target/linux/generic/pending-4.4/304-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 Date:   Mon,  7 Apr 2014 12:57:04 +0200
   4 Message-Id: <1396868224-252888-2-git-send-email-manuel.lauss@gmail.com>
   5
   6 This small patch makes the MIPS FPU emulator optional. The kernel
   7 kills float-users on systems without a hardware FPU by sending a SIGILL.
   8
   9 Disabling the emulator shrinks vmlinux by about 54kBytes (32bit,
  10 optimizing for size).
  11
  12 Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
  13 ---
  14 v4: rediffed because of patch 1/2, should now work with micromips as well
  15 v3: updated patch description with size savings.
  16 v2: incorporated changes suggested by Jonas Gorski
  17     force the fpu emulator on for micromips: relocating the parts
  18     of the mmips code in the emulator to other areas would be a
  19     much larger change; I went the cheap route instead with this.
  20
  21  arch/mips/Kbuild                     |  2 +-
  22  arch/mips/Kconfig                    | 14 ++++++++++++++
  23  arch/mips/include/asm/fpu.h          |  5 +++--
  24  arch/mips/include/asm/fpu_emulator.h | 15 +++++++++++++++
  25  4 files changed, 33 insertions(+), 3 deletions(-)
  26
  27 --- a/arch/mips/Kconfig
  28 +++ b/arch/mips/Kconfig
  29 @@ -2725,6 +2725,20 @@ config MIPS_O32_FP64_SUPPORT
  30
  31           If unsure, say N.
  32
  33 +config MIPS_FPU_EMULATOR
  34 +       bool "MIPS FPU Emulator"
  35 +       default y
  36 +       help
  37 +         This option lets you disable the built-in MIPS FPU (Coprocessor 1)
  38 +         emulator, which handles floating-point instructions on processors
  39 +         without a hardware FPU.  It is generally a good idea to keep the
  40 +         emulator built-in, unless you are perfectly sure you have a
  41 +         complete soft-float environment.  With the emulator disabled, all
  42 +         users of float operations will be killed with an illegal instr-
  43 +         uction exception.
  44 +
  45 +         Say Y, please.
  46 +
  47  config USE_OF
  48         bool
  49         select OF
  50 --- a/arch/mips/Makefile
  51 +++ b/arch/mips/Makefile
  52 @@ -285,7 +285,7 @@ OBJCOPYFLAGS                += --remove-section=.regin
  53  head-y := arch/mips/kernel/head.o
  54
  55  libs-y                 += arch/mips/lib/
  56 -libs-y                 += arch/mips/math-emu/
  57 +libs-$(CONFIG_MIPS_FPU_EMULATOR)       += arch/mips/math-emu/
  58
  59  # See arch/mips/Kbuild for content of core part of the kernel
  60  core-y += arch/mips/
  61 --- a/arch/mips/include/asm/fpu.h
  62 +++ b/arch/mips/include/asm/fpu.h
  63 @@ -223,8 +223,10 @@ static inline int init_fpu(void)
  64                 /* Restore FRE */
  65                 write_c0_config5(config5);
  66                 enable_fpu_hazard();
  67 -       } else
  68 +       } else if (IS_ENABLED(CONFIG_MIPS_FPU_EMULATOR))
  69                 fpu_emulator_init_fpu();
  70 +       else
  71 +               ret = SIGILL;
  72
  73         return ret;
  74  }
  75 --- a/arch/mips/include/asm/fpu_emulator.h
  76 +++ b/arch/mips/include/asm/fpu_emulator.h
  77 @@ -30,6 +30,7 @@
  78  #include <asm/local.h>
  79  #include <asm/processor.h>
  80
  81 +#ifdef CONFIG_MIPS_FPU_EMULATOR
  82  #ifdef CONFIG_DEBUG_FS
  83
  84  struct mips_fpu_emulator_stats {
  85 @@ -66,6 +67,21 @@ extern int do_dsemulret(struct pt_regs *
  86  extern int fpu_emulator_cop1Handler(struct pt_regs *xcp,
  87                                     struct mips_fpu_struct *ctx, int has_fpu,
  88                                     void *__user *fault_addr);
  89 +#else  /* no CONFIG_MIPS_FPU_EMULATOR */
  90 +static inline int do_dsemulret(struct pt_regs *xcp)
  91 +{
  92 +       return 0;       /* 0 means error, should never get here anyway */
  93 +}
  94 +
  95 +static inline int fpu_emulator_cop1Handler(struct pt_regs *xcp,
  96 +                               struct mips_fpu_struct *ctx, int has_fpu,
  97 +                               void *__user *fault_addr)
  98 +{
  99 +       *fault_addr = NULL;
 100 +       return SIGILL;  /* we don't speak MIPS FPU */
 101 +}
 102 +#endif /* CONFIG_MIPS_FPU_EMULATOR */
 103 +
 104  int process_fpemu_return(int sig, void __user *fault_addr,
 105                          unsigned long fcr31);
 106  int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,