ARM kprobes: instruction single-stepping support

This is the code implementing instruction single-stepping for kprobes
on ARM.

To get around the limitation of no Next-PC and no hardware single-
stepping, all kprobe'd instructions are split into three camps:
simulation, emulation, and rejected. "Simulated" instructions are
those instructions which behavior is reproduced by straight C code.
"Emulated" instructions are ones that are copied, slightly altered
and executed directly in the instruction slot to reproduce their
behavior.  "Rejected" instructions are ones that could be simulated,
but work hasn't been put into simulating them. These instructions
should be very rare, if not unencountered, in the kernel. If ever
needed, code could be added to simulate them.

One might wonder why this and the ptrace singlestep facility are not
sharing some code.  Both approaches are fundamentally different because
the ptrace code regains control after the stepped instruction by installing
a breakpoint after the instruction itself, and possibly at the location
where the instruction might be branching to, instead of simulating or
emulating the target instruction.

The ptrace approach isn't suitable for kprobes because the breakpoints
would have to be moved back, and the icache flushed, everytime the
probe is hit to let normal code execution resume, which would have a
significant performance impact. It is also racy on SMP since another
CPU could, with the right timing, sail through the probe point without
being caught.  Because ptrace single-stepping always result in a
different process to be scheduled, the concern for performance is much
less significant.

On the other hand, the kprobes approach isn't (currently) suitable for
ptrace because it has no provision for proper user space memory
protection and translation, and even if that was implemented, the gain
wouldn't be worth the added complexity in the ptrace path compared to
the current approach.

So, until kprobes does support user space, both kprobes and ptrace are
best kept independent and separate.

Signed-off-by: Quentin Barnes <qbarnes@gmail.com>
Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>

2 files changed, 1530 insertions, 0 deletions

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 593b56509f4..9e0eebacd3d 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -19,6 +19,7 @@ obj-$(CONFIG_ISA_DMA)		+= dma-isa.o
 obj-$(CONFIG_PCI)		+= bios32.o isa.o
 obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
+obj-$(CONFIG_KPROBES)		+= kprobes-decode.o
 obj-$(CONFIG_OABI_COMPAT)	+= sys_oabi-compat.o
 
 obj-$(CONFIG_CRUNCH)		+= crunch.o crunch-bits.o
diff --git a/arch/arm/kernel/kprobes-decode.c b/arch/arm/kernel/kprobes-decode.c
new file mode 100644
index 00000000000..d51bc8b6055
--- /dev/null
+++ b/arch/arm/kernel/kprobes-decode.c
@@ -0,0 +1,1529 @@
+/*
+ * arch/arm/kernel/kprobes-decode.c
+ *
+ * Copyright (C) 2006, 2007 Motorola Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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.  See the GNU
+ * General Public License for more details.
+ */
+
+/*
+ * We do not have hardware single-stepping on ARM, This
+ * effort is further complicated by the ARM not having a
+ * "next PC" register.  Instructions that change the PC
+ * can't be safely single-stepped in a MP environment, so
+ * we have a lot of work to do:
+ *
+ * In the prepare phase:
+ *   *) If it is an instruction that does anything
+ *      with the CPU mode, we reject it for a kprobe.
+ *      (This is out of laziness rather than need.  The
+ *      instructions could be simulated.)
+ *
+ *   *) Otherwise, decode the instruction rewriting its
+ *      registers to take fixed, ordered registers and
+ *      setting a handler for it to run the instruction.
+ *
+ * In the execution phase by an instruction's handler:
+ *
+ *   *) If the PC is written to by the instruction, the
+ *      instruction must be fully simulated in software.
+ *      If it is a conditional instruction, the handler
+ *      will use insn[0] to copy its condition code to
+ *	set r0 to 1 and insn[1] to "mov pc, lr" to return.
+ *
+ *   *) Otherwise, a modified form of the instruction is
+ *      directly executed.  Its handler calls the
+ *      instruction in insn[0].  In insn[1] is a
+ *      "mov pc, lr" to return.
+ *
+ *      Before calling, load up the reordered registers
+ *      from the original instruction's registers.  If one
+ *      of the original input registers is the PC, compute
+ *      and adjust the appropriate input register.
+ *
+ *	After call completes, copy the output registers to
+ *      the original instruction's original registers.
+ *
+ * We don't use a real breakpoint instruction since that
+ * would have us in the kernel go from SVC mode to SVC
+ * mode losing the link register.  Instead we use an
+ * undefined instruction.  To simplify processing, the
+ * undefined instruction used for kprobes must be reserved
+ * exclusively for kprobes use.
