning-3 += $(call cc-option, -Wconstant-conversion) warning-3 += -Wpacked warning-3 += -Wpadded warning-3 += -Wpointer-arith -- 2.20.1
From e958c1b7b3353372a8f6de87c55ffa95392314e6 Mon Sep 17 00:00:00 2001 From: Sedat Dilek <sedat.dilek@credativ.de> Date: Tue, 19 Mar 2019 23:39:32 +0100 Subject: [PATCH] x86: kvm: clang: Disable -Wconstant-conversion warning --- arch/x86/kvm/Makefile | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile index 31ecf7a76d5a..54dd52c2e927 100644 --- a/arch/x86/kvm/Makefile +++ b/arch/x86/kvm/Makefile @@ -1,6 +1,7 @@ # SPDX-License-Identifier: GPL-2.0 ccflags-y += -Iarch/x86/kvm +ccflags-y += $(call cc-disable-warning, constant-conversion) KVM := ../../../virt/kvm -- 2.20.1
