Re: [PATCH] x86: Fix early boot crash on gcc-10, next try

[Borislav Petkov]

On Sat, Apr 25, 2020 at 11:04:40AM -0400, Arvind Sankar wrote:
> I'd put the clause about stack protector being disabled and the
> tail-call one together, to make clear that you still need the never
> return and always inline bits.

Done.

> Also, this function is implemented by multiple arch's and they all
> have similar comments -- might be better to consolidate the comment in
> the generic (dummy) one in include/linux/stackprotector.h laying out
> the restrictions that arch implementations should follow?

I'm not sure gcc-10 does the same thing on other arches - I'd let gcc
guys chime in here and other arch maintainers to decide what to do.

> There's also the one in init/main.c which is used by multiple
> architectures. On x86 at least, the call to arch_call_rest_init at the
> end of start_kernel does not get tail-call optimized by gcc-10, but I
> don't see anything that actually prevents that from happening. We should
> add the asm("") there as well I think, unless the compiler guys see
> something about this function that will always prevent the optimization?

Hmm, that's what I was afraid of - having to sprinkle this around. Yah, let's
wait for compiler guys to have a look here and then maybe I'll convert that
thing to a macro called

	compiler_prevent_tail_call_opt()

or so, so that it can be sprinkled around. ;-\

-- 
Regards/Gruss,
    Boris.

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