+ *
+ * TODO: ifdef out some instruction decoding based on architecture.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+
+#define sign_extend(x, signbit) ((x) | (0 - ((x) & (1 << (signbit)))))
+
+#define branch_displacement(insn) sign_extend(((insn) & 0xffffff) << 2, 25)
+
+#define PSR_fs	(PSR_f|PSR_s)
+
+#define KPROBE_RETURN_INSTRUCTION	0xe1a0f00e	/* mov pc, lr */
+#define SET_R0_TRUE_INSTRUCTION		0xe3a00001	/* mov	r0, #1 */
+
+#define	truecc_insn(insn)	(((insn) & 0xf0000000) | \
+				 (SET_R0_TRUE_INSTRUCTION & 0x0fffffff))
+
+typedef long (insn_0arg_fn_t)(void);
+typedef long (insn_1arg_fn_t)(long);
+typedef long (insn_2arg_fn_t)(long, long);
+typedef long (insn_3arg_fn_t)(long, long, long);
+typedef long (insn_4arg_fn_t)(long, long, long, long);
+typedef long long (insn_llret_0arg_fn_t)(void);
+typedef long long (insn_llret_3arg_fn_t)(long, long, long);
+typedef long long (insn_llret_4arg_fn_t)(long, long, long, long);
+
+union reg_pair {
+	long long	dr;
+#ifdef __LITTLE_ENDIAN
+	struct { long	r0, r1; };
+#else
+	struct { long	r1, r0; };
+#endif
+};
+
+/*
+ * For STR and STM instructions, an ARM core may choose to use either
+ * a +8 or a +12 displacement from the current instruction's address.
+ * Whichever value is chosen for a given core, it must be the same for
+ * both instructions and may not change.  This function measures it.
+ */
+
+static int str_pc_offset;
+
+static void __init find_str_pc_offset(void)
+{
+	int addr, scratch, ret;
+
+	__asm__ (
+		"sub	%[ret], pc, #4		\n\t"
+		"str	pc, %[addr]		\n\t"
+		"ldr	%[scr], %[addr]		\n\t"
+		"sub	%[ret], %[scr], %[ret]	\n\t"
+		: [ret] "=r" (ret), [scr] "=r" (scratch), [addr] "+m" (addr));
+
+	str_pc_offset = ret;
+}
+
+/*
+ * The insnslot_?arg_r[w]flags() functions below are to keep the
+ * msr -> *fn -> mrs instruction sequences indivisible so that
+ * the state of the CPSR flags aren't inadvertently modified
+ * just before or just after the call.
+ */
+
+static inline long __kprobes
+insnslot_0arg_rflags(long cpsr, insn_0arg_fn_t *fn)
+{
+	register long ret asm("r0");
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[cpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		: "=r" (ret)
+		: [cpsr] "r" (cpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	return ret;
+}
+
+static inline long long __kprobes
+insnslot_llret_0arg_rflags(long cpsr, insn_llret_0arg_fn_t *fn)
+{
+	register long ret0 asm("r0");
+	register long ret1 asm("r1");
+	union reg_pair fnr;
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[cpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		: "=r" (ret0), "=r" (ret1)
+		: [cpsr] "r" (cpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	fnr.r0 = ret0;
+	fnr.r1 = ret1;
+	return fnr.dr;
+}
+
+static inline long __kprobes
+insnslot_1arg_rflags(long r0, long cpsr, insn_1arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long ret asm("r0");
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[cpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		: "=r" (ret)
+		: "0" (rr0), [cpsr] "r" (cpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	return ret;
+}
+
+static inline long __kprobes
+insnslot_2arg_rflags(long r0, long r1, long cpsr, insn_2arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long rr1 asm("r1") = r1;
+	register long ret asm("r0");
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[cpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		: "=r" (ret)
+		: "0" (rr0), "r" (rr1),
+		  [cpsr] "r" (cpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	return ret;
+}
+
+static inline long __kprobes
+insnslot_3arg_rflags(long r0, long r1, long r2, long cpsr, insn_3arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long rr1 asm("r1") = r1;
+	register long rr2 asm("r2") = r2;
+	register long ret asm("r0");
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[cpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		: "=r" (ret)
+		: "0" (rr0), "r" (rr1), "r" (rr2),
+		  [cpsr] "r" (cpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	return ret;
+}
+
+static inline long long __kprobes
+insnslot_llret_3arg_rflags(long r0, long r1, long r2, long cpsr,
+			   insn_llret_3arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long rr1 asm("r1") = r1;
+	register long rr2 asm("r2") = r2;
+	register long ret0 asm("r0");
+	register long ret1 asm("r1");
+	union reg_pair fnr;
