linuxdebug/arch/arm/kernel/ptrace.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/arch/arm/kernel/ptrace.c
 *
 *  By Ross Biro 1/23/92
 * edited by Linus Torvalds
 * ARM modifications Copyright (C) 2000 Russell King
 */
#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/sched/task_stack.h>
#include <linux/mm.h>
#include <linux/elf.h>
#include <linux/smp.h>
#include <linux/ptrace.h>
#include <linux/user.h>
#include <linux/security.h>
#include <linux/init.h>
#include <linux/signal.h>
#include <linux/uaccess.h>
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
#include <linux/regset.h>
#include <linux/audit.h>
#include <linux/unistd.h>

#include <asm/syscall.h>
#include <asm/traps.h>

#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>

#define REG_PC	15
#define REG_PSR	16
/*
 * does not yet catch signals sent when the child dies.
 * in exit.c or in signal.c.
 */

#if 0
/*
 * Breakpoint SWI instruction: SWI &9F0001
 */
#define BREAKINST_ARM	0xef9f0001
#define BREAKINST_THUMB	0xdf00		/* fill this in later */
#else
/*
 * New breakpoints - use an undefined instruction.  The ARM architecture
 * reference manual guarantees that the following instruction space
 * will produce an undefined instruction exception on all CPUs:
 *
 *  ARM:   xxxx 0111 1111 xxxx xxxx xxxx 1111 xxxx
 *  Thumb: 1101 1110 xxxx xxxx
 */
#define BREAKINST_ARM	0xe7f001f0
#define BREAKINST_THUMB	0xde01
#endif

struct pt_regs_offset {
	const char *name;
	int offset;
};

#define REG_OFFSET_NAME(r) \
	{.name = #r, .offset = offsetof(struct pt_regs, ARM_##r)}
#define REG_OFFSET_END {.name = NULL, .offset = 0}

static const struct pt_regs_offset regoffset_table[] = {
	REG_OFFSET_NAME(r0),
	REG_OFFSET_NAME(r1),
	REG_OFFSET_NAME(r2),
	REG_OFFSET_NAME(r3),
	REG_OFFSET_NAME(r4),
	REG_OFFSET_NAME(r5),
	REG_OFFSET_NAME(r6),
	REG_OFFSET_NAME(r7),
	REG_OFFSET_NAME(r8),
	REG_OFFSET_NAME(r9),
	REG_OFFSET_NAME(r10),
	REG_OFFSET_NAME(fp),
	REG_OFFSET_NAME(ip),
	REG_OFFSET_NAME(sp),
	REG_OFFSET_NAME(lr),
	REG_OFFSET_NAME(pc),
	REG_OFFSET_NAME(cpsr),
	REG_OFFSET_NAME(ORIG_r0),
	REG_OFFSET_END,
};

/**
 * regs_query_register_offset() - query register offset from its name
 * @name:	the name of a register
 *
 * regs_query_register_offset() returns the offset of a register in struct
 * pt_regs from its name. If the name is invalid, this returns -EINVAL;
 */
int regs_query_register_offset(const char *name)
{
	const struct pt_regs_offset *roff;
	for (roff = regoffset_table; roff->name != NULL; roff++)
		if (!strcmp(roff->name, name))
			return roff->offset;
	return -EINVAL;
}

/**
 * regs_query_register_name() - query register name from its offset
 * @offset:	the offset of a register in struct pt_regs.
 *
 * regs_query_register_name() returns the name of a register from its
 * offset in struct pt_regs. If the @offset is invalid, this returns NULL;
 */
const char *regs_query_register_name(unsigned int offset)
{
	const struct pt_regs_offset *roff;
	for (roff = regoffset_table; roff->name != NULL; roff++)
		if (roff->offset == offset)
			return roff->name;
	return NULL;
}

/**
 * regs_within_kernel_stack() - check the address in the stack
 * @regs:      pt_regs which contains kernel stack pointer.
 * @addr:      address which is checked.
 *
 * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
 * If @addr is within the kernel stack, it returns true. If not, returns false.
 */
bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
{
	return ((addr & ~(THREAD_SIZE - 1))  ==
		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
}

/**
 * regs_get_kernel_stack_nth() - get Nth entry of the stack
 * @regs:	pt_regs which contains kernel stack pointer.
 * @n:		stack entry number.
 *
 * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
 * is specified by @regs. If the @n th entry is NOT in the kernel stack,
 * this returns 0.
 */
unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
{
	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
	addr += n;
	if (regs_within_kernel_stack(regs, (unsigned long)addr))
		return *addr;
	else
		return 0;
}

