Merge tag 'microblaze-4.16-rc1' of git://git.monstr.eu/linux-2.6-microblaze

[sfrench/cifs-2.6.git] / arch / arm / net / bpf_jit_32.c

/*
 * 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"

/*
 * eBPF prog stack layout:
 *
 *                         high
 * original ARM_SP =>     +-----+
 *                        |     | callee saved registers
 *                        +-----+ <= (BPF_FP + SCRATCH_SIZE)
 *                        | ... | eBPF JIT scratch space
 * eBPF fp register =>    +-----+
 *   (BPF_FP)             | ... | eBPF prog stack
 *                        +-----+
 *                        |RSVD | JIT scratchpad
 * current ARM_SP =>      +-----+ <= (BPF_FP - STACK_SIZE + SCRATCH_SIZE)
 *                        |     |
 *                        | ... | Function call stack
 *                        |     |
 *                        +-----+
 *                          low
 *
 * The callee saved registers depends on whether frame pointers are enabled.
 * With frame pointers (to be compliant with the ABI):
 *
 *                                high
 * original ARM_SP =>     +------------------+ \
 *                        |        pc        | |
 * current ARM_FP =>      +------------------+ } callee saved registers
 *                        |r4-r8,r10,fp,ip,lr| |
 *                        +------------------+ /
 *                                low
 *
 * Without frame pointers:
 *
 *                                high
 * original ARM_SP =>     +------------------+
 *                        | r4-r8,r10,fp,lr  | callee saved registers
 * current ARM_FP =>      +------------------+
 *                                low
 *
 * When popping registers off the stack at the end of a BPF function, we
 * reference them via the current ARM_FP register.
 */
#define CALLEE_MASK     (1 << ARM_R4 | 1 << ARM_R5 | 1 << ARM_R6 | \
                         1 << ARM_R7 | 1 << ARM_R8 | 1 << ARM_R10 | \
                         1 << ARM_FP)
#define CALLEE_PUSH_MASK (CALLEE_MASK | 1 << ARM_LR)
#define CALLEE_POP_MASK  (CALLEE_MASK | 1 << ARM_PC)

#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 */

#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.
 * 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 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);
}

#if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5)
/* EABI requires the stack to be aligned to 64-bit boundaries */
#define STACK_ALIGNMENT 8
#else
/* Stack must be aligned to 32-bit boundaries */
#define STACK_ALIGNMENT 4
#endif

/* 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 ALIGN(_STACK_SIZE, STACK_ALIGNMENT)

/* 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 void emit_bx_r(u8 tgt_reg, struct jit_ctx *ctx)
{
        if (elf_hwcap & HWCAP_THUMB)
                emit(ARM_BX(tgt_reg), ctx);
        else
                emit(ARM_MOV_R(ARM_PC, tgt_reg), ctx);
}

static inline void emit_blx_r(u8 tgt_reg, struct jit_ctx *ctx)
{
#if __LINUX_ARM_ARCH__ < 5
        emit(ARM_MOV_R(ARM_LR, ARM_PC), ctx);
        emit_bx_r(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];

#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 */
        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);
        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);
        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);
        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);
        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,
                              s32 off, struct jit_ctx *ctx, const u8 sz){
        const u8 *tmp = bpf2a32[TMP_REG_1];
        const u8 *rd = dstk ? tmp : dst;
        u8 rm = src;
        s32 off_max;

        if (sz == BPF_H)
                off_max = 0xff;
        else
                off_max = 0xfff;

        if (off < 0 || off > off_max) {
                emit_a32_mov_i(tmp[0], off, false, ctx);
                emit(ARM_ADD_R(tmp[0], tmp[0], src), ctx);
                rm = tmp[0];
                off = 0;
        } else if (rd[1] == rm) {
                emit(ARM_MOV_R(tmp[0], rm), ctx);
                rm = tmp[0];
        }
        switch (sz) {
        case BPF_B:
                /* Load a Byte */
                emit(ARM_LDRB_I(rd[1], rm, off), ctx);
                emit_a32_mov_i(dst[0], 0, dstk, ctx);
                break;
        case BPF_H:
                /* Load a HalfWord */
                emit(ARM_LDRH_I(rd[1], rm, off), ctx);
                emit_a32_mov_i(dst[0], 0, dstk, ctx);
                break;
        case BPF_W:
                /* Load a Word */
                emit(ARM_LDR_I(rd[1], rm, off), ctx);
                emit_a32_mov_i(dst[0], 0, dstk, ctx);
                break;
        case BPF_DW:
                /* Load a Double Word */
                emit(ARM_LDR_I(rd[1], rm, off), ctx);
                emit(ARM_LDR_I(rd[0], rm, off + 4), ctx);
                break;
        }
        if (dstk)
                emit(ARM_STR_I(rd[1], ARM_SP, STACK_VAR(dst[1])), ctx);
        if (dstk && sz == BPF_DW)
                emit(ARM_STR_I(rd[0], ARM_SP, STACK_VAR(dst[0])), 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:
                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) - 2)
        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 is 32-bit for arrays */
        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_bx_r(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 fplo = bpf2a32[BPF_REG_FP][1];
        const u8 fphi = bpf2a32[BPF_REG_FP][0];
        const u8 *tcc = bpf2a32[TCALL_CNT];

        /* Save callee saved registers. */
#ifdef CONFIG_FRAME_POINTER
        u16 reg_set = CALLEE_PUSH_MASK | 1 << ARM_IP | 1 << ARM_PC;
        emit(ARM_MOV_R(ARM_IP, ARM_SP), ctx);
        emit(ARM_PUSH(reg_set), ctx);
        emit(ARM_SUB_I(ARM_FP, ARM_IP, 4), ctx);
#else
        emit(ARM_PUSH(CALLEE_PUSH_MASK), ctx);
        emit(ARM_MOV_R(ARM_FP, ARM_SP), ctx);
#endif
        /* Save frame pointer for later */
        emit(ARM_SUB_I(ARM_IP, ARM_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 */
}

/* restore callee saved registers. */
static void build_epilogue(struct jit_ctx *ctx)
{
#ifdef CONFIG_FRAME_POINTER
        /* When using frame pointers, some additional registers need to
         * be loaded. */
        u16 reg_set = CALLEE_POP_MASK | 1 << ARM_SP;
        emit(ARM_SUB_I(ARM_SP, ARM_FP, hweight16(reg_set) * 4), ctx);
        emit(ARM_LDM(ARM_SP, reg_set), ctx);
#else
        /* Restore callee saved registers. */
        emit(ARM_MOV_R(ARM_SP, ARM_FP), ctx);
        emit(ARM_POP(CALLEE_POP_MASK), 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:
                        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);
                emit_ldx_r(dst, rn, dstk, off, ctx, BPF_SIZE(code));
                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 (!prog->jit_requested)
                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;
}