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[cpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		: "=r" (ret0), "=r" (ret1)
+		: "0" (rr0), "r" (rr1), "r" (rr2),
+		  [cpsr] "r" (cpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	fnr.r0 = ret0;
+	fnr.r1 = ret1;
+	return fnr.dr;
+}
+
+static inline long __kprobes
+insnslot_4arg_rflags(long r0, long r1, long r2, long r3, long cpsr,
+		     insn_4arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long rr1 asm("r1") = r1;
+	register long rr2 asm("r2") = r2;
+	register long rr3 asm("r3") = r3;
+	register long ret asm("r0");
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[cpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		: "=r" (ret)
+		: "0" (rr0), "r" (rr1), "r" (rr2), "r" (rr3),
+		  [cpsr] "r" (cpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	return ret;
+}
+
+static inline long __kprobes
+insnslot_1arg_rwflags(long r0, long *cpsr, insn_1arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long ret asm("r0");
+	long oldcpsr = *cpsr;
+	long newcpsr;
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[oldcpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		"mrs	%[newcpsr], cpsr	\n\t"
+		: "=r" (ret), [newcpsr] "=r" (newcpsr)
+		: "0" (rr0), [oldcpsr] "r" (oldcpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	*cpsr = (oldcpsr & ~PSR_fs) | (newcpsr & PSR_fs);
+	return ret;
+}
+
+static inline long __kprobes
+insnslot_2arg_rwflags(long r0, long r1, long *cpsr, insn_2arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long rr1 asm("r1") = r1;
+	register long ret asm("r0");
+	long oldcpsr = *cpsr;
+	long newcpsr;
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[oldcpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		"mrs	%[newcpsr], cpsr	\n\t"
+		: "=r" (ret), [newcpsr] "=r" (newcpsr)
+		: "0" (rr0), "r" (rr1), [oldcpsr] "r" (oldcpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	*cpsr = (oldcpsr & ~PSR_fs) | (newcpsr & PSR_fs);
+	return ret;
+}
+
+static inline long __kprobes
+insnslot_3arg_rwflags(long r0, long r1, long r2, long *cpsr,
+		      insn_3arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long rr1 asm("r1") = r1;
+	register long rr2 asm("r2") = r2;
+	register long ret asm("r0");
+	long oldcpsr = *cpsr;
+	long newcpsr;
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[oldcpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		"mrs	%[newcpsr], cpsr	\n\t"
+		: "=r" (ret), [newcpsr] "=r" (newcpsr)
+		: "0" (rr0), "r" (rr1), "r" (rr2),
+		  [oldcpsr] "r" (oldcpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	*cpsr = (oldcpsr & ~PSR_fs) | (newcpsr & PSR_fs);
+	return ret;
+}
+
+static inline long __kprobes
+insnslot_4arg_rwflags(long r0, long r1, long r2, long r3, long *cpsr,
+		      insn_4arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long rr1 asm("r1") = r1;
+	register long rr2 asm("r2") = r2;
+	register long rr3 asm("r3") = r3;
+	register long ret asm("r0");
+	long oldcpsr = *cpsr;
+	long newcpsr;
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[oldcpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		"mrs	%[newcpsr], cpsr	\n\t"
+		: "=r" (ret), [newcpsr] "=r" (newcpsr)
+		: "0" (rr0), "r" (rr1), "r" (rr2), "r" (rr3),
+		  [oldcpsr] "r" (oldcpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	*cpsr = (oldcpsr & ~PSR_fs) | (newcpsr & PSR_fs);
+	return ret;
+}
+
+static inline long long __kprobes
+insnslot_llret_4arg_rwflags(long r0, long r1, long r2, long r3, long *cpsr,
+			    insn_llret_4arg_fn_t *fn)
+{
+	register long rr0 asm("r0") = r0;
+	register long rr1 asm("r1") = r1;
+	register long rr2 asm("r2") = r2;
+	register long rr3 asm("r3") = r3;
+	register long ret0 asm("r0");
+	register long ret1 asm("r1");
+	long oldcpsr = *cpsr;
+	long newcpsr;
+	union reg_pair fnr;
+
+	__asm__ __volatile__ (
+		"msr	cpsr_fs, %[oldcpsr]	\n\t"
+		"mov	lr, pc			\n\t"
+		"mov	pc, %[fn]		\n\t"
+		"mrs	%[newcpsr], cpsr	\n\t"
+		: "=r" (ret0), "=r" (ret1), [newcpsr] "=r" (newcpsr)
+		: "0" (rr0), "r" (rr1), "r" (rr2), "r" (rr3),
+		  [oldcpsr] "r" (oldcpsr), [fn] "r" (fn)
+		: "lr", "cc"
+	);
+	*cpsr = (oldcpsr & ~PSR_fs) | (newcpsr & PSR_fs);
+	fnr.r0 = ret0;
+	fnr.r1 = ret1;
+	return fnr.dr;
+}
+
+/*
+ * To avoid the complications of mimicing single-stepping on a
+ * processor without a Next-PC or a single-step mode, and to
+ * avoid having to deal with the side-effects of boosting, we
+ * simulate or emulate (almost) all ARM instructions.
