On Sun, Apr 6, 2014 at 12:52 AM, Manuel Lauss <manuel.lauss@xxxxxxxxx> wrote:
> Add a config option to disable the FPU emulator.
> Saves around 56kB on 32bit, and kills FPU users with SIGILL.
Looks similar to what we do in OpenWrt[1]. Main differences are we
also stub out process_fpemu_return and emit a notice into the kernel
log that the FPU emulator is disabled.
> Signed-off-by: Manuel Lauss <manuel.lauss@xxxxxxxxx>
> ---
> arch/mips/Kbuild | 2 ++
> arch/mips/Kconfig | 14 ++++++++++++++
> arch/mips/include/asm/fpu.h | 2 ++
> arch/mips/include/asm/fpu_emulator.h | 24 +++++++++++++++++++++++-
> 4 files changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/Kbuild b/arch/mips/Kbuild
> index d2cfe45..da76dc0 100644
> --- a/arch/mips/Kbuild
> +++ b/arch/mips/Kbuild
> @@ -16,7 +16,9 @@ obj- := $(platform-)
>
> obj-y += kernel/
> obj-y += mm/
> +ifdef CONFIG_MIPS_FPU_EMULATOR
> obj-y += math-emu/
> +endif
You can write this as obj-$(CONFIG_MIPS_FPU_EMULATOR) += math-emu/
>
> ifdef CONFIG_KVM
> obj-y += kvm/
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 9b53358..9a8d7ed 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -2482,6 +2482,20 @@ config MIPS_O32_FP64_SUPPORT
>
> If unsure, say N.
>
> +config MIPS_FPU_EMULATOR
> + bool "Support for MIPS FPU Emulator"
> + default y
> + help
> + This option lets you disable the built-in MIPS FPU (Cop1)
> + Emulator. This emulator executes floating-point instructions on
> + processors which don't have a built-in floating point unit.
> + It is generally a very good idea to keep this support built in,
> + only disable it if you have a complete soft-float userland.
> + Any use of floating point operations in userspace will result in
> + the process being killed with an illegal instruction exception.
> +
> + Say Y, please.
> +
> config USE_OF
> bool
> select OF
> diff --git a/arch/mips/include/asm/fpu.h b/arch/mips/include/asm/fpu.h
> index 4d86b72..d6c3d97 100644
> --- a/arch/mips/include/asm/fpu.h
> +++ b/arch/mips/include/asm/fpu.h
> @@ -161,7 +161,9 @@ static inline int init_fpu(void)
> if (!ret)
> _init_fpu();
> } else {
> +#ifdef CONFIG_MIPS_FPU_EMULATOR
> fpu_emulator_init_fpu();
> +#endif
Maybe do something like
} else if (IS_ENABLED(CONFIG_MIPS_FPU_EMULATOR)) {
fpu_emulator_init_fpu();
which kooks a bit nicer IMHO.
> }
>
> preempt_enable();
> diff --git a/arch/mips/include/asm/fpu_emulator.h b/arch/mips/include/asm/fpu_emulator.h
> index 2abb587..b2c1524 100644
> --- a/arch/mips/include/asm/fpu_emulator.h
> +++ b/arch/mips/include/asm/fpu_emulator.h
> @@ -53,13 +53,35 @@ do { \
>
> extern int mips_dsemul(struct pt_regs *regs, mips_instruction ir,
> unsigned long cpc);
> +int process_fpemu_return(int sig, void __user *fault_addr);
> +
> +#ifdef CONFIG_MIPS_FPU_EMULATOR
> extern int do_dsemulret(struct pt_regs *xcp);
> extern int fpu_emulator_cop1Handler(struct pt_regs *xcp,
> struct mips_fpu_struct *ctx, int has_fpu,
> void *__user *fault_addr);
> -int process_fpemu_return(int sig, void __user *fault_addr);
> int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
> unsigned long *contpc);
> +#else /* no CONFIG_MIPS_FPU_EMULATOR */
> +static inline int do_dsemulret(struct pt_regs *xcp)
> +{
> + return 0; /* 0 means error, should never get here anyway */
> +}
> +
> +static inline int fpu_emulator_cop1Handler(struct pt_regs *xcp,
> + struct mips_fpu_struct *ctx, int has_fpu,
> + void *__user *fault_addr)
> +{
> + return SIGILL; /* we don't speak MIPS FPU */
> +}
> +
> +static inline int mm_isBranchInstr(struct pt_regs *regs,
> + struct mm_decoded_insn dec_insn,
> + unsigned long *contpc)
> +{
> + return 0;
> +}
Won't this break micromips support? mm_isBranchInstr is called from a
few other places outside the FPU emulator.
Regards
Jonas
[1] http://git.openwrt.org/?p=openwrt.git;a=blob;f=target/linux/generic/patches-3.14/304-mips_disable_fpu.patch;h=4536ce6dae80710e530dd7c67c8c8728f95ee3e6;hb=HEAD
