[RFC PATCH v5 1/2] MIPS: move mmips branch support code out of the fpu emu code

[RFC PATCH v5 1/2] MIPS: move mmips branch support code out of the fpu emu code

[Manuel Lauss]

moves mm_isBranchInstr() from math-emu code to branch code.  Required
for a follow-on patch to disable the math-emu code completely.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
---
v4/v5: initial patch, no changes

 arch/mips/include/asm/branch.h       |   2 +
 arch/mips/include/asm/fpu_emulator.h |   2 -
 arch/mips/kernel/branch.c            | 200 +++++++++++++++++++++++++++++++++++
 arch/mips/math-emu/cp1emu.c          | 198 ----------------------------------
 4 files changed, 202 insertions(+), 200 deletions(-)

diff --git a/arch/mips/include/asm/branch.h b/arch/mips/include/asm/branch.h
index e28a3e0..1c6b5c2 100644
--- a/arch/mips/include/asm/branch.h
+++ b/arch/mips/include/asm/branch.h
@@ -17,6 +17,8 @@ extern int __compute_return_epc_for_insn(struct pt_regs *regs,
 					 union mips_instruction insn);
 extern int __microMIPS_compute_return_epc(struct pt_regs *regs);
 extern int __MIPS16e_compute_return_epc(struct pt_regs *regs);
+int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
+		     unsigned long *contpc);
 
 
 static inline int delay_slot(struct pt_regs *regs)
diff --git a/arch/mips/include/asm/fpu_emulator.h b/arch/mips/include/asm/fpu_emulator.h
index 2abb587..283e6f3 100644
--- a/arch/mips/include/asm/fpu_emulator.h
+++ b/arch/mips/include/asm/fpu_emulator.h
@@ -58,8 +58,6 @@ 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);
 
 /*
  * Instruction inserted following the badinst to further tag the sequence
diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index 4d78bf4..47eadf0 100644
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -19,6 +19,13 @@
 #include <asm/ptrace.h>
 #include <asm/uaccess.h>
 
+/* microMIPS bitfields */
+#define MM_POOL32A_MINOR_MASK	0x3f
+#define MM_POOL32A_MINOR_SHIFT	0x6
+
+/* (microMIPS) Convert 16-bit register encoding to 32-bit register encoding. */
+static const unsigned int reg16to32map[8] = {16, 17, 2, 3, 4, 5, 6, 7};
+
 /*
  * Calculate and return exception PC in case of branch delay slot
  * for microMIPS and MIPS16e. It does not clear the ISA mode bit.
@@ -48,6 +55,199 @@ int __isa_exception_epc(struct pt_regs *regs)
 	return epc;
 }
 
