diff --git a/arch/tile/kernel/single_step.c b/arch/tile/kernel/single_step.c
new file mode 100644
index 0000000..266aae1
--- /dev/null
+++ b/arch/tile/kernel/single_step.c
@@ -0,0 +1,656 @@
+/*
+ * Copyright 2010 Tilera Corporation. All Rights Reserved.
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program is distributed in the hope that it will be useful, but
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ *   NON INFRINGEMENT.  See the GNU General Public License for
+ *   more details.
+ *
+ * A code-rewriter that enables instruction single-stepping.
+ * Derived from iLib's single-stepping code.
+ */
+
+#ifndef __tilegx__   /* No support for single-step yet. */
+
+/* These functions are only used on the TILE platform */
+#include <linux/slab.h>
+#include <linux/thread_info.h>
+#include <linux/uaccess.h>
+#include <linux/mman.h>
+#include <linux/types.h>
+#include <asm/cacheflush.h>
+#include <asm/opcode-tile.h>
+#include <asm/opcode_constants.h>
+#include <arch/abi.h>
+
+#define signExtend17(val) sign_extend((val), 17)
+#define TILE_X1_MASK (0xffffffffULL << 31)
+
+int unaligned_printk;
+
+static int __init setup_unaligned_printk(char *str)
+{
+	long val;
+	if (strict_strtol(str, 0, &val) != 0)
+		return 0;
+	unaligned_printk = val;
+	printk("Printk for each unaligned data accesses is %s\n",
+	       unaligned_printk ? "enabled" : "disabled");
+	return 1;
+}
+__setup("unaligned_printk=", setup_unaligned_printk);
+
+unsigned int unaligned_fixup_count;
+
+enum mem_op {
+	MEMOP_NONE,
+	MEMOP_LOAD,
+	MEMOP_STORE,
+	MEMOP_LOAD_POSTINCR,
+	MEMOP_STORE_POSTINCR
+};
+
+static inline tile_bundle_bits set_BrOff_X1(tile_bundle_bits n, int32_t offset)
+{
+	tile_bundle_bits result;
+
+	/* mask out the old offset */
+	tile_bundle_bits mask = create_BrOff_X1(-1);
+	result = n & (~mask);
+
+	/* or in the new offset */
+	result |= create_BrOff_X1(offset);
+
+	return result;
+}
+
+static inline tile_bundle_bits move_X1(tile_bundle_bits n, int dest, int src)
+{
+	tile_bundle_bits result;
+	tile_bundle_bits op;
+
+	result = n & (~TILE_X1_MASK);
+
+	op = create_Opcode_X1(SPECIAL_0_OPCODE_X1) |
+		create_RRROpcodeExtension_X1(OR_SPECIAL_0_OPCODE_X1) |
+		create_Dest_X1(dest) |
+		create_SrcB_X1(TREG_ZERO) |
+		create_SrcA_X1(src) ;
+
+	result |= op;
+	return result;
+}
+
+static inline tile_bundle_bits nop_X1(tile_bundle_bits n)
+{
+	return move_X1(n, TREG_ZERO, TREG_ZERO);
+}
+
+static inline tile_bundle_bits addi_X1(
+	tile_bundle_bits n, int dest, int src, int imm)
+{
+	n &= ~TILE_X1_MASK;
+
+	n |=  (create_SrcA_X1(src) |
+	       create_Dest_X1(dest) |
+	       create_Imm8_X1(imm) |
+	       create_S_X1(0) |
+	       create_Opcode_X1(IMM_0_OPCODE_X1) |
+	       create_ImmOpcodeExtension_X1(ADDI_IMM_0_OPCODE_X1));
+
+	return n;
+}
+
+static tile_bundle_bits rewrite_load_store_unaligned(
+	struct single_step_state *state,
+	tile_bundle_bits bundle,
+	struct pt_regs *regs,
+	enum mem_op mem_op,
+	int size, int sign_ext)
+{
+	unsigned char *addr;
+	int val_reg, addr_reg, err, val;
+
+	/* Get address and value registers */
+	if (bundle & TILE_BUNDLE_Y_ENCODING_MASK) {
+		addr_reg = get_SrcA_Y2(bundle);
+		val_reg = get_SrcBDest_Y2(bundle);
+	} else if (mem_op == MEMOP_LOAD || mem_op == MEMOP_LOAD_POSTINCR) {
+		addr_reg = get_SrcA_X1(bundle);
+		val_reg  = get_Dest_X1(bundle);
+	} else {
+		addr_reg = get_SrcA_X1(bundle);
+		val_reg  = get_SrcB_X1(bundle);
+	}
+
+	/*
+	 * If registers are not GPRs, don't try to handle it.
