Re: 4.14.9 with CONFIG_MCORE2 fails to boot

From: Linus Torvalds
Date: Fri Dec 29 2017 - 15:34:49 EST

On Fri, Dec 29, 2017 at 12:22 PM, Alexander Tsoy <alexander@xxxxxxx> wrote:
>> But double-checking that "-march=core2" case is definitely worth
>> looking into. Especially since there are clear indications that it's
>> gcc version-dependent anyway. Alexander?
> Yes, the change suggested by Dave makes the problem go away.

Ok, that's good information.

It doesn't really explain *why* that commit 7f2590a110b8
("x86/entry/64: Use a per-CPU trampoline stack for IDT entries") ends
up being sensitive to that compiler option, though.

So it narrows the cause down, but it doesn't really root-cause the
problem. It tends to be almost impossible to find differences in code
generation, because they are generally all over.

Ho humm. What happens if you change the "-march=core2" to
"-mtune=core2"? Does it still boot?

Because maybe the actual differences that "-march=core2" generates
might be easier to see when compared to "-mtune=core2".