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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Brian Gerst' <brgerst@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>
CC:     Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "Peter Zijlstra" <peterz@infradead.org>,
        Uros Bizjak <ubizjak@gmail.com>
Subject: RE: [PATCH v2 00/11] x86-64: Stack protector and percpu improvements
Thread-Topic: [PATCH v2 00/11] x86-64: Stack protector and percpu improvements
Thread-Index: AQHaCCWwM6Gzma9PGEyZRt5JZqLOarBhUF8A
Date:   Sun, 29 Oct 2023 21:42:41 +0000
Message-ID: <a094c7da294a4827994af72249262593@AcuMS.aculab.com>
References: <20231026160100.195099-1-brgerst@gmail.com>
In-Reply-To: <20231026160100.195099-1-brgerst@gmail.com>
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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.

	David

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