+int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
+		     unsigned long *contpc)
+{
+	union mips_instruction insn = (union mips_instruction)dec_insn.insn;
+	int bc_false = 0;
+	unsigned int fcr31;
+	unsigned int bit;
+
+	if (!cpu_has_mmips)
+		return 0;
+
+	switch (insn.mm_i_format.opcode) {
+	case mm_pool32a_op:
+		if ((insn.mm_i_format.simmediate & MM_POOL32A_MINOR_MASK) ==
+		    mm_pool32axf_op) {
+			switch (insn.mm_i_format.simmediate >>
+				MM_POOL32A_MINOR_SHIFT) {
+			case mm_jalr_op:
+			case mm_jalrhb_op:
+			case mm_jalrs_op:
+			case mm_jalrshb_op:
+				if (insn.mm_i_format.rt != 0)	/* Not mm_jr */
+					regs->regs[insn.mm_i_format.rt] =
+						regs->cp0_epc +
+						dec_insn.pc_inc +
+						dec_insn.next_pc_inc;
+				*contpc = regs->regs[insn.mm_i_format.rs];
+				return 1;
+			}
+		}
+		break;
+	case mm_pool32i_op:
+		switch (insn.mm_i_format.rt) {
+		case mm_bltzals_op:
+		case mm_bltzal_op:
+			regs->regs[31] = regs->cp0_epc +
+				dec_insn.pc_inc +
+				dec_insn.next_pc_inc;
+			/* Fall through */
+		case mm_bltz_op:
+			if ((long)regs->regs[insn.mm_i_format.rs] < 0)
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					(insn.mm_i_format.simmediate << 1);
+			else
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					dec_insn.next_pc_inc;
+			return 1;
+		case mm_bgezals_op:
+		case mm_bgezal_op:
+			regs->regs[31] = regs->cp0_epc +
+					dec_insn.pc_inc +
+					dec_insn.next_pc_inc;
+			/* Fall through */
+		case mm_bgez_op:
+			if ((long)regs->regs[insn.mm_i_format.rs] >= 0)
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					(insn.mm_i_format.simmediate << 1);
+			else
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					dec_insn.next_pc_inc;
+			return 1;
+		case mm_blez_op:
+			if ((long)regs->regs[insn.mm_i_format.rs] <= 0)
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					(insn.mm_i_format.simmediate << 1);
+			else
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					dec_insn.next_pc_inc;
+			return 1;
+		case mm_bgtz_op:
+			if ((long)regs->regs[insn.mm_i_format.rs] <= 0)
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					(insn.mm_i_format.simmediate << 1);
+			else
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					dec_insn.next_pc_inc;
+			return 1;
+		case mm_bc2f_op:
+		case mm_bc1f_op:
+			bc_false = 1;
+			/* Fall through */
+		case mm_bc2t_op:
+		case mm_bc1t_op:
+			preempt_disable();
+			if (is_fpu_owner())
+				asm volatile("cfc1\t%0,$31" : "=r" (fcr31));
+			else
+				fcr31 = current->thread.fpu.fcr31;
+			preempt_enable();
+
+			if (bc_false)
+				fcr31 = ~fcr31;
+
+			bit = (insn.mm_i_format.rs >> 2);
+			bit += (bit != 0);
+			bit += 23;
+			if (fcr31 & (1 << bit))
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc +
+					(insn.mm_i_format.simmediate << 1);
+			else
+				*contpc = regs->cp0_epc +
+					dec_insn.pc_inc + dec_insn.next_pc_inc;
+			return 1;
+		}
+		break;
+	case mm_pool16c_op:
+		switch (insn.mm_i_format.rt) {
+		case mm_jalr16_op:
+		case mm_jalrs16_op:
+			regs->regs[31] = regs->cp0_epc +
+				dec_insn.pc_inc + dec_insn.next_pc_inc;
+			/* Fall through */
+		case mm_jr16_op:
+			*contpc = regs->regs[insn.mm_i_format.rs];
+			return 1;
+		}
+		break;
+	case mm_beqz16_op:
+		if ((long)regs->regs[reg16to32map[insn.mm_b1_format.rs]] == 0)
+			*contpc = regs->cp0_epc +
+				dec_insn.pc_inc +
+				(insn.mm_b1_format.simmediate << 1);
+		else
+			*contpc = regs->cp0_epc +
+				dec_insn.pc_inc + dec_insn.next_pc_inc;
+		return 1;
+	case mm_bnez16_op:
+		if ((long)regs->regs[reg16to32map[insn.mm_b1_format.rs]] != 0)
+			*contpc = regs->cp0_epc +
+				dec_insn.pc_inc +
+				(insn.mm_b1_format.simmediate << 1);
+		else
+			*contpc = regs->cp0_epc +
+				dec_insn.pc_inc + dec_insn.next_pc_inc;
+		return 1;
+	case mm_b16_op:
+		*contpc = regs->cp0_epc + dec_insn.pc_inc +
+			 (insn.mm_b0_format.simmediate << 1);
+		return 1;
+	case mm_beq32_op:
+		if (regs->regs[insn.mm_i_format.rs] ==
+		    regs->regs[insn.mm_i_format.rt])
+			*contpc = regs->cp0_epc +
+				dec_insn.pc_inc +
+				(insn.mm_i_format.simmediate << 1);
+		else
+			*contpc = regs->cp0_epc +
+				dec_insn.pc_inc +
+				dec_insn.next_pc_inc;
+		return 1;
+	case mm_bne32_op:
+		if (regs->regs[insn.mm_i_format.rs] !=
+		    regs->regs[insn.mm_i_format.rt])
+			*contpc = regs->cp0_epc +
+				dec_insn.pc_inc +
+				(insn.mm_i_format.simmediate << 1);
+		else
+			*contpc = regs->cp0_epc +
+				dec_insn.pc_inc + dec_insn.next_pc_inc;
+		return 1;
+	case mm_jalx32_op:
+		regs->regs[31] = regs->cp0_epc +
+			dec_insn.pc_inc + dec_insn.next_pc_inc;
+		*contpc = regs->cp0_epc + dec_insn.pc_inc;
+		*contpc >>= 28;
+		*contpc <<= 28;
+		*contpc |= (insn.j_format.target << 2);
+		return 1;
+	case mm_jals32_op:
+	case mm_jal32_op:
+		regs->regs[31] = regs->cp0_epc +
+			dec_insn.pc_inc + dec_insn.next_pc_inc;
+		/* Fall through */
+	case mm_j32_op:
+		*contpc = regs->cp0_epc + dec_insn.pc_inc;
+		*contpc >>= 27;
+		*contpc <<= 27;
+		*contpc |= (insn.j_format.target << 1);
+		set_isa16_mode(*contpc);
+		return 1;
+	}
+	return 0;
+}
+
 /*
  * Compute return address and emulate branch in microMIPS mode after an
  * exception only. It does not handle compact branches/jumps and cannot
diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index 7b3c9ac..8f36146 100644
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -83,8 +83,6 @@ DEFINE_PER_CPU(struct mips_fpu_emulator_stats, fpuemustats);
 #define modeindex(v) ((v) & FPU_CSR_RM)
 