+ *
+ * "Simulation" is where the instruction's behavior is duplicated in
+ * C code.  "Emulation" is where the original instruction is rewritten
+ * and executed, often by altering its registers.
+ *
+ * By having all behavior of the kprobe'd instruction completed before
+ * returning from the kprobe_handler(), all locks (scheduler and
+ * interrupt) can safely be released.  There is no need for secondary
+ * breakpoints, no race with MP or preemptable kernels, nor having to
+ * clean up resources counts at a later time impacting overall system
+ * performance.  By rewriting the instruction, only the minimum registers
+ * need to be loaded and saved back optimizing performance.
+ *
+ * Calling the insnslot_*_rwflags version of a function doesn't hurt
+ * anything even when the CPSR flags aren't updated by the
+ * instruction.  It's just a little slower in return for saving
+ * a little space by not having a duplicate function that doesn't
+ * update the flags.  (The same optimization can be said for
+ * instructions that do or don't perform register writeback)
+ * Also, instructions can either read the flags, only write the
+ * flags, or read and write the flags.  To save combinations
+ * rather than for sheer performance, flag functions just assume
+ * read and write of flags.
+ */
+
+static void __kprobes simulate_bbl(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	long iaddr = (long)p->addr;
+	int disp  = branch_displacement(insn);
+
+	if (!insnslot_1arg_rflags(0, regs->ARM_cpsr, i_fn))
+		return;
+
+	if (insn & (1 << 24))
+		regs->ARM_lr = iaddr + 4;
+
+	regs->ARM_pc = iaddr + 8 + disp;
+}
+
+static void __kprobes simulate_blx1(struct kprobe *p, struct pt_regs *regs)
+{
+	kprobe_opcode_t insn = p->opcode;
+	long iaddr = (long)p->addr;
+	int disp = branch_displacement(insn);
+
+	regs->ARM_lr = iaddr + 4;
+	regs->ARM_pc = iaddr + 8 + disp + ((insn >> 23) & 0x2);
+	regs->ARM_cpsr |= PSR_T_BIT;
+}
+
+static void __kprobes simulate_blx2bx(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rm = insn & 0xf;
+	long rmv = regs->uregs[rm];
+
+	if (!insnslot_1arg_rflags(0, regs->ARM_cpsr, i_fn))
+		return;
+
+	if (insn & (1 << 5))
+		regs->ARM_lr = (long)p->addr + 4;
+
+	regs->ARM_pc = rmv & ~0x1;
+	regs->ARM_cpsr &= ~PSR_T_BIT;
+	if (rmv & 0x1)
+		regs->ARM_cpsr |= PSR_T_BIT;
+}
+
+static void __kprobes simulate_ldm1stm1(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rn = (insn >> 16) & 0xf;
+	int lbit = insn & (1 << 20);
+	int wbit = insn & (1 << 21);
+	int ubit = insn & (1 << 23);
+	int pbit = insn & (1 << 24);
+	long *addr = (long *)regs->uregs[rn];
+	int reg_bit_vector;
+	int reg_count;
+
+	if (!insnslot_1arg_rflags(0, regs->ARM_cpsr, i_fn))
+		return;
+
+	reg_count = 0;
+	reg_bit_vector = insn & 0xffff;
+	while (reg_bit_vector) {
+		reg_bit_vector &= (reg_bit_vector - 1);
+		++reg_count;
+	}
+
+	if (!ubit)
+		addr -= reg_count;
+	addr += (!pbit ^ !ubit);
+
+	reg_bit_vector = insn & 0xffff;
+	while (reg_bit_vector) {
+		int reg = __ffs(reg_bit_vector);
+		reg_bit_vector &= (reg_bit_vector - 1);
+		if (lbit)
+			regs->uregs[reg] = *addr++;
+		else
+			*addr++ = regs->uregs[reg];
+	}
+
+	if (wbit) {
+		if (!ubit)
+			addr -= reg_count;
+		addr -= (!pbit ^ !ubit);
+		regs->uregs[rn] = (long)addr;
+	}
+}
+
+static void __kprobes simulate_stm1_pc(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+
+	if (!insnslot_1arg_rflags(0, regs->ARM_cpsr, i_fn))
+		return;
+
+	regs->ARM_pc = (long)p->addr + str_pc_offset;
+	simulate_ldm1stm1(p, regs);
+	regs->ARM_pc = (long)p->addr + 4;
+}
+
+static void __kprobes simulate_mov_ipsp(struct kprobe *p, struct pt_regs *regs)
+{
+	regs->uregs[12] = regs->uregs[13];
+}
+
+static void __kprobes emulate_ldcstc(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rn = (insn >> 16) & 0xf;
