Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h

Vincenzo Frascino
2020-03-16T10:54:39Z

Hi Catalin,

On 3/16/20 10:34 AM, Catalin Marinas wrote:
[...]

>>
>> I tried to fine grain the headers as much as I could in order to avoid
>> unneeded/unwanted inclusions:
>> * TASK_SIZE_32 is used to verify ABI consistency on vdso32 (please refer to
>> arch/arm64/kernel/vdso32/vgettimeofday.c).
>
> I see. But the test is probably useless. With 4K pages, TASK_SIZE_32 is
> 1UL << 32, so you can't have a u32 greater than this. So I'd argue that
> the ABI compatibility here doesn't matter.
>
> With 16K or 64K pages, TASK_SIZE_32 is slightly smaller but arm32 never
> supported it.
>
> What's the side-effect of dropping this check altogether?
>

The main side-effect is that arm32 and arm64 compat have a different behavior,
that it is what we want to avoid.

The vdsotest [1] I am using, verifies all the side conditions with respect to
the ABI, which we are now compatible with. Removing those checks would break
this condition.

[1] https://github.com/nlynch-mentor/vdsotest

--
Regards,
Vincenzo