 /* microMIPS bitfields */
-#define MM_POOL32A_MINOR_MASK	0x3f
-#define MM_POOL32A_MINOR_SHIFT	0x6
 #define MM_MIPS32_COND_FC	0x30
 
 /* Convert Mips rounding mode (0..3) to IEEE library modes. */
@@ -116,9 +114,6 @@ static const unsigned int fpucondbit[8] = {
 };
 #endif
 
-/* (microMIPS) Convert 16-bit register encoding to 32-bit register encoding. */
-static const unsigned int reg16to32map[8] = {16, 17, 2, 3, 4, 5, 6, 7};
-
 /* (microMIPS) Convert certain microMIPS instructions to MIPS32 format. */
 static const int sd_format[] = {16, 17, 0, 0, 0, 0, 0, 0};
 static const int sdps_format[] = {16, 17, 22, 0, 0, 0, 0, 0};
@@ -466,199 +461,6 @@ static int microMIPS32_to_MIPS32(union mips_instruction *insn_ptr)
 	return 0;
 }
 
-int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
-		     unsigned long *contpc)
-{
-	union mips_instruction insn = (union mips_instruction)dec_insn.insn;
-	int bc_false = 0;
-	unsigned int fcr31;
-	unsigned int bit;
-
-	if (!cpu_has_mmips)
-		return 0;
-
-	switch (insn.mm_i_format.opcode) {
-	case mm_pool32a_op:
-		if ((insn.mm_i_format.simmediate & MM_POOL32A_MINOR_MASK) ==
-		    mm_pool32axf_op) {
-			switch (insn.mm_i_format.simmediate >>
-				MM_POOL32A_MINOR_SHIFT) {
-			case mm_jalr_op:
-			case mm_jalrhb_op:
-			case mm_jalrs_op:
-			case mm_jalrshb_op:
-				if (insn.mm_i_format.rt != 0)	/* Not mm_jr */
-					regs->regs[insn.mm_i_format.rt] =
-						regs->cp0_epc +
-						dec_insn.pc_inc +
-						dec_insn.next_pc_inc;
-				*contpc = regs->regs[insn.mm_i_format.rs];
-				return 1;
-			}
-		}
-		break;
-	case mm_pool32i_op:
-		switch (insn.mm_i_format.rt) {
-		case mm_bltzals_op:
-		case mm_bltzal_op:
-			regs->regs[31] = regs->cp0_epc +
-				dec_insn.pc_inc +
-				dec_insn.next_pc_inc;
-			/* Fall through */
-		case mm_bltz_op:
-			if ((long)regs->regs[insn.mm_i_format.rs] < 0)
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					(insn.mm_i_format.simmediate << 1);
-			else
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					dec_insn.next_pc_inc;
-			return 1;
-		case mm_bgezals_op:
-		case mm_bgezal_op:
-			regs->regs[31] = regs->cp0_epc +
-					dec_insn.pc_inc +
-					dec_insn.next_pc_inc;
-			/* Fall through */
-		case mm_bgez_op:
-			if ((long)regs->regs[insn.mm_i_format.rs] >= 0)
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					(insn.mm_i_format.simmediate << 1);
-			else
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					dec_insn.next_pc_inc;
-			return 1;
-		case mm_blez_op:
-			if ((long)regs->regs[insn.mm_i_format.rs] <= 0)
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					(insn.mm_i_format.simmediate << 1);
-			else
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					dec_insn.next_pc_inc;
-			return 1;
-		case mm_bgtz_op:
-			if ((long)regs->regs[insn.mm_i_format.rs] <= 0)
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					(insn.mm_i_format.simmediate << 1);
-			else
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					dec_insn.next_pc_inc;
