linux-kernel - Re: [PATCH v2] ARM: Use udiv/sdiv for __aeabi

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Message-ID: <alpine.LFD.2.10.1311120924330.9667@knanqh.ubzr>
Date:	Tue, 12 Nov 2013 09:32:03 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Ben Dooks <ben.dooks@...ethink.co.uk>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Måns Rullgård <mans@...sr.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org,
	Christopher Covington <cov@...eaurora.org>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library
 functions

On Tue, 12 Nov 2013, Ben Dooks wrote:

> Given these are single instructoins for ARM, is it possible we could
> make a table of all the callers and fix them up when we initialise
> as we do for the SMP/UP case and for page-offset?

Not really.  Calls to those functions are generated by the compiler 
implicitly when a divisor operand is used and therefore we cannot 
annotate those calls.  We'd have to use special accessors everywhere to 
replace the standard division operand (like we do for 64 by 32 bit 
divisions) but I doubt that people would accept that.

You cannot just scan the binary for the appropriate branch opcode either 
as you may turn up false positives in literal pools.

Nicolas
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