| Message ID | 20190712091239.716978-2-arnd@arndb.de |
|---|---|
| State | Accepted |
| Commit | a6a6d3b1f867d34ba5bd61aa7bb056b48ca67cff |
| Headers | show |
| Series | [1/2] x86: kvm: avoid -Wsometimes-uninitized warning | expand |
On Fri, Jul 12, 2019 at 11:12 AM Arnd Bergmann <arnd@arndb.de> 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@arndb.de> > --- > 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@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20190712091239.716978-2-arnd%40arndb.de.
On 12/07/19 11:12, Arnd Bergmann wrote: > clang finds a contruct suspicious that converts an unsigned > character to a signed integer and back, causing an overflow: I like how the commit message conveys the braindead-ness of the warning. Queued, thanks. Paolo > 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. > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > 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 */ >
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 */
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. Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- arch/x86/kvm/mmu.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) -- 2.20.0