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.
Disabling the emulator shrinks vmlinux by about 54kBytes (32bit,
optimizing for size).
Signed-off-by: Manuel Lauss <manuel.lauss@xxxxxxxxx>
---
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 | 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
