* Julia Lawall <julia.lawall@xxxxxxx> wrote:
>
>
> On Thu, 28 Dec 2017, Ingo Molnar wrote:
>
> >
> > * Julia Lawall <julia.lawall@xxxxxxx> wrote:
> >
> > > > > [...] There does seem to be a few cases where the field actually does hold an
> > > > > integer. I guess this is not a problem?
> > > >
> > > > Could you point to such an example?
> > >
> > > drivers/thermal/intel_soc_dts_thermal.c:#define BYT_SOC_DTS_APIC_IRQ 86
> > >
> > > and then:
> > >
> > > static const struct x86_cpu_id soc_thermal_ids[] = {
> > > { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT1, 0,
> > > BYT_SOC_DTS_APIC_IRQ},
> > > {}
> > > };
> > >
> > > and finally:
> > >
> > > soc_dts_thres_irq = (int)match_cpu->driver_data;
> > >
> > > Also:
> > >
> > > arch/x86/kernel/apic/apic.c
> > >
> > > #define DEADLINE_MODEL_MATCH_REV(model, rev) \
> > > { X86_VENDOR_INTEL, 6, model, X86_FEATURE_ANY, (unsigned long)rev
> > > }
> > >
> > > DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_BROADWELL_X, 0x0b000020),
> > > DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_HASWELL_CORE, 0x22),
> > > etc. (all 2-digit numbers in the remaining case).
> >
> > Ok - I think in these cases the resulting long->pointer type conversion is a _lot_
> > less dangerous than the pointer->long conversion which caused the regression.
> >
> > So unless the resulting code is excessively ugly, this feels like the right
> > approach to me.
>
> The problem is that this case will inevitably have a cast somewhere.
That's OK as long as the cast is dominantly (long)->(pointer), because that
doesn't really risk losing the underlying type.
It's the (pointer)->(pointer) and (pointer)->(long) conversions that are the most
dangerous ones.
> [...] Many of the values put into the driver_data field really are const, so
> the type has to be const void *. When the value is extracted from the
> structure, there will thus need to be a cast on it, and the current cast
>
> ddata = (struct bt_sfi_data *)id->driver_data;
>
> works fine, whether the original structure is const or not.
So since this data structure is not size critical, I'd really suggest using two or
three fields:
->driver_data.ptr
->driver_data.const_ptr
->driver_data.long
that way the fundamental types remains.
>
> I also got a couple of complaints about non-pointer types:
>
> arch/x86/kernel/apic/apic.c:621:9: warning: cast from pointer to integer
> of different size [-Wpointer-to-int-cast]
> rev = (u32)m->driver_data;
>
> drivers/thermal/intel_soc_dts_thermal.c:68:22: warning: cast from pointer
> to integer of different size [-Wpointer-to-int-cast]
> soc_dts_thres_irq = (int)match_cpu->driver_data;
These could use driver_data.long or so?
Thanks,
Ingo
