/*
 * Just-In-Time compiler for BPF filters on MIPS
 *
 * Copyright (c) 2014 Imagination Technologies Ltd.
 * Author: Markos Chandras <markos.chandras@imgtec.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/bitops.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/filter.h>
#include <linux/if_vlan.h>
#include <linux/kconfig.h>
#include <linux/moduleloader.h>
#include <linux/netdevice.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <asm/bitops.h>
#include <asm/cacheflush.h>
#include <asm/cpu-features.h>
#include <asm/uasm.h>

#include "bpf_jit.h"

/* ABI
 *
 * s0   1st scratch register
 * s1   2nd scratch register
 * s2   offset register
 * s3   BPF register A
 * s4   BPF register X
 * s5   *skb
 * s6   *scratch memory
 *
 * On entry (*bpf_func)(*skb, *filter)
 * a0 = MIPS_R_A0 = skb;
 * a1 = MIPS_R_A1 = filter;
 *
 * Stack
 * ...
 * M[15]
 * M[14]
 * M[13]
 * ...
 * M[0] <-- r_M
 * saved reg k-1
 * saved reg k-2
 * ...
 * saved reg 0 <-- r_sp
 * <no argument area>
 *
 *                     Packet layout
 *
 * <--------------------- len ------------------------>
 * <--skb-len(r_skb_hl)-->< ----- skb->data_len ------>
 * ----------------------------------------------------
 * |                  skb->data                       |
 * ----------------------------------------------------
 */

#define RSIZE   (sizeof(unsigned long))
#define ptr typeof(unsigned long)

/* ABI specific return values */
#ifdef CONFIG_32BIT /* O32 */
#ifdef CONFIG_CPU_LITTLE_ENDIAN
#define r_err   MIPS_R_V1
#define r_val   MIPS_R_V0
#else /* CONFIG_CPU_LITTLE_ENDIAN */
#define r_err   MIPS_R_V0
#define r_val   MIPS_R_V1
#endif
#else /* N64 */
#define r_err   MIPS_R_V0
#define r_val   MIPS_R_V0
#endif

#define r_ret   MIPS_R_V0

/*
 * Use 2 scratch registers to avoid pipeline interlocks.
 * There is no overhead during epilogue and prologue since
 * any of the $s0-$s6 registers will only be preserved if
 * they are going to actually be used.
 */
#define r_s0            MIPS_R_S0 /* scratch reg 1 */
#define r_s1            MIPS_R_S1 /* scratch reg 2 */
#define r_off           MIPS_R_S2
#define r_A             MIPS_R_S3
#define r_X             MIPS_R_S4
#define r_skb           MIPS_R_S5
#define r_M             MIPS_R_S6
#define r_tmp_imm       MIPS_R_T6 /* No need to preserve this */
#define r_tmp           MIPS_R_T7 /* No need to preserve this */
#define r_zero          MIPS_R_ZERO
#define r_sp            MIPS_R_SP
#define r_ra            MIPS_R_RA

#define SCRATCH_OFF(k)          (4 * (k))

/* JIT flags */
#define SEEN_CALL               (1 << BPF_MEMWORDS)
#define SEEN_SREG_SFT           (BPF_MEMWORDS + 1)
#define SEEN_SREG_BASE          (1 << SEEN_SREG_SFT)
#define SEEN_SREG(x)            (SEEN_SREG_BASE << (x))
#define SEEN_S0                 SEEN_SREG(0)
#define SEEN_S1                 SEEN_SREG(1)
#define SEEN_OFF                SEEN_SREG(2)
#define SEEN_A                  SEEN_SREG(3)
#define SEEN_X                  SEEN_SREG(4)
#define SEEN_SKB                SEEN_SREG(5)
#define SEEN_MEM                SEEN_SREG(6)

/* Arguments used by JIT */
#define ARGS_USED_BY_JIT        2 /* only applicable to 64-bit */

#define SBIT(x)                 (1 << (x)) /* Signed version of BIT() */

/**
 * struct jit_ctx - JIT context
 * @skf:                The sk_filter
 * @prologue_bytes:     Number of bytes for prologue
 * @idx:                Instruction index
 * @flags:              JIT flags
 * @offsets:            Instruction offsets
 * @target:             Memory location for the compiled filter
 */
struct jit_ctx {
        const struct bpf_prog *skf;
        unsigned int prologue_bytes;
        u32 idx;
        u32 flags;
        u32 *offsets;
        u32 *target;
};


static inline int optimize_div(u32 *k)
{
        /* power of 2 divides can be implemented with right shift */
        if (!(*k & (*k-1))) {
                *k = ilog2(*k);
                return 1;
        }

        return 0;
}

static inline void emit_jit_reg_move(ptr dst, ptr src, struct jit_ctx *ctx);

/* Simply emit the instruction if the JIT memory space has been allocated */
#define emit_instr(ctx, func, ...)                      \
do {                                                    \
        if ((ctx)->target != NULL) {                    \
                u32 *p = &(ctx)->target[ctx->idx];      \
                uasm_i_##func(&p, ##__VA_ARGS__);       \
        }                                               \
        (ctx)->idx++;                                   \
} while (0)

/*
 * Similar to emit_instr but it must be used when we need to emit
 * 32-bit or 64-bit instructions
 */
#define emit_long_instr(ctx, func, ...)                 \
do {                                                    \
        if ((ctx)->target != NULL) {                    \
                u32 *p = &(ctx)->target[ctx->idx];      \
                UASM_i_##func(&p, ##__VA_ARGS__);       \
        }                                               \
        (ctx)->idx++;                                   \
} while (0)

