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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 7 Sep 2021 14:12:01 -0700
Message-ID: <CAKwvOd=HfA-08N6LqCS54QcYBcuRgqjcuhVk0dioEte_DxqVqg@mail.gmail.com>
Subject: Re: [PATCH 02/24] x86/traps: Move arch/x86/kernel/traps.c to arch/x86/entry/
To:     =?UTF-8?Q?Martin_Li=C5=A1ka?= <mliska@suse.cz>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Miguel Ojeda <ojeda@kernel.org>,
        Lai Jiangshan <laijs@linux.alibaba.com>,
        Joerg Roedel <jroedel@suse.de>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Chester Lin <clin@suse.com>, Juergen Gross <jgross@suse.com>,
        andrew.cooper3@citrix.com, linux-toolchains@vger.kernel.org
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On Fri, Sep 3, 2021 at 12:36 AM Martin Li=C5=A1ka <mliska@suse.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 relea=
se:
> 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.  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.

> 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...:( ).
--=20
Thanks,
~Nick Desaulniers