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

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Message-ID: <20200317143602.GC15609@zn.tnic>
Date:   Tue, 17 Mar 2020 15:36:02 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Jakub Jelinek <jakub@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Sergei Trofimovich <slyfox@...too.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Michael Matz <matz@...e.de>
Subject: Re: [PATCH] x86: fix early boot crash on gcc-10

On Mon, Mar 16, 2020 at 07:03:03PM +0100, Jakub Jelinek wrote:
> On Mon, Mar 16, 2020 at 06:54:50PM +0100, Borislav Petkov wrote:
> > So having a way to state "do not add stack canary checking to this
> > particular function" would be optimal. And since you already have the
> > "stack_protect" function attribute I figure adding a "no_stack_protect"
> > one should be easy...
> 
> Easy, but a waste when GCC already has the optimize attribute that can
> handle also ~450 other options that are per-function rather than per-TU.

Ok, Micha explained to me what you mean here and I did:

static void __attribute__((optimize("no-stack-protect"))) notrace start_secondary(void *unused)
{

but it said

arch/x86/kernel/smpboot.c:216:1: warning: bad option ‘-fno-stack-protect’ to attribute ‘optimize’ [-Wattributes]
  216 | {
      | ^

because -fno-stack-protect is not implemented yet.

Regardless, yes, that can work too, if we had the -fno-stack-protect
variant.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette