-----Original Message----- From: Qian Cai [mailto:cai@xxxxxx] Sent: Wednesday, July 24, 2019 6:40 AM To: Moore, Robert <robert.moore@xxxxxxxxx>; Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Wysocki, Rafael J <rafael.j.wysocki@xxxxxxxxx>; Schmauss, Erik <erik.schmauss@xxxxxxxxx>; jkim@xxxxxxxxxxx; Len Brown <lenb@xxxxxxxxxx>; linux-acpi@xxxxxxxxxxxxxxx; devel@xxxxxxxxxx; clang-built-linux <clang-built-linux@xxxxxxxxxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx> Subject: Re: [PATCH] acpica: fix -Wnull-pointer-arithmetic warnings On Tue, 2019-07-23 at 20:49 +0000, Moore, Robert wrote: > > > Signed-off-by: Qian Cai <cai@xxxxxx> > > > --- > > > include/acpi/actypes.h | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index > > > ad6892a24015..25b4a32da177 100644 > > > --- a/include/acpi/actypes.h > > > +++ b/include/acpi/actypes.h > > > @@ -500,13 +500,13 @@ typedef u64 acpi_integer; > > > > > > #define ACPI_CAST_PTR(t, p) ((t *) (acpi_uintptr_t) > > > (p)) #define ACPI_CAST_INDIRECT_PTR(t, p) ((t **) > > > (acpi_uintptr_t) (p)) -#define ACPI_ADD_PTR(t, a, b) > > > ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) + (acpi_size)(b))) > > > +#define ACPI_ADD_PTR(t, a, b) ACPI_CAST_PTR (t, (a) + > > > (acpi_size)(b)) > > We have some questions concerning this change. If (a) is not cast to a > u8, the addition will be in whatever units are appropriate for (a) > i.e., the type of (a). However, we want ACPI_ADD_PTR (And > ACPI_SUB_PTR) to simply perform a byte addition or subtraction - thus > the cast to u8. I believe that is the original thinking behind the macros. I posted a v2 a while ago, and should clear this concern. OK then this change only affects ACPI_TO_POINTER? +#define ACPI_TO_POINTER(i) ACPI_CAST_PTR (void, i) > > > > #define ACPI_SUB_PTR(t, a, b) ACPI_CAST_PTR (t, > > > (ACPI_CAST_PTR (u8, (a)) - (acpi_size)(b))) #define > > > ACPI_PTR_DIFF(a, b) ((acpi_size) (ACPI_CAST_PTR (u8, > > > (a)) - ACPI_CAST_PTR (u8, (b)))) > > > > > > /* Pointer/Integer type conversions */ > > > > > > -#define ACPI_TO_POINTER(i) ACPI_ADD_PTR (void, (void > > > *) 0, > > > (acpi_size) (i)) > > > +#define ACPI_TO_POINTER(i) ACPI_ADD_PTR (void, 0, > > > (acpi_size) (i)) > > > > IIUC, these are adding `i` to NULL (or (void*)0)? X + 0 == X ? > > -- > > Thanks, > > ~Nick Desaulniers > >
