Re: [PATCH v2] x86: fix early boot crash on gcc-10

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Apr 17, 2020 at 09:57:39AM +0200, Borislav Petkov wrote:
> On Wed, Apr 15, 2020 at 11:19:30PM +0100, Sergei Trofimovich wrote:
> > Ah, that makes sense. Borislav, should I send a fix forward against
> > x86 tree to move -fno-stack-protector as it was in v1 patch?
> > Or you'll revert v2 and apply v1 ~as is? Or should I send those myself?
> 
> Yeah, Peter and I have been discussing something like the below
> yesterday. I don't like the additional exports too much but would
> disable stack protector only for the one function...

If you want minimal changes, you can as I said earlier either
mark cpu_startup_entry noreturn (in the declaration in some header so that
smpboot.c sees it), or you could add something after the cpu_startup_entry
call to ensure it is not tail call optimized (e.g. just
	/* Prevent tail call to cpu_startup_entry because the stack
	   protector guard has been changed in the middle of this function
	   and must not be checked before tail calling another function.  */
	asm ("");
would do, or for (;;); , or combine both, mark cpu_startup_entry noreturn and
add asm (""); (which most GCC versions will optimize away as unreachable).

	Jakub