linux-kernel - Re: [PATCH v3] ia64: fix module loading for gcc-5.4+

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Date:   Mon, 10 Apr 2017 22:53:36 +0100
From:   Sergei Trofimovich <slyfox@...too.org>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:     linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H. J. Lu" <hjl.tools@...il.com>, Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v3] ia64: fix module loading for gcc-5.4+

On Mon, 10 Apr 2017 19:23:28 +0200
SF Markus Elfring <elfring@...rs.sourceforge.net> wrote:

> > -	if (slot(insn) != 2) {
> > +	if (slot(insn) != 1 && slot(insn) != 2) {  
> 
> +	int const s = slot(insn);
> +	if (s < 1 || s > 2) {
> 
> Do run time characteristics matter for such a condition check here?

It's done once at kernel module load time. My guess would be
"not critical at all".

slot() is a pure arithmetic static inline function. You can compare
assembly output before and after your change.

You can measure the difference yourself using 'ski' emulator.
That's for example how I debugged and tested the patch:
     http://trofi.github.io/posts/199-ia64-machine-emulation.html

-- 

  Sergei

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