On Tue, 2014-10-28 at 23:25 +0100, Jakub Jermar wrote: > Hi Jano, > > On 10/28/2014 10:57 PM, Jan Vesely wrote: > > sorry for taking so long to look into this, the time I can work on > > HelenOS is really scarce. > > > > the reason is that vmrs is ARMv7 only. as is probably the rest of the > > arm FPU support on HelenOS. qemu probably just checks better (kudos to > > them) > > > > The solution is to disable FPU on armv6-, until somebody implements > > properly, I enabled it on "it happens to work" basis. > > This got fixed in the meantime - it was actually a bug in QEMU, > something along the lines they completely forgot about ARMv5. But the > latest released QEMU should have this fixed. ARMv5 does not have vmrs, > but is has something else (I guess the normal FPU instructions) that, > IIRC, share the same opcode, so it is expected to work.
ah, good :). thanks for pointing it out. It still means that HelenOS FPU code works by accident (accidental forward compatibility). ideally we'd have comments explaining why armv6/7 code is OK on older devices with CONFIG_FPU. > > Here is the respective QEMU commit that fixed this again: > > commit ed1f13d607e2c64c66bea49d6f4edaf278d3d246 > Author: Peter Maydell <[email protected]> > Date: Fri Aug 29 15:00:28 2014 +0100 > > target-arm: Fix regression that disabled VFP for ARMv5 CPUs > > Commit 2c7ffc414 added support for honouring the CPACR coprocessor > access control register bits which may disable access to VFP > and Neon instructions. However it failed to account for the > fact that the CPACR is only present starting from the ARMv6 > architecture version, so it accidentally disabled VFP completely > for ARMv5 CPUs like the ARM926. Linux would detect this as > "no VFP present" and probably fall back to its own emulation, > but other guest OSes might crash or misbehave. > > This fixes bug LP:1359930. > > > I would commit the fix directly but icp crashes in bootloader on both > > qemu-2.1.1, and git, so I can not verify. > > Strange, my QEMU 2.1.1 runs just fine. Anyone else has the same problem? > > Jakub > > > _______________________________________________ > HelenOS-devel mailing list > [email protected] > http://lists.modry.cz/listinfo/helenos-devel
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