/*
 * this routine will get a word off of the processes privileged stack.
 * the offset is how far from the base addr as stored in the THREAD.
 * this routine assumes that all the privileged stacks are in our
 * data space.
 */
static inline long get_user_reg(struct task_struct *task, int offset)
{
	return task_pt_regs(task)->uregs[offset];
}

/*
 * this routine will put a word on the processes privileged stack.
 * the offset is how far from the base addr as stored in the THREAD.
 * this routine assumes that all the privileged stacks are in our
 * data space.
 */
static inline int
put_user_reg(struct task_struct *task, int offset, long data)
{
	struct pt_regs newregs, *regs = task_pt_regs(task);
	int ret = -EINVAL;

	newregs = *regs;
	newregs.uregs[offset] = data;

	if (valid_user_regs(&newregs)) {
		regs->uregs[offset] = data;
		ret = 0;
	}

	return ret;
}

/*
 * Called by kernel/ptrace.c when detaching..
 */
void ptrace_disable(struct task_struct *child)
{
	/* Nothing to do. */
}

/*
 * Handle hitting a breakpoint.
 */
void ptrace_break(struct pt_regs *regs)
{
	force_sig_fault(SIGTRAP, TRAP_BRKPT,
			(void __user *)instruction_pointer(regs));
}

static int break_trap(struct pt_regs *regs, unsigned int instr)
{
	ptrace_break(regs);
	return 0;
}

static struct undef_hook arm_break_hook = {
	.instr_mask	= 0x0fffffff,
	.instr_val	= 0x07f001f0,
	.cpsr_mask	= PSR_T_BIT,
	.cpsr_val	= 0,
	.fn		= break_trap,
};

static struct undef_hook thumb_break_hook = {
	.instr_mask	= 0xffffffff,
	.instr_val	= 0x0000de01,
	.cpsr_mask	= PSR_T_BIT,
	.cpsr_val	= PSR_T_BIT,
	.fn		= break_trap,
};

static struct undef_hook thumb2_break_hook = {
	.instr_mask	= 0xffffffff,
	.instr_val	= 0xf7f0a000,
	.cpsr_mask	= PSR_T_BIT,
	.cpsr_val	= PSR_T_BIT,
	.fn		= break_trap,
};

static int __init ptrace_break_init(void)
{
	register_undef_hook(&arm_break_hook);
	register_undef_hook(&thumb_break_hook);
	register_undef_hook(&thumb2_break_hook);
	return 0;
}

core_initcall(ptrace_break_init);

/*
 * Read the word at offset "off" into the "struct user".  We
 * actually access the pt_regs stored on the kernel stack.
 */
static int ptrace_read_user(struct task_struct *tsk, unsigned long off,
			    unsigned long __user *ret)
{
	unsigned long tmp;

	if (off & 3)
		return -EIO;

	tmp = 0;
	if (off == PT_TEXT_ADDR)
		tmp = tsk->mm->start_code;
	else if (off == PT_DATA_ADDR)
		tmp = tsk->mm->start_data;
	else if (off == PT_TEXT_END_ADDR)
		tmp = tsk->mm->end_code;
	else if (off < sizeof(struct pt_regs))
		tmp = get_user_reg(tsk, off >> 2);
	else if (off >= sizeof(struct user))
		return -EIO;

	return put_user(tmp, ret);
}

/*
 * Write the word at offset "off" into "struct user".  We
 * actually access the pt_regs stored on the kernel stack.
 */
static int ptrace_write_user(struct task_struct *tsk, unsigned long off,
			     unsigned long val)
{
	if (off & 3 || off >= sizeof(struct user))
		return -EIO;

	if (off >= sizeof(struct pt_regs))
		return 0;

	return put_user_reg(tsk, off >> 2, val);
}

#ifdef CONFIG_IWMMXT

/*
 * Get the child iWMMXt state.
 */
static int ptrace_getwmmxregs(struct task_struct *tsk, void __user *ufp)
{
	struct thread_info *thread = task_thread_info(tsk);

	if (!test_ti_thread_flag(thread, TIF_USING_IWMMXT))
		return -ENODATA;
	iwmmxt_task_disable(thread);  /* force it to ram */
	return copy_to_user(ufp, &thread->fpstate.iwmmxt, IWMMXT_SIZE)
		? -EFAULT : 0;
}

