/*
 * Just-In-Time compiler for eBPF filters on 32bit ARM
 *
 * Copyright (c) 2017 Shubham Bansal <illusionist.neo@gmail.com>
 * Copyright (c) 2011 Mircea Gherzan <mgherzan@gmail.com>
 *
 * 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 of the License.
 */

#include <linux/bpf.h>
#include <linux/bitops.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/filter.h>
#include <linux/netdevice.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/if_vlan.h>

#include <asm/cacheflush.h>
#include <asm/hwcap.h>
#include <asm/opcodes.h>

#include "bpf_jit_32.h"

int bpf_jit_enable __read_mostly;

#define STACK_OFFSET(k)	(k)
#define TMP_REG_1	(MAX_BPF_JIT_REG + 0)	/* TEMP Register 1 */
#define TMP_REG_2	(MAX_BPF_JIT_REG + 1)	/* TEMP Register 2 */
#define TCALL_CNT	(MAX_BPF_JIT_REG + 2)	/* Tail Call Count */

/* Flags used for JIT optimization */
#define SEEN_CALL	(1 << 0)

#define FLAG_IMM_OVERFLOW	(1 << 0)

/*
 * Map eBPF registers to ARM 32bit registers or stack scratch space.
 *
 * 1. First argument is passed using the arm 32bit registers and rest of the
 * arguments are passed on stack scratch space.
 * 2. First callee-saved arugument is mapped to arm 32 bit registers and rest
 * arguments are mapped to scratch space on stack.
 * 3. We need two 64 bit temp registers to do complex operations on eBPF
 * registers.
 *
 * As the eBPF registers are all 64 bit registers and arm has only 32 bit
 * registers, we have to map each eBPF registers with two arm 32 bit regs or
 * scratch memory space and we have to build eBPF 64 bit register from those.
 *
 */
static const u8 bpf2a32[][2] = {
	/* return value from in-kernel function, and exit value from eBPF */
	[BPF_REG_0] = {ARM_R1, ARM_R0},
	/* arguments from eBPF program to in-kernel function */
	[BPF_REG_1] = {ARM_R3, ARM_R2},
	/* Stored on stack scratch space */
	[BPF_REG_2] = {STACK_OFFSET(0), STACK_OFFSET(4)},
	[BPF_REG_3] = {STACK_OFFSET(8), STACK_OFFSET(12)},
	[BPF_REG_4] = {STACK_OFFSET(16), STACK_OFFSET(20)},
	[BPF_REG_5] = {STACK_OFFSET(24), STACK_OFFSET(28)},
	/* callee saved registers that in-kernel function will preserve */
	[BPF_REG_6] = {ARM_R5, ARM_R4},
	/* Stored on stack scratch space */
	[BPF_REG_7] = {STACK_OFFSET(32), STACK_OFFSET(36)},
	[BPF_REG_8] = {STACK_OFFSET(40), STACK_OFFSET(44)},
	[BPF_REG_9] = {STACK_OFFSET(48), STACK_OFFSET(52)},
	/* Read only Frame Pointer to access Stack */
	[BPF_REG_FP] = {STACK_OFFSET(56), STACK_OFFSET(60)},
	/* Temporary Register for internal BPF JIT, can be used
	 * for constant blindings and others.
	 */
	[TMP_REG_1] = {ARM_R7, ARM_R6},
	[TMP_REG_2] = {ARM_R10, ARM_R8},
	/* Tail call count. Stored on stack scratch space. */
	[TCALL_CNT] = {STACK_OFFSET(64), STACK_OFFSET(68)},
	/* temporary register for blinding constants.
	 * Stored on stack scratch space.
	 */
	[BPF_REG_AX] = {STACK_OFFSET(72), STACK_OFFSET(76)},
};

#define	dst_lo	dst[1]
#define dst_hi	dst[0]
#define src_lo	src[1]
#define src_hi	src[0]

/*
 * JIT Context:
 *
 * prog			:	bpf_prog
 * idx			:	index of current last JITed instruction.
 * prologue_bytes	:	bytes used in prologue.
 * epilogue_offset	:	offset of epilogue starting.
 * seen			:	bit mask used for JIT optimization.
 * offsets		:	array of eBPF instruction offsets in
 *				JITed code.
 * target		:	final JITed code.
 * epilogue_bytes	:	no of bytes used in epilogue.
 * imm_count		:	no of immediate counts used for global
 *				variables.
 * imms			:	array of global variable addresses.
 */

struct jit_ctx {
	const struct bpf_prog *prog;
	unsigned int idx;
	unsigned int prologue_bytes;
	unsigned int epilogue_offset;
	u32 seen;
	u32 flags;
	u32 *offsets;
	u32 *target;
	u32 stack_size;
#if __LINUX_ARM_ARCH__ < 7
	u16 epilogue_bytes;
	u16 imm_count;
	u32 *imms;
#endif
};

/*
 * Wrappers which handle both OABI and EABI and assures Thumb2 interworking
 * (where the assembly routines like __aeabi_uidiv could cause problems).
 */
static u32 jit_udiv32(u32 dividend, u32 divisor)
{
	return dividend / divisor;
}

static u32 jit_mod32(u32 dividend, u32 divisor)
{
	return dividend % divisor;
}

static inline void _emit(int cond, u32 inst, struct jit_ctx *ctx)
{
	inst |= (cond << 28);
	inst = __opcode_to_mem_arm(inst);

	if (ctx->target != NULL)
		ctx->target[ctx->idx] = inst;

	ctx->idx++;
}

/*
 * Emit an instruction that will be executed unconditionally.
 */
static inline void emit(u32 inst, struct jit_ctx *ctx)
{
	_emit(ARM_COND_AL, inst, ctx);
}

/*
 * Checks if immediate value can be converted to imm12(12 bits) value.
 */
static int16_t imm8m(u32 x)
{
	u32 rot;

	for (rot = 0; rot < 16; rot++)
		if ((x & ~ror32(0xff, 2 * rot)) == 0)
			return rol32(x, 2 * rot) | (rot << 8);
	return -1;
}

/*
 * Initializes the JIT space with undefined instructions.
 */
static void jit_fill_hole(void *area, unsigned int size)
{
	u32 *ptr;
	/* We are guaranteed to have aligned memory. */
	for (ptr = area; size >= sizeof(u32); size -= sizeof(u32))
		*ptr++ = __opcode_to_mem_arm(ARM_INST_UDF);
}

/* Stack must be multiples of 16 Bytes */
#define STACK_ALIGN(sz) (((sz) + 3) & ~3)

/* Stack space for BPF_REG_2, BPF_REG_3, BPF_REG_4,
 * BPF_REG_5, BPF_REG_7, BPF_REG_8, BPF_REG_9,
 * BPF_REG_FP and Tail call counts.
 */
#define SCRATCH_SIZE 80

/* total stack size used in JITed code */
#define _STACK_SIZE \
	(ctx->prog->aux->stack_depth + \
	 + SCRATCH_SIZE + \
	 + 4 /* extra for skb_copy_bits buffer */)

#define STACK_SIZE STACK_ALIGN(_STACK_SIZE)

/* Get the offset of eBPF REGISTERs stored on scratch space. */
#define STACK_VAR(off) (STACK_SIZE-off-4)

/* Offset of skb_copy_bits buffer */
#define SKB_BUFFER STACK_VAR(SCRATCH_SIZE)

#if __LINUX_ARM_ARCH__ < 7

static u16 imm_offset(u32 k, struct jit_ctx *ctx)
{
	unsigned int i = 0, offset;
	u16 imm;

	/* on the "fake" run we just count them (duplicates included) */
	if (ctx->target == NULL) {
		ctx->imm_count++;
		return 0;
	}

	while ((i < ctx->imm_count) && ctx->imms[i]) {
		if (ctx->imms[i] == k)
			break;
		i++;
	}

	if (ctx->imms[i] == 0)
		ctx->imms[i] = k;

	/* constants go just after the epilogue */
	offset =  ctx->offsets[ctx->prog->len - 1] * 4;
	offset += ctx->prologue_bytes;
	offset += ctx->epilogue_bytes;
	offset += i * 4;

	ctx->target[offset / 4] = k;

	/* PC in ARM mode == address of the instruction + 8 */
	imm = offset - (8 + ctx->idx * 4);

	if (imm & ~0xfff) {
		/*
		 * literal pool is too far, signal it into flags. we
		 * can only detect it on the second pass unfortunately.
		 */
		ctx->flags |= FLAG_IMM_OVERFLOW;
		return 0;
	}

	return imm;
}

#endif /* __LINUX_ARM_ARCH__ */

static inline int bpf2a32_offset(int bpf_to, int bpf_from,
				 const struct jit_ctx *ctx) {
	int to, from;

	if (ctx->target == NULL)
		return 0;
	to = ctx->offsets[bpf_to];
	from = ctx->offsets[bpf_from];

	return to - from - 1;
}

/*
 * Move an immediate that's not an imm8m to a core register.
 */
static inline void emit_mov_i_no8m(const u8 rd, u32 val, struct jit_ctx *ctx)
{
#if __LINUX_ARM_ARCH__ < 7
	emit(ARM_LDR_I(rd, ARM_PC, imm_offset(val, ctx)), ctx);
#else
	emit(ARM_MOVW(rd, val & 0xffff), ctx);
	if (val > 0xffff)
		emit(ARM_MOVT(rd, val >> 16), ctx);
#endif
}

static inline void emit_mov_i(const u8 rd, u32 val, struct jit_ctx *ctx)
{
	int imm12 = imm8m(val);

	if (imm12 >= 0)
		emit(ARM_MOV_I(rd, imm12), ctx);
	else
		emit_mov_i_no8m(rd, val, ctx);
}

static inline void emit_blx_r(u8 tgt_reg, struct jit_ctx *ctx)
{
	ctx->seen |= SEEN_CALL;
#if __LINUX_ARM_ARCH__ < 5
	emit(ARM_MOV_R(ARM_LR, ARM_PC), ctx);

	if (elf_hwcap & HWCAP_THUMB)
		emit(ARM_BX(tgt_reg), ctx);
	else
		emit(ARM_MOV_R(ARM_PC, tgt_reg), ctx);
#else
	emit(ARM_BLX_R(tgt_reg), ctx);
#endif
}

static inline int epilogue_offset(const struct jit_ctx *ctx)
{
	int to, from;
	/* No need for 1st dummy run */
	if (ctx->target == NULL)
		return 0;
	to = ctx->epilogue_offset;
	from = ctx->idx;

	return to - from - 2;
}

static inline void emit_udivmod(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx, u8 op)
{
	const u8 *tmp = bpf2a32[TMP_REG_1];
	s32 jmp_offset;

