openwrt/target/linux/generic/patches-3.18/304-mips_disable_fpu.patch

MIPS: allow disabling the kernel FPU emulator

This patch allows turning off the in-kernel Algorithmics
FPU emulator support, which allows one to save a couple of
precious blocks on an embedded system.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
--
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -934,6 +934,17 @@ config I8259
 config MIPS_BONITO64
 	bool
 
+config MIPS_FPU_EMU
+	bool "Enable FPU emulation"
+	default y
+	help
+	   This option allows building a kernel with or without the Algorithmics
+	   FPU emulator enabled. Turning off this option results in a kernel which
+	   does not catch floating operations exceptions. Make sure that your toolchain
+	   is configured to enable software floating point emulation in that case.
+
+	   If unsure say Y here.
+
 config MIPS_MSC
 	bool
 
--- a/arch/mips/math-emu/Makefile
+++ b/arch/mips/math-emu/Makefile
@@ -2,10 +2,12 @@
 # Makefile for the Linux/MIPS kernel FPU emulation.
 #
 
-obj-y	:= cp1emu.o ieee754m.o ieee754d.o ieee754dp.o ieee754sp.o ieee754.o \
+obj-y	:= kernel_linkage.o
+
+obj-$(CONFIG_MIPS_FPU_EMU)	+= ieee754m.o ieee754d.o ieee754dp.o ieee754sp.o ieee754.o \
 	   ieee754xcpt.o dp_frexp.o dp_modf.o dp_div.o dp_mul.o dp_sub.o \
 	   dp_add.o dp_fsp.o dp_cmp.o dp_logb.o dp_scalb.o dp_simple.o \
 	   dp_tint.o dp_fint.o dp_tlong.o dp_flong.o sp_frexp.o sp_modf.o \
 	   sp_div.o sp_mul.o sp_sub.o sp_add.o sp_fdp.o sp_cmp.o sp_logb.o \
 	   sp_scalb.o sp_simple.o sp_tint.o sp_fint.o sp_tlong.o sp_flong.o \
-	   dp_sqrt.o sp_sqrt.o kernel_linkage.o dsemul.o
+	   dp_sqrt.o sp_sqrt.o dsemul.o cp1emu.o
--- a/arch/mips/math-emu/kernel_linkage.c
+++ b/arch/mips/math-emu/kernel_linkage.c
@@ -29,6 +29,7 @@
 
 #define SIGNALLING_NAN 0x7ff800007ff80000LL
 
+#ifdef CONFIG_MIPS_FPU_EMU
 void fpu_emulator_init_fpu(void)
 {
 	static int first = 1;
@@ -115,3 +116,36 @@ int fpu_emulator_restore_context32(struc
 	return err;
 }
 #endif
+
+#else
+
+void fpu_emulator_init_fpu(void)
+{
+	printk(KERN_INFO "FPU emulator disabled, make sure your toolchain"
+		"was compiled with software floating point support (soft-float)\n");
+	return;
+}
+
+int fpu_emulator_save_context(struct sigcontext __user *sc)
+{
+	return 0;
+}
+
+int fpu_emulator_restore_context(struct sigcontext __user *sc)
+{
+	return 0;
+}
+
+#ifdef CONFIG_64BIT
+int fpu_emulator_save_context32(struct sigcontext32 __user *sc)
+{
+	return 0;
+}
+
+int fpu_emulator_restore_context32(struct sigcontext32 __user *sc)
+{
+	return 0;
+}
+#endif /* CONFIG_64BIT */
+
+#endif /* CONFIG_MIPS_FPU_EMU */
--- a/arch/mips/include/asm/fpu_emulator.h
+++ b/arch/mips/include/asm/fpu_emulator.h
@@ -27,6 +27,8 @@
 #include <asm/inst.h>
 #include <asm/local.h>
 
+#ifdef CONFIG_MIPS_FPU_EMU
+
 #ifdef CONFIG_DEBUG_FS
 
 struct mips_fpu_emulator_stats {
@@ -60,6 +62,38 @@ extern int fpu_emulator_cop1Handler(stru
 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
+static inline int mips_dsemul(struct pt_regs *regs, mips_instruction ir,
+			      unsigned long cpc)
+{
+	return 0;
+}
+
+static inline int do_dsemulret(struct pt_regs *xcp)
+{
+	return 0;
+}
+
+static inline int fpu_emulator_cop1Handler(struct pt_regs *xcp,
+					   struct mips_fpu_struct *ctx,
+					   int has_fpu,
+					   void *__user *fault_addr)
+{
+	return 0;
+}
+
+static inline int process_fpemu_return(int sig, void __user *fault_addr)
+{
+	return -EINVAL;
+}
+
+static inline int mm_isBranchInstr(struct pt_regs *regs,
+				   struct mm_decoded_insn dec_insn,
+				   unsigned long *contpc)
+{
+	return 0;
+}
+#endif /* CONFIG_MIPS_FPU_EMU */
 
 /*
  * Instruction inserted following the badinst to further tag the sequence
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -701,6 +701,7 @@ asmlinkage void do_ov(struct pt_regs *re
 	exception_exit(prev_state);
 }
 
+#ifdef CONFIG_MIPS_FPU_EMU
 int process_fpemu_return(int sig, void __user *fault_addr)
 {
 	if (sig == SIGSEGV || sig == SIGBUS) {
@@ -724,6 +725,7 @@ int process_fpemu_return(int sig, void _
 		return 0;
 	}
 }
+#endif /* CONFIG_MIPS_FPU_EMU */
 
 /*
  * XXX Delayed fp exceptions when doing a lazy ctx switch XXX