linux-kernel - Re: [PATCH] x86: Implement Linear Address Masking support

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Message-ID: <Yn0bI2W7JnZnHmj+@hirez.programming.kicks-ass.net>
Date:   Thu, 12 May 2022 16:35:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     "'Kirill A. Shutemov'" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Implement Linear Address Masking support

On Thu, May 12, 2022 at 01:01:07PM +0000, David Laight wrote:

> > +static inline int64_t sign_extend64(uint64_t value, int index)
> > +{
> > +    int shift = 63 - index;
> > +    return (int64_t)(value << shift) >> shift;
> > +}
> 
> Shift of signed integers are UB.

The kernel uses -fno-strict-overflow, all the signed UB is gone.