	/* checks if divisor is zero or not. If it is, then
	 * exit directly.
	 */
	emit(ARM_CMP_I(rn, 0), ctx);
	_emit(ARM_COND_EQ, ARM_MOV_I(ARM_R0, 0), ctx);
	jmp_offset = epilogue_offset(ctx);
	_emit(ARM_COND_EQ, ARM_B(jmp_offset), ctx);
#if __LINUX_ARM_ARCH__ == 7
	if (elf_hwcap & HWCAP_IDIVA) {
		if (op == BPF_DIV)
			emit(ARM_UDIV(rd, rm, rn), ctx);
		else {
			emit(ARM_UDIV(ARM_IP, rm, rn), ctx);
			emit(ARM_MLS(rd, rn, ARM_IP, rm), ctx);
		}
		return;
	}
#endif

	/*
	 * For BPF_ALU | BPF_DIV | BPF_K instructions
	 * As ARM_R1 and ARM_R0 contains 1st argument of bpf
	 * function, we need to save it on caller side to save
	 * it from getting destroyed within callee.
	 * After the return from the callee, we restore ARM_R0
	 * ARM_R1.
	 */
	if (rn != ARM_R1) {
		emit(ARM_MOV_R(tmp[0], ARM_R1), ctx);
		emit(ARM_MOV_R(ARM_R1, rn), ctx);
	}
	if (rm != ARM_R0) {
		emit(ARM_MOV_R(tmp[1], ARM_R0), ctx);
		emit(ARM_MOV_R(ARM_R0, rm), ctx);
	}

	/* Call appropriate function */
	ctx->seen |= SEEN_CALL;
	emit_mov_i(ARM_IP, op == BPF_DIV ?
		   (u32)jit_udiv32 : (u32)jit_mod32, ctx);
	emit_blx_r(ARM_IP, ctx);

	/* Save return value */
	if (rd != ARM_R0)
		emit(ARM_MOV_R(rd, ARM_R0), ctx);

	/* Restore ARM_R0 and ARM_R1 */
	if (rn != ARM_R1)
		emit(ARM_MOV_R(ARM_R1, tmp[0]), ctx);
	if (rm != ARM_R0)
		emit(ARM_MOV_R(ARM_R0, tmp[1]), ctx);
}

/* Checks whether BPF register is on scratch stack space or not. */
static inline bool is_on_stack(u8 bpf_reg)
{
	static u8 stack_regs[] = {BPF_REG_AX, BPF_REG_3, BPF_REG_4, BPF_REG_5,
				BPF_REG_7, BPF_REG_8, BPF_REG_9, TCALL_CNT,
				BPF_REG_2, BPF_REG_FP};
	int i, reg_len = sizeof(stack_regs);

	for (i = 0 ; i < reg_len ; i++) {
		if (bpf_reg == stack_regs[i])
			return true;
	}
	return false;
}

static inline void emit_a32_mov_i(const u8 dst, const u32 val,
				  bool dstk, struct jit_ctx *ctx)
{
	const u8 *tmp = bpf2a32[TMP_REG_1];

	if (dstk) {
		emit_mov_i(tmp[1], val, ctx);
		emit(ARM_STR_I(tmp[1], ARM_SP, STACK_VAR(dst)), ctx);
	} else {
		emit_mov_i(dst, val, ctx);
	}
}

/* Sign extended move */
static inline void emit_a32_mov_i64(const bool is64, const u8 dst[],
				  const u32 val, bool dstk,
				  struct jit_ctx *ctx) {
	u32 hi = 0;

	if (is64 && (val & (1<<31)))
		hi = (u32)~0;
	emit_a32_mov_i(dst_lo, val, dstk, ctx);
	emit_a32_mov_i(dst_hi, hi, dstk, ctx);
}

static inline void emit_a32_add_r(const u8 dst, const u8 src,
			      const bool is64, const bool hi,
			      struct jit_ctx *ctx) {
	/* 64 bit :
	 *	adds dst_lo, dst_lo, src_lo
	 *	adc dst_hi, dst_hi, src_hi
	 * 32 bit :
	 *	add dst_lo, dst_lo, src_lo
	 */
	if (!hi && is64)
		emit(ARM_ADDS_R(dst, dst, src), ctx);
	else if (hi && is64)
		emit(ARM_ADC_R(dst, dst, src), ctx);
	else
		emit(ARM_ADD_R(dst, dst, src), ctx);
}

static inline void emit_a32_sub_r(const u8 dst, const u8 src,
				  const bool is64, const bool hi,
				  struct jit_ctx *ctx) {
	/* 64 bit :
	 *	subs dst_lo, dst_lo, src_lo
	 *	sbc dst_hi, dst_hi, src_hi
	 * 32 bit :
	 *	sub dst_lo, dst_lo, src_lo
	 */
	if (!hi && is64)
		emit(ARM_SUBS_R(dst, dst, src), ctx);
	else if (hi && is64)
		emit(ARM_SBC_R(dst, dst, src), ctx);
	else
		emit(ARM_SUB_R(dst, dst, src), ctx);
}

static inline void emit_alu_r(const u8 dst, const u8 src, const bool is64,
			      const bool hi, const u8 op, struct jit_ctx *ctx){
	switch (BPF_OP(op)) {
	/* dst = dst + src */
	case BPF_ADD:
		emit_a32_add_r(dst, src, is64, hi, ctx);
		break;
	/* dst = dst - src */
	case BPF_SUB:
		emit_a32_sub_r(dst, src, is64, hi, ctx);
		break;
	/* dst = dst | src */
	case BPF_OR:
		emit(ARM_ORR_R(dst, dst, src), ctx);
		break;
	/* dst = dst & src */
	case BPF_AND:
		emit(ARM_AND_R(dst, dst, src), ctx);
		break;
	/* dst = dst ^ src */
	case BPF_XOR:
		emit(ARM_EOR_R(dst, dst, src), ctx);
		break;
	/* dst = dst * src */
	case BPF_MUL:
		emit(ARM_MUL(dst, dst, src), ctx);
		break;
	/* dst = dst << src */
	case BPF_LSH:
		emit(ARM_LSL_R(dst, dst, src), ctx);
		break;
	/* dst = dst >> src */
	case BPF_RSH:
		emit(ARM_LSR_R(dst, dst, src), ctx);
		break;
	/* dst = dst >> src (signed)*/
	case BPF_ARSH:
		emit(ARM_MOV_SR(dst, dst, SRTYPE_ASR, src), ctx);
		break;
	}
}

/* ALU operation (32 bit)
 * dst = dst (op) src
 */
static inline void emit_a32_alu_r(const u8 dst, const u8 src,
				  bool dstk, bool sstk,
				  struct jit_ctx *ctx, const bool is64,
				  const bool hi, const u8 op) {
	const u8 *tmp = bpf2a32[TMP_REG_1];
	u8 rn = sstk ? tmp[1] : src;

	if (sstk)
		emit(ARM_LDR_I(rn, ARM_SP, STACK_VAR(src)), ctx);

	/* ALU operation */
	if (dstk) {
		emit(ARM_LDR_I(tmp[0], ARM_SP, STACK_VAR(dst)), ctx);
		emit_alu_r(tmp[0], rn, is64, hi, op, ctx);
		emit(ARM_STR_I(tmp[0], ARM_SP, STACK_VAR(dst)), ctx);
	} else {
		emit_alu_r(dst, rn, is64, hi, op, ctx);
	}
}

/* ALU operation (64 bit) */
static inline void emit_a32_alu_r64(const bool is64, const u8 dst[],
				  const u8 src[], bool dstk,
				  bool sstk, struct jit_ctx *ctx,
				  const u8 op) {
	emit_a32_alu_r(dst_lo, src_lo, dstk, sstk, ctx, is64, false, op);
	if (is64)
		emit_a32_alu_r(dst_hi, src_hi, dstk, sstk, ctx, is64, true, op);
	else
		emit_a32_mov_i(dst_hi, 0, dstk, ctx);
}

/* dst = imm (4 bytes)*/
static inline void emit_a32_mov_r(const u8 dst, const u8 src,
				  bool dstk, bool sstk,
				  struct jit_ctx *ctx) {
	const u8 *tmp = bpf2a32[TMP_REG_1];
	u8 rt = sstk ? tmp[0] : src;

	if (sstk)
		emit(ARM_LDR_I(tmp[0], ARM_SP, STACK_VAR(src)), ctx);
	if (dstk)
		emit(ARM_STR_I(rt, ARM_SP, STACK_VAR(dst)), ctx);
	else
		emit(ARM_MOV_R(dst, rt), ctx);
}