/* Determine if immediate is within the 16-bit signed range */
static inline bool is_range16(s32 imm)
{
        return !(imm >= SBIT(15) || imm < -SBIT(15));
}

static inline void emit_addu(unsigned int dst, unsigned int src1,
                             unsigned int src2, struct jit_ctx *ctx)
{
        emit_instr(ctx, addu, dst, src1, src2);
}

static inline void emit_nop(struct jit_ctx *ctx)
{
        emit_instr(ctx, nop);
}

/* Load a u32 immediate to a register */
static inline void emit_load_imm(unsigned int dst, u32 imm, struct jit_ctx *ctx)
{
        if (ctx->target != NULL) {
                /* addiu can only handle s16 */
                if (!is_range16(imm)) {
                        u32 *p = &ctx->target[ctx->idx];
                        uasm_i_lui(&p, r_tmp_imm, (s32)imm >> 16);
                        p = &ctx->target[ctx->idx + 1];
                        uasm_i_ori(&p, dst, r_tmp_imm, imm & 0xffff);
                } else {
                        u32 *p = &ctx->target[ctx->idx];
                        uasm_i_addiu(&p, dst, r_zero, imm);
                }
        }
        ctx->idx++;

        if (!is_range16(imm))
                ctx->idx++;
}

static inline void emit_or(unsigned int dst, unsigned int src1,
                           unsigned int src2, struct jit_ctx *ctx)
{
        emit_instr(ctx, or, dst, src1, src2);
}

static inline void emit_ori(unsigned int dst, unsigned src, u32 imm,
                            struct jit_ctx *ctx)
{
        if (imm >= BIT(16)) {
                emit_load_imm(r_tmp, imm, ctx);
                emit_or(dst, src, r_tmp, ctx);
        } else {
                emit_instr(ctx, ori, dst, src, imm);
        }
}

static inline void emit_daddiu(unsigned int dst, unsigned int src,
                               int imm, struct jit_ctx *ctx)
{
        /*
         * Only used for stack, so the imm is relatively small
         * and it fits in 15-bits
         */
        emit_instr(ctx, daddiu, dst, src, imm);
}

static inline void emit_addiu(unsigned int dst, unsigned int src,
                              u32 imm, struct jit_ctx *ctx)
{
        if (!is_range16(imm)) {
                emit_load_imm(r_tmp, imm, ctx);
                emit_addu(dst, r_tmp, src, ctx);
        } else {
                emit_instr(ctx, addiu, dst, src, imm);
        }
}

static inline void emit_and(unsigned int dst, unsigned int src1,
                            unsigned int src2, struct jit_ctx *ctx)
{
        emit_instr(ctx, and, dst, src1, src2);
}

static inline void emit_andi(unsigned int dst, unsigned int src,
                             u32 imm, struct jit_ctx *ctx)
{
        /* If imm does not fit in u16 then load it to register */
        if (imm >= BIT(16)) {
                emit_load_imm(r_tmp, imm, ctx);
                emit_and(dst, src, r_tmp, ctx);
        } else {
                emit_instr(ctx, andi, dst, src, imm);
        }
}

static inline void emit_xor(unsigned int dst, unsigned int src1,
                            unsigned int src2, struct jit_ctx *ctx)
{
        emit_instr(ctx, xor, dst, src1, src2);
}

static inline void emit_xori(ptr dst, ptr src, u32 imm, struct jit_ctx *ctx)
{
        /* If imm does not fit in u16 then load it to register */
        if (imm >= BIT(16)) {
                emit_load_imm(r_tmp, imm, ctx);
                emit_xor(dst, src, r_tmp, ctx);
        } else {
                emit_instr(ctx, xori, dst, src, imm);
        }
}

static inline void emit_stack_offset(int offset, struct jit_ctx *ctx)
{
        emit_long_instr(ctx, ADDIU, r_sp, r_sp, offset);
}

static inline void emit_subu(unsigned int dst, unsigned int src1,
                             unsigned int src2, struct jit_ctx *ctx)
{
        emit_instr(ctx, subu, dst, src1, src2);
}

static inline void emit_neg(unsigned int reg, struct jit_ctx *ctx)
{
        emit_subu(reg, r_zero, reg, ctx);
}

static inline void emit_sllv(unsigned int dst, unsigned int src,
                             unsigned int sa, struct jit_ctx *ctx)
{
        emit_instr(ctx, sllv, dst, src, sa);
}

static inline void emit_sll(unsigned int dst, unsigned int src,
                            unsigned int sa, struct jit_ctx *ctx)
{
        /* sa is 5-bits long */
        if (sa >= BIT(5))
                /* Shifting >= 32 results in zero */
                emit_jit_reg_move(dst, r_zero, ctx);
        else
                emit_instr(ctx, sll, dst, src, sa);
}

static inline void emit_srlv(unsigned int dst, unsigned int src,
                             unsigned int sa, struct jit_ctx *ctx)
{
        emit_instr(ctx, srlv, dst, src, sa);
}

static inline void emit_srl(unsigned int dst, unsigned int src,
                            unsigned int sa, struct jit_ctx *ctx)
{
        /* sa is 5-bits long */
        if (sa >= BIT(5))
                /* Shifting >= 32 results in zero */
                emit_jit_reg_move(dst, r_zero, ctx);
        else
                emit_instr(ctx, srl, dst, src, sa);
}

static inline void emit_slt(unsigned int dst, unsigned int src1,
                            unsigned int src2, struct jit_ctx *ctx)
{
        emit_instr(ctx, slt, dst, src1, src2);
}

static inline void emit_sltu(unsigned int dst, unsigned int src1,
                             unsigned int src2, struct jit_ctx *ctx)
{
        emit_instr(ctx, sltu, dst, src1, src2);
}

static inline void emit_sltiu(unsigned dst, unsigned int src,
                              unsigned int imm, struct jit_ctx *ctx)
{
        /* 16 bit immediate */
        if (!is_range16((s32)imm)) {
                emit_load_imm(r_tmp, imm, ctx);
                emit_sltu(dst, src, r_tmp, ctx);
        } else {
                emit_instr(ctx, sltiu, dst, src, imm);
        }

