linux-kernel - Re: [PATCH v2 00/11] x86-64: Stack protector and percpu improvements

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Date:   Sun, 29 Oct 2023 19:19:56 -0400
From:   Brian Gerst <brgerst@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Uros Bizjak <ubizjak@...il.com>
Subject: Re: [PATCH v2 00/11] x86-64: Stack protector and percpu improvements

On Sun, Oct 29, 2023 at 5:42 PM David Laight <David.Laight@...lab.com> wrote:
>
> From: Brian Gerst
> > Sent: 26 October 2023 17:01
> >
> > Currently, x86-64 uses an unusual percpu layout, where the percpu section
> > is linked at absolute address 0.  The reason behind this is that older GCC
> > versions placed the stack protector (if enabled) at a fixed offset from the
> > GS segment base.  Since the GS segement is also used for percpu variables,
> > this forced the current layout.
> >
> > GCC since version 8.1 supports a configurable location for the stack
> > protector value, which allows removal of the restriction on how the percpu
> > section is linked.  This allows the percpu section to be linked
> > normally, like most other architectures.  In turn, this allows removal
> > of code that was needed to support the zero-based percpu section.
>
> I didn't think the minimum gcc version was anything like 8.1.
> I'm using 7.5.0 and I don't think that is the oldest version.

What distribution are you using that still relies on that old of a compiler?

Brian Gerst