/* dst = src */
static inline void emit_a32_mov_r64(const bool is64, const u8 dst[],
				  const u8 src[], bool dstk,
				  bool sstk, struct jit_ctx *ctx) {
	emit_a32_mov_r(dst_lo, src_lo, dstk, sstk, ctx);
	if (is64) {
		/* complete 8 byte move */
		emit_a32_mov_r(dst_hi, src_hi, dstk, sstk, ctx);
	} else {
		/* Zero out high 4 bytes */
		emit_a32_mov_i(dst_hi, 0, dstk, ctx);
	}
}

/* Shift operations */
static inline void emit_a32_alu_i(const u8 dst, const u32 val, bool dstk,
				struct jit_ctx *ctx, const u8 op) {
	const u8 *tmp = bpf2a32[TMP_REG_1];
	u8 rd = dstk ? tmp[0] : dst;

	if (dstk)
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst)), ctx);

	/* Do shift operation */
	switch (op) {
	case BPF_LSH:
		emit(ARM_LSL_I(rd, rd, val), ctx);
		break;
	case BPF_RSH:
		emit(ARM_LSR_I(rd, rd, val), ctx);
		break;
	case BPF_NEG:
		emit(ARM_RSB_I(rd, rd, val), ctx);
		break;
	}

	if (dstk)
		emit(ARM_STR_I(rd, ARM_SP, STACK_VAR(dst)), ctx);
}

/* dst = ~dst (64 bit) */
static inline void emit_a32_neg64(const u8 dst[], bool dstk,
				struct jit_ctx *ctx){
	const u8 *tmp = bpf2a32[TMP_REG_1];
	u8 rd = dstk ? tmp[1] : dst[1];
	u8 rm = dstk ? tmp[0] : dst[0];

	/* Setup Operand */
	if (dstk) {
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}

	/* Do Negate Operation */
	emit(ARM_RSBS_I(rd, rd, 0), ctx);
	emit(ARM_RSC_I(rm, rm, 0), ctx);

	if (dstk) {
		emit(ARM_STR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_STR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}
}

/* dst = dst << src */
static inline void emit_a32_lsh_r64(const u8 dst[], const u8 src[], bool dstk,
				    bool sstk, struct jit_ctx *ctx) {
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];

	/* Setup Operands */
	u8 rt = sstk ? tmp2[1] : src_lo;
	u8 rd = dstk ? tmp[1] : dst_lo;
	u8 rm = dstk ? tmp[0] : dst_hi;

	if (sstk)
		emit(ARM_LDR_I(rt, ARM_SP, STACK_VAR(src_lo)), ctx);
	if (dstk) {
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}

	/* Do LSH operation */
	emit(ARM_SUB_I(ARM_IP, rt, 32), ctx);
	emit(ARM_RSB_I(tmp2[0], rt, 32), ctx);
	/* As we are using ARM_LR */
	ctx->seen |= SEEN_CALL;
	emit(ARM_MOV_SR(ARM_LR, rm, SRTYPE_ASL, rt), ctx);
	emit(ARM_ORR_SR(ARM_LR, ARM_LR, rd, SRTYPE_ASL, ARM_IP), ctx);
	emit(ARM_ORR_SR(ARM_IP, ARM_LR, rd, SRTYPE_LSR, tmp2[0]), ctx);
	emit(ARM_MOV_SR(ARM_LR, rd, SRTYPE_ASL, rt), ctx);

	if (dstk) {
		emit(ARM_STR_I(ARM_LR, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_STR_I(ARM_IP, ARM_SP, STACK_VAR(dst_hi)), ctx);
	} else {
		emit(ARM_MOV_R(rd, ARM_LR), ctx);
		emit(ARM_MOV_R(rm, ARM_IP), ctx);
	}
}

/* dst = dst >> src (signed)*/
static inline void emit_a32_arsh_r64(const u8 dst[], const u8 src[], bool dstk,
				    bool sstk, struct jit_ctx *ctx) {
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	/* Setup Operands */
	u8 rt = sstk ? tmp2[1] : src_lo;
	u8 rd = dstk ? tmp[1] : dst_lo;
	u8 rm = dstk ? tmp[0] : dst_hi;

	if (sstk)
		emit(ARM_LDR_I(rt, ARM_SP, STACK_VAR(src_lo)), ctx);
	if (dstk) {
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}

	/* Do the ARSH operation */
	emit(ARM_RSB_I(ARM_IP, rt, 32), ctx);
	emit(ARM_SUBS_I(tmp2[0], rt, 32), ctx);
	/* As we are using ARM_LR */
	ctx->seen |= SEEN_CALL;
	emit(ARM_MOV_SR(ARM_LR, rd, SRTYPE_LSR, rt), ctx);
	emit(ARM_ORR_SR(ARM_LR, ARM_LR, rm, SRTYPE_ASL, ARM_IP), ctx);
	_emit(ARM_COND_MI, ARM_B(0), ctx);
	emit(ARM_ORR_SR(ARM_LR, ARM_LR, rm, SRTYPE_ASR, tmp2[0]), ctx);
	emit(ARM_MOV_SR(ARM_IP, rm, SRTYPE_ASR, rt), ctx);
	if (dstk) {
		emit(ARM_STR_I(ARM_LR, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_STR_I(ARM_IP, ARM_SP, STACK_VAR(dst_hi)), ctx);
	} else {
		emit(ARM_MOV_R(rd, ARM_LR), ctx);
		emit(ARM_MOV_R(rm, ARM_IP), ctx);
	}
}

/* dst = dst >> src */
static inline void emit_a32_lsr_r64(const u8 dst[], const u8 src[], bool dstk,
				     bool sstk, struct jit_ctx *ctx) {
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	/* Setup Operands */
	u8 rt = sstk ? tmp2[1] : src_lo;
	u8 rd = dstk ? tmp[1] : dst_lo;
	u8 rm = dstk ? tmp[0] : dst_hi;

	if (sstk)
		emit(ARM_LDR_I(rt, ARM_SP, STACK_VAR(src_lo)), ctx);
	if (dstk) {
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}

	/* Do LSH operation */
	emit(ARM_RSB_I(ARM_IP, rt, 32), ctx);
	emit(ARM_SUBS_I(tmp2[0], rt, 32), ctx);
	/* As we are using ARM_LR */
	ctx->seen |= SEEN_CALL;
	emit(ARM_MOV_SR(ARM_LR, rd, SRTYPE_LSR, rt), ctx);
	emit(ARM_ORR_SR(ARM_LR, ARM_LR, rm, SRTYPE_ASL, ARM_IP), ctx);
	emit(ARM_ORR_SR(ARM_LR, ARM_LR, rm, SRTYPE_LSR, tmp2[0]), ctx);
	emit(ARM_MOV_SR(ARM_IP, rm, SRTYPE_LSR, rt), ctx);
	if (dstk) {
		emit(ARM_STR_I(ARM_LR, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_STR_I(ARM_IP, ARM_SP, STACK_VAR(dst_hi)), ctx);
	} else {
		emit(ARM_MOV_R(rd, ARM_LR), ctx);
		emit(ARM_MOV_R(rm, ARM_IP), ctx);
	}
}

/* dst = dst << val */
static inline void emit_a32_lsh_i64(const u8 dst[], bool dstk,
				     const u32 val, struct jit_ctx *ctx){
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	/* Setup operands */
	u8 rd = dstk ? tmp[1] : dst_lo;
	u8 rm = dstk ? tmp[0] : dst_hi;

	if (dstk) {
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}

	/* Do LSH operation */
	if (val < 32) {
		emit(ARM_MOV_SI(tmp2[0], rm, SRTYPE_ASL, val), ctx);
		emit(ARM_ORR_SI(rm, tmp2[0], rd, SRTYPE_LSR, 32 - val), ctx);
		emit(ARM_MOV_SI(rd, rd, SRTYPE_ASL, val), ctx);
	} else {
		if (val == 32)
			emit(ARM_MOV_R(rm, rd), ctx);
		else
			emit(ARM_MOV_SI(rm, rd, SRTYPE_ASL, val - 32), ctx);
		emit(ARM_EOR_R(rd, rd, rd), ctx);
	}

	if (dstk) {
		emit(ARM_STR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_STR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}
}

/* dst = dst >> val */
static inline void emit_a32_lsr_i64(const u8 dst[], bool dstk,
				    const u32 val, struct jit_ctx *ctx) {
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	/* Setup operands */
	u8 rd = dstk ? tmp[1] : dst_lo;
	u8 rm = dstk ? tmp[0] : dst_hi;

	if (dstk) {
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}

	/* Do LSR operation */
	if (val < 32) {
		emit(ARM_MOV_SI(tmp2[1], rd, SRTYPE_LSR, val), ctx);
		emit(ARM_ORR_SI(rd, tmp2[1], rm, SRTYPE_ASL, 32 - val), ctx);
		emit(ARM_MOV_SI(rm, rm, SRTYPE_LSR, val), ctx);
	} else if (val == 32) {
		emit(ARM_MOV_R(rd, rm), ctx);
		emit(ARM_MOV_I(rm, 0), ctx);
	} else {
		emit(ARM_MOV_SI(rd, rm, SRTYPE_LSR, val - 32), ctx);
		emit(ARM_MOV_I(rm, 0), ctx);
	}

	if (dstk) {
		emit(ARM_STR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_STR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}
}

