[PATCH] arm64: Work around broken GCC handling of "S" constraint

[Robin Murphy]

On 2020-12-07 19:04, Marc Zyngier wrote:
> Hi Robin,
> 
> On Mon, 07 Dec 2020 18:42:23 +0000,
> Robin Murphy <robin.murphy at arm.com> wrote:
>>
>> On 2020-12-07 17:47, Ard Biesheuvel wrote:
>>> On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz at kernel.org> wrote:
>>>>
>>>> On 2020-12-07 17:19, Ard Biesheuvel wrote:
>>>>> (resend with David's email address fixed)
>>>>
>>>> Irk. Thanks for that.
>>>>
>>>>>>> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
>>>>>>> +#define SYM_CONSTRAINT "i"
>>>>>>> +#else
>>>>>>> +#define SYM_CONSTRAINT "S"
>>>>>>> +#endif
>>>>>>> +
>>>>>>
>>>>>> Could we just check GCC_VERSION here?
>>>>
>>>> I guess we could. But I haven't investigated which exact range of
>>>> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
>>>> I have apart from the offending 4.9).
>>>>
>>>
>>> I tried 5.4 on godbolt, and it seems happy. And the failure will be
>>> obvious, so we can afford to get it slightly wrong and refine it
>>> later.
>>
>> FWIW the Linaro 14.11, 15.02 and 15.05 releases of GCC 4.9.3 seem to
>> build rc7 without complaint. The only thing older that I have to hand
>> is Ubuntu's GCC 4.8.4, which Kbuild chokes on entirely now.
> 
> Can you try kvmarm/next? David's PSCI relay is breaking badly here.

Ah, gotcha... Yes, they're all falling over on that :(

The 15.08 release of 5.1.1 is happy though, so Ard's probably right 
about generalising it to 4.x.

Cheers,
Robin.