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Re: [PATCH] x86/apic: Fix function typechecking in TSC Deadline errata check
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 21 Mar 2022 15:26:58 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 21 Mar 2022 14:27:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.03.2022 15:12, Andrew Cooper wrote:
> --- a/xen/arch/x86/apic.c
> +++ b/xen/arch/x86/apic.c
> @@ -1092,12 +1092,17 @@ static void setup_APIC_timer(void)
> local_irq_restore(flags);
> }
>
> +#define DEADLINE_MODEL_FUNCT(m, fn) \
> + { .vendor = X86_VENDOR_INTEL, .family = 6, .model = (m), \
> + .feature = X86_FEATURE_TSC_DEADLINE, \
> + .driver_data = fn + (0 * sizeof(fn == ((unsigned int (*)(void))NULL)))
> }
Are you sure all compiler versions we support are happy about +
of a function pointer and a constant? Even if that constant is zero,
this is not legal as per the plain C spec.
Also strictly speaking you would want to parenthesize both uses of
fn.
> #define DEADLINE_MODEL_MATCH(m, fr) \
> { .vendor = X86_VENDOR_INTEL, .family = 6, .model = (m), \
> .feature = X86_FEATURE_TSC_DEADLINE, \
> .driver_data = (void *)(unsigned long)(fr) }
As long as we leave this in place, there's a (small) risk of the
wrong macro being used again if another hook would need adding here.
We might be safer if driver_data became "unsigned long" and the
void * cast was dropped from here (with an "unsigned long" cast
added in the new macro, which at the same time would address my
other concern above).
Jan
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