diff options
| author | Paul Burton <paul.burton@imgtec.com> | 2013-11-22 13:12:07 +0000 |
|---|---|---|
| committer | Ralf Baechle <ralf@linux-mips.org> | 2014-01-13 23:40:56 +0100 |
| commit | 597ce1723e0fa0bdbe2ae4c94f18da6e29b92635 (patch) | |
| tree | 21f67268915b8457dd305c6bcf7ac905772fd0ee /arch/mips/Kconfig | |
| parent | 56a22d21bf9744315f56b2bbd6416170f27b7765 (diff) | |
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>
Diffstat (limited to 'arch/mips/Kconfig')
| -rw-r--r-- | arch/mips/Kconfig | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index 650de3976e7a..c12d9c807d09 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -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 |