/*
 * Set the child iWMMXt state.
 */
static int ptrace_setwmmxregs(struct task_struct *tsk, void __user *ufp)
{
	struct thread_info *thread = task_thread_info(tsk);

	if (!test_ti_thread_flag(thread, TIF_USING_IWMMXT))
		return -EACCES;
	iwmmxt_task_release(thread);  /* force a reload */
	return copy_from_user(&thread->fpstate.iwmmxt, ufp, IWMMXT_SIZE)
		? -EFAULT : 0;
}

#endif

#ifdef CONFIG_HAVE_HW_BREAKPOINT
/*
 * Convert a virtual register number into an index for a thread_info
 * breakpoint array. Breakpoints are identified using positive numbers
 * whilst watchpoints are negative. The registers are laid out as pairs
 * of (address, control), each pair mapping to a unique hw_breakpoint struct.
 * Register 0 is reserved for describing resource information.
 */
static int ptrace_hbp_num_to_idx(long num)
{
	if (num < 0)
		num = (ARM_MAX_BRP << 1) - num;
	return (num - 1) >> 1;
}

/*
 * Returns the virtual register number for the address of the
 * breakpoint at index idx.
 */
static long ptrace_hbp_idx_to_num(int idx)
{
	long mid = ARM_MAX_BRP << 1;
	long num = (idx << 1) + 1;
	return num > mid ? mid - num : num;
}

/*
 * Handle hitting a HW-breakpoint.
 */
static void ptrace_hbptriggered(struct perf_event *bp,
				     struct perf_sample_data *data,
				     struct pt_regs *regs)
{
	struct arch_hw_breakpoint *bkpt = counter_arch_bp(bp);
	long num;
	int i;

	for (i = 0; i < ARM_MAX_HBP_SLOTS; ++i)
		if (current->thread.debug.hbp[i] == bp)
			break;

	num = (i == ARM_MAX_HBP_SLOTS) ? 0 : ptrace_hbp_idx_to_num(i);

	force_sig_ptrace_errno_trap((int)num, (void __user *)(bkpt->trigger));
}

/*
 * Set ptrace breakpoint pointers to zero for this task.
 * This is required in order to prevent child processes from unregistering
 * breakpoints held by their parent.
 */
void clear_ptrace_hw_breakpoint(struct task_struct *tsk)
{
	memset(tsk->thread.debug.hbp, 0, sizeof(tsk->thread.debug.hbp));
}

/*
 * Unregister breakpoints from this task and reset the pointers in
 * the thread_struct.
 */
void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
{
	int i;
	struct thread_struct *t = &tsk->thread;

	for (i = 0; i < ARM_MAX_HBP_SLOTS; i++) {
		if (t->debug.hbp[i]) {
			unregister_hw_breakpoint(t->debug.hbp[i]);
			t->debug.hbp[i] = NULL;
		}
	}
}

static u32 ptrace_get_hbp_resource_info(void)
{
	u8 num_brps, num_wrps, debug_arch, wp_len;
	u32 reg = 0;

	num_brps	= hw_breakpoint_slots(TYPE_INST);
	num_wrps	= hw_breakpoint_slots(TYPE_DATA);
	debug_arch	= arch_get_debug_arch();
	wp_len		= arch_get_max_wp_len();

	reg		|= debug_arch;
	reg		<<= 8;
	reg		|= wp_len;
	reg		<<= 8;
	reg		|= num_wrps;
	reg		<<= 8;
	reg		|= num_brps;

	return reg;
}

static struct perf_event *ptrace_hbp_create(struct task_struct *tsk, int type)
{
	struct perf_event_attr attr;

	ptrace_breakpoint_init(&attr);

	/* Initialise fields to sane defaults. */
	attr.bp_addr	= 0;
	attr.bp_len	= HW_BREAKPOINT_LEN_4;
	attr.bp_type	= type;
	attr.disabled	= 1;

	return register_user_hw_breakpoint(&attr, ptrace_hbptriggered, NULL,
					   tsk);
}

static int ptrace_gethbpregs(struct task_struct *tsk, long num,
			     unsigned long  __user *data)
{
	u32 reg;
	int idx, ret = 0;
	struct perf_event *bp;
	struct arch_hw_breakpoint_ctrl arch_ctrl;

	if (num == 0) {
		reg = ptrace_get_hbp_resource_info();
	} else {
		idx = ptrace_hbp_num_to_idx(num);
		if (idx < 0 || idx >= ARM_MAX_HBP_SLOTS) {
			ret = -EINVAL;
			goto out;
		}

		bp = tsk->thread.debug.hbp[idx];
		if (!bp) {
			reg = 0;
			goto put;
		}

		arch_ctrl = counter_arch_bp(bp)->ctrl;

