[PATCH] arm: add SDIV/UDIV emulation for ARMv7 processors

[will.deacon@arm.com (Will Deacon)]

On Sat, Sep 22, 2012 at 01:57:37PM +0100, Russell King - ARM Linux wrote:
> On Sat, Sep 22, 2012 at 03:49:23PM +0400, Vladimir Murzin wrote:
> > The Virtualization Extensions introduce the requirement for an ARMv7-A
> > implementation to include SDIV and UDIV.  Any implementation of the
> > Virtualization Extensions must include the SDIV and UDIV instructions
> > in the Thumb and ARM instruction sets.
> > 
> > In an ARMv7-A implementation that does not include the Virtualization
> > Extensions, it is IMPLEMENTATION DEFINED whether:
> >  *  SDIV and UDIV are not implemented
> >  *  SDIV and UDIV are implemented only in the Thumb instruction set
> >  *  SDIV and UDIV are implemented in the Thumb and ARM instruction sets.
> 
> We don't want to do emulation of instructions in the kernel because it's
> slow.  It's far better for userspace to figure this stuff out itself and
> select appropriate libraries and instructions to use than to have the CPU
> take an exception, have to save a lot of state, and then emulate the
> instruction.

I added some hwcaps for precisely this purpose. Please see idiva and idivt.

Will