+	long rnv = regs->uregs[rn];
+
+	/* Save Rn in case of writeback. */
+	regs->uregs[rn] = insnslot_1arg_rflags(rnv, regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_ldrd(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_2arg_fn_t *i_fn = (insn_2arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	int rm = insn & 0xf;  /* rm may be invalid, don't care. */
+
+	/* Not following the C calling convention here, so need asm(). */
+	__asm__ __volatile__ (
+		"ldr	r0, %[rn]	\n\t"
+		"ldr	r1, %[rm]	\n\t"
+		"msr	cpsr_fs, %[cpsr]\n\t"
+		"mov	lr, pc		\n\t"
+		"mov	pc, %[i_fn]	\n\t"
+		"str	r0, %[rn]	\n\t"	/* in case of writeback */
+		"str	r2, %[rd0]	\n\t"
+		"str	r3, %[rd1]	\n\t"
+		: [rn]  "+m" (regs->uregs[rn]),
+		  [rd0] "=m" (regs->uregs[rd]),
+		  [rd1] "=m" (regs->uregs[rd+1])
+		: [rm]   "m" (regs->uregs[rm]),
+		  [cpsr] "r" (regs->ARM_cpsr),
+		  [i_fn] "r" (i_fn)
+		: "r0", "r1", "r2", "r3", "lr", "cc"
+	);
+}
+
+static void __kprobes emulate_strd(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_4arg_fn_t *i_fn = (insn_4arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	int rm  = insn & 0xf;
+	long rnv = regs->uregs[rn];
+	long rmv = regs->uregs[rm];  /* rm/rmv may be invalid, don't care. */
+
+	regs->uregs[rn] = insnslot_4arg_rflags(rnv, rmv, regs->uregs[rd],
+					       regs->uregs[rd+1],
+					       regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_ldr(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_llret_3arg_fn_t *i_fn = (insn_llret_3arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	union reg_pair fnr;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	int rm = insn & 0xf;
+	long rdv;
+	long rnv  = regs->uregs[rn];
+	long rmv  = regs->uregs[rm]; /* rm/rmv may be invalid, don't care. */
+	long cpsr = regs->ARM_cpsr;
+
+	fnr.dr = insnslot_llret_3arg_rflags(rnv, 0, rmv, cpsr, i_fn);
+	regs->uregs[rn] = fnr.r0;  /* Save Rn in case of writeback. */
+	rdv = fnr.r1;
+
+	if (rd == 15) {
+#if __LINUX_ARM_ARCH__ >= 5
+		cpsr &= ~PSR_T_BIT;
+		if (rdv & 0x1)
+			cpsr |= PSR_T_BIT;
+		regs->ARM_cpsr = cpsr;
+		rdv &= ~0x1;
+#else
+		rdv &= ~0x2;
+#endif
+	}
+	regs->uregs[rd] = rdv;
+}
+
+static void __kprobes emulate_str(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_3arg_fn_t *i_fn = (insn_3arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	long iaddr = (long)p->addr;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	int rm = insn & 0xf;
+	long rdv = (rd == 15) ? iaddr + str_pc_offset : regs->uregs[rd];
+	long rnv = (rn == 15) ? iaddr +  8 : regs->uregs[rn];
+	long rmv = regs->uregs[rm];  /* rm/rmv may be invalid, don't care. */
+
+	/* Save Rn in case of writeback. */
+	regs->uregs[rn] =
+		insnslot_3arg_rflags(rnv, rdv, rmv, regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_mrrc(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_llret_0arg_fn_t *i_fn = (insn_llret_0arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	union reg_pair fnr;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+
+	fnr.dr = insnslot_llret_0arg_rflags(regs->ARM_cpsr, i_fn);
+	regs->uregs[rn] = fnr.r0;
+	regs->uregs[rd] = fnr.r1;
+}
+
+static void __kprobes emulate_mcrr(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_2arg_fn_t *i_fn = (insn_2arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	long rnv = regs->uregs[rn];
+	long rdv = regs->uregs[rd];
+
+	insnslot_2arg_rflags(rnv, rdv, regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_sat(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rm = insn & 0xf;
+	long rmv = regs->uregs[rm];
+
+	/* Writes Q flag */
+	regs->uregs[rd] = insnslot_1arg_rwflags(rmv, &regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_sel(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_2arg_fn_t *i_fn = (insn_2arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	int rm = insn & 0xf;
