On Fri, 25 Jan 2013, Josh Boyer wrote: > On Fri, Jan 25, 2013 at 1:10 PM, Nicolas Pitre <nico@xxxxxxxxxxx> wrote: > > On Fri, 25 Jan 2013, Josh Boyer wrote: > > > >> On Fri, Jan 25, 2013 at 11:22 AM, Dennis Gilmore <dennis@xxxxxxxx> wrote: > >> > Hi all, > >> > > >> > I wanted to kick off a discussion, I think that with the work that > >> > Seneca is doing for armv6hl to support the Raspberry Pi most of the > >> > need for building sfp has gone away. I would like us to drop support > >> > for sfp in F19 that means that anyone running a kirkwood based system > >> > would get supported software updates for approximately 13 months from > >> > now. with cubie boards and other devices coming around that are cheap > >> > and more powerful and similar options I think there is little benefit > >> > to continuing to support sfp. > >> > >> I'm not overly familiar with arm, but from a kernel standpoint you might > >> be able to enable floating point emulation. That would let you run the > >> hardfp binaries on the boards without an FPU. > > > > No, you can't. > > OK. > > > The only FP emulation the ARM kernel provide is for the antique FPA > > instruction set that almost never got implemented in hardware, except > > for a few exceptions that Linux never supported anyway. > > Ah. See, that would be where I point back to me knowning almost nothing > about ARM ;). > > > All modern EABI compliant binaries are using the VFP instruction set, > > and the only thing the kernel implements is the processing of > > exceptions for them. To have a full VFP emulation support in the > > kernel, significant development effort would be needed. > > I find this slightly interesting to be honest. In the embedded powerpc > world, math emulation is used as a last ditch effort but it does exist. > I would have thought the proliferation of ARM devices would generate some > amount of interest in getting similar support in-kernel, but apparently > not. Thing is: a soft float library in user space is 8 to 25 times faster than any kernel emulation of machine FP instructions. I know that as I wrote that soft-float library myself. ;-) Before EABI, it was common to have user space binaryes compiled for FPA and those instructions were always emulated by the kernel, since, as I said, there were no actual FPA hardware that Linux supported. When EABI was introduced, it was decided to go with the soft-float library given the ABI was different anyway and performances were much better than any emulation. That was before VFP became a reality. With VFP hardware you then had the ability to still use the same procedure call convention but the ability to implement the intra procedure code using actual VFP instructions. That is what most ARMv6+ binary distributions did prior the HF variant to remain compatible with the soft-float ABI. But given that hardware VFP is now prevalent, going with full FP even at the function call level was implemented and deployed. Nicolas _______________________________________________ arm mailing list arm@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/arm
