linux-kernel - Re: [PATCH 3/5] MIPS: Only change $28 to thread

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Message-ID: <alpine.DEB.2.00.1612051733070.6743@tp.orcam.me.uk>
Date:   Mon, 5 Dec 2016 17:41:49 +0000
From:   "Maciej W. Rozycki" <macro@...tec.com>
To:     Paul Burton <paul.burton@...tec.com>
CC:     Matt Redfearn <matt.redfearn@...tec.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        <linux-mips@...ux-mips.org>,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>,
        James Hogan <james.hogan@...tec.com>
Subject: Re: [PATCH 3/5] MIPS: Only change $28 to thread_info if coming from
 user mode

On Mon, 5 Dec 2016, Paul Burton wrote:

> Agreed we ought to use .set reorder (or rather, not use .set noreorder) 
> wherever possible but FYI one thing I've only noticed recently is that we 
> don't actually get any reordering anyway, presumably because we don't provide 
> any -O flags when building asm source. I haven't yet done the legwork or 
> figuring out whether we've ever had optimisation & if so what changed...

 Reordering or `-O2' is the default for GAS, you actually have to pass a 
different `-O*' option explicitly to GAS to disable it.  NB it's *not* the 
same as passing one of the `-O*' options to GCC, you'd need e.g. `-Wa,-O'.

 So perhaps one of our Makefiles or a particular configuration of the GCC 
driver does the wrong thing?

  Maciej