/* dst = dst >> val (signed) */
static inline void emit_a32_arsh_i64(const u8 dst[], bool dstk,
				     const u32 val, struct jit_ctx *ctx){
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	 /* Setup operands */
	u8 rd = dstk ? tmp[1] : dst_lo;
	u8 rm = dstk ? tmp[0] : dst_hi;

	if (dstk) {
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}

	/* Do ARSH operation */
	if (val < 32) {
		emit(ARM_MOV_SI(tmp2[1], rd, SRTYPE_LSR, val), ctx);
		emit(ARM_ORR_SI(rd, tmp2[1], rm, SRTYPE_ASL, 32 - val), ctx);
		emit(ARM_MOV_SI(rm, rm, SRTYPE_ASR, val), ctx);
	} else if (val == 32) {
		emit(ARM_MOV_R(rd, rm), ctx);
		emit(ARM_MOV_SI(rm, rm, SRTYPE_ASR, 31), ctx);
	} else {
		emit(ARM_MOV_SI(rd, rm, SRTYPE_ASR, val - 32), ctx);
		emit(ARM_MOV_SI(rm, rm, SRTYPE_ASR, 31), ctx);
	}

	if (dstk) {
		emit(ARM_STR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_STR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}
}

static inline void emit_a32_mul_r64(const u8 dst[], const u8 src[], bool dstk,
				    bool sstk, struct jit_ctx *ctx) {
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	/* Setup operands for multiplication */
	u8 rd = dstk ? tmp[1] : dst_lo;
	u8 rm = dstk ? tmp[0] : dst_hi;
	u8 rt = sstk ? tmp2[1] : src_lo;
	u8 rn = sstk ? tmp2[0] : src_hi;

	if (dstk) {
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	}
	if (sstk) {
		emit(ARM_LDR_I(rt, ARM_SP, STACK_VAR(src_lo)), ctx);
		emit(ARM_LDR_I(rn, ARM_SP, STACK_VAR(src_hi)), ctx);
	}

	/* Do Multiplication */
	emit(ARM_MUL(ARM_IP, rd, rn), ctx);
	emit(ARM_MUL(ARM_LR, rm, rt), ctx);
	/* As we are using ARM_LR */
	ctx->seen |= SEEN_CALL;
	emit(ARM_ADD_R(ARM_LR, ARM_IP, ARM_LR), ctx);

	emit(ARM_UMULL(ARM_IP, rm, rd, rt), ctx);
	emit(ARM_ADD_R(rm, ARM_LR, rm), ctx);
	if (dstk) {
		emit(ARM_STR_I(ARM_IP, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit(ARM_STR_I(rm, ARM_SP, STACK_VAR(dst_hi)), ctx);
	} else {
		emit(ARM_MOV_R(rd, ARM_IP), ctx);
	}
}

/* *(size *)(dst + off) = src */
static inline void emit_str_r(const u8 dst, const u8 src, bool dstk,
			      const s32 off, struct jit_ctx *ctx, const u8 sz){
	const u8 *tmp = bpf2a32[TMP_REG_1];
	u8 rd = dstk ? tmp[1] : dst;

	if (dstk)
		emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst)), ctx);
	if (off) {
		emit_a32_mov_i(tmp[0], off, false, ctx);
		emit(ARM_ADD_R(tmp[0], rd, tmp[0]), ctx);
		rd = tmp[0];
	}
	switch (sz) {
	case BPF_W:
		/* Store a Word */
		emit(ARM_STR_I(src, rd, 0), ctx);
		break;
	case BPF_H:
		/* Store a HalfWord */
		emit(ARM_STRH_I(src, rd, 0), ctx);
		break;
	case BPF_B:
		/* Store a Byte */
		emit(ARM_STRB_I(src, rd, 0), ctx);
		break;
	}
}

/* dst = *(size*)(src + off) */
static inline void emit_ldx_r(const u8 dst, const u8 src, bool dstk,
			      const s32 off, struct jit_ctx *ctx, const u8 sz){
	const u8 *tmp = bpf2a32[TMP_REG_1];
	u8 rd = dstk ? tmp[1] : dst;
	u8 rm = src;

	if (off) {
		emit_a32_mov_i(tmp[0], off, false, ctx);
		emit(ARM_ADD_R(tmp[0], tmp[0], src), ctx);
		rm = tmp[0];
	}
	switch (sz) {
	case BPF_W:
		/* Load a Word */
		emit(ARM_LDR_I(rd, rm, 0), ctx);
		break;
	case BPF_H:
		/* Load a HalfWord */
		emit(ARM_LDRH_I(rd, rm, 0), ctx);
		break;
	case BPF_B:
		/* Load a Byte */
		emit(ARM_LDRB_I(rd, rm, 0), ctx);
		break;
	}
	if (dstk)
		emit(ARM_STR_I(rd, ARM_SP, STACK_VAR(dst)), ctx);
}

/* Arithmatic Operation */
static inline void emit_ar_r(const u8 rd, const u8 rt, const u8 rm,
			     const u8 rn, struct jit_ctx *ctx, u8 op) {
	switch (op) {
	case BPF_JSET:
		ctx->seen |= SEEN_CALL;
		emit(ARM_AND_R(ARM_IP, rt, rn), ctx);
		emit(ARM_AND_R(ARM_LR, rd, rm), ctx);
		emit(ARM_ORRS_R(ARM_IP, ARM_LR, ARM_IP), ctx);
		break;
	case BPF_JEQ:
	case BPF_JNE:
	case BPF_JGT:
	case BPF_JGE:
	case BPF_JLE:
	case BPF_JLT:
		emit(ARM_CMP_R(rd, rm), ctx);
		_emit(ARM_COND_EQ, ARM_CMP_R(rt, rn), ctx);
		break;
	case BPF_JSLE:
	case BPF_JSGT:
		emit(ARM_CMP_R(rn, rt), ctx);
		emit(ARM_SBCS_R(ARM_IP, rm, rd), ctx);
		break;
	case BPF_JSLT:
	case BPF_JSGE:
		emit(ARM_CMP_R(rt, rn), ctx);
		emit(ARM_SBCS_R(ARM_IP, rd, rm), ctx);
		break;
	}
}

static int out_offset = -1; /* initialized on the first pass of build_body() */
static int emit_bpf_tail_call(struct jit_ctx *ctx)
{

	/* bpf_tail_call(void *prog_ctx, struct bpf_array *array, u64 index) */
	const u8 *r2 = bpf2a32[BPF_REG_2];
	const u8 *r3 = bpf2a32[BPF_REG_3];
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	const u8 *tcc = bpf2a32[TCALL_CNT];
	const int idx0 = ctx->idx;
#define cur_offset (ctx->idx - idx0)
#define jmp_offset (out_offset - (cur_offset))
	u32 off, lo, hi;

	/* if (index >= array->map.max_entries)
	 *	goto out;
	 */
	off = offsetof(struct bpf_array, map.max_entries);
	/* array->map.max_entries */
	emit_a32_mov_i(tmp[1], off, false, ctx);
	emit(ARM_LDR_I(tmp2[1], ARM_SP, STACK_VAR(r2[1])), ctx);
	emit(ARM_LDR_R(tmp[1], tmp2[1], tmp[1]), ctx);
	/* index (64 bit) */
	emit(ARM_LDR_I(tmp2[1], ARM_SP, STACK_VAR(r3[1])), ctx);
	/* index >= array->map.max_entries */
	emit(ARM_CMP_R(tmp2[1], tmp[1]), ctx);
	_emit(ARM_COND_CS, ARM_B(jmp_offset), ctx);

	/* if (tail_call_cnt > MAX_TAIL_CALL_CNT)
	 *	goto out;
	 * tail_call_cnt++;
	 */
	lo = (u32)MAX_TAIL_CALL_CNT;
	hi = (u32)((u64)MAX_TAIL_CALL_CNT >> 32);
	emit(ARM_LDR_I(tmp[1], ARM_SP, STACK_VAR(tcc[1])), ctx);
	emit(ARM_LDR_I(tmp[0], ARM_SP, STACK_VAR(tcc[0])), ctx);
	emit(ARM_CMP_I(tmp[0], hi), ctx);
	_emit(ARM_COND_EQ, ARM_CMP_I(tmp[1], lo), ctx);
	_emit(ARM_COND_HI, ARM_B(jmp_offset), ctx);
	emit(ARM_ADDS_I(tmp[1], tmp[1], 1), ctx);
	emit(ARM_ADC_I(tmp[0], tmp[0], 0), ctx);
	emit(ARM_STR_I(tmp[1], ARM_SP, STACK_VAR(tcc[1])), ctx);
	emit(ARM_STR_I(tmp[0], ARM_SP, STACK_VAR(tcc[0])), ctx);

	/* prog = array->ptrs[index]
	 * if (prog == NULL)
	 *	goto out;
	 */
	off = offsetof(struct bpf_array, ptrs);
	emit_a32_mov_i(tmp[1], off, false, ctx);
	emit(ARM_LDR_I(tmp2[1], ARM_SP, STACK_VAR(r2[1])), ctx);
	emit(ARM_ADD_R(tmp[1], tmp2[1], tmp[1]), ctx);
	emit(ARM_LDR_I(tmp2[1], ARM_SP, STACK_VAR(r3[1])), ctx);
	emit(ARM_MOV_SI(tmp[0], tmp2[1], SRTYPE_ASL, 2), ctx);
	emit(ARM_LDR_R(tmp[1], tmp[1], tmp[0]), ctx);
	emit(ARM_CMP_I(tmp[1], 0), ctx);
	_emit(ARM_COND_EQ, ARM_B(jmp_offset), ctx);

	/* goto *(prog->bpf_func + prologue_size); */
	off = offsetof(struct bpf_prog, bpf_func);
	emit_a32_mov_i(tmp2[1], off, false, ctx);
	emit(ARM_LDR_R(tmp[1], tmp[1], tmp2[1]), ctx);
	emit(ARM_ADD_I(tmp[1], tmp[1], ctx->prologue_bytes), ctx);
	emit(ARM_BX(tmp[1]), ctx);

