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MIPS: Allow FP support to be disabled

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Allow the user to configure the kernel to omit support for floating
point, by setting CONFIG_MIPS_FP_SUPPORT=n. In an attempt to avoid
problems for users who don't understand the impact of this, only expose
the option when CONFIG_EXPERT=y.

When CONFIG_MIPS_FP_SUPPORT=n all support for FPU hardware, FPU
emulation & FP context will be removed from the kernel. If a userland
program attempts to execute a floating point instruction it will receive
a SIGILL.

Setting CONFIG_MIPS_FP_SUPPORT=n shaves around 112KB from a
64r6el_defconfig build using GCC 8.1.0.

This also helps prepare us for supporting the nanoMIPS ISA, for which
floating point support has not been finalized.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21014/
Cc: linux-mips@linux-mips.org
This commit is contained in:
Paul Burton 2018-11-07 23:14:11 +00:00
parent 2725f3778f
commit 183b40f992
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1 changed files with 13 additions and 1 deletions
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arch/mips/Kconfig
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@ -2256,7 +2256,19 @@ config CPU_GENERIC_DUMP_TLB
default y if !(CPU_R3000 || CPU_R8000 || CPU_TX39XX)
config MIPS_FP_SUPPORT
def_bool y
bool "Floating Point support" if EXPERT
default y
help
Select y to include support for floating point in the kernel
including initialization of FPU hardware, FP context save & restore
and emulation of an FPU where necessary. Without this support any
userland program attempting to use floating point instructions will
receive a SIGILL.
If you know that your userland will not attempt to use floating point
instructions then you can say n here to shrink the kernel a little.
If unsure, say y.
config CPU_R2300_FPU
bool