Commit 597ce1723 (MIPS: Support for 64-bit FP with O32 binaries) causing qemu hang with mips64 kernels

[Guenter Roeck <linux@roeck-us.net>]

Hi all,

in 3.14-rc1, my mips64 qemu test fails. The image boots and then hangs.
Bisect points to commit 597ce1723 (MIPS: Support for 64-bit FP with O32 binaries).
Reverting this commit fixes the problem. Disabling MIPS_O32_FP64_SUPPORT
in my test image does _not_ solve the problem. The qemu version does not seem
to make a difference; I tested with qemu 1.6.0 and 1.7.0.

Console log output is available in
http://server.roeck-us.net:8010/builders/qemu-mips64-master/builds/34/steps/buildcommand/logs/stdio

When the problem is seen, the emulation hangs as can be seen in the log,
and the qemu process consumes 100% CPU until it is killed.

qemu command line is

qemu-system-mips64 -kernel vmlinux -M malta -hda core-image-minimal-qemumips64.ext3 \
-vga cirrus -usb -usbdevice wacom-tablet -no-reboot -m 128 --append "root=/dev/hda \
rw mem=128M console=ttyS0 console=tty" -nographic

The same configuration works fine with earlier kernels. I'll be happy to provide
the detailed configuration as well as the root file system for testing if needed.

Obviously I have no idea if this is a problem with the patch or with qemu.
If there is anything I can do to help tracking down the problem further,
please let me know.

Thanks,
Guenter