Rework `process_fpemu_return' and move IEEE 754 exception interpretation
there, from `do_fpe'.  Record the cause bits set in FCSR before they are
cleared and pass them through to `process_fpemu_return' so as to set
`si_code' correctly too for SIGFPE signals sent from emulation rather
than those issued by hardware with the FPE processor exception only.

For simplicity `mipsr2_decoder' assumes `*fcr31' has been preinitialised
and only sets it to anything if an FPU instruction has been emulated,
which in turn is the only case SIGFPE can be issued for here.
Signed-off-by: NMaciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9705/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Clear any FCSR cause bits recorded in the saved FPU context after
emulation in all cases rather than in `do_fpe' only, so that any
unmasked IEEE 754 exception left from emulation does not cause a fatal
kernel-mode FPE hardware exception with the CTC1 instruction used by the
kernel to subsequently restore FCSR hardware from the saved FPU context.
Signed-off-by: NMaciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9704/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Correct a copy-and-paste issue with the description for `movf_func'
referring to `movt_func'.  Reformat the former function to match the
latter.
Signed-off-by: NMaciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9675/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

MIPS R6 removed quite a few R2 instructions. However, there
is plenty of <R6 userland code so we add an in-kernel emulator
so we can still be able to execute all R2 userland out there.

The emulator comes with a handy debugfs under /mips/ directory
(r2-emul-stats) to provide some basic statistics of the
instructions that are being emulated.

Below are some statistics from booting a minimal buildroot image:

Instruction     Total   BDslot
------------------------------
movs            236969  0
hilo            56686   0
muls            55279   0
divs            10941   0
dsps            0       0
bops            1       0
traps           0       0
fpus            0       0
loads           214981  17
stores          103364  0
llsc            56898   0
dsemul          150418  0
jr              370158
bltzl           43
bgezl           1594
bltzll          0
bgezll          0
bltzal          39
bgezal          39
beql            14503
bnel            138741
blezl           0
bgtzl           3988
Signed-off-by: NLeonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: NMarkos Chandras <markos.chandras@imgtec.com>