}

/* Store register on the stack */
static inline void emit_store_stack_reg(ptr reg, ptr base,
                                        unsigned int offset,
                                        struct jit_ctx *ctx)
{
        emit_long_instr(ctx, SW, reg, offset, base);
}

static inline void emit_store(ptr reg, ptr base, unsigned int offset,
                              struct jit_ctx *ctx)
{
        emit_instr(ctx, sw, reg, offset, base);
}

static inline void emit_load_stack_reg(ptr reg, ptr base,
                                       unsigned int offset,
                                       struct jit_ctx *ctx)
{
        emit_long_instr(ctx, LW, reg, offset, base);
}

static inline void emit_load(unsigned int reg, unsigned int base,
                             unsigned int offset, struct jit_ctx *ctx)
{
        emit_instr(ctx, lw, reg, offset, base);
}

static inline void emit_load_byte(unsigned int reg, unsigned int base,
                                  unsigned int offset, struct jit_ctx *ctx)
{
        emit_instr(ctx, lb, reg, offset, base);
}

static inline void emit_half_load(unsigned int reg, unsigned int base,
                                  unsigned int offset, struct jit_ctx *ctx)
{
        emit_instr(ctx, lh, reg, offset, base);
}

static inline void emit_mul(unsigned int dst, unsigned int src1,
                            unsigned int src2, struct jit_ctx *ctx)
{
        emit_instr(ctx, mul, dst, src1, src2);
}

static inline void emit_div(unsigned int dst, unsigned int src,
                            struct jit_ctx *ctx)
{
        if (ctx->target != NULL) {
                u32 *p = &ctx->target[ctx->idx];
                uasm_i_divu(&p, dst, src);
                p = &ctx->target[ctx->idx + 1];
                uasm_i_mflo(&p, dst);
        }
        ctx->idx += 2; /* 2 insts */
}

static inline void emit_mod(unsigned int dst, unsigned int src,
                            struct jit_ctx *ctx)
{
        if (ctx->target != NULL) {
                u32 *p = &ctx->target[ctx->idx];
                uasm_i_divu(&p, dst, src);
                p = &ctx->target[ctx->idx + 1];
                uasm_i_mfhi(&p, dst);
        }
        ctx->idx += 2; /* 2 insts */
}

static inline void emit_dsll(unsigned int dst, unsigned int src,
                             unsigned int sa, struct jit_ctx *ctx)
{
        emit_instr(ctx, dsll, dst, src, sa);
}

static inline void emit_dsrl32(unsigned int dst, unsigned int src,
                               unsigned int sa, struct jit_ctx *ctx)
{
        emit_instr(ctx, dsrl32, dst, src, sa);
}

static inline void emit_wsbh(unsigned int dst, unsigned int src,
                             struct jit_ctx *ctx)
{
        emit_instr(ctx, wsbh, dst, src);
}

/* load pointer to register */
static inline void emit_load_ptr(unsigned int dst, unsigned int src,
                                     int imm, struct jit_ctx *ctx)
{
        /* src contains the base addr of the 32/64-pointer */
        emit_long_instr(ctx, LW, dst, imm, src);
}

/* load a function pointer to register */
static inline void emit_load_func(unsigned int reg, ptr imm,
                                  struct jit_ctx *ctx)
{
        if (config_enabled(CONFIG_64BIT)) {
                /* At this point imm is always 64-bit */
                emit_load_imm(r_tmp, (u64)imm >> 32, ctx);
                emit_dsll(r_tmp_imm, r_tmp, 16, ctx); /* left shift by 16 */
                emit_ori(r_tmp, r_tmp_imm, (imm >> 16) & 0xffff, ctx);
                emit_dsll(r_tmp_imm, r_tmp, 16, ctx); /* left shift by 16 */
                emit_ori(reg, r_tmp_imm, imm & 0xffff, ctx);
        } else {
                emit_load_imm(reg, imm, ctx);
        }
}

/* Move to real MIPS register */
static inline void emit_reg_move(ptr dst, ptr src, struct jit_ctx *ctx)
{
        emit_long_instr(ctx, ADDU, dst, src, r_zero);
}

/* Move to JIT (32-bit) register */
static inline void emit_jit_reg_move(ptr dst, ptr src, struct jit_ctx *ctx)
{
        emit_addu(dst, src, r_zero, ctx);
}

/* Compute the immediate value for PC-relative branches. */
static inline u32 b_imm(unsigned int tgt, struct jit_ctx *ctx)
{
        if (ctx->target == NULL)
                return 0;

        /*
         * We want a pc-relative branch. We only do forward branches
         * so tgt is always after pc. tgt is the instruction offset
         * we want to jump to.

