Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions

Arnd Bergmann
2015-11-22T20:37:49Z

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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@cubox:~# 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@cubox:~# 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@wuerfel:/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@wuerfel:/tmp$ arm-linux-gnueabihf-gcc -Wall -O2 -mcpu=cortex-a15 idiv.c -c -o idiv-arm.o
arnd@wuerfel:/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@wuerfel:/tmp$ arm-linux-gnueabihf-gcc -Wall -O2 -mcpu=cortex-a15 idiv.c -c -o idiv-thumb.o -mthumb
arnd@wuerfel:/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

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unsigned int udiv(unsigned int a, unsigned int b)
{
return a / b;
}

int sdiv(int a, int b)
{
return a / b;
}