-			return 1;
-		case mm_bc2f_op:
-		case mm_bc1f_op:
-			bc_false = 1;
-			/* Fall through */
-		case mm_bc2t_op:
-		case mm_bc1t_op:
-			preempt_disable();
-			if (is_fpu_owner())
-				asm volatile("cfc1\t%0,$31" : "=r" (fcr31));
-			else
-				fcr31 = current->thread.fpu.fcr31;
-			preempt_enable();
-
-			if (bc_false)
-				fcr31 = ~fcr31;
-
-			bit = (insn.mm_i_format.rs >> 2);
-			bit += (bit != 0);
-			bit += 23;
-			if (fcr31 & (1 << bit))
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc +
-					(insn.mm_i_format.simmediate << 1);
-			else
-				*contpc = regs->cp0_epc +
-					dec_insn.pc_inc + dec_insn.next_pc_inc;
-			return 1;
-		}
-		break;
-	case mm_pool16c_op:
-		switch (insn.mm_i_format.rt) {
-		case mm_jalr16_op:
-		case mm_jalrs16_op:
-			regs->regs[31] = regs->cp0_epc +
-				dec_insn.pc_inc + dec_insn.next_pc_inc;
-			/* Fall through */
-		case mm_jr16_op:
-			*contpc = regs->regs[insn.mm_i_format.rs];
-			return 1;
-		}
-		break;
-	case mm_beqz16_op:
-		if ((long)regs->regs[reg16to32map[insn.mm_b1_format.rs]] == 0)
-			*contpc = regs->cp0_epc +
-				dec_insn.pc_inc +
-				(insn.mm_b1_format.simmediate << 1);
-		else
-			*contpc = regs->cp0_epc +
-				dec_insn.pc_inc + dec_insn.next_pc_inc;
-		return 1;
-	case mm_bnez16_op:
-		if ((long)regs->regs[reg16to32map[insn.mm_b1_format.rs]] != 0)
-			*contpc = regs->cp0_epc +
-				dec_insn.pc_inc +
-				(insn.mm_b1_format.simmediate << 1);
-		else
-			*contpc = regs->cp0_epc +
-				dec_insn.pc_inc + dec_insn.next_pc_inc;
-		return 1;
-	case mm_b16_op:
-		*contpc = regs->cp0_epc + dec_insn.pc_inc +
-			 (insn.mm_b0_format.simmediate << 1);
-		return 1;
-	case mm_beq32_op:
-		if (regs->regs[insn.mm_i_format.rs] ==
-		    regs->regs[insn.mm_i_format.rt])
-			*contpc = regs->cp0_epc +
-				dec_insn.pc_inc +
-				(insn.mm_i_format.simmediate << 1);
-		else
-			*contpc = regs->cp0_epc +
-				dec_insn.pc_inc +
-				dec_insn.next_pc_inc;
-		return 1;
-	case mm_bne32_op:
-		if (regs->regs[insn.mm_i_format.rs] !=
-		    regs->regs[insn.mm_i_format.rt])
-			*contpc = regs->cp0_epc +
-				dec_insn.pc_inc +
-				(insn.mm_i_format.simmediate << 1);
-		else
-			*contpc = regs->cp0_epc +
-				dec_insn.pc_inc + dec_insn.next_pc_inc;
-		return 1;
-	case mm_jalx32_op:
-		regs->regs[31] = regs->cp0_epc +
-			dec_insn.pc_inc + dec_insn.next_pc_inc;
-		*contpc = regs->cp0_epc + dec_insn.pc_inc;
-		*contpc >>= 28;
-		*contpc <<= 28;
-		*contpc |= (insn.j_format.target << 2);
-		return 1;
-	case mm_jals32_op:
-	case mm_jal32_op:
-		regs->regs[31] = regs->cp0_epc +
-			dec_insn.pc_inc + dec_insn.next_pc_inc;
-		/* Fall through */
-	case mm_j32_op:
-		*contpc = regs->cp0_epc + dec_insn.pc_inc;
-		*contpc >>= 27;
-		*contpc <<= 27;
-		*contpc |= (insn.j_format.target << 1);
-		set_isa16_mode(*contpc);
-		return 1;
-	}
-	return 0;
-}
-
 /*
  * Redundant with logic already in kernel/branch.c,
  * embedded in compute_return_epc.  At some point,
-- 
1.9.1