         * Branch on MIPS:
         * I: target_offset <- sign_extend(offset)
         * I+1: PC += target_offset (delay slot)
         *
         * ctx->idx currently points to the branch instruction
         * but the offset is added to the delay slot so we need
         * to subtract 4.
         */
        return ctx->offsets[tgt] -
                (ctx->idx * 4 - ctx->prologue_bytes) - 4;
}

static inline void emit_bcond(int cond, unsigned int reg1, unsigned int reg2,
                             unsigned int imm, struct jit_ctx *ctx)
{
        if (ctx->target != NULL) {
                u32 *p = &ctx->target[ctx->idx];

                switch (cond) {
                case MIPS_COND_EQ:
                        uasm_i_beq(&p, reg1, reg2, imm);
                        break;
                case MIPS_COND_NE:
                        uasm_i_bne(&p, reg1, reg2, imm);
                        break;
                case MIPS_COND_ALL:
                        uasm_i_b(&p, imm);
                        break;
                default:
                        pr_warn("%s: Unhandled branch conditional: %d\n",
                                __func__, cond);
                }
        }
        ctx->idx++;
}

static inline void emit_b(unsigned int imm, struct jit_ctx *ctx)
{
        emit_bcond(MIPS_COND_ALL, r_zero, r_zero, imm, ctx);
}

static inline void emit_jalr(unsigned int link, unsigned int reg,
                             struct jit_ctx *ctx)
{
        emit_instr(ctx, jalr, link, reg);
}

static inline void emit_jr(unsigned int reg, struct jit_ctx *ctx)
{
        emit_instr(ctx, jr, reg);
}

static inline u16 align_sp(unsigned int num)
{
        /* Double word alignment for 32-bit, quadword for 64-bit */
        unsigned int align = config_enabled(CONFIG_64BIT) ? 16 : 8;
        num = (num + (align - 1)) & -align;
        return num;
}

static bool is_load_to_a(u16 inst)
{
        switch (inst) {
        case BPF_LD | BPF_W | BPF_LEN:
        case BPF_LD | BPF_W | BPF_ABS:
        case BPF_LD | BPF_H | BPF_ABS:
        case BPF_LD | BPF_B | BPF_ABS:
                return true;
        default:
                return false;
        }
}

static void save_bpf_jit_regs(struct jit_ctx *ctx, unsigned offset)
{
        int i = 0, real_off = 0;
        u32 sflags, tmp_flags;

        /* Adjust the stack pointer */
        emit_stack_offset(-align_sp(offset), ctx);

        if (ctx->flags & SEEN_CALL) {
                /* Argument save area */
                if (config_enabled(CONFIG_64BIT))
                        /* Bottom of current frame */
                        real_off = align_sp(offset) - RSIZE;
                else
                        /* Top of previous frame */
                        real_off = align_sp(offset) + RSIZE;
                emit_store_stack_reg(MIPS_R_A0, r_sp, real_off, ctx);
                emit_store_stack_reg(MIPS_R_A1, r_sp, real_off + RSIZE, ctx);

                real_off = 0;
        }

        tmp_flags = sflags = ctx->flags >> SEEN_SREG_SFT;
        /* sflags is essentially a bitmap */
        while (tmp_flags) {
                if ((sflags >> i) & 0x1) {
                        emit_store_stack_reg(MIPS_R_S0 + i, r_sp, real_off,
                                             ctx);
                        real_off += RSIZE;
                }
                i++;
                tmp_flags >>= 1;
        }

        /* save return address */
        if (ctx->flags & SEEN_CALL) {
                emit_store_stack_reg(r_ra, r_sp, real_off, ctx);
                real_off += RSIZE;
        }

        /* Setup r_M leaving the alignment gap if necessary */
        if (ctx->flags & SEEN_MEM) {
                if (real_off % (RSIZE * 2))
                        real_off += RSIZE;
                emit_long_instr(ctx, ADDIU, r_M, r_sp, real_off);
        }
}

static void restore_bpf_jit_regs(struct jit_ctx *ctx,
                                 unsigned int offset)
{
        int i, real_off = 0;
        u32 sflags, tmp_flags;

        if (ctx->flags & SEEN_CALL) {
                if (config_enabled(CONFIG_64BIT))
                        /* Bottom of current frame */
                        real_off = align_sp(offset) - RSIZE;
                else
                        /* Top of previous frame */
                        real_off = align_sp(offset) + RSIZE;
                emit_load_stack_reg(MIPS_R_A0, r_sp, real_off, ctx);
                emit_load_stack_reg(MIPS_R_A1, r_sp, real_off + RSIZE, ctx);

                real_off = 0;
        }

        tmp_flags = sflags = ctx->flags >> SEEN_SREG_SFT;
        /* sflags is a bitmap */
        i = 0;
        while (tmp_flags) {
                if ((sflags >> i) & 0x1) {
                        emit_load_stack_reg(MIPS_R_S0 + i, r_sp, real_off,
                                            ctx);
                        real_off += RSIZE;
                }
                i++;
                tmp_flags >>= 1;
        }

        /* restore return address */
        if (ctx->flags & SEEN_CALL)
                emit_load_stack_reg(r_ra, r_sp, real_off, ctx);

        /* Restore the sp and discard the scrach memory */
        emit_stack_offset(align_sp(offset), ctx);
}

static unsigned int get_stack_depth(struct jit_ctx *ctx)
{
        int sp_off = 0;