+	 *
+	 * FIXME: we could handle non-GPR loads by getting the real value
+	 * from memory, writing it to the single step buffer, using a
+	 * temp_reg to hold a pointer to that memory, then executing that
+	 * instruction and resetting temp_reg.  For non-GPR stores, it's a
+	 * little trickier; we could use the single step buffer for that
+	 * too, but we'd have to add some more state bits so that we could
+	 * call back in here to copy that value to the real target.  For
+	 * now, we just handle the simple case.
+	 */
+	if ((val_reg >= PTREGS_NR_GPRS &&
+	     (val_reg != TREG_ZERO ||
+	      mem_op == MEMOP_LOAD ||
+	      mem_op == MEMOP_LOAD_POSTINCR)) ||
+	    addr_reg >= PTREGS_NR_GPRS)
+		return bundle;
+
+	/* If it's aligned, don't handle it specially */
+	addr = (void *)regs->regs[addr_reg];
+	if (((unsigned long)addr % size) == 0)
+		return bundle;
+
+#ifndef __LITTLE_ENDIAN
+# error We assume little-endian representation with copy_xx_user size 2 here
+#endif
+	/* Handle unaligned load/store */
+	if (mem_op == MEMOP_LOAD || mem_op == MEMOP_LOAD_POSTINCR) {
+		unsigned short val_16;
+		switch (size) {
+		case 2:
+			err = copy_from_user(&val_16, addr, sizeof(val_16));
+			val = sign_ext ? ((short)val_16) : val_16;
+			break;
+		case 4:
+			err = copy_from_user(&val, addr, sizeof(val));
+			break;
+		default:
+			BUG();
+		}
+		if (err == 0) {
+			state->update_reg = val_reg;
+			state->update_value = val;
+			state->update = 1;
+		}
+	} else {
+		val = (val_reg == TREG_ZERO) ? 0 : regs->regs[val_reg];
+		err = copy_to_user(addr, &val, size);
+	}
+
+	if (err) {
+		siginfo_t info = {
+			.si_signo = SIGSEGV,
+			.si_code = SEGV_MAPERR,
+			.si_addr = (void __user *)addr
+		};
+		force_sig_info(info.si_signo, &info, current);
+		return (tile_bundle_bits) 0;
+	}
+
+	if (unaligned_fixup == 0) {
+		siginfo_t info = {
+			.si_signo = SIGBUS,
+			.si_code = BUS_ADRALN,
+			.si_addr = (void __user *)addr
+		};
+		force_sig_info(info.si_signo, &info, current);
+		return (tile_bundle_bits) 0;
+	}
+
+	if (unaligned_printk || unaligned_fixup_count == 0) {
+		printk("Process %d/%s: PC %#lx: Fixup of"
+		       " unaligned %s at %#lx.\n",
+		       current->pid, current->comm, regs->pc,
+		       (mem_op == MEMOP_LOAD || mem_op == MEMOP_LOAD_POSTINCR) ?