		/*
		 * Fix up the len because we may have adjusted it
		 * to compensate for an unaligned address.
		 */
		while (!(arch_ctrl.len & 0x1))
			arch_ctrl.len >>= 1;

		if (num & 0x1)
			reg = bp->attr.bp_addr;
		else
			reg = encode_ctrl_reg(arch_ctrl);
	}

put:
	if (put_user(reg, data))
		ret = -EFAULT;

out:
	return ret;
}

static int ptrace_sethbpregs(struct task_struct *tsk, long num,
			     unsigned long __user *data)
{
	int idx, gen_len, gen_type, implied_type, ret = 0;
	u32 user_val;
	struct perf_event *bp;
	struct arch_hw_breakpoint_ctrl ctrl;
	struct perf_event_attr attr;

	if (num == 0)
		goto out;
	else if (num < 0)
		implied_type = HW_BREAKPOINT_RW;
	else
		implied_type = HW_BREAKPOINT_X;

	idx = ptrace_hbp_num_to_idx(num);
	if (idx < 0 || idx >= ARM_MAX_HBP_SLOTS) {
		ret = -EINVAL;
		goto out;
	}

	if (get_user(user_val, data)) {
		ret = -EFAULT;
		goto out;
	}

	bp = tsk->thread.debug.hbp[idx];
	if (!bp) {
		bp = ptrace_hbp_create(tsk, implied_type);
		if (IS_ERR(bp)) {
			ret = PTR_ERR(bp);
			goto out;
		}
		tsk->thread.debug.hbp[idx] = bp;
	}

	attr = bp->attr;

	if (num & 0x1) {
		/* Address */
		attr.bp_addr	= user_val;
	} else {
		/* Control */
		decode_ctrl_reg(user_val, &ctrl);
		ret = arch_bp_generic_fields(ctrl, &gen_len, &gen_type);
		if (ret)
			goto out;

		if ((gen_type & implied_type) != gen_type) {
			ret = -EINVAL;
			goto out;
		}

		attr.bp_len	= gen_len;
		attr.bp_type	= gen_type;
		attr.disabled	= !ctrl.enabled;
	}

	ret = modify_user_hw_breakpoint(bp, &attr);
out:
	return ret;
}
#endif

/* regset get/set implementations */

static int gpr_get(struct task_struct *target,
		   const struct user_regset *regset,
		   struct membuf to)
{
	return membuf_write(&to, task_pt_regs(target), sizeof(struct pt_regs));
}

static int gpr_set(struct task_struct *target,
		   const struct user_regset *regset,
		   unsigned int pos, unsigned int count,
		   const void *kbuf, const void __user *ubuf)
{
	int ret;
	struct pt_regs newregs = *task_pt_regs(target);

	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
				 &newregs,
				 0, sizeof(newregs));
	if (ret)
		return ret;

	if (!valid_user_regs(&newregs))
		return -EINVAL;

	*task_pt_regs(target) = newregs;
	return 0;
}

static int fpa_get(struct task_struct *target,
		   const struct user_regset *regset,
		   struct membuf to)
{
	return membuf_write(&to, &task_thread_info(target)->fpstate,
				 sizeof(struct user_fp));
}

static int fpa_set(struct task_struct *target,
		   const struct user_regset *regset,
		   unsigned int pos, unsigned int count,
		   const void *kbuf, const void __user *ubuf)
{
	struct thread_info *thread = task_thread_info(target);

	thread->used_cp[1] = thread->used_cp[2] = 1;

	return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
		&thread->fpstate,
		0, sizeof(struct user_fp));
}