        /* How may s* regs do we need to preserved? */
        sp_off += hweight32(ctx->flags >> SEEN_SREG_SFT) * RSIZE;

        if (ctx->flags & SEEN_MEM)
                sp_off += 4 * BPF_MEMWORDS; /* BPF_MEMWORDS are 32-bit */

        if (ctx->flags & SEEN_CALL)
                /*
                 * The JIT code make calls to external functions using 2
                 * arguments. Therefore, for o32 we don't need to allocate
                 * space because we don't care if the argumetns are lost
                 * across calls. We do need however to preserve incoming
                 * arguments but the space is already allocated for us by
                 * the caller. On the other hand, for n64, we need to allocate
                 * this space ourselves. We need to preserve $ra as well.
                 */
                sp_off += config_enabled(CONFIG_64BIT) ?
                        (ARGS_USED_BY_JIT + 1) * RSIZE : RSIZE;

        return sp_off;
}

static void build_prologue(struct jit_ctx *ctx)
{
        u16 first_inst = ctx->skf->insns[0].code;
        int sp_off;

        /* Calculate the total offset for the stack pointer */
        sp_off = get_stack_depth(ctx);
        save_bpf_jit_regs(ctx, sp_off);

        if (ctx->flags & SEEN_SKB)
                emit_reg_move(r_skb, MIPS_R_A0, ctx);

        if (ctx->flags & SEEN_X)
                emit_jit_reg_move(r_X, r_zero, ctx);

        /* Do not leak kernel data to userspace */
        if ((first_inst != (BPF_RET | BPF_K)) && !(is_load_to_a(first_inst)))
                emit_jit_reg_move(r_A, r_zero, ctx);
}

static void build_epilogue(struct jit_ctx *ctx)
{
        unsigned int sp_off;

        /* Calculate the total offset for the stack pointer */

        sp_off = get_stack_depth(ctx);
        restore_bpf_jit_regs(ctx, sp_off);

        /* Return */
        emit_jr(r_ra, ctx);
        emit_nop(ctx);
}

static u64 jit_get_skb_b(struct sk_buff *skb, unsigned offset)
{
        u8 ret;
        int err;

        err = skb_copy_bits(skb, offset, &ret, 1);

        return (u64)err << 32 | ret;
}

static u64 jit_get_skb_h(struct sk_buff *skb, unsigned offset)
{
        u16 ret;
        int err;

        err = skb_copy_bits(skb, offset, &ret, 2);

        return (u64)err << 32 | ntohs(ret);
}

static u64 jit_get_skb_w(struct sk_buff *skb, unsigned offset)
{
        u32 ret;
        int err;

        err = skb_copy_bits(skb, offset, &ret, 4);

        return (u64)err << 32 | ntohl(ret);
}

static int build_body(struct jit_ctx *ctx)
{
        void *load_func[] = {jit_get_skb_b, jit_get_skb_h, jit_get_skb_w};
        const struct bpf_prog *prog = ctx->skf;
        const struct sock_filter *inst;
        unsigned int i, off, load_order, condt;
        u32 k, b_off __maybe_unused;

        for (i = 0; i < prog->len; i++) {
                u16 code;

                inst = &(prog->insns[i]);
                pr_debug("%s: code->0x%02x, jt->0x%x, jf->0x%x, k->0x%x\n",
                         __func__, inst->code, inst->jt, inst->jf, inst->k);
                k = inst->k;
                code = bpf_anc_helper(inst);

                if (ctx->target == NULL)
                        ctx->offsets[i] = ctx->idx * 4;

                switch (code) {
                case BPF_LD | BPF_IMM:
                        /* A <- k ==> li r_A, k */
                        ctx->flags |= SEEN_A;
                        emit_load_imm(r_A, k, ctx);
                        break;
                case BPF_LD | BPF_W | BPF_LEN:
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
                        /* A <- len ==> lw r_A, offset(skb) */
                        ctx->flags |= SEEN_SKB | SEEN_A;
                        off = offsetof(struct sk_buff, len);
                        emit_load(r_A, r_skb, off, ctx);
                        break;
                case BPF_LD | BPF_MEM:
                        /* A <- M[k] ==> lw r_A, offset(M) */
                        ctx->flags |= SEEN_MEM | SEEN_A;
                        emit_load(r_A, r_M, SCRATCH_OFF(k), ctx);
                        break;
                case BPF_LD | BPF_W | BPF_ABS:
                        /* A <- P[k:4] */
                        load_order = 2;
                        goto load;
                case BPF_LD | BPF_H | BPF_ABS:
                        /* A <- P[k:2] */
                        load_order = 1;
                        goto load;
                case BPF_LD | BPF_B | BPF_ABS:
                        /* A <- P[k:1] */
                        load_order = 0;
load:
                        /* the interpreter will deal with the negative K */
                        if ((int)k < 0)
                                return -ENOTSUPP;

                        emit_load_imm(r_off, k, ctx);
load_common:
                        /*
                         * We may got here from the indirect loads so
                         * return if offset is negative.
                         */
                        emit_slt(r_s0, r_off, r_zero, ctx);
                        emit_bcond(MIPS_COND_NE, r_s0, r_zero,
                                   b_imm(prog->len, ctx), ctx);
                        emit_reg_move(r_ret, r_zero, ctx);

                        ctx->flags |= SEEN_CALL | SEEN_OFF | SEEN_S0 |
                                SEEN_SKB | SEEN_A;