+			 "load" : "store",
+		       (unsigned long)addr);
+		if (!unaligned_printk) {
+			printk("\n"
+"Unaligned fixups in the kernel will slow your application considerably.\n"
+"You can find them by writing \"1\" to /proc/sys/tile/unaligned_fixup/printk,\n"
+"which requests the kernel show all unaligned fixups, or writing a \"0\"\n"
+"to /proc/sys/tile/unaligned_fixup/enabled, in which case each unaligned\n"
+"access will become a SIGBUS you can debug. No further warnings will be\n"
+"shown so as to avoid additional slowdown, but you can track the number\n"
+"of fixups performed via /proc/sys/tile/unaligned_fixup/count.\n"
+"Use the tile-addr2line command (see \"info addr2line\") to decode PCs.\n"
+				"\n");
+		}
+	}
+	++unaligned_fixup_count;
+
+	if (bundle & TILE_BUNDLE_Y_ENCODING_MASK) {
+		/* Convert the Y2 instruction to a prefetch. */
+		bundle &= ~(create_SrcBDest_Y2(-1) |
+			    create_Opcode_Y2(-1));
+		bundle |= (create_SrcBDest_Y2(TREG_ZERO) |
+			   create_Opcode_Y2(LW_OPCODE_Y2));
+	/* Replace the load postincr with an addi */
+	} else if (mem_op == MEMOP_LOAD_POSTINCR) {
+		bundle = addi_X1(bundle, addr_reg, addr_reg,
+				 get_Imm8_X1(bundle));
+	/* Replace the store postincr with an addi */
+	} else if (mem_op == MEMOP_STORE_POSTINCR) {
+		bundle = addi_X1(bundle, addr_reg, addr_reg,
+				 get_Dest_Imm8_X1(bundle));
+	} else {
+		/* Convert the X1 instruction to a nop. */
+		bundle &= ~(create_Opcode_X1(-1) |
+			    create_UnShOpcodeExtension_X1(-1) |
+			    create_UnOpcodeExtension_X1(-1));
+		bundle |= (create_Opcode_X1(SHUN_0_OPCODE_X1) |
+			   create_UnShOpcodeExtension_X1(
+				   UN_0_SHUN_0_OPCODE_X1) |
+			   create_UnOpcodeExtension_X1(
+				   NOP_UN_0_SHUN_0_OPCODE_X1));
+	}
+
+	return bundle;
+}
+
+/**
+ * single_step_once() - entry point when single stepping has been triggered.
+ * @regs: The machine register state
+ *
+ *  When we arrive at this routine via a trampoline, the single step
+ *  engine copies the executing bundle to the single step buffer.
+ *  If the instruction is a condition branch, then the target is
+ *  reset to one past the next instruction. If the instruction
+ *  sets the lr, then that is noted. If the instruction is a jump
+ *  or call, then the new target pc is preserved and the current
+ *  bundle instruction set to null.
+ *
+ *  The necessary post-single-step rewriting information is stored in
+ *  single_step_state->  We use data segment values because the
+ *  stack will be rewound when we run the rewritten single-stepped
+ *  instruction.
+ */
+void single_step_once(struct pt_regs *regs)
+{
+	extern tile_bundle_bits __single_step_ill_insn;
+	extern tile_bundle_bits __single_step_j_insn;
+	extern tile_bundle_bits __single_step_addli_insn;
+	extern tile_bundle_bits __single_step_auli_insn;
+	struct thread_info *info = (void *)current_thread_info();
+	struct single_step_state *state = info->step_state;
+	int is_single_step = test_ti_thread_flag(info, TIF_SINGLESTEP);
+	tile_bundle_bits *buffer, *pc;
+	tile_bundle_bits bundle;
+	int temp_reg;
+	int target_reg = TREG_LR;
+	int err;
+	enum mem_op mem_op = MEMOP_NONE;
+	int size = 0, sign_ext = 0;  /* happy compiler */
+
+	asm(
+"    .pushsection .rodata.single_step\n"
+"    .align 8\n"
+"    .globl    __single_step_ill_insn\n"
+"__single_step_ill_insn:\n"
+"    ill\n"
+"    .globl    __single_step_addli_insn\n"