	/* out: */
	if (out_offset == -1)
		out_offset = cur_offset;
	if (cur_offset != out_offset) {
		pr_err_once("tail_call out_offset = %d, expected %d!\n",
			    cur_offset, out_offset);
		return -1;
	}
	return 0;
#undef cur_offset
#undef jmp_offset
}

/* 0xabcd => 0xcdab */
static inline void emit_rev16(const u8 rd, const u8 rn, struct jit_ctx *ctx)
{
#if __LINUX_ARM_ARCH__ < 6
	const u8 *tmp2 = bpf2a32[TMP_REG_2];

	emit(ARM_AND_I(tmp2[1], rn, 0xff), ctx);
	emit(ARM_MOV_SI(tmp2[0], rn, SRTYPE_LSR, 8), ctx);
	emit(ARM_AND_I(tmp2[0], tmp2[0], 0xff), ctx);
	emit(ARM_ORR_SI(rd, tmp2[0], tmp2[1], SRTYPE_LSL, 8), ctx);
#else /* ARMv6+ */
	emit(ARM_REV16(rd, rn), ctx);
#endif
}

/* 0xabcdefgh => 0xghefcdab */
static inline void emit_rev32(const u8 rd, const u8 rn, struct jit_ctx *ctx)
{
#if __LINUX_ARM_ARCH__ < 6
	const u8 *tmp2 = bpf2a32[TMP_REG_2];

	emit(ARM_AND_I(tmp2[1], rn, 0xff), ctx);
	emit(ARM_MOV_SI(tmp2[0], rn, SRTYPE_LSR, 24), ctx);
	emit(ARM_ORR_SI(ARM_IP, tmp2[0], tmp2[1], SRTYPE_LSL, 24), ctx);

	emit(ARM_MOV_SI(tmp2[1], rn, SRTYPE_LSR, 8), ctx);
	emit(ARM_AND_I(tmp2[1], tmp2[1], 0xff), ctx);
	emit(ARM_MOV_SI(tmp2[0], rn, SRTYPE_LSR, 16), ctx);
	emit(ARM_AND_I(tmp2[0], tmp2[0], 0xff), ctx);
	emit(ARM_MOV_SI(tmp2[0], tmp2[0], SRTYPE_LSL, 8), ctx);
	emit(ARM_ORR_SI(tmp2[0], tmp2[0], tmp2[1], SRTYPE_LSL, 16), ctx);
	emit(ARM_ORR_R(rd, ARM_IP, tmp2[0]), ctx);

#else /* ARMv6+ */
	emit(ARM_REV(rd, rn), ctx);
#endif
}

// push the scratch stack register on top of the stack
static inline void emit_push_r64(const u8 src[], const u8 shift,
		struct jit_ctx *ctx)
{
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	u16 reg_set = 0;

	emit(ARM_LDR_I(tmp2[1], ARM_SP, STACK_VAR(src[1]+shift)), ctx);
	emit(ARM_LDR_I(tmp2[0], ARM_SP, STACK_VAR(src[0]+shift)), ctx);

	reg_set = (1 << tmp2[1]) | (1 << tmp2[0]);
	emit(ARM_PUSH(reg_set), ctx);
}

static void build_prologue(struct jit_ctx *ctx)
{
	const u8 r0 = bpf2a32[BPF_REG_0][1];
	const u8 r2 = bpf2a32[BPF_REG_1][1];
	const u8 r3 = bpf2a32[BPF_REG_1][0];
	const u8 r4 = bpf2a32[BPF_REG_6][1];
	const u8 r5 = bpf2a32[BPF_REG_6][0];
	const u8 r6 = bpf2a32[TMP_REG_1][1];
	const u8 r7 = bpf2a32[TMP_REG_1][0];
	const u8 r8 = bpf2a32[TMP_REG_2][1];
	const u8 r10 = bpf2a32[TMP_REG_2][0];
	const u8 fplo = bpf2a32[BPF_REG_FP][1];
	const u8 fphi = bpf2a32[BPF_REG_FP][0];
	const u8 sp = ARM_SP;
	const u8 *tcc = bpf2a32[TCALL_CNT];

	u16 reg_set = 0;

	/*
	 * eBPF prog stack layout
	 *
	 *                         high
	 * original ARM_SP =>     +-----+ eBPF prologue
	 *                        |FP/LR|
	 * current ARM_FP =>      +-----+
	 *                        | ... | callee saved registers
	 * eBPF fp register =>    +-----+ <= (BPF_FP)
	 *                        | ... | eBPF JIT scratch space
	 *                        |     | eBPF prog stack
	 *                        +-----+
	 *			  |RSVD | JIT scratchpad
	 * current A64_SP =>      +-----+ <= (BPF_FP - STACK_SIZE)
	 *                        |     |
	 *                        | ... | Function call stack
	 *                        |     |
	 *                        +-----+
	 *                          low
	 */

	/* Save callee saved registers. */
	reg_set |= (1<<r4) | (1<<r5) | (1<<r6) | (1<<r7) | (1<<r8) | (1<<r10);
#ifdef CONFIG_FRAME_POINTER
	reg_set |= (1<<ARM_FP) | (1<<ARM_IP) | (1<<ARM_LR) | (1<<ARM_PC);
	emit(ARM_MOV_R(ARM_IP, sp), ctx);
	emit(ARM_PUSH(reg_set), ctx);
	emit(ARM_SUB_I(ARM_FP, ARM_IP, 4), ctx);
#else
	/* Check if call instruction exists in BPF body */
	if (ctx->seen & SEEN_CALL)
		reg_set |= (1<<ARM_LR);
	emit(ARM_PUSH(reg_set), ctx);
#endif
	/* Save frame pointer for later */
	emit(ARM_SUB_I(ARM_IP, sp, SCRATCH_SIZE), ctx);

	ctx->stack_size = imm8m(STACK_SIZE);

	/* Set up function call stack */
	emit(ARM_SUB_I(ARM_SP, ARM_SP, ctx->stack_size), ctx);

	/* Set up BPF prog stack base register */
	emit_a32_mov_r(fplo, ARM_IP, true, false, ctx);
	emit_a32_mov_i(fphi, 0, true, ctx);

	/* mov r4, 0 */
	emit(ARM_MOV_I(r4, 0), ctx);

	/* Move BPF_CTX to BPF_R1 */
	emit(ARM_MOV_R(r3, r4), ctx);
	emit(ARM_MOV_R(r2, r0), ctx);
	/* Initialize Tail Count */
	emit(ARM_STR_I(r4, ARM_SP, STACK_VAR(tcc[0])), ctx);
	emit(ARM_STR_I(r4, ARM_SP, STACK_VAR(tcc[1])), ctx);
	/* end of prologue */
}

static void build_epilogue(struct jit_ctx *ctx)
{
	const u8 r4 = bpf2a32[BPF_REG_6][1];
	const u8 r5 = bpf2a32[BPF_REG_6][0];
	const u8 r6 = bpf2a32[TMP_REG_1][1];
	const u8 r7 = bpf2a32[TMP_REG_1][0];
	const u8 r8 = bpf2a32[TMP_REG_2][1];
	const u8 r10 = bpf2a32[TMP_REG_2][0];
	u16 reg_set = 0;

	/* unwind function call stack */
	emit(ARM_ADD_I(ARM_SP, ARM_SP, ctx->stack_size), ctx);

	/* restore callee saved registers. */
	reg_set |= (1<<r4) | (1<<r5) | (1<<r6) | (1<<r7) | (1<<r8) | (1<<r10);
#ifdef CONFIG_FRAME_POINTER
	/* the first instruction of the prologue was: mov ip, sp */
	reg_set |= (1<<ARM_FP) | (1<<ARM_SP) | (1<<ARM_PC);
	emit(ARM_LDM(ARM_SP, reg_set), ctx);
#else
	if (ctx->seen & SEEN_CALL)
		reg_set |= (1<<ARM_PC);
	/* Restore callee saved registers. */
	emit(ARM_POP(reg_set), ctx);
	/* Return back to the callee function */
	if (!(ctx->seen & SEEN_CALL))
		emit(ARM_BX(ARM_LR), ctx);
#endif
}

/*
 * Convert an eBPF instruction to native instruction, i.e
 * JITs an eBPF instruction.
 * Returns :
 *	0  - Successfully JITed an 8-byte eBPF instruction
 *	>0 - Successfully JITed a 16-byte eBPF instruction
 *	<0 - Failed to JIT.
 */
static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
{
	const u8 code = insn->code;
	const u8 *dst = bpf2a32[insn->dst_reg];
	const u8 *src = bpf2a32[insn->src_reg];
	const u8 *tmp = bpf2a32[TMP_REG_1];
	const u8 *tmp2 = bpf2a32[TMP_REG_2];
	const s16 off = insn->off;
	const s32 imm = insn->imm;
	const int i = insn - ctx->prog->insnsi;
	const bool is64 = BPF_CLASS(code) == BPF_ALU64;
	const bool dstk = is_on_stack(insn->dst_reg);
	const bool sstk = is_on_stack(insn->src_reg);
	u8 rd, rt, rm, rn;
	s32 jmp_offset;

