Re: [PATCH] x86/srat: Conditional apic_id vs MAX_LOCAL_APIC comparison

[Ingo Molnar <mingo@kernel.org>]

* WangYuli <wangyuli@uniontech.com> wrote:

> The apic_id employed within the acpi_numa_processor_affinity_init()
> function is derived from the acpi_srat_cpu_affinity structure defined
> in acpi/actbl3.h.
> 
> When CONFIG_X86_X2APIC is not enabled, its maximum value is limited
> to 255.

How does the compiler know the value is limited to 0-255?

<acpi/actbl3.h> has an u32 apic_id field:

 struct acpi_srat_x2apic_cpu_affinity {
        struct acpi_subtable_header header;
        u16 reserved;           /* Reserved, must be zero */
        u32 proximity_domain;
        u32 apic_id;
        ^^^^^^^^^^^^
        u32 flags;
        u32 clock_domain;
        u32 reserved2;
 };

and the apic_id local variable in acpi_numa_processor_affinity_init() 
is an 'int':

        int apic_id;

Neither is limited to 0-255.

Thanks,

	Ingo