+	long rnv = regs->uregs[rn];
+	long rmv = regs->uregs[rm];
+
+	/* Reads GE bits */
+	regs->uregs[rd] = insnslot_2arg_rflags(rnv, rmv, regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_none(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_0arg_fn_t *i_fn = (insn_0arg_fn_t *)&p->ainsn.insn[0];
+
+	insnslot_0arg_rflags(regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_rd12(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_0arg_fn_t *i_fn = (insn_0arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+
+	regs->uregs[rd] = insnslot_0arg_rflags(regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_ird12(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int ird = (insn >> 12) & 0xf;
+
+	insnslot_1arg_rflags(regs->uregs[ird], regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_rn16(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rn = (insn >> 16) & 0xf;
+	long rnv = regs->uregs[rn];
+
+	insnslot_1arg_rflags(rnv, regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes emulate_rd12rm0(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rm = insn & 0xf;
+	long rmv = regs->uregs[rm];
+
+	regs->uregs[rd] = insnslot_1arg_rflags(rmv, regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes
+emulate_rd12rn16rm0_rwflags(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_2arg_fn_t *i_fn = (insn_2arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	int rm = insn & 0xf;
+	long rnv = regs->uregs[rn];
+	long rmv = regs->uregs[rm];
+
+	regs->uregs[rd] =
+		insnslot_2arg_rwflags(rnv, rmv, &regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes
+emulate_rd16rn12rs8rm0_rwflags(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_3arg_fn_t *i_fn = (insn_3arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 16) & 0xf;
+	int rn = (insn >> 12) & 0xf;
+	int rs = (insn >> 8) & 0xf;
+	int rm = insn & 0xf;
+	long rnv = regs->uregs[rn];
+	long rsv = regs->uregs[rs];
+	long rmv = regs->uregs[rm];
+
+	regs->uregs[rd] =
+		insnslot_3arg_rwflags(rnv, rsv, rmv, &regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes
+emulate_rd16rs8rm0_rwflags(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_2arg_fn_t *i_fn = (insn_2arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 16) & 0xf;
+	int rs = (insn >> 8) & 0xf;
+	int rm = insn & 0xf;
+	long rsv = regs->uregs[rs];
+	long rmv = regs->uregs[rm];
+
+	regs->uregs[rd] =
+		insnslot_2arg_rwflags(rsv, rmv, &regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes
+emulate_rdhi16rdlo12rs8rm0_rwflags(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_llret_4arg_fn_t *i_fn = (insn_llret_4arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	union reg_pair fnr;
+	int rdhi = (insn >> 16) & 0xf;
+	int rdlo = (insn >> 12) & 0xf;
+	int rs   = (insn >> 8) & 0xf;
+	int rm   = insn & 0xf;
+	long rsv = regs->uregs[rs];
+	long rmv = regs->uregs[rm];
+
+	fnr.dr = insnslot_llret_4arg_rwflags(regs->uregs[rdhi],
+					     regs->uregs[rdlo], rsv, rmv,
+					     &regs->ARM_cpsr, i_fn);
+	regs->uregs[rdhi] = fnr.r0;
+	regs->uregs[rdlo] = fnr.r1;
+}
+
+static void __kprobes
+emulate_alu_imm_rflags(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	long rnv = (rn == 15) ? (long)p->addr + 8 : regs->uregs[rn];
+
+	regs->uregs[rd] = insnslot_1arg_rflags(rnv, regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes
+emulate_alu_imm_rwflags(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_1arg_fn_t *i_fn = (insn_1arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;
+	long rnv = (rn == 15) ? (long)p->addr + 8 : regs->uregs[rn];
+
+	regs->uregs[rd] = insnslot_1arg_rwflags(rnv, &regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes
