target/linux/generic/pending-4.14/304-mips_disable_fpu.patch

   1 From:   Manuel Lauss <manuel.lauss@gmail.com>
   2 Subject: [RFC PATCH v4 2/2] MIPS: make FPU emulator optional
   3
   4 This small patch makes the MIPS FPU emulator optional. The kernel
   5 kills float-users on systems without a hardware FPU by sending a SIGILL.
   6
   7 Disabling the emulator shrinks vmlinux by about 54kBytes (32bit,
   8 optimizing for size).
   9
  10 Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
  11 ---
  12 v4: rediffed because of patch 1/2, should now work with micromips as well
  13 v3: updated patch description with size savings.
  14 v2: incorporated changes suggested by Jonas Gorski
  15     force the fpu emulator on for micromips: relocating the parts
  16     of the mmips code in the emulator to other areas would be a
  17     much larger change; I went the cheap route instead with this.
  18
  19  arch/mips/Kbuild                     |  2 +-
  20  arch/mips/Kconfig                    | 14 ++++++++++++++
  21  arch/mips/include/asm/fpu.h          |  5 +++--
  22  arch/mips/include/asm/fpu_emulator.h | 15 +++++++++++++++
  23  4 files changed, 33 insertions(+), 3 deletions(-)
  24
  25 --- a/arch/mips/Kconfig
  26 +++ b/arch/mips/Kconfig
  27 @@ -2891,6 +2891,20 @@ config MIPS_O32_FP64_SUPPORT
  28
  29           If unsure, say N.
  30
  31 +config MIPS_FPU_EMULATOR
  32 +       bool "MIPS FPU Emulator"
  33 +       default y
  34 +       help
  35 +         This option lets you disable the built-in MIPS FPU (Coprocessor 1)
  36 +         emulator, which handles floating-point instructions on processors
  37 +         without a hardware FPU.  It is generally a good idea to keep the
  38 +         emulator built-in, unless you are perfectly sure you have a
  39 +         complete soft-float environment.  With the emulator disabled, all
  40 +         users of float operations will be killed with an illegal instr-
  41 +         uction exception.
  42 +
  43 +         Say Y, please.
  44 +
  45  config USE_OF
  46         bool
  47         select OF
  48 --- a/arch/mips/Makefile
  49 +++ b/arch/mips/Makefile
  50 @@ -315,7 +315,7 @@ OBJCOPYFLAGS                += --remove-section=.regin
  51  head-y := arch/mips/kernel/head.o
  52
  53  libs-y                 += arch/mips/lib/
  54 -libs-y                 += arch/mips/math-emu/
  55 +libs-$(CONFIG_MIPS_FPU_EMULATOR)       += arch/mips/math-emu/
  56
  57  # See arch/mips/Kbuild for content of core part of the kernel
  58  core-y += arch/mips/
  59 --- a/arch/mips/include/asm/fpu.h
  60 +++ b/arch/mips/include/asm/fpu.h
  61 @@ -230,8 +230,10 @@ static inline int init_fpu(void)
  62                 /* Restore FRE */
  63                 write_c0_config5(config5);
  64                 enable_fpu_hazard();
  65 -       } else
  66 +       } else if (IS_ENABLED(CONFIG_MIPS_FPU_EMULATOR))
  67                 fpu_emulator_init_fpu();
  68 +       else
  69 +               ret = SIGILL;
  70
  71         return ret;
  72  }
  73 --- a/arch/mips/include/asm/fpu_emulator.h
  74 +++ b/arch/mips/include/asm/fpu_emulator.h
  75 @@ -30,6 +30,7 @@
  76  #include <asm/local.h>
  77  #include <asm/processor.h>
  78
  79 +#ifdef CONFIG_MIPS_FPU_EMULATOR
  80  #ifdef CONFIG_DEBUG_FS
  81
  82  struct mips_fpu_emulator_stats {
  83 @@ -179,6 +180,16 @@ do {                                                                       \
  84  extern int fpu_emulator_cop1Handler(struct pt_regs *xcp,
  85                                     struct mips_fpu_struct *ctx, int has_fpu,
  86                                     void __user **fault_addr);
  87 +#else  /* no CONFIG_MIPS_FPU_EMULATOR */
  88 +static inline int fpu_emulator_cop1Handler(struct pt_regs *xcp,
  89 +                               struct mips_fpu_struct *ctx, int has_fpu,
  90 +                               void __user **fault_addr)
  91 +{
  92 +       *fault_addr = NULL;
  93 +       return SIGILL;  /* we don't speak MIPS FPU */
  94 +}
  95 +#endif /* CONFIG_MIPS_FPU_EMULATOR */
  96 +
  97  void force_fcr31_sig(unsigned long fcr31, void __user *fault_addr,
  98                      struct task_struct *tsk);
  99  int process_fpemu_return(int sig, void __user *fault_addr,
 100 --- a/arch/mips/include/asm/dsemul.h
 101 +++ b/arch/mips/include/asm/dsemul.h
 102 @@ -41,6 +41,7 @@ struct task_struct;
 103  extern int mips_dsemul(struct pt_regs *regs, mips_instruction ir,
 104                        unsigned long branch_pc, unsigned long cont_pc);
 105
 106 +#ifdef CONFIG_MIPS_FPU_EMULATOR
 107  /**
 108   * do_dsemulret() - Return from a delay slot 'emulation' frame
 109   * @xcp:       User thread register context.
 110 @@ -88,5 +89,27 @@ extern bool dsemul_thread_rollback(struc
 111   * before @mm is freed in order to avoid memory leaks.
 112   */
 113  extern void dsemul_mm_cleanup(struct mm_struct *mm);
 114 +#else
 115 +static inline bool do_dsemulret(struct pt_regs *xcp)
 116 +{
 117 +       return false;
 118 +}
 119 +
 120 +static inline bool dsemul_thread_cleanup(struct task_struct *tsk)
 121 +{
 122 +       return false;
 123 +}
 124 +
 125 +static inline bool dsemul_thread_rollback(struct pt_regs *regs)
 126 +{
 127 +       return false;
 128 +}
 129 +
 130 +static inline void dsemul_mm_cleanup(struct mm_struct *mm)
 131 +{
 132 +
 133 +}
 134 +
 135 +#endif
 136
 137  #endif /* __MIPS_ASM_DSEMUL_H__ */