                        emit_load_func(r_s0, (ptr)load_func[load_order],
                                      ctx);
                        emit_reg_move(MIPS_R_A0, r_skb, ctx);
                        emit_jalr(MIPS_R_RA, r_s0, ctx);
                        /* Load second argument to delay slot */
                        emit_reg_move(MIPS_R_A1, r_off, ctx);
                        /* Check the error value */
                        if (config_enabled(CONFIG_64BIT)) {
                                /* Get error code from the top 32-bits */
                                emit_dsrl32(r_s0, r_val, 0, ctx);
                                /* Branch to 3 instructions ahead */
                                emit_bcond(MIPS_COND_NE, r_s0, r_zero, 3 << 2,
                                           ctx);
                        } else {
                                /* Branch to 3 instructions ahead */
                                emit_bcond(MIPS_COND_NE, r_err, r_zero, 3 << 2,
                                           ctx);
                        }
                        emit_nop(ctx);
                        /* We are good */
                        emit_b(b_imm(i + 1, ctx), ctx);
                        emit_jit_reg_move(r_A, r_val, ctx);
                        /* Return with error */
                        emit_b(b_imm(prog->len, ctx), ctx);
                        emit_reg_move(r_ret, r_zero, ctx);
                        break;
                case BPF_LD | BPF_W | BPF_IND:
                        /* A <- P[X + k:4] */
                        load_order = 2;
                        goto load_ind;
                case BPF_LD | BPF_H | BPF_IND:
                        /* A <- P[X + k:2] */
                        load_order = 1;
                        goto load_ind;
                case BPF_LD | BPF_B | BPF_IND:
                        /* A <- P[X + k:1] */
                        load_order = 0;
load_ind:
                        ctx->flags |= SEEN_OFF | SEEN_X;
                        emit_addiu(r_off, r_X, k, ctx);
                        goto load_common;
                case BPF_LDX | BPF_IMM:
                        /* X <- k */
                        ctx->flags |= SEEN_X;
                        emit_load_imm(r_X, k, ctx);
                        break;
                case BPF_LDX | BPF_MEM:
                        /* X <- M[k] */
                        ctx->flags |= SEEN_X | SEEN_MEM;
                        emit_load(r_X, r_M, SCRATCH_OFF(k), ctx);
                        break;
                case BPF_LDX | BPF_W | BPF_LEN:
                        /* X <- len */
                        ctx->flags |= SEEN_X | SEEN_SKB;
                        off = offsetof(struct sk_buff, len);
                        emit_load(r_X, r_skb, off, ctx);
                        break;
                case BPF_LDX | BPF_B | BPF_MSH:
                        /* the interpreter will deal with the negative K */
                        if ((int)k < 0)
                                return -ENOTSUPP;

                        /* X <- 4 * (P[k:1] & 0xf) */
                        ctx->flags |= SEEN_X | SEEN_CALL | SEEN_S0 | SEEN_SKB;
                        /* Load offset to a1 */
                        emit_load_func(r_s0, (ptr)jit_get_skb_b, ctx);
                        /*
                         * This may emit two instructions so it may not fit
                         * in the delay slot. So use a0 in the delay slot.
                         */
                        emit_load_imm(MIPS_R_A1, k, ctx);
                        emit_jalr(MIPS_R_RA, r_s0, ctx);
                        emit_reg_move(MIPS_R_A0, r_skb, ctx); /* delay slot */
                        /* Check the error value */
                        if (config_enabled(CONFIG_64BIT)) {
                                /* Top 32-bits of $v0 on 64-bit */
                                emit_dsrl32(r_s0, r_val, 0, ctx);
                                emit_bcond(MIPS_COND_NE, r_s0, r_zero,
                                           3 << 2, ctx);
                        } else {
                                emit_bcond(MIPS_COND_NE, r_err, r_zero,
                                           3 << 2, ctx);
                        }
                        /* No need for delay slot */
                        /* We are good */
                        /* X <- P[1:K] & 0xf */
                        emit_andi(r_X, r_val, 0xf, ctx);
                        /* X << 2 */
                        emit_b(b_imm(i + 1, ctx), ctx);
                        emit_sll(r_X, r_X, 2, ctx); /* delay slot */
                        /* Return with error */
                        emit_b(b_imm(prog->len, ctx), ctx);
                        emit_load_imm(r_ret, 0, ctx); /* delay slot */
                        break;
                case BPF_ST:
                        /* M[k] <- A */
                        ctx->flags |= SEEN_MEM | SEEN_A;
                        emit_store(r_A, r_M, SCRATCH_OFF(k), ctx);
                        break;
                case BPF_STX:
                        /* M[k] <- X */
                        ctx->flags |= SEEN_MEM | SEEN_X;
                        emit_store(r_X, r_M, SCRATCH_OFF(k), ctx);
                        break;
                case BPF_ALU | BPF_ADD | BPF_K:
                        /* A += K */
                        ctx->flags |= SEEN_A;
                        emit_addiu(r_A, r_A, k, ctx);
                        break;
                case BPF_ALU | BPF_ADD | BPF_X:
                        /* A += X */
                        ctx->flags |= SEEN_A | SEEN_X;
                        emit_addu(r_A, r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_SUB | BPF_K:
                        /* A -= K */
                        ctx->flags |= SEEN_A;
                        emit_addiu(r_A, r_A, -k, ctx);
                        break;
                case BPF_ALU | BPF_SUB | BPF_X:
                        /* A -= X */
                        ctx->flags |= SEEN_A | SEEN_X;
                        emit_subu(r_A, r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_MUL | BPF_K:
                        /* A *= K */
                        /* Load K to scratch register before MUL */
                        ctx->flags |= SEEN_A | SEEN_S0;
                        emit_load_imm(r_s0, k, ctx);
                        emit_mul(r_A, r_A, r_s0, ctx);
                        break;
                case BPF_ALU | BPF_MUL | BPF_X:
                        /* A *= X */
                        ctx->flags |= SEEN_A | SEEN_X;
                        emit_mul(r_A, r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_DIV | BPF_K:
                        /* A /= k */
                        if (k == 1)
                                break;
                        if (optimize_div(&k)) {
                                ctx->flags |= SEEN_A;
                                emit_srl(r_A, r_A, k, ctx);
                                break;
                        }
                        ctx->flags |= SEEN_A | SEEN_S0;
                        emit_load_imm(r_s0, k, ctx);
                        emit_div(r_A, r_s0, ctx);
                        break;
                case BPF_ALU | BPF_MOD | BPF_K:
                        /* A %= k */
                        if (k == 1) {
                                ctx->flags |= SEEN_A;
                                emit_jit_reg_move(r_A, r_zero, ctx);
                        } else {
                                ctx->flags |= SEEN_A | SEEN_S0;
                                emit_load_imm(r_s0, k, ctx);
                                emit_mod(r_A, r_s0, ctx);
                        }
                        break;
                case BPF_ALU | BPF_DIV | BPF_X:
                        /* A /= X */
                        ctx->flags |= SEEN_X | SEEN_A;
                        /* Check if r_X is zero */
                        emit_bcond(MIPS_COND_EQ, r_X, r_zero,
                                   b_imm(prog->len, ctx), ctx);
                        emit_load_imm(r_val, 0, ctx); /* delay slot */
                        emit_div(r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_MOD | BPF_X:
                        /* A %= X */
                        ctx->flags |= SEEN_X | SEEN_A;
                        /* Check if r_X is zero */
                        emit_bcond(MIPS_COND_EQ, r_X, r_zero,
                                   b_imm(prog->len, ctx), ctx);
                        emit_load_imm(r_val, 0, ctx); /* delay slot */
                        emit_mod(r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_OR | BPF_K:
                        /* A |= K */
                        ctx->flags |= SEEN_A;
                        emit_ori(r_A, r_A, k, ctx);