+emulate_alu_rflags(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_3arg_fn_t *i_fn = (insn_3arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	long ppc = (long)p->addr + 8;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;	/* rn/rnv/rs/rsv may be */
+	int rs = (insn >> 8) & 0xf;	/* invalid, don't care. */
+	int rm = insn & 0xf;
+	long rnv = (rn == 15) ? ppc : regs->uregs[rn];
+	long rmv = (rm == 15) ? ppc : regs->uregs[rm];
+	long rsv = regs->uregs[rs];
+
+	regs->uregs[rd] =
+		insnslot_3arg_rflags(rnv, rmv, rsv, regs->ARM_cpsr, i_fn);
+}
+
+static void __kprobes
+emulate_alu_rwflags(struct kprobe *p, struct pt_regs *regs)
+{
+	insn_3arg_fn_t *i_fn = (insn_3arg_fn_t *)&p->ainsn.insn[0];
+	kprobe_opcode_t insn = p->opcode;
+	long ppc = (long)p->addr + 8;
+	int rd = (insn >> 12) & 0xf;
+	int rn = (insn >> 16) & 0xf;	/* rn/rnv/rs/rsv may be */
+	int rs = (insn >> 8) & 0xf;	/* invalid, don't care. */
+	int rm = insn & 0xf;
+	long rnv = (rn == 15) ? ppc : regs->uregs[rn];
+	long rmv = (rm == 15) ? ppc : regs->uregs[rm];
+	long rsv = regs->uregs[rs];
+
+	regs->uregs[rd] =
+		insnslot_3arg_rwflags(rnv, rmv, rsv, &regs->ARM_cpsr, i_fn);
+}
+
+static enum kprobe_insn __kprobes
+prep_emulate_ldr_str(kprobe_opcode_t insn, struct arch_specific_insn *asi)
+{
+	int ibit = (insn & (1 << 26)) ? 25 : 22;
+
+	insn &= 0xfff00fff;
+	insn |= 0x00001000;	/* Rn = r0, Rd = r1 */
+	if (insn & (1 << ibit)) {
+		insn &= ~0xf;
+		insn |= 2;	/* Rm = r2 */
+	}
+	asi->insn[0] = insn;
+	asi->insn_handler = (insn & (1 << 20)) ? emulate_ldr : emulate_str;
+	return INSN_GOOD;
+}
+
+static enum kprobe_insn __kprobes
+prep_emulate_rd12rm0(kprobe_opcode_t insn, struct arch_specific_insn *asi)
+{
+	insn &= 0xffff0ff0;	/* Rd = r0, Rm = r0 */
+	asi->insn[0] = insn;
+	asi->insn_handler = emulate_rd12rm0;
+	return INSN_GOOD;
+}
+
+static enum kprobe_insn __kprobes
+prep_emulate_rd12(kprobe_opcode_t insn, struct arch_specific_insn *asi)
+{
+	insn &= 0xffff0fff;	/* Rd = r0 */
+	asi->insn[0] = insn;
+	asi->insn_handler = emulate_rd12;
+	return INSN_GOOD;
+}
+
+static enum kprobe_insn __kprobes
+prep_emulate_rd12rn16rm0_wflags(kprobe_opcode_t insn,
+				struct arch_specific_insn *asi)
+{
+	insn &= 0xfff00ff0;	/* Rd = r0, Rn = r0 */
+	insn |= 0x00000001;	/* Rm = r1 */
+	asi->insn[0] = insn;
+	asi->insn_handler = emulate_rd12rn16rm0_rwflags;
+	return INSN_GOOD;
+}
+
+static enum kprobe_insn __kprobes
+prep_emulate_rd16rs8rm0_wflags(kprobe_opcode_t insn,
+			       struct arch_specific_insn *asi)
+{
+	insn &= 0xfff0f0f0;	/* Rd = r0, Rs = r0 */
+	insn |= 0x00000001;	/* Rm = r1          */
+	asi->insn[0] = insn;
+	asi->insn_handler = emulate_rd16rs8rm0_rwflags;
+	return INSN_GOOD;
+}
+
+static enum kprobe_insn __kprobes
+prep_emulate_rd16rn12rs8rm0_wflags(kprobe_opcode_t insn,
+				   struct arch_specific_insn *asi)
+{
+	insn &= 0xfff000f0;	/* Rd = r0, Rn = r0 */
+	insn |= 0x00000102;	/* Rs = r1, Rm = r2 */
+	asi->insn[0] = insn;
+	asi->insn_handler = emulate_rd16rn12rs8rm0_rwflags;
+	return INSN_GOOD;
+}
+
+static enum kprobe_insn __kprobes
+prep_emulate_rdhi16rdlo12rs8rm0_wflags(kprobe_opcode_t insn,
+				       struct arch_specific_insn *asi)
+{
+	insn &= 0xfff000f0;	/* RdHi = r0, RdLo = r1 */
+	insn |= 0x00001203;	/* Rs = r2, Rm = r3 */
+	asi->insn[0] = insn;
+	asi->insn_handler = emulate_rdhi16rdlo12rs8rm0_rwflags;
+	return INSN_GOOD;
+}
+
+/*
+ * For the instruction masking and comparisons in all the "space_*"
+ * functions below, Do _not_ rearrange the order of tests unless
+ * you're very, very sure of what you are doing.  For the sake of
+ * efficiency, the masks for some tests sometimes assume other test
+ * have been done prior to them so the number of patterns to test
+ * for an instruction set can be as broad as possible to reduce the
+ * number of tests needed.