#define check_imm(bits, imm) do {				\
	if ((((imm) > 0) && ((imm) >> (bits))) ||		\
	    (((imm) < 0) && (~(imm) >> (bits)))) {		\
		pr_info("[%2d] imm=%d(0x%x) out of range\n",	\
			i, imm, imm);				\
		return -EINVAL;					\
	}							\
} while (0)
#define check_imm24(imm) check_imm(24, imm)

	switch (code) {
	/* ALU operations */

	/* dst = src */
	case BPF_ALU | BPF_MOV | BPF_K:
	case BPF_ALU | BPF_MOV | BPF_X:
	case BPF_ALU64 | BPF_MOV | BPF_K:
	case BPF_ALU64 | BPF_MOV | BPF_X:
		switch (BPF_SRC(code)) {
		case BPF_X:
			emit_a32_mov_r64(is64, dst, src, dstk, sstk, ctx);
			break;
		case BPF_K:
			/* Sign-extend immediate value to destination reg */
			emit_a32_mov_i64(is64, dst, imm, dstk, ctx);
			break;
		}
		break;
	/* dst = dst + src/imm */
	/* dst = dst - src/imm */
	/* dst = dst | src/imm */
	/* dst = dst & src/imm */
	/* dst = dst ^ src/imm */
	/* dst = dst * src/imm */
	/* dst = dst << src */
	/* dst = dst >> src */
	case BPF_ALU | BPF_ADD | BPF_K:
	case BPF_ALU | BPF_ADD | BPF_X:
	case BPF_ALU | BPF_SUB | BPF_K:
	case BPF_ALU | BPF_SUB | BPF_X:
	case BPF_ALU | BPF_OR | BPF_K:
	case BPF_ALU | BPF_OR | BPF_X:
	case BPF_ALU | BPF_AND | BPF_K:
	case BPF_ALU | BPF_AND | BPF_X:
	case BPF_ALU | BPF_XOR | BPF_K:
	case BPF_ALU | BPF_XOR | BPF_X:
	case BPF_ALU | BPF_MUL | BPF_K:
	case BPF_ALU | BPF_MUL | BPF_X:
	case BPF_ALU | BPF_LSH | BPF_X:
	case BPF_ALU | BPF_RSH | BPF_X:
	case BPF_ALU | BPF_ARSH | BPF_K:
	case BPF_ALU | BPF_ARSH | BPF_X:
	case BPF_ALU64 | BPF_ADD | BPF_K:
	case BPF_ALU64 | BPF_ADD | BPF_X:
	case BPF_ALU64 | BPF_SUB | BPF_K:
	case BPF_ALU64 | BPF_SUB | BPF_X:
	case BPF_ALU64 | BPF_OR | BPF_K:
	case BPF_ALU64 | BPF_OR | BPF_X:
	case BPF_ALU64 | BPF_AND | BPF_K:
	case BPF_ALU64 | BPF_AND | BPF_X:
	case BPF_ALU64 | BPF_XOR | BPF_K:
	case BPF_ALU64 | BPF_XOR | BPF_X:
		switch (BPF_SRC(code)) {
		case BPF_X:
			emit_a32_alu_r64(is64, dst, src, dstk, sstk,
					 ctx, BPF_OP(code));
			break;
		case BPF_K:
			/* Move immediate value to the temporary register
			 * and then do the ALU operation on the temporary
			 * register as this will sign-extend the immediate
			 * value into temporary reg and then it would be
			 * safe to do the operation on it.
			 */
			emit_a32_mov_i64(is64, tmp2, imm, false, ctx);
			emit_a32_alu_r64(is64, dst, tmp2, dstk, false,
					 ctx, BPF_OP(code));
			break;
		}
		break;
	/* dst = dst / src(imm) */
	/* dst = dst % src(imm) */
	case BPF_ALU | BPF_DIV | BPF_K:
	case BPF_ALU | BPF_DIV | BPF_X:
	case BPF_ALU | BPF_MOD | BPF_K:
	case BPF_ALU | BPF_MOD | BPF_X:
		rt = src_lo;
		rd = dstk ? tmp2[1] : dst_lo;
		if (dstk)
			emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		switch (BPF_SRC(code)) {
		case BPF_X:
			rt = sstk ? tmp2[0] : rt;
			if (sstk)
				emit(ARM_LDR_I(rt, ARM_SP, STACK_VAR(src_lo)),
				     ctx);
			break;
		case BPF_K:
			rt = tmp2[0];
			emit_a32_mov_i(rt, imm, false, ctx);
			break;
		}
		emit_udivmod(rd, rd, rt, ctx, BPF_OP(code));
		if (dstk)
			emit(ARM_STR_I(rd, ARM_SP, STACK_VAR(dst_lo)), ctx);
		emit_a32_mov_i(dst_hi, 0, dstk, ctx);
		break;
	case BPF_ALU64 | BPF_DIV | BPF_K:
	case BPF_ALU64 | BPF_DIV | BPF_X:
	case BPF_ALU64 | BPF_MOD | BPF_K:
	case BPF_ALU64 | BPF_MOD | BPF_X:
		goto notyet;
	/* dst = dst >> imm */
	/* dst = dst << imm */
	case BPF_ALU | BPF_RSH | BPF_K:
	case BPF_ALU | BPF_LSH | BPF_K:
		if (unlikely(imm > 31))
			return -EINVAL;
		if (imm)
			emit_a32_alu_i(dst_lo, imm, dstk, ctx, BPF_OP(code));
		emit_a32_mov_i(dst_hi, 0, dstk, ctx);
		break;
	/* dst = dst << imm */
	case BPF_ALU64 | BPF_LSH | BPF_K:
		if (unlikely(imm > 63))
			return -EINVAL;
		emit_a32_lsh_i64(dst, dstk, imm, ctx);
		break;
	/* dst = dst >> imm */
	case BPF_ALU64 | BPF_RSH | BPF_K:
		if (unlikely(imm > 63))
			return -EINVAL;
		emit_a32_lsr_i64(dst, dstk, imm, ctx);
		break;
	/* dst = dst << src */
	case BPF_ALU64 | BPF_LSH | BPF_X:
		emit_a32_lsh_r64(dst, src, dstk, sstk, ctx);
		break;
	/* dst = dst >> src */
	case BPF_ALU64 | BPF_RSH | BPF_X:
		emit_a32_lsr_r64(dst, src, dstk, sstk, ctx);
		break;
	/* dst = dst >> src (signed) */
	case BPF_ALU64 | BPF_ARSH | BPF_X:
		emit_a32_arsh_r64(dst, src, dstk, sstk, ctx);
		break;
	/* dst = dst >> imm (signed) */
	case BPF_ALU64 | BPF_ARSH | BPF_K:
		if (unlikely(imm > 63))
			return -EINVAL;
		emit_a32_arsh_i64(dst, dstk, imm, ctx);
		break;
	/* dst = ~dst */
	case BPF_ALU | BPF_NEG:
		emit_a32_alu_i(dst_lo, 0, dstk, ctx, BPF_OP(code));
		emit_a32_mov_i(dst_hi, 0, dstk, ctx);
		break;
	/* dst = ~dst (64 bit) */
	case BPF_ALU64 | BPF_NEG:
		emit_a32_neg64(dst, dstk, ctx);
		break;
	/* dst = dst * src/imm */
	case BPF_ALU64 | BPF_MUL | BPF_X:
	case BPF_ALU64 | BPF_MUL | BPF_K:
		switch (BPF_SRC(code)) {
		case BPF_X:
			emit_a32_mul_r64(dst, src, dstk, sstk, ctx);
			break;
		case BPF_K:
			/* Move immediate value to the temporary register
			 * and then do the multiplication on it as this
			 * will sign-extend the immediate value into temp
			 * reg then it would be safe to do the operation
			 * on it.
			 */
			emit_a32_mov_i64(is64, tmp2, imm, false, ctx);
			emit_a32_mul_r64(dst, tmp2, dstk, false, ctx);
			break;
		}
		break;
	/* dst = htole(dst) */
	/* dst = htobe(dst) */
	case BPF_ALU | BPF_END | BPF_FROM_LE:
	case BPF_ALU | BPF_END | BPF_FROM_BE:
		rd = dstk ? tmp[0] : dst_hi;
		rt = dstk ? tmp[1] : dst_lo;
		if (dstk) {
			emit(ARM_LDR_I(rt, ARM_SP, STACK_VAR(dst_lo)), ctx);
			emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_hi)), ctx);
		}
		if (BPF_SRC(code) == BPF_FROM_LE)
			goto emit_bswap_uxt;
		switch (imm) {
		case 16:
			emit_rev16(rt, rt, ctx);
			goto emit_bswap_uxt;
		case 32:
			emit_rev32(rt, rt, ctx);
			goto emit_bswap_uxt;
		case 64:
			/* Because of the usage of ARM_LR */
			ctx->seen |= SEEN_CALL;
			emit_rev32(ARM_LR, rt, ctx);
			emit_rev32(rt, rd, ctx);
			emit(ARM_MOV_R(rd, ARM_LR), ctx);
			break;
		}
		goto exit;
emit_bswap_uxt:
		switch (imm) {
		case 16:
			/* zero-extend 16 bits into 64 bits */
#if __LINUX_ARM_ARCH__ < 6
			emit_a32_mov_i(tmp2[1], 0xffff, false, ctx);
			emit(ARM_AND_R(rt, rt, tmp2[1]), ctx);
#else /* ARMv6+ */
			emit(ARM_UXTH(rt, rt), ctx);
#endif
			emit(ARM_EOR_R(rd, rd, rd), ctx);
			break;
		case 32:
			/* zero-extend 32 bits into 64 bits */
			emit(ARM_EOR_R(rd, rd, rd), ctx);
			break;
		case 64:
			/* nop */
			break;
		}
exit:
		if (dstk) {
			emit(ARM_STR_I(rt, ARM_SP, STACK_VAR(dst_lo)), ctx);
			emit(ARM_STR_I(rd, ARM_SP, STACK_VAR(dst_hi)), ctx);
		}
		break;
	/* dst = imm64 */
	case BPF_LD | BPF_IMM | BPF_DW:
	{
		const struct bpf_insn insn1 = insn[1];
		u32 hi, lo = imm;

