linux-kernel - Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi

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Message-ID: <yw1xsi3vr42t.fsf@unicorn.mansr.com>
Date:	Tue, 24 Nov 2015 12:10:02 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	Stephen Boyd <sboyd@...eaurora.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Peter Maydell <peter.maydell@...aro.org>,
	"linux-arm-msm\@vger.kernel.org" <linux-arm-msm@...r.kernel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Christopher Covington <cov@...eaurora.org>
Subject: Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions

Russell King - ARM Linux <linux@....linux.org.uk> writes:

> On Tue, Nov 24, 2015 at 11:38:53AM +0100, Arnd Bergmann wrote:
>> I suggested using -mcpu=cortex-a15 because there are old gcc versions
>> that don't know about -march=armv7ve or -march=armv7-a+idiv yet, but
>> that do understand -mcpu=cortex-a15.
>
> That's not all.  The bigger problem is that there are toolchains out
> there which accept these options, but do _not_ support IDIV in either
> ARM or Thumb mode.  I'm afraid that makes it impossible to add this
> feature to the mainline kernel in this form: we need to run a test
> build to check that -march=armv7ve or what-not really does work
> through both GCC and GAS.

If the compiler accepts the option but doesn't actually emit any div
instructions, is there any real harm?

-- 
Måns Rullgård
mans@...sr.com
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