                        break;
                case BPF_ALU | BPF_OR | BPF_X:
                        /* A |= X */
                        ctx->flags |= SEEN_A;
                        emit_ori(r_A, r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_XOR | BPF_K:
                        /* A ^= k */
                        ctx->flags |= SEEN_A;
                        emit_xori(r_A, r_A, k, ctx);
                        break;
                case BPF_ANC | SKF_AD_ALU_XOR_X:
                case BPF_ALU | BPF_XOR | BPF_X:
                        /* A ^= X */
                        ctx->flags |= SEEN_A;
                        emit_xor(r_A, r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_AND | BPF_K:
                        /* A &= K */
                        ctx->flags |= SEEN_A;
                        emit_andi(r_A, r_A, k, ctx);
                        break;
                case BPF_ALU | BPF_AND | BPF_X:
                        /* A &= X */
                        ctx->flags |= SEEN_A | SEEN_X;
                        emit_and(r_A, r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_LSH | BPF_K:
                        /* A <<= K */
                        ctx->flags |= SEEN_A;
                        emit_sll(r_A, r_A, k, ctx);
                        break;
                case BPF_ALU | BPF_LSH | BPF_X:
                        /* A <<= X */
                        ctx->flags |= SEEN_A | SEEN_X;
                        emit_sllv(r_A, r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_RSH | BPF_K:
                        /* A >>= K */
                        ctx->flags |= SEEN_A;
                        emit_srl(r_A, r_A, k, ctx);
                        break;
                case BPF_ALU | BPF_RSH | BPF_X:
                        ctx->flags |= SEEN_A | SEEN_X;
                        emit_srlv(r_A, r_A, r_X, ctx);
                        break;
                case BPF_ALU | BPF_NEG:
                        /* A = -A */
                        ctx->flags |= SEEN_A;
                        emit_neg(r_A, ctx);
                        break;
                case BPF_JMP | BPF_JA:
                        /* pc += K */
                        emit_b(b_imm(i + k + 1, ctx), ctx);
                        emit_nop(ctx);
                        break;
                case BPF_JMP | BPF_JEQ | BPF_K:
                        /* pc += ( A == K ) ? pc->jt : pc->jf */
                        condt = MIPS_COND_EQ | MIPS_COND_K;
                        goto jmp_cmp;
                case BPF_JMP | BPF_JEQ | BPF_X:
                        ctx->flags |= SEEN_X;
                        /* pc += ( A == X ) ? pc->jt : pc->jf */
                        condt = MIPS_COND_EQ | MIPS_COND_X;
                        goto jmp_cmp;
                case BPF_JMP | BPF_JGE | BPF_K:
                        /* pc += ( A >= K ) ? pc->jt : pc->jf */
                        condt = MIPS_COND_GE | MIPS_COND_K;
                        goto jmp_cmp;
                case BPF_JMP | BPF_JGE | BPF_X:
                        ctx->flags |= SEEN_X;
                        /* pc += ( A >= X ) ? pc->jt : pc->jf */
                        condt = MIPS_COND_GE | MIPS_COND_X;
                        goto jmp_cmp;
                case BPF_JMP | BPF_JGT | BPF_K:
                        /* pc += ( A > K ) ? pc->jt : pc->jf */
                        condt = MIPS_COND_GT | MIPS_COND_K;
                        goto jmp_cmp;
                case BPF_JMP | BPF_JGT | BPF_X:
                        ctx->flags |= SEEN_X;
                        /* pc += ( A > X ) ? pc->jt : pc->jf */
                        condt = MIPS_COND_GT | MIPS_COND_X;
jmp_cmp:
                        /* Greater or Equal */
                        if ((condt & MIPS_COND_GE) ||
                            (condt & MIPS_COND_GT)) {
                                if (condt & MIPS_COND_K) { /* K */
                                        ctx->flags |= SEEN_S0 | SEEN_A;
                                        emit_sltiu(r_s0, r_A, k, ctx);
                                } else { /* X */
                                        ctx->flags |= SEEN_S0 | SEEN_A |
                                                SEEN_X;
                                        emit_sltu(r_s0, r_A, r_X, ctx);
                                }
                                /* A < (K|X) ? r_scrach = 1 */
                                b_off = b_imm(i + inst->jf + 1, ctx);
                                emit_bcond(MIPS_COND_NE, r_s0, r_zero, b_off,
                                           ctx);
                                emit_nop(ctx);
                                /* A > (K|X) ? scratch = 0 */
                                if (condt & MIPS_COND_GT) {
                                        /* Checking for equality */
                                        ctx->flags |= SEEN_S0 | SEEN_A | SEEN_X;
                                        if (condt & MIPS_COND_K)
                                                emit_load_imm(r_s0, k, ctx);
                                        else
                                                emit_jit_reg_move(r_s0, r_X,
                                                                  ctx);