[RFC PATCH v5 2/2] MIPS: optional floating point support

[Manuel Lauss]

Makes floating point support a selectable kernel option. Disabling
this option will make the kernel 50kB lighter and kill all float
uses with an illegal instruction exception.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
---
v5: now disable float support completely to avoid sudden program crashes
    on buggy fpus when the fpu emulator cannot take over (suggested by
    Paul Burton).
v4: rediffed because of patch 1/2, should now work with micromips as well
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                    | 11 +++++++++++
 arch/mips/include/asm/fpu.h          | 20 +++++++++++---------
 arch/mips/include/asm/fpu_emulator.h | 15 +++++++++++++++
 4 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/arch/mips/Kbuild b/arch/mips/Kbuild
index d2cfe45..730e0a7 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_SUPPORT) += math-emu/
 
 ifdef CONFIG_KVM
 obj-y += kvm/
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 9b53358..c8040db 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2482,6 +2482,17 @@ config MIPS_O32_FP64_SUPPORT
 
 	  If unsure, say N.
 
+config MIPS_FPU_SUPPORT
+	bool "MIPS FPU Support"
+	default y
+	help
+	  Support for floating point registers and FP-hardware, and also
+	  the in-kernel FPU emulator.  Disabling this option will result
+	  in all uses of floating point hardware to be killed with an
+	  illegal instruction exception, and about a 50kB smaller kernel.
+
+	  Say Y.
+
 config USE_OF
 	bool
 	select OF
diff --git a/arch/mips/include/asm/fpu.h b/arch/mips/include/asm/fpu.h
index 4d86b72..f0ea5ae 100644
--- a/arch/mips/include/asm/fpu.h
+++ b/arch/mips/include/asm/fpu.h
@@ -155,16 +155,18 @@ static inline int init_fpu(void)
 {
 	int ret = 0;
 
-	preempt_disable();
-	if (cpu_has_fpu) {
-		ret = __own_fpu();
-		if (!ret)
-			_init_fpu();
-	} else {
-		fpu_emulator_init_fpu();
-	}
+	if (IS_ENABLED(CONFIG_MIPS_FPU_SUPPORT)) {
+		preempt_disable();
+		if (cpu_has_fpu) {
+			ret = __own_fpu();
+			if (!ret)
+				_init_fpu();
+		} else
+			fpu_emulator_init_fpu();
+		preempt_enable();
+	} 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 283e6f3..552a054 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_SUPPORT
 #ifdef CONFIG_DEBUG_FS
 
 struct mips_fpu_emulator_stats {
@@ -57,6 +58,20 @@ 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);
+#else	/* no CONFIG_MIPS_FPU_SUPPORT */
+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 */
+}
+#endif	/* CONFIG_MIPS_FPU_SUPPORT */
+
 int process_fpemu_return(int sig, void __user *fault_addr);
 
 /*
-- 
1.9.1

Re: [RFC PATCH v5 2/2] MIPS: optional floating point support

[David Daney]

On 04/07/2014 10:53 AM, Manuel Lauss wrote:
[...]
> +#else	/* no CONFIG_MIPS_FPU_SUPPORT */
> +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 */

In a message in the other branch, Ralf suggested emitting very ugly 
messages in the case that something tries to use the FPU.

This code doesn't quite satisfy that request.


> +}
> +#endif	/* CONFIG_MIPS_FPU_SUPPORT */
> +
>   int process_fpemu_return(int sig, void __user *fault_addr);
>
>   /*
>