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MIPS: Support for 64-bit FP with O32 binaries

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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>
This commit is contained in:
Paul Burton
2013-11-22 13:12:07 +00:00
committed by Ralf Baechle
parent 56a22d21bf
commit 597ce1723e
19 changed files with 449 additions and 236 deletions
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arch/mips/Kconfig
+17
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@@ -2335,6 +2335,23 @@ config CC_STACKPROTECTOR
This feature requires gcc version 4.2 or above.
config MIPS_O32_FP64_SUPPORT
bool "Support for O32 binaries using 64-bit FP"
depends on 32BIT || MIPS32_O32
default y
help
When this is enabled, the kernel will support use of 64-bit floating
point registers with binaries using the O32 ABI along with the
EF_MIPS_FP64 ELF header flag (typically built with -mfp64). On
32-bit MIPS systems this support is at the cost of increasing the
size and complexity of the compiled FPU emulator. Thus if you are
running a MIPS32 system and know that none of your userland binaries
will require 64-bit floating point, you may wish to reduce the size
of your kernel & potentially improve FP emulation performance by
saying N here.
If unsure, say Y.
config USE_OF
bool
select OF