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

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Message-ID: <alpine.LFD.2.10.1311121014530.9667@knanqh.ubzr>
Date:	Tue, 12 Nov 2013 10:20:10 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Måns Rullgård <mans@...sr.com>
cc:	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	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, Nicolas Pitre wrote:

> On Tue, 12 Nov 2013, Måns Rullgård wrote:
> 
> > It might be possible to extract this information from relocation tables.
> 
> True, but only for individual .o files.  Once the linker puts them 
> together the information is lost, and trying to infer what the linker 
> has done is insane.
> 
> Filtering the compiler output to annotate idiv calls before it is 
> assembled would probably be a better solution.

Another solution is to patch the call site from within __aeabi_idiv at 
run time using lr.  That wouldn't work in the presence of tail call 
optimization though.

Again this might not be worth it and patching __aeabi_idiv instead might 
be a good enough compromize.


Nicolas