MIPS: Allow FP support to be disabled
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
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 378379c..9006ae1 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2256,7 +2256,19 @@
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