                                        b_off = b_imm(i + inst->jf + 1, ctx);
                                        emit_bcond(MIPS_COND_EQ, r_A, r_s0,
                                                   b_off, ctx);
                                        emit_nop(ctx);
                                        /* Finally, A > K|X */
                                        b_off = b_imm(i + inst->jt + 1, ctx);
                                        emit_b(b_off, ctx);
                                        emit_nop(ctx);
                                } else {
                                        /* A >= (K|X) so jump */
                                        b_off = b_imm(i + inst->jt + 1, ctx);
                                        emit_b(b_off, ctx);
                                        emit_nop(ctx);
                                }
                        } else {
                                /* A == K|X */
                                if (condt & MIPS_COND_K) { /* K */
                                        ctx->flags |= SEEN_S0 | SEEN_A;
                                        emit_load_imm(r_s0, k, ctx);
                                        /* jump true */
                                        b_off = b_imm(i + inst->jt + 1, ctx);
                                        emit_bcond(MIPS_COND_EQ, r_A, r_s0,
                                                   b_off, ctx);
                                        emit_nop(ctx);
                                        /* jump false */
                                        b_off = b_imm(i + inst->jf + 1,
                                                      ctx);
                                        emit_bcond(MIPS_COND_NE, r_A, r_s0,
                                                   b_off, ctx);
                                        emit_nop(ctx);
                                } else { /* X */
                                        /* jump true */
                                        ctx->flags |= SEEN_A | SEEN_X;
                                        b_off = b_imm(i + inst->jt + 1,
                                                      ctx);
                                        emit_bcond(MIPS_COND_EQ, r_A, r_X,
                                                   b_off, ctx);
                                        emit_nop(ctx);
                                        /* jump false */
                                        b_off = b_imm(i + inst->jf + 1, ctx);
                                        emit_bcond(MIPS_COND_NE, r_A, r_X,
                                                   b_off, ctx);
                                        emit_nop(ctx);
                                }
                        }
                        break;
                case BPF_JMP | BPF_JSET | BPF_K:
                        ctx->flags |= SEEN_S0 | SEEN_S1 | SEEN_A;
                        /* pc += (A & K) ? pc -> jt : pc -> jf */
                        emit_load_imm(r_s1, k, ctx);
                        emit_and(r_s0, r_A, r_s1, ctx);
                        /* jump true */
                        b_off = b_imm(i + inst->jt + 1, ctx);
                        emit_bcond(MIPS_COND_NE, r_s0, r_zero, b_off, ctx);
                        emit_nop(ctx);
                        /* jump false */
                        b_off = b_imm(i + inst->jf + 1, ctx);
                        emit_b(b_off, ctx);
                        emit_nop(ctx);
                        break;
                case BPF_JMP | BPF_JSET | BPF_X:
                        ctx->flags |= SEEN_S0 | SEEN_X | SEEN_A;
                        /* pc += (A & X) ? pc -> jt : pc -> jf */
                        emit_and(r_s0, r_A, r_X, ctx);
                        /* jump true */
                        b_off = b_imm(i + inst->jt + 1, ctx);
                        emit_bcond(MIPS_COND_NE, r_s0, r_zero, b_off, ctx);
                        emit_nop(ctx);
                        /* jump false */
                        b_off = b_imm(i + inst->jf + 1, ctx);
                        emit_b(b_off, ctx);
                        emit_nop(ctx);
                        break;
                case BPF_RET | BPF_A:
                        ctx->flags |= SEEN_A;
                        if (i != prog->len - 1)
                                /*
                                 * If this is not the last instruction
                                 * then jump to the epilogue
                                 */
                                emit_b(b_imm(prog->len, ctx), ctx);
                        emit_reg_move(r_ret, r_A, ctx); /* delay slot */
                        break;
                case BPF_RET | BPF_K:
                        /*
                         * It can emit two instructions so it does not fit on
                         * the delay slot.
                         */
                        emit_load_imm(r_ret, k, ctx);
                        if (i != prog->len - 1) {
                                /*
                                 * If this is not the last instruction
                                 * then jump to the epilogue
                                 */
                                emit_b(b_imm(prog->len, ctx), ctx);
                                emit_nop