+ */
+
+static enum kprobe_insn __kprobes
+space_1111(kprobe_opcode_t insn, struct arch_specific_insn *asi)
+{
+	/* CPS mmod == 1 : 1111 0001 0000 xx10 xxxx xxxx xx0x xxxx */
+	/* RFE           : 1111 100x x0x1 xxxx xxxx 1010 xxxx xxxx */
+	/* SRS           : 1111 100x x1x0 1101 xxxx 0101 xxxx xxxx */
+	if ((insn & 0xfff30020) == 0xf1020000 ||
+	    (insn & 0xfe500f00) == 0xf8100a00 ||
+	    (insn & 0xfe5f0f00) == 0xf84d0500)
+		return INSN_REJECTED;
+
+	/* PLD : 1111 01x1 x101 xxxx xxxx xxxx xxxx xxxx : */
+	if ((insn & 0xfd700000) == 0xf4500000) {
+		insn &= 0xfff0ffff;	/* Rn = r0 */
+		asi->insn[0] = insn;
+		asi->insn_handler = emulate_rn16;
+		return INSN_GOOD;
+	}
+
+	/* BLX(1) : 1111 101x xxxx xxxx xxxx xxxx xxxx xxxx : */
+	if ((insn & 0xfe000000) == 0xfa000000) {
+		asi->insn_handler = simulate_blx1;
+		return INSN_GOOD_NO_SLOT;
+	}
+
+	/* SETEND : 1111 0001 0000 0001 xxxx xxxx 0000 xxxx */
+	/* CDP2   : 1111 1110 xxxx xxxx xxxx xxxx xxx0 xxxx */
+	if ((insn & 0xffff00f0) == 0xf1010000 ||
+	    (insn & 0xff000010) == 0xfe000000) {
+		asi->insn[0] = insn;
+		asi->insn_handler = emulate_none;
+		return INSN_GOOD;
+	}
+
+	/* MCRR2 : 1111 1100 0100 xxxx xxxx xxxx xxxx xxxx : (Rd != Rn) */
+	/* MRRC2 : 1111 1100 0101 xxxx xxxx xxxx xxxx xxxx : (Rd != Rn) */
+	if ((insn & 0xffe00000) == 0xfc400000) {
+		insn &= 0xfff00fff;	/* Rn = r0 */
+		insn |= 0x00001000;	/* Rd = r1 */
+		asi->insn[0] = insn;
+		asi->insn_handler =
+			(insn & (1 << 20)) ? emulate_mrrc : emulate_mcrr;
+		return INSN_GOOD;
+	}
+
+	/* LDC2 : 1111 110x xxx1 xxxx xxxx xxxx xxxx xxxx */
+	/* STC2 : 1111 110x xxx0 xxxx xxxx xxxx xxxx xxxx */
+	if ((insn & 0xfe000000) == 0xfc000000) {
+		insn &= 0xfff0ffff;      /* Rn = r0 */
+		asi->insn[0] = insn;
+		asi->insn_handler = emulate_ldcstc;
+		return INSN_GOOD;
+	}
+
+	/* MCR2 : 1111 1110 xxx0 xxxx xxxx xxxx xxx1 xxxx */
+	/* MRC2 : 1111 1110 xxx1 xxxx xxxx xxxx xxx1 xxxx */
+	insn &= 0xffff0fff;	/* Rd = r0 */
+	asi->insn[0]      = insn;
+	asi->insn_handler = (insn & (1 << 20)) ? emulate_rd12 : emulate_ird12;
+	return INSN_GOOD;
+}
+
+static enum kprobe_insn __kprobes
+space_cccc_000x(kprobe_opcode_t insn, struct arch_specific_insn *asi)
+{
+	/* cccc 0001 0xx0 xxxx xxxx xxxx xxxx xxx0 xxxx */
+	if ((insn & 0x0f900010) == 0x01000000) {
+
+		/* BXJ  : cccc 0001 0010 xxxx xxxx xxxx 0010 xxxx */
+		/* MSR  : cccc 0001 0x10 xxxx xxxx xxxx 0000 xxxx */
+		if ((insn & 0x0ff000f0) == 0x01200020 ||
+		    (insn & 0x0fb000f0) == 0x01200000)
+			return INSN_REJECTED;
+
+		/* MRS : cccc 0001 0x00 xxxx xxxx xxxx 0000 xxxx */
+		if ((insn & 0x0fb00010) == 0x01000000)
+			return prep_emulate_rd12(insn, asi);
+
+		/* SMLALxy : cccc 0001 0100 xxxx xxxx xxxx 1xx0 xxxx */
+		if ((insn & 0x0ff00090) == 0x01400080)
+			return prep_emulate_rdhi16rdlo12rs8rm0_wflags(insn, asi);
+
+		/* SMULWy : cccc 0001 0010 xxxx xxxx xxxx 1x10 xxxx */
+		/* SMULxy : cccc 0001 0110 xxxx xxxx xxxx 1xx0 xxxx */
+		if ((insn & 0x0ff000b0) == 0x012000a0 ||
+		    (insn & 0x0ff00090) == 0x01600080)
+			return prep_emulate_rd16rs8rm0_wflags(insn, asi);
+
+		/* SMLAxy : cccc 0001 0000 xxxx xxxx xxxx 1xx0 xxxx : Q */