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.
Disabling the emulator saves about 54kBytes (32bit, optimizing for size).
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
--
1.9.1
