linux-kernel - Re: [PATCH] x86/retpoline: Fix forcing me to update my compiler

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Message-ID: <20181208132005.GA658@kroah.com>
Date:   Sat, 8 Dec 2018 14:20:05 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Kirill Marinushkin <k.marinushkin@...il.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/retpoline: Fix forcing me to update my compiler

On Sat, Dec 08, 2018 at 02:14:47PM +0100, Kirill Marinushkin wrote:
> >> First problem: I cannot compile the kernel with my version of compiler
> 
> >> Second problem: when I disable the feature - it cannot take effect,
> >> because the parse-time error happens before `syncconfig`
> 
> On 12/08/18 13:42, Borislav Petkov wrote:
> > Does this help?
> > 
> > https://git.kernel.org/tip/25896d073d8a0403b07e6dec56f58e6c33678207
> > 
> 
> The patch which you mentioned fixes the second problem: now I can disable
> CONFIG_RETPOLINE.
> But, the first problem is still here: with defconfig and gcc v6.4.0, kernel
> doesn't build, with this message:
> 
> ~~~~
> $ make
> scripts/kconfig/conf  --syncconfig Kconfig
> You are building kernel with non-retpoline compiler.
> Please update your compiler.
> make: *** [arch/x86/Makefile:311: checkbin] Error 1
> ~~~~
> 
> I don't think that this is a proper behavior. I suggest to allow compilation

No, you asked for retpoline, and your compiler can not provide that, so
erroring out is the correct behavior.  It is worse for you to have an
option enabled and it not being enabled just because your compiler does
not support it.  That way you do not have the false sense of security.

thanks,

greg k-h