		hi = insn1.imm;
		emit_a32_mov_i(dst_lo, lo, dstk, ctx);
		emit_a32_mov_i(dst_hi, hi, dstk, ctx);

		return 1;
	}
	/* LDX: dst = *(size *)(src + off) */
	case BPF_LDX | BPF_MEM | BPF_W:
	case BPF_LDX | BPF_MEM | BPF_H:
	case BPF_LDX | BPF_MEM | BPF_B:
	case BPF_LDX | BPF_MEM | BPF_DW:
		rn = sstk ? tmp2[1] : src_lo;
		if (sstk)
			emit(ARM_LDR_I(rn, ARM_SP, STACK_VAR(src_lo)), ctx);
		switch (BPF_SIZE(code)) {
		case BPF_W:
			/* Load a Word */
		case BPF_H:
			/* Load a Half-Word */
		case BPF_B:
			/* Load a Byte */
			emit_ldx_r(dst_lo, rn, dstk, off, ctx, BPF_SIZE(code));
			emit_a32_mov_i(dst_hi, 0, dstk, ctx);
			break;
		case BPF_DW:
			/* Load a double word */
			emit_ldx_r(dst_lo, rn, dstk, off, ctx, BPF_W);
			emit_ldx_r(dst_hi, rn, dstk, off+4, ctx, BPF_W);
			break;
		}
		break;
	/* R0 = ntohx(*(size *)(((struct sk_buff *)R6)->data + imm)) */
	case BPF_LD | BPF_ABS | BPF_W:
	case BPF_LD | BPF_ABS | BPF_H:
	case BPF_LD | BPF_ABS | BPF_B:
	/* R0 = ntohx(*(size *)(((struct sk_buff *)R6)->data + src + imm)) */
	case BPF_LD | BPF_IND | BPF_W:
	case BPF_LD | BPF_IND | BPF_H:
	case BPF_LD | BPF_IND | BPF_B:
	{
		const u8 r4 = bpf2a32[BPF_REG_6][1]; /* r4 = ptr to sk_buff */
		const u8 r0 = bpf2a32[BPF_REG_0][1]; /*r0: struct sk_buff *skb*/
						     /* rtn value */
		const u8 r1 = bpf2a32[BPF_REG_0][0]; /* r1: int k */
		const u8 r2 = bpf2a32[BPF_REG_1][1]; /* r2: unsigned int size */
		const u8 r3 = bpf2a32[BPF_REG_1][0]; /* r3: void *buffer */
		const u8 r6 = bpf2a32[TMP_REG_1][1]; /* r6: void *(*func)(..) */
		int size;

		/* Setting up first argument */
		emit(ARM_MOV_R(r0, r4), ctx);

		/* Setting up second argument */
		emit_a32_mov_i(r1, imm, false, ctx);
		if (BPF_MODE(code) == BPF_IND)
			emit_a32_alu_r(r1, src_lo, false, sstk, ctx,
				       false, false, BPF_ADD);

		/* Setting up third argument */
		switch (BPF_SIZE(code)) {
		case BPF_W:
			size = 4;
			break;
		case BPF_H:
			size = 2;
			break;
		case BPF_B:
			size = 1;
			break;
		default:
			return -EINVAL;
		}
		emit_a32_mov_i(r2, size, false, ctx);

		/* Setting up fourth argument */
		emit(ARM_ADD_I(r3, ARM_SP, imm8m(SKB_BUFFER)), ctx);

		/* Setting up function pointer to call */
		emit_a32_mov_i(r6, (unsigned int)bpf_load_pointer, false, ctx);
		emit_blx_r(r6, ctx);

		emit(ARM_EOR_R(r1, r1, r1), ctx);
		/* Check if return address is NULL or not.
		 * if NULL then jump to epilogue
		 * else continue to load the value from retn address
		 */
		emit(ARM_CMP_I(r0, 0), ctx);
		jmp_offset = epilogue_offset(ctx);
		check_imm24(jmp_offset);
		_emit(ARM_COND_EQ, ARM_B(jmp_offset), ctx);

		/* Load value from the address */
		switch (BPF_SIZE(code)) {
		case BPF_W:
			emit(ARM_LDR_I(r0, r0, 0), ctx);
			emit_rev32(r0, r0, ctx);
			break;
		case BPF_H:
			emit(ARM_LDRH_I(r0, r0, 0), ctx);
			emit_rev16(r0, r0, ctx);
			break;
		case BPF_B:
			emit(ARM_LDRB_I(r0, r0, 0), ctx);
			/* No need to reverse */
			break;
		}
		break;
	}
	/* ST: *(size *)(dst + off) = imm */
	case BPF_ST | BPF_MEM | BPF_W:
	case BPF_ST | BPF_MEM | BPF_H:
	case BPF_ST | BPF_MEM | BPF_B:
	case BPF_ST | BPF_MEM | BPF_DW:
		switch (BPF_SIZE(code)) {
		case BPF_DW:
			/* Sign-extend immediate value into temp reg */
			emit_a32_mov_i64(true, tmp2, imm, false, ctx);
			emit_str_r(dst_lo, tmp2[1], dstk, off, ctx, BPF_W);
			emit_str_r(dst_lo, tmp2[0], dstk, off+4, ctx, BPF_W);
			break;
		case BPF_W:
		case BPF_H:
		case BPF_B:
			emit_a32_mov_i(tmp2[1], imm, false, ctx);
			emit_str_r(dst_lo, tmp2[1], dstk, off, ctx,
				   BPF_SIZE(code));
			break;
		}
		break;
	/* STX XADD: lock *(u32 *)(dst + off) += src */
	case BPF_STX | BPF_XADD | BPF_W:
	/* STX XADD: lock *(u64 *)(dst + off) += src */
	case BPF_STX | BPF_XADD | BPF_DW:
		goto notyet;
	/* STX: *(size *)(dst + off) = src */
	case BPF_STX | BPF_MEM | BPF_W:
	case BPF_STX | BPF_MEM | BPF_H:
	case BPF_STX | BPF_MEM | BPF_B:
	case BPF_STX | BPF_MEM | BPF_DW:
	{
		u8 sz = BPF_SIZE(code);

		rn = sstk ? tmp2[1] : src_lo;
		rm = sstk ? tmp2[0] : src_hi;
		if (sstk) {
			emit(ARM_LDR_I(rn, ARM_SP, STACK_VAR(src_lo)), ctx);
			emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(src_hi)), ctx);
		}

		/* Store the value */
		if (BPF_SIZE(code) == BPF_DW) {
			emit_str_r(dst_lo, rn, dstk, off, ctx, BPF_W);
			emit_str_r(dst_lo, rm, dstk, off+4, ctx, BPF_W);
		} else {
			emit_str_r(dst_lo, rn, dstk, off, ctx, sz);
		}
		break;
	}
	/* PC += off if dst == src */
	/* PC += off if dst > src */
	/* PC += off if dst >= src */
	/* PC += off if dst < src */
	/* PC += off if dst <= src */
	/* PC += off if dst != src */
	/* PC += off if dst > src (signed) */
	/* PC += off if dst >= src (signed) */
	/* PC += off if dst < src (signed) */
	/* PC += off if dst <= src (signed) */
	/* PC += off if dst & src */
	case BPF_JMP | BPF_JEQ | BPF_X:
	case BPF_JMP | BPF_JGT | BPF_X:
	case BPF_JMP | BPF_JGE | BPF_X:
	case BPF_JMP | BPF_JNE | BPF_X:
	case BPF_JMP | BPF_JSGT | BPF_X:
	case BPF_JMP | BPF_JSGE | BPF_X:
	case BPF_JMP | BPF_JSET | BPF_X:
	case BPF_JMP | BPF_JLE | BPF_X:
	case BPF_JMP | BPF_JLT | BPF_X:
	case BPF_JMP | BPF_JSLT | BPF_X:
	case BPF_JMP | BPF_JSLE | BPF_X:
		/* Setup source registers */
		rm = sstk ? tmp2[0] : src_hi;
		rn = sstk ? tmp2[1] : src_lo;
		if (sstk) {
			emit(ARM_LDR_I(rn, ARM_SP, STACK_VAR(src_lo)), ctx);
			emit(ARM_LDR_I(rm, ARM_SP, STACK_VAR(src_hi)), ctx);
		}
		goto go_jmp;
	/* PC += off if dst == imm */
	/* PC += off if dst > imm */
	/* PC += off if dst >= imm */
	/* PC += off if dst < imm */
	/* PC += off if dst <= imm */
	/* PC += off if dst != imm */
	/* PC += off if dst > imm (signed) */
	/* PC += off if dst >= imm (signed) */
	/* PC += off if dst < imm (signed) */
	/* PC += off if dst <= imm (signed) */
	/* PC += off if dst & imm */
	case BPF_JMP | BPF_JEQ | BPF_K:
	case BPF_JMP | BPF_JGT | BPF_K:
	case BPF_JMP | BPF_JGE | BPF_K:
	case BPF_JMP | BPF_JNE | BPF_K:
	case BPF_JMP | BPF_JSGT | BPF_K:
	case BPF_JMP | BPF_JSGE | BPF_K:
	case BPF_JMP | BPF_JSET | BPF_K:
	case BPF_JMP | BPF_JLT | BPF_K:
	case BPF_JMP | BPF_JLE | BPF_K:
	case BPF_JMP | BPF_JSLT | BPF_K:
	case BPF_JMP | BPF_JSLE | BPF_K:
		if (off == 0)
			break;
		rm = tmp2[0];
		rn = tmp2[1];
		/* Sign-extend immediate value */
		emit_a32_mov_i64(true, tmp2, imm, false, ctx);
go_jmp:
		/* Setup destination register */
		rd = dstk ? tmp[0] : dst_hi;
		rt = dstk ? tmp[1] : dst_lo;
		if (dstk) {
			emit(ARM_LDR_I(rt, ARM_SP, STACK_VAR(dst_lo)), ctx);
			emit(ARM_LDR_I(rd, ARM_SP, STACK_VAR(dst_hi)), ctx);
		}

