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

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Subject: Commit 597ce1723 (MIPS: Support for 64-bit FP with O32 binaries) causing qemu hang with mips64 kernels
From: Guenter Roeck <linux@roeck-us.net>
Date: Fri, 07 Feb 2014 19:39:26 -0800
Cc: Paul Burton <paul.burton@imgtec.com>, Ralf Baechle <ralf@linux-mips.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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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

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