linux-kernel - Re: [RFR] Store tearing

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Date:   Sun, 28 Oct 2018 18:20:42 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Josh Triplett <josh@...htriplett.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFR] Store tearing

On Mon, Oct 29, 2018 at 12:10:03AM +0100, Andrea Parri wrote:
> Hopefully, with Paul's proper email address this time,
> 
>   Andrea
> 
> On Mon, Oct 29, 2018 at 12:06:27AM +0100, Andrea Parri wrote:
> > Hi,
> > 
> > memory-barriers.txt says:
> > 
> >   [on "store tearing"]
> > 
> >   "In fact, a recent bug (since fixed) caused GCC to incorrectly use
> >    this optimization in a volatile store.".
> > 
> > I was wondering if you could help me retrieve some reference/discussions
> > about this?

This was quite some time ago, but it involved a 32-bit volatile store
of a constant such as 0x10001.  The machine in question had a narrow
store-immediate instruction, so the compiler emitted  a pair of 16-bit
store-immediate instructions.  This bug was fixed, though only after
significant screaming and shouting.

							Thanx, Paul