linux-kernel - RE: [PATCH 02/11] x86: tboot: avoid Wstringop-overread-warning

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Date:   Wed, 24 Mar 2021 10:39:57 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     David Laight <David.Laight@...LAB.COM>,
        'Martin Sebor' <msebor@...il.com>,
        Ingo Molnar <mingo@...nel.org>, Arnd Bergmann <arnd@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Martin Sebor" <msebor@....gnu.org>, Ning Sun <ning.sun@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Simon Kelley <simon@...kelleys.org.uk>,
        James Smart <james.smart@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Anders Larsen <al@...rsen.net>, Tejun Heo <tj@...nel.org>,
        Serge Hallyn <serge@...lyn.com>,
        Imre Deak <imre.deak@...el.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "tboot-devel@...ts.sourceforge.net" 
        <tboot-devel@...ts.sourceforge.net>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "ath11k@...ts.infradead.org" <ath11k@...ts.infradead.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Will Deacon <will@...nel.org>
Subject: RE: [PATCH 02/11] x86: tboot: avoid Wstringop-overread-warning

From: David Laight
> Sent: 24 March 2021 09:12
> 
> From: Martin Sebor
> > Sent: 22 March 2021 22:08
> ...
> > In GCC 11, all access warnings expect objects to be either declared
> > or allocated.  Pointers with constant values are taken to point to
> > nothing valid (as Arnd mentioned above, this is to detect invalid
> > accesses to members of structs at address zero).
> >
> > One possible solution to the known address problem is to extend GCC
> > attributes address and io that pin an object to a hardwired address
> > to all targets (at the moment they're supported on just one or two
> > targets).  I'm not sure this can still happen before GCC 11 releases
> > sometime in April or May.
> 
> A different solution is to define a normal C external data item
> and then assign a fixed address with an asm statement or in
> the linker script.

Or stop gcc tracking the value by using:
	struct foo *foo = (void *)xxxxx;
	asm ("", "+r" (foo));

If the address is used more than once forcing it into
a register is also likely to generate better code.

	David

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