On 04/06/2014 12:51 PM, Manuel Lauss wrote:
> This small patch makes the MIPS FPU emulator optional. The kernel
> kills float-users on systems without a hardware FPU by sending a SIGILL.
>
> The Emulator can't be turned off on systems which support microMIPS
> because parts of the microMIPS support code live in the emu code.
>
> Signed-off-by: Manuel Lauss <manuel.lauss@xxxxxxxxx>
> ---
> v2: incorporated changes suggested by Hauke Mehrtens,
> force the fpu emulator on for micromips: relocating the parts
> of the mmips code in the emulator to other areas would be a
> much larger change; I went the cheap route instead with this.
Did I suggest anything? I was planing to point you to the patch in
OpenWrt, but Jonas already did so.
> Disabling the emulator saves about 54kBytes (32bit, optimizing for size).
What about putting this number into the commit message or into the help
text.
> arch/mips/Kbuild | 2 +-
> arch/mips/Kconfig | 15 +++++++++++++++
> arch/mips/include/asm/fpu.h | 5 +++--
> arch/mips/include/asm/fpu_emulator.h | 27 ++++++++++++++++++++++++++-
> 4 files changed, 45 insertions(+), 4 deletions(-)
>
> diff --git a/arch/mips/Kbuild b/arch/mips/Kbuild
> index d2cfe45..426c264 100644
> --- a/arch/mips/Kbuild
> +++ b/arch/mips/Kbuild
> @@ -16,7 +16,7 @@ obj- := $(platform-)
>
> obj-y += kernel/
> obj-y += mm/
> -obj-y += math-emu/
> +obj-$(CONFIG_MIPS_FPU_EMULATOR) += math-emu/
>
> ifdef CONFIG_KVM
> obj-y += kvm/
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 9b53358..e9dd80e 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -2208,6 +2208,7 @@ config SYS_SUPPORTS_SMARTMIPS
>
> config SYS_SUPPORTS_MICROMIPS
> bool
> + select MIPS_FPU_EMULATOR # houses tiny parts of the mmips code
>
> config CPU_SUPPORTS_MSA
> bool
> @@ -2482,6 +2483,20 @@ config MIPS_O32_FP64_SUPPORT
>
> If unsure, say N.
>
> +config MIPS_FPU_EMULATOR
> + bool "MIPS FPU Emulator"
> + default y
> + help
> + This option lets you disable the built-in MIPS FPU (Coprocessor 1)
> + emulator, which handles floating-point instructions on processors
> + without a hardware FPU. It is generally a good idea to keep the
> + emulator built-in, unless you are perfectly sure you have a
> + complete soft-float environment. With the emulator disabled, all
> + users of float operations will be killed with an illegal instr-
> + uction 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..c5203bb 100644
> --- a/arch/mips/include/asm/fpu.h
> +++ b/arch/mips/include/asm/fpu.h
> @@ -160,9 +160,10 @@ static inline int init_fpu(void)
> ret = __own_fpu();
> if (!ret)
> _init_fpu();
> - } else {
> + } else if (IS_ENABLED(CONFIG_MIPS_FPU_EMULATOR))
> fpu_emulator_init_fpu();
> - }
> + else
> + ret = SIGILL;
>
> preempt_enable();
> return ret;
> diff --git a/arch/mips/include/asm/fpu_emulator.h b/arch/mips/include/asm/fpu_emulator.h
> index 2abb587..26a71ba 100644
> --- a/arch/mips/include/asm/fpu_emulator.h
> +++ b/arch/mips/include/asm/fpu_emulator.h
> @@ -27,6 +27,7 @@
> #include <asm/inst.h>
> #include <asm/local.h>
>
> +#ifdef CONFIG_MIPS_FPU_EMULATOR
> #ifdef CONFIG_DEBUG_FS
>
> struct mips_fpu_emulator_stats {
> @@ -57,9 +58,33 @@ 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)
> +{
> + BUG(); /* should never ever get here */
> + return 0;
> +}
> +#endif /* CONFIG_MIPS_FPU_EMULATOR */
> +
> +
> +int process_fpemu_return(int sig, void __user *fault_addr);
> +
>
> /*
> * Instruction inserted following the badinst to further tag the sequence
>
