linux-kernel - Re: [PATCH] x86: add the flag -fno-reorder-blocks-and-partition

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Date:   Tue, 15 May 2018 07:33:57 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Mikulas Patocka <mpatocka@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: add the flag -fno-reorder-blocks-and-partition


* Mikulas Patocka <mpatocka@...hat.com> wrote:

> GCC 8 turns on -freorder-blocks-and-partition by default, the ORC unwinder 
> can't deal with it and it results in a lot of warnings "sibling call from 
> callable instruction with modified stack frame". This patch adds the 
> -fno-reorder-blocks-and-partition option to KBUILD_CFLAGS.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> Cc: stable@...r.kernel.org
> 
> ---
>  arch/x86/Makefile |    1 +
>  1 file changed, 1 insertion(+)
> 
> Index: linux-2.6/arch/x86/Makefile
> ===================================================================
> --- linux-2.6.orig/arch/x86/Makefile	2018-05-15 07:19:40.000000000 +0200
> +++ linux-2.6/arch/x86/Makefile	2018-05-15 07:19:40.000000000 +0200
> @@ -59,6 +59,7 @@ endif
>  #
>  KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow
>  KBUILD_CFLAGS += $(call cc-option,-mno-avx,)
> +KBUILD_CFLAGS += $(call cc-option,-fno-reorder-blocks-and-partition,)

Could you check whether the latest objtool fixes in -tip:

  git git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git master

solves those warnings?

Thanks,

	Ingo