+"__single_step_addli_insn:\n"
+"    { nop; addli r0, zero, 0 }\n"
+"    .globl    __single_step_auli_insn\n"
+"__single_step_auli_insn:\n"
+"    { nop; auli r0, r0, 0 }\n"
+"    .globl    __single_step_j_insn\n"
+"__single_step_j_insn:\n"
+"    j .\n"
+"    .popsection\n"
+	);
+
+	if (state == NULL) {
+		/* allocate a page of writable, executable memory */
+		state = kmalloc(sizeof(struct single_step_state), GFP_KERNEL);
+		if (state == NULL) {
+			printk("Out of kernel memory trying to single-step\n");
+			return;
+		}
+
+		/* allocate a cache line of writable, executable memory */
+		down_write(&current->mm->mmap_sem);
+		buffer = (void *) do_mmap(0, 0, 64,
+					  PROT_EXEC | PROT_READ | PROT_WRITE,
+					  MAP_PRIVATE | MAP_ANONYMOUS,
+					  0);
+		up_write(&current->mm->mmap_sem);
+
+		if ((int)buffer < 0 && (int)buffer > -PAGE_SIZE) {
+			kfree(state);
+			printk("Out of kernel pages trying to single-step\n");
+			return;
+		}
+
+		state->buffer = buffer;
+		state->is_enabled = 0;
+
+		info->step_state = state;
+
+		/* Validate our stored instruction patterns */
+		BUG_ON(get_Opcode_X1(__single_step_addli_insn) !=
+		       ADDLI_OPCODE_X1);
+		BUG_ON(get_Opcode_X1(__single_step_auli_insn) !=
+		       AULI_OPCODE_X1);
+		BUG_ON(get_SrcA_X1(__single_step_addli_insn) != TREG_ZERO);
+		BUG_ON(get_Dest_X1(__single_step_addli_insn) != 0);
+		BUG_ON(get_JOffLong_X1(__single_step_j_insn) != 0);
+	}
+
+	/*
+	 * If we are returning from a syscall, we still haven't hit the
+	 * "ill" for the swint1 instruction.  So back the PC up to be
+	 * pointing at the swint1, but we'll actually return directly
+	 * back to the "ill" so we come back in via SIGILL as if we
+	 * had "executed" the swint1 without ever being in kernel space.
+	 */
+	if (regs->faultnum == INT_SWINT_1)
+		regs->pc -= 8;
+
+	pc = (tile_bundle_bits *)(regs->pc);
+	bundle = pc[0];
+
+	/* We'll follow the instruction with 2 ill op bundles */
+	state->orig_pc = (unsigned long) pc;
+	state->next_pc = (unsigned long)(pc + 1);
+	state->branch_next_pc = 0;
+	state->update = 0;
+
+	if (!(bundle & TILE_BUNDLE_Y_ENCODING_MASK)) {
+		/* two wide, check for control flow */
+		int opcode = get_Opcode_X1(bundle);
+
+		switch (opcode) {
+		/* branches */
+		case BRANCH_OPCODE_X1:
+		{
+			int32_t offset = signExtend17(get_BrOff_X1(bundle));
+
+			/*
+			 * For branches, we use a rewriting trick to let the
+			 * hardware evaluate whether the branch is taken or
+			 * untaken.  We record the target offset and then
+			 * rewrite the branch instruction to target 1 insn
+			 * ahead if the branch is taken.  We then follow the
+			 * rewritten branch with two bundles, each containing
+			 * an "ill" instruction. The supervisor examines the
+			 * pc after the single step code is executed, and if
+			 * the pc is the first ill instruction, then the
+			 * branch (if any) was not taken.  If the pc is the
+			 * second ill instruction, then the branch was
+			 * taken. The new pc is computed for these cases, and
+			 * inserted into the registers for the thread.  If
+			 * the pc is the start of the single step code, then
+			 * an exception or interrupt was taken before the
+			 * code started processing, and the same "original"
+			 * pc is restored.  This change, different from the
+			 * original implementation, has the advantage of
+			 * executing a single user instruction.
