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:     Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
        "Thomas Gleixner" <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "Peter Zijlstra" <peterz@infradead.org>
Subject: RE: [PATCH v2 2/6] x86-64: Convert stack protector to normal percpu
 variable
Thread-Topic: [PATCH v2 2/6] x86-64: Convert stack protector to normal percpu
 variable
Thread-Index: AQHX5i01pws/jQEaYE+x2M5p3Mzw46wdZTkg
Date:   Wed, 1 Dec 2021 09:50:57 +0000
Message-ID: <2c23335e98bc4a66b1fd779a78ddd821@AcuMS.aculab.com>
References: <20211130205549.116673-1-brgerst@gmail.com>
 <20211130205549.116673-3-brgerst@gmail.com>
In-Reply-To: <20211130205549.116673-3-brgerst@gmail.com>
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From: Brian Gerst
> Sent: 30 November 2021 20:56
> 
> Older versions of GCC fixed the location of the stack protector canary
> at %gs:40.  This constraint forced the percpu section to be linked at
> virtual address 0 so that the canary could be the first data object in
> the percpu section.  Supporting the zero-based percpu section requires
> additional code to handle relocations for RIP-relative references to
> percpu data, extra complexity to kallsyms, and workarounds for linker
> bugs due to the use of absolute symbols.
> 
> Since version 8.1, GCC has options to configure the location of the
> canary value.  This allows the canary to be turned into a normal
> percpu variable and removes the constraint that the percpu section
> be zero-based.

I didn't think the minimum gcc version has been raised as far as 8.1?

	David

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