		/* Check for the condition */
		emit_ar_r(rd, rt, rm, rn, ctx, BPF_OP(code));

		/* Setup JUMP instruction */
		jmp_offset = bpf2a32_offset(i+off, i, ctx);
		switch (BPF_OP(code)) {
		case BPF_JNE:
		case BPF_JSET:
			_emit(ARM_COND_NE, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JEQ:
			_emit(ARM_COND_EQ, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JGT:
			_emit(ARM_COND_HI, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JGE:
			_emit(ARM_COND_CS, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JSGT:
			_emit(ARM_COND_LT, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JSGE:
			_emit(ARM_COND_GE, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JLE:
			_emit(ARM_COND_LS, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JLT:
			_emit(ARM_COND_CC, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JSLT:
			_emit(ARM_COND_LT, ARM_B(jmp_offset), ctx);
			break;
		case BPF_JSLE:
			_emit(ARM_COND_GE, ARM_B(jmp_offset), ctx);
			break;
		}
		break;
	/* JMP OFF */
	case BPF_JMP | BPF_JA:
	{
		if (off == 0)
			break;
		jmp_offset = bpf2a32_offset(i+off, i, ctx);
		check_imm24(jmp_offset);
		emit(ARM_B(jmp_offset), ctx);
		break;
	}
	/* tail call */
	case BPF_JMP | BPF_TAIL_CALL:
		if (emit_bpf_tail_call(ctx))
			return -EFAULT;
		break;
	/* function call */
	case BPF_JMP | BPF_CALL:
	{
		const u8 *r0 = bpf2a32[BPF_REG_0];
		const u8 *r1 = bpf2a32[BPF_REG_1];
		const u8 *r2 = bpf2a32[BPF_REG_2];
		const u8 *r3 = bpf2a32[BPF_REG_3];
		const u8 *r4 = bpf2a32[BPF_REG_4];
		const u8 *r5 = bpf2a32[BPF_REG_5];
		const u32 func = (u32)__bpf_call_base + (u32)imm;

		emit_a32_mov_r64(true, r0, r1, false, false, ctx);
		emit_a32_mov_r64(true, r1, r2, false, true, ctx);
		emit_push_r64(r5, 0, ctx);
		emit_push_r64(r4, 8, ctx);
		emit_push_r64(r3, 16, ctx);

		emit_a32_mov_i(tmp[1], func, false, ctx);
		emit_blx_r(tmp[1], ctx);

		emit(ARM_ADD_I(ARM_SP, ARM_SP, imm8m(24)), ctx); // callee clean
		break;
	}
	/* function return */
	case BPF_JMP | BPF_EXIT:
		/* Optimization: when last instruction is EXIT
		 * simply fallthrough to epilogue.
		 */
		if (i == ctx->prog->len - 1)
			break;
		jmp_offset = epilogue_offset(ctx);
		check_imm24(jmp_offset);
		emit(ARM_B(jmp_offset), ctx);
		break;
notyet:
		pr_info_once("*** NOT YET: opcode %02x ***\n", code);
		return -EFAULT;
	default:
		pr_err_once("unknown opcode %02x\n", code);
		return -EINVAL;
	}

	if (ctx->flags & FLAG_IMM_OVERFLOW)
		/*
		 * this instruction generated an overflow when
		 * trying to access the literal pool, so
		 * delegate this filter to the kernel interpreter.
		 */
		return -1;
	return 0;
}

static int build_body(struct jit_ctx *ctx)
{
	const struct bpf_prog *prog = ctx->prog;
	unsigned int i;

	for (i = 0; i < prog->len; i++) {
		const struct bpf_insn *insn = &(prog->insnsi[i]);
		int ret;

		ret = build_insn(insn, ctx);

		/* It's used with loading the 64 bit immediate value. */
		if (ret > 0) {
			i++;
			if (ctx->target == NULL)
				ctx->offsets[i] = ctx->idx;
			continue;
		}

		if (ctx->target == NULL)
			ctx->offsets[i] = ctx->idx;

		/* If unsuccesfull, return with error code */
		if (ret)
			return ret;
	}
	return 0;
}

static int validate_code(struct jit_ctx *ctx)
{
	int i;

	for (i = 0; i < ctx->idx; i++) {
		if (ctx->target[i] == __opcode_to_mem_arm(ARM_INST_UDF))
			return -1;
	}

	return 0;
}

void bpf_jit_compile(struct bpf_prog *prog)
{
	/* Nothing to do here. We support Internal BPF. */
}

struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
{
	struct bpf_prog *tmp, *orig_prog = prog;
	struct bpf_binary_header *header;
	bool tmp_blinded = false;
	struct jit_ctx ctx;
	unsigned int tmp_idx;
	unsigned int image_size;
	u8 *image_ptr;

	/* If BPF JIT was not enabled then we must fall back to
	 * the interpreter.
	 */
	if (!bpf_jit_enable)
		return orig_prog;

	/* If constant blinding was enabled and we failed during blinding
	 * then we must fall back to the interpreter. Otherwise, we save
	 * the new JITed code.
	 */
	tmp = bpf_jit_blind_constants(prog);

	if (IS_ERR(tmp))
		return orig_prog;
	if (tmp != prog) {
		tmp_blinded = true;
		prog = tmp;
	}

	memset(&ctx, 0, sizeof(ctx));
	ctx.prog = prog;

	/* Not able to allocate memory for offsets[] , then
	 * we must fall back to the interpreter
	 */
	ctx.offsets = kcalloc(prog->len, sizeof(int), GFP_KERNEL);
	if (ctx.offsets == NULL) {
		prog = orig_prog;
		goto out;
	}

	/* 1) fake pass to find in the length of the JITed code,
	 * to compute ctx->offsets and other context variables
	 * needed to compute final JITed code.
	 * Also, calculate random starting pointer/start of JITed code
	 * which is prefixed by random number of fault instructions.
	 *
	 * If the first pass fails then there is no chance of it
	 * being successful in the second pass, so just fall back
	 * to the interpreter.
	 */
	if (build_body(&ctx)) {
		prog = orig_prog;
		goto out_off;
	}

	tmp_idx = ctx.idx;
	build_prologue(&ctx);
	ctx.prologue_bytes = (ctx.idx - tmp_idx) * 4;

	ctx.epilogue_offset = ctx.idx;

#if __LINUX_ARM_ARCH__ < 7
	tmp_idx = ctx.idx;
	build_epilogue(&ctx);
	ctx.epilogue_bytes = (ctx.idx - tmp_idx) * 4;

	ctx.idx += ctx.imm_count;
	if (ctx.imm_count) {
		ctx.imms = kcalloc(ctx.imm_count, sizeof(u32), GFP_KERNEL);
		if (ctx.imms == NULL) {
			prog = orig_prog;
			goto out_off;
		}
	}
#else
	/* there's nothing about the epilogue on ARMv7 */
	build_epilogue(&ctx);
#endif
	/* Now we can get the actual image size of the JITed arm code.
	 * Currently, we are not considering the THUMB-2 instructions
	 * for jit, although it can decrease the size of the image.
	 *
	 * As each arm instruction is of length 32bit, we are translating
	 * number of JITed intructions into the size required to store these
	 * JITed code.
	 */
	image_size = sizeof(u32) * ctx.idx;

	/* Now we know the size of the structure to make */
	header = bpf_jit_binary_alloc(image_size, &image_ptr,
				      sizeof(u32), jit_fill_hole);
	/* Not able to allocate memory for the structure then
	 * we must fall back to the interpretation
	 */
	if (header == NULL) {
		prog = orig_prog;
		goto out_imms;
	}

	/* 2.) Actual pass to generate final JIT code */
	ctx.target = (u32 *) image_ptr;
	ctx.idx = 0;

	build_prologue(&ctx);

	/* If building the body of the JITed code fails somehow,
	 * we fall back to the interpretation.
	 */
	if (build_body(&ctx) < 0) {
		image_ptr = NULL;
		bpf_jit_binary_free(header);
		prog = orig_prog;
		goto out_imms;
	}
	build_epilogue(&ctx);

	/* 3.) Extra pass to validate JITed Code */
	if (validate_code(&ctx)) {
		image_ptr = NULL;
		bpf_jit_binary_free(header);
		prog = orig_prog;
		goto out_imms;
	}
	flush_icache_range((u32)header, (u32)(ctx.target + ctx.idx));

	if (bpf_jit_enable > 1)
		/* there are 2 passes here */
		bpf_jit_dump(prog->len, image_size, 2, ctx.target);

	set_memory_ro((unsigned long)header, header->pages);
	prog->bpf_func = (void *)ctx.target;
	prog->jited = 1;
	prog->jited_len = image_size;

out_imms:
#if __LINUX_ARM_ARCH__ < 7
	if (ctx.imm_count)
		kfree(ctx.imms);
#endif
out_off:
	kfree(ctx.offsets);
out:
	if (tmp_blinded)
		bpf_jit_prog_release_other(prog, prog == orig_prog ?
					   tmp : orig_prog);
	return prog;
}