#ifdef CONFIG_VFP
/*
 * VFP register get/set implementations.
 *
 * With respect to the kernel, struct user_fp is divided into three chunks:
 * 16 or 32 real VFP registers (d0-d15 or d0-31)
 *	These are transferred to/from the real registers in the task's
 *	vfp_hard_struct.  The number of registers depends on the kernel
 *	configuration.
 *
 * 16 or 0 fake VFP registers (d16-d31 or empty)
 *	i.e., the user_vfp structure has space for 32 registers even if
 *	the kernel doesn't have them all.
 *
 *	vfp_get() reads this chunk as zero where applicable
 *	vfp_set() ignores this chunk
 *
 * 1 word for the FPSCR
 */
static int vfp_get(struct task_struct *target,
		   const struct user_regset *regset,
		   struct membuf to)
{
	struct thread_info *thread = task_thread_info(target);
	struct vfp_hard_struct const *vfp = &thread->vfpstate.hard;
	const size_t user_fpscr_offset = offsetof(struct user_vfp, fpscr);

	vfp_sync_hwstate(thread);

	membuf_write(&to, vfp->fpregs, sizeof(vfp->fpregs));
	membuf_zero(&to, user_fpscr_offset - sizeof(vfp->fpregs));
	return membuf_store(&to, vfp->fpscr);
}

/*
 * For vfp_set() a read-modify-write is done on the VFP registers,
 * in order to avoid writing back a half-modified set of registers on
 * failure.
 */
static int vfp_set(struct task_struct *target,
			  const struct user_regset *regset,
			  unsigned int pos, unsigned int count,
			  const void *kbuf, const void __user *ubuf)
{
	int ret;
	struct thread_info *thread = task_thread_info(target);
	struct vfp_hard_struct new_vfp;
	const size_t user_fpregs_offset = offsetof(struct user_vfp, fpregs);
	const size_t user_fpscr_offset = offsetof(struct user_vfp, fpscr);

	vfp_sync_hwstate(thread);
	new_vfp = thread->vfpstate.hard;

	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
				  &new_vfp.fpregs,
				  user_fpregs_offset,
				  user_fpregs_offset + sizeof(new_vfp.fpregs));
	if (ret)
		return ret;

	ret = user_regset_copyin_ignore(&pos, &count, &kbuf, &ubuf,
				user_fpregs_offset + sizeof(new_vfp.fpregs),
				user_fpscr_offset);
	if (ret)
		return ret;

	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
				 &new_vfp.fpscr,
				 user_fpscr_offset,
				 user_fpscr_offset + sizeof(new_vfp.fpscr));
	if (ret)
		return ret;

	thread->vfpstate.hard = new_vfp;
	vfp_flush_hwstate(thread);

	return 0;
}
#endif /* CONFIG_VFP */

enum arm_regset {
	REGSET_GPR,
	REGSET_FPR,
#ifdef CONFIG_VFP
	REGSET_VFP,
#endif
};

static const struct user_regset arm_regsets[] = {
	[REGSET_GPR] = {
		.core_note_type = NT_PRSTATUS,
		.n = ELF_NGREG,
		.size = sizeof(u32),
		.align = sizeof(u32),
		.regset_get = gpr_get,
		.set = gpr_set
	},
	[REGSET_FPR] = {
		/*
		 * For the FPA regs in fpstate, the real fields are a mixture
		 * of sizes, so pretend that the registers are word-sized:
		 */
		.core_note_type = NT_PRFPREG,
		.n = sizeof(struct user_fp) / sizeof(u32),
		.size = sizeof(u32),
		.align = sizeof(u32),
		.regset_get = fpa_get,
		.set = fpa_set
	},
#ifdef CONFIG_VFP
	[REGSET_VFP] = {
		/*
		 * Pretend that the VFP regs are word-sized, since the FPSCR is
		 * a single word dangling at the end of struct user_vfp:
		 */
		.core_note_type = NT_ARM_VFP,
		.n = ARM_VFPREGS_SIZE / sizeof(u32),
		.size = sizeof(u32),
		.align = sizeof(u32),
		.regset_get = vfp_get,
		.set = vfp_set
	},
#endif /* CONFIG_VFP */
};

static const struct user_regset_view user_arm_view = {
	.name = "arm", .e_machine = ELF_ARCH, .ei_osabi = ELF_OSABI,
	.regsets = arm_regsets, .n = ARRAY_SIZE(arm_regsets)
};

const struct user_regset_view *task_user_regset_view(struct task_struct *task)
{
	return &user_arm_view;
}

long arch_ptrace(struct task_struct *child, long request,
		 unsigned long addr, unsigned long data)
{
	int ret;
	unsigned long __user *datap = (unsigned long __user *) data;

	switch (request) {
		case PTRACE_PEEKUSR:
			ret = ptrace_read_user(child, addr, datap);
			break;

		case PTRACE_POKEUSR:
			ret = ptrace_write_user(child, addr, data);
			break;

		case PTRACE_GETREGS:
			ret = copy_regset_to_user(child,
						  &user_arm_view, REGSET_GPR,
						  0, sizeof(struct pt_regs),
						  datap);
			break;

		case PTRACE_SETREGS:
			ret = copy_regset_from_user(child,
						    &user_arm_view, REGSET_GPR,
						    0, sizeof(struct pt_regs),
						    datap);
			break;

		case PTRACE_GETFPREGS:
			ret = copy_regset_to_user(child,
						  &user_arm_view, REGSET_FPR,
						  0, sizeof(union fp_state),
						  datap);
			break;

		case PTRACE_SETFPREGS:
			ret = copy_regset_from_user(child,
						    &user_arm_view, REGSET_FPR,
						    0, sizeof(union fp_state),
						    datap);
			break;

