Re: [patch 05/12] x86/irq: Provide macro for inlining irq stack switching

[Thomas Gleixner]

On Mon, Feb 08 2021 at 14:42, Josh Poimboeuf wrote:
> On Thu, Feb 04, 2021 at 09:49:08PM +0100, Thomas Gleixner wrote:
>>  #ifdef CONFIG_X86_64
>> +
>> +#ifdef CONFIG_UNWINDER_FRAME_POINTER
>> +# define IRQSTACK_CALL_CONSTRAINT	, ASM_CALL_CONSTRAINT
>> +#else
>> +# define IRQSTACK_CALL_CONSTRAINT
>> +#endif
>
> Is this really needed?  i.e. does ASM_CALL_CONSTRAINT actually affect
> code generation with !FRAME_POINTER?

The problem is that if the asm inline is the first operation in a
function some compilers insert the asm inline before setting up the
frame pointer.

That's actualy irrelevant here as the compiler cannot reorder against
the C code leading to the asm inline. So we can probably replace it with
a big fat comment.

Thanks,

        tglx