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

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Date:	Sun, 22 Nov 2015 21:37 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Peter Maydell <peter.maydell@...aro.org>,
	Måns Rullgård <mans@...sr.com>,
	Nicolas Pitre <nico@...xnic.net>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	arm-mail-list <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions

On Sunday 22 November 2015 20:03:26 Russell King - ARM Linux wrote:
> On Sun, Nov 22, 2015 at 08:58:08PM +0100, Arnd Bergmann wrote:
> > does it work with -mcpu=cortex-a15?  I've tried crosstool as versions
> > 2.23.52.20130913, 2.24.0.20141017 and 2.25.51.20150518, and they
> > all seem to behave as expected, failing with -mcpu=cortex-a9 and
> > marvell-pj4 but succeeding with -mcpu=cortex-a15 or marvell-pj4+idiv.
> 
> Appears not:
> 
> root@...ox:~# gcc -O2 -o idiv idiv.c -Wa,-mcpu='cortex-a15+idiv' -marm
> /tmp/ccSovg32.s: Assembler messages:
> /tmp/ccSovg32.s:32: Error: selected processor does not support ARM mode `udiv ip,r5,r4'
> root@...ox:~# gcc -O2 -o idiv idiv.c -Wa,-mcpu='cortex-a15+idiv' -mthumb
> /tmp/cchbT3EE.s: Assembler messages:
> /tmp/cchbT3EE.s:36: Error: selected processor does not support Thumb mode `udiv r6,r5,r4'
> 
> Same without the +idiv.

I've attached files with those instructions, maybe that helps.

> > I've also found some /proc/cpuinfo output to cross-reference SoCs
> > to their core names.
> > 
> > 		variant	part	revision	name		features
> > mmp2:		0	0x581	5		PJ4		idivt
> > dove:		0	0x581	5		PJ4		idivt
> 
> Yes, that agrees with my dove.

ok.

arnd@...rfel:/tmp$ cat idiv.c 
unsigned int udiv(unsigned int a, unsigned int b)
{
        return a / b;
}

int sdiv(int a, int b)
{
        return a / b;
}
arnd@...rfel:/tmp$ arm-linux-gnueabihf-gcc -Wall -O2 -mcpu=cortex-a15 idiv.c -c -o idiv-arm.o
arnd@...rfel:/tmp$ objdump -dr idiv-arm.o   

idiv-arm.o:     file format elf32-littlearm


Disassembly of section .text:

00000000 <udiv>:
   0:   fbb0 f0f1       udiv    r0, r0, r1
   4:   4770            bx      lr
   6:   bf00            nop

00000008 <sdiv>:
   8:   fb90 f0f1       sdiv    r0, r0, r1
   c:   4770            bx      lr
   e:   bf00            nop
arnd@...rfel:/tmp$ arm-linux-gnueabihf-gcc -Wall -O2 -mcpu=cortex-a15 idiv.c -c -o idiv-thumb.o -mthumb
arnd@...rfel:/tmp$ objdump -dr idiv-thumb.o 

idiv-thumb.o:     file format elf32-littlearm


Disassembly of section .text:

00000000 <udiv>:
   0:   fbb0 f0f1       udiv    r0, r0, r1
   4:   4770            bx      lr
   6:   bf00            nop

00000008 <sdiv>:
   8:   fb90 f0f1       sdiv    r0, r0, r1
   c:   4770            bx      lr
   e:   bf00            nop


	Arnd
Download attachment "idiv-arm.o" of type "application/x-object" (861 bytes)

Download attachment "idiv-thumb.o" of type "application/x-object" (861 bytes)

View attachment "idiv.c" of type "text/x-csrc" (113 bytes)