#ifdef CONFIG_IWMMXT
		case PTRACE_GETWMMXREGS:
			ret = ptrace_getwmmxregs(child, datap);
			break;

		case PTRACE_SETWMMXREGS:
			ret = ptrace_setwmmxregs(child, datap);
			break;
#endif

		case PTRACE_GET_THREAD_AREA:
			ret = put_user(task_thread_info(child)->tp_value[0],
				       datap);
			break;

		case PTRACE_SET_SYSCALL:
			if (data != -1)
				data &= __NR_SYSCALL_MASK;
			task_thread_info(child)->abi_syscall = data;
			ret = 0;
			break;

#ifdef CONFIG_VFP
		case PTRACE_GETVFPREGS:
			ret = copy_regset_to_user(child,
						  &user_arm_view, REGSET_VFP,
						  0, ARM_VFPREGS_SIZE,
						  datap);
			break;

		case PTRACE_SETVFPREGS:
			ret = copy_regset_from_user(child,
						    &user_arm_view, REGSET_VFP,
						    0, ARM_VFPREGS_SIZE,
						    datap);
			break;
#endif

#ifdef CONFIG_HAVE_HW_BREAKPOINT
		case PTRACE_GETHBPREGS:
			ret = ptrace_gethbpregs(child, addr,
						(unsigned long __user *)data);
			break;
		case PTRACE_SETHBPREGS:
			ret = ptrace_sethbpregs(child, addr,
						(unsigned long __user *)data);
			break;
#endif

		default:
			ret = ptrace_request(child, request, addr, data);
			break;
	}

	return ret;
}

enum ptrace_syscall_dir {
	PTRACE_SYSCALL_ENTER = 0,
	PTRACE_SYSCALL_EXIT,
};

static void report_syscall(struct pt_regs *regs, enum ptrace_syscall_dir dir)
{
	unsigned long ip;

	/*
	 * IP is used to denote syscall entry/exit:
	 * IP = 0 -> entry, =1 -> exit
	 */
	ip = regs->ARM_ip;
	regs->ARM_ip = dir;

	if (dir == PTRACE_SYSCALL_EXIT)
		ptrace_report_syscall_exit(regs, 0);
	else if (ptrace_report_syscall_entry(regs))
		current_thread_info()->abi_syscall = -1;

	regs->ARM_ip = ip;
}

asmlinkage int syscall_trace_enter(struct pt_regs *regs)
{
	int scno;

	if (test_thread_flag(TIF_SYSCALL_TRACE))
		report_syscall(regs, PTRACE_SYSCALL_ENTER);

	/* Do seccomp after ptrace; syscall may have changed. */
#ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
	if (secure_computing() == -1)
		return -1;
#else
	/* XXX: remove this once OABI gets fixed */
	secure_computing_strict(syscall_get_nr(current, regs));
#endif

	/* Tracer or seccomp may have changed syscall. */
	scno = syscall_get_nr(current, regs);

	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
		trace_sys_enter(regs, scno);

	audit_syscall_entry(scno, regs->ARM_r0, regs->ARM_r1, regs->ARM_r2,
			    regs->ARM_r3);

	return scno;
}

asmlinkage void syscall_trace_exit(struct pt_regs *regs)
{
	/*
	 * Audit the syscall before anything else, as a debugger may
	 * come in and change the current registers.
	 */
	audit_syscall_exit(regs);

	/*
	 * Note that we haven't updated the ->syscall field for the
	 * current thread. This isn't a problem because it will have
	 * been set on syscall entry and there hasn't been an opportunity
	 * for a PTRACE_SET_SYSCALL since then.
	 */
	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
		trace_sys_exit(regs, regs_return_value(regs));

	if (test_thread_flag(TIF_SYSCALL_TRACE))
		report_syscall(regs, PTRACE_SYSCALL_EXIT);
}