From: Manuel Lauss <manuel.lauss@gmail.com> Subject: [RFC PATCH v4 2/2] MIPS: make FPU emulator optional Date: Mon, 7 Apr 2014 12:57:04 +0200 Message-Id: <1396868224-252888-2-git-send-email-manuel.lauss@gmail.com> This small patch makes the MIPS FPU emulator optional. The kernel kills float-users on systems without a hardware FPU by sending a SIGILL. Disabling the emulator shrinks vmlinux by about 54kBytes (32bit, optimizing for size). Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com> --- v4: rediffed because of patch 1/2, should now work with micromips as well v3: updated patch description with size savings. v2: incorporated changes suggested by Jonas Gorski 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. arch/mips/Kbuild | 2 +- arch/mips/Kconfig | 14 ++++++++++++++ arch/mips/include/asm/fpu.h | 5 +++-- arch/mips/include/asm/fpu_emulator.h | 15 +++++++++++++++ 4 files changed, 33 insertions(+), 3 deletions(-) --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -2586,6 +2586,20 @@ 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 --- a/arch/mips/Makefile +++ b/arch/mips/Makefile @@ -292,7 +292,7 @@ OBJCOPYFLAGS += --remove-section=.regin head-y := arch/mips/kernel/head.o libs-y += arch/mips/lib/ -libs-y += arch/mips/math-emu/ +libs-$(CONFIG_MIPS_FPU_EMULATOR) += arch/mips/math-emu/ # See arch/mips/Kbuild for content of core part of the kernel core-y += arch/mips/ --- a/arch/mips/include/asm/fpu.h +++ b/arch/mips/include/asm/fpu.h @@ -212,8 +212,10 @@ static inline int init_fpu(void) /* Restore FRE */ write_c0_config5(config5); enable_fpu_hazard(); - } else + } else if (IS_ENABLED(CONFIG_MIPS_FPU_EMULATOR)) fpu_emulator_init_fpu(); + else + ret = SIGILL; return ret; } --- a/arch/mips/include/asm/fpu_emulator.h +++ b/arch/mips/include/asm/fpu_emulator.h @@ -30,6 +30,7 @@ #include <asm/local.h> #include <asm/processor.h> +#ifdef CONFIG_MIPS_FPU_EMULATOR #ifdef CONFIG_DEBUG_FS struct mips_fpu_emulator_stats { @@ -65,6 +66,20 @@ extern int do_dsemulret(struct pt_regs * extern int fpu_emulator_cop1Handler(struct pt_regs *xcp, struct mips_fpu_struct *ctx, int has_fpu, void *__user *fault_addr); +#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 */ +} +#endif /* CONFIG_MIPS_FPU_EMULATOR */ + 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);