MIPS: Support for 64-bit FP with O32 binaries

CPUs implementing MIPS32 R2 may include a 64-bit FPU, just as MIPS64 CPUs
do. In order to preserve backwards compatibility a 64-bit FPU will act
like a 32-bit FPU (by accessing doubles from the least significant 32
bits of an even-odd pair of FP registers) when the Status.FR bit is
zero, again just like a mips64 CPU. The standard O32 ABI is defined
expecting a 32-bit FPU, however recent toolchains support use of a
64-bit FPU from an O32 MIPS32 executable. When an ELF executable is
built to use a 64-bit FPU a new flag (EF_MIPS_FP64) is set in the ELF
header.

With this patch the kernel will check the EF_MIPS_FP64 flag when
executing an O32 binary, and set Status.FR accordingly. The addition
of O32 64-bit FP support lessens the opportunity for optimisation in
the FPU emulator, so a CONFIG_MIPS_O32_FP64_SUPPORT Kconfig option is
introduced to allow this support to be disabled for those that don't
require it.

Inspired by an earlier patch by Leonid Yegoshin, but implemented more
cleanly & correctly.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Paul Burton <paul.burton@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/6154/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --cc arch/mips/Kconfig
Simple merge

diff --cc arch/mips/include/asm/asmmacro-32.h
Simple merge

diff --cc arch/mips/include/asm/asmmacro-64.h
Simple merge

diff --cc arch/mips/include/asm/asmmacro.h
Simple merge

diff --cc arch/mips/include/asm/elf.h
Simple merge

diff --cc arch/mips/include/asm/fpu.h
Simple merge

diff --cc arch/mips/include/asm/thread_info.h
Simple merge

diff --cc arch/mips/kernel/binfmt_elfo32.c
Simple merge

diff --cc arch/mips/kernel/cpu-probe.c
Simple merge

diff --cc arch/mips/kernel/process.c
Simple merge

diff --cc arch/mips/kernel/ptrace.c
Simple merge

diff --cc arch/mips/kernel/ptrace32.c
Simple merge

diff --cc arch/mips/kernel/r4k_fpu.S
Simple merge

diff --cc arch/mips/kernel/r4k_switch.S
Simple merge

diff --cc arch/mips/kernel/signal.c
Simple merge

diff --cc arch/mips/kernel/signal32.c
Simple merge

diff --cc arch/mips/kernel/traps.c
Simple merge

diff --cc arch/mips/math-emu/cp1emu.c
Simple merge

diff --cc arch/mips/math-emu/kernel_linkage.c
Simple merge