+			 */
+			state->branch_next_pc = (unsigned long)(pc + offset);
+
+			/* rewrite branch offset to go forward one bundle */
+			bundle = set_BrOff_X1(bundle, 2);
+		}
+		break;
+
+		/* jumps */
+		case JALB_OPCODE_X1:
+		case JALF_OPCODE_X1:
+			state->update = 1;
+			state->next_pc =
+				(unsigned long) (pc + get_JOffLong_X1(bundle));
+			break;
+
+		case JB_OPCODE_X1:
+		case JF_OPCODE_X1:
+			state->next_pc =
+				(unsigned long) (pc + get_JOffLong_X1(bundle));
+			bundle = nop_X1(bundle);
+			break;
+
+		case SPECIAL_0_OPCODE_X1:
+			switch (get_RRROpcodeExtension_X1(bundle)) {
+			/* jump-register */
+			case JALRP_SPECIAL_0_OPCODE_X1:
+			case JALR_SPECIAL_0_OPCODE_X1:
+				state->update = 1;
+				state->next_pc =
+					regs->regs[get_SrcA_X1(bundle)];
+				break;
+
+			case JRP_SPECIAL_0_OPCODE_X1:
+			case JR_SPECIAL_0_OPCODE_X1:
+				state->next_pc =
+					regs->regs[get_SrcA_X1(bundle)];
+				bundle = nop_X1(bundle);
+				break;
+
+			case LNK_SPECIAL_0_OPCODE_X1:
+				state->update = 1;
+				target_reg = get_Dest_X1(bundle);
+				break;
+
+			/* stores */
+			case SH_SPECIAL_0_OPCODE_X1:
+				mem_op = MEMOP_STORE;
+				size = 2;
+				break;
+
+			case SW_SPECIAL_0_OPCODE_X1:
+				mem_op = MEMOP_STORE;
+				size = 4;
+				break;
+			}
+			break;
+
+		/* loads and iret */
+		case SHUN_0_OPCODE_X1:
+			if (get_UnShOpcodeExtension_X1(bundle) ==
+			    UN_0_SHUN_0_OPCODE_X1) {
+				switch (get_UnOpcodeExtension_X1(bundle)) {
+				case LH_UN_0_SHUN_0_OPCODE_X1:
+					mem_op = MEMOP_LOAD;
+					size = 2;
+					sign_ext = 1;
+					break;
+
+				case LH_U_UN_0_SHUN_0_OPCODE_X1:
+					mem_op = MEMOP_LOAD;
+					size = 2;
+					sign_ext = 0;
+					break;
+
+				case LW_UN_0_SHUN_0_OPCODE_X1:
+					mem_op = MEMOP_LOAD;
+					size = 4;
+					break;
+
+				case IRET_UN_0_SHUN_0_OPCODE_X1:
+				{
+					unsigned long ex0_0 = __insn_mfspr(
+						SPR_EX_CONTEXT_0_0);
+					unsigned long ex0_1 = __insn_mfspr(
+						SPR_EX_CONTEXT_0_1);
+					/*
+					 * Special-case it if we're iret'ing
+					 * to PL0 again.  Otherwise just let
+					 * it run and it will generate SIGILL.
+					 */
+					if (EX1_PL(ex0_1) == USER_PL) {
+						state->next_pc = ex0_0;
+						regs->ex1 = ex0_1;
+						bundle = nop_X1(bundle);
+					}
+				}
+				}
+			}
+			break;
+
+#if CHIP_HAS_WH64()
+		/* postincrement operations */
+		case IMM_0_OPCODE_X1:
+			switch (get_ImmOpcodeExtension_X1(bundle)) {
+			case LWADD_IMM_0_OPCODE_X1:
+				mem_op = MEMOP_LOAD_POSTINCR;
+				size = 4;
+				break;
+
+			case LHADD_IMM_0_OPCODE_X1:
+				mem_op = MEMOP_LOAD_POSTINCR;
+				size = 2;
+				sign_ext = 1;
+				break;
+
+			case LHADD_U_IMM_0_OPCODE_X1:
+				mem_op = MEMOP_LOAD_POSTINCR;
+				size = 2;
+				sign_ext = 0;
+				break;
+
+			case SWADD_IMM_0_OPCODE_X1:
+				mem_op = MEMOP_STORE_POSTINCR;
+				size = 4;
+				break;
+
+			case SHADD_IMM_0_OPCODE_X1:
+				mem_op = MEMOP_STORE_POSTINCR;
+				size = 2;
+				break;
+
+			default:
+				break;
+			}
+			break;
+#endif /* CHIP_HAS_WH64() */
+		}
+
+		if (state->update) {
+			/*
+			 * Get an available register.  We start with a
+			 * bitmask with 1's for available registers.
+			 * We truncate to the low 32 registers since
+			 * we are guaranteed to have set bits in the
+			 * low 32 bits, then use ctz to pick the first.
