linux-kernel - Re: [PATCH 02/24] x86/traps: Move arch/x86/kernel/traps.c to arch/x86/entry/

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Message-ID: <124a19ef-0b50-2cf2-c6cc-12f443706883@suse.cz>
Date:   Wed, 8 Sep 2021 09:33:37 +0200
From:   Martin Liška <mliska@...e.cz>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Joerg Roedel <jroedel@...e.de>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Chester Lin <clin@...e.com>, Juergen Gross <jgross@...e.com>,
        andrew.cooper3@...rix.com, linux-toolchains@...r.kernel.org
Subject: Re: [PATCH 02/24] x86/traps: Move arch/x86/kernel/traps.c to
 arch/x86/entry/

On 9/7/21 23:12, Nick Desaulniers wrote:
> On Fri, Sep 3, 2021 at 12:36 AM Martin Liška <mliska@...e.cz> wrote:
>>
>> On 9/2/21 19:05, Nick Desaulniers wrote:
>>> IIRC GCC only
>>> added the attribute recently in the 10.X release, so it might be too
>>> new to rely on quite yet.
>>
>> The no_stack_protector attribute was actually added in the GCC 11.x release:
>> https://gcc.gnu.org/gcc-11/changes.html
> 
> Ah right, that lays more weight though that this feature is still too
> new to rely on quite yet.

Sure.

> Martin, do you know if what happens with
> regards to inlining when the callee and caller mismatch on this
> function attribute in GCC?  This is very much a problem for the
> kernel.

That's a know issue that was already discusses both in a Kernel mailing and
GCC bugzilla:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94722#c9

Martin

> 
>> Note the compiler is definitely used by Fedora, openSUSE Tumbleweed
>> and other cutting edge distributions.
> 
> Kernel supports GCC 4.9+ currently. This feature can only be emulated
> with the coarse grain -fno-stack-protector (or gnu_inline with out of
> line assembler definition...:( ).
>