+			 */
+			u32 mask = (u32) ~((1ULL << get_Dest_X0(bundle)) |
+					   (1ULL << get_SrcA_X0(bundle)) |
+					   (1ULL << get_SrcB_X0(bundle)) |
+					   (1ULL << target_reg));
+			temp_reg = __builtin_ctz(mask);
+			state->update_reg = temp_reg;
+			state->update_value = regs->regs[temp_reg];
+			regs->regs[temp_reg] = (unsigned long) (pc+1);
+			regs->flags |= PT_FLAGS_RESTORE_REGS;
+			bundle = move_X1(bundle, target_reg, temp_reg);
+		}
+	} else {
+		int opcode = get_Opcode_Y2(bundle);
+
+		switch (opcode) {
+		/* loads */
+		case LH_OPCODE_Y2:
+			mem_op = MEMOP_LOAD;
+			size = 2;
+			sign_ext = 1;
+			break;
+
+		case LH_U_OPCODE_Y2:
+			mem_op = MEMOP_LOAD;
+			size = 2;
+			sign_ext = 0;
+			break;
+
+		case LW_OPCODE_Y2:
+			mem_op = MEMOP_LOAD;
+			size = 4;
+			break;
+
+		/* stores */
+		case SH_OPCODE_Y2:
+			mem_op = MEMOP_STORE;
+			size = 2;
+			break;
+
+		case SW_OPCODE_Y2:
+			mem_op = MEMOP_STORE;
+			size = 4;
+			break;
+		}
+	}
+
+	/*
+	 * Check if we need to rewrite an unaligned load/store.
+	 * Returning zero is a special value meaning we need to SIGSEGV.
+	 */
+	if (mem_op != MEMOP_NONE && unaligned_fixup >= 0) {
+		bundle = rewrite_load_store_unaligned(state, bundle, regs,
+						      mem_op, size, sign_ext);
+		if (bundle == 0)
+			return;
+	}
+
+	/* write the bundle to our execution area */
+	buffer = state->buffer;
+	err = __put_user(bundle, buffer++);
+
+	/*
+	 * If we're really single-stepping, we take an INT_ILL after.
+	 * If we're just handling an unaligned access, we can just
+	 * jump directly back to where we were in user code.
+	 */
+	if (is_single_step) {
+		err |= __put_user(__single_step_ill_insn, buffer++);
+		err |= __put_user(__single_step_ill_insn, buffer++);
+	} else {
+		long delta;
+
+		if (state->update) {
+			/* We have some state to update; do it inline */
+			int ha16;
+			bundle = __single_step_addli_insn;
+			bundle |= create_Dest_X1(state->update_reg);
+			bundle |= create_Imm16_X1(state->update_value);
+			err |= __put_user(bundle, buffer++);
+			bundle = __single_step_auli_insn;
+			bundle |= create_Dest_X1(state->update_reg);
+			bundle |= create_SrcA_X1(state->update_reg);
+			ha16 = (state->update_value + 0x8000) >> 16;
+			bundle |= create_Imm16_X1(ha16);
+			err |= __put_user(bundle, buffer++);
+			state->update = 0;
+		}
+
+		/* End with a jump back to the next instruction */
+		delta = ((regs->pc + TILE_BUNDLE_SIZE_IN_BYTES) -
+			(unsigned long)buffer) >>
+			TILE_LOG2_BUNDLE_ALIGNMENT_IN_BYTES;
+		bundle = __single_step_j_insn;
+		bundle |= create_JOffLong_X1(delta);
+		err |= __put_user(bundle, buffer++);
+	}
+
+	if (err) {
+		printk("Fault when writing to single-step buffer\n");
+		return;
+	}
+
+	/*
+	 * Flush the buffer.
+	 * We do a local flush only, since this is a thread-specific buffer.
+	 */
+	__flush_icache_range((unsigned long) state->buffer,
+			     (unsigned long) buffer);
+
+	/* Indicate enabled */
+	state->is_enabled = is_single_step;
+	regs->pc = (unsigned long) state->buffer;
+
+	/* Fault immediately if we are coming back from a syscall. */
+	if (regs->faultnum == INT_SWINT_1)
+		regs->pc += 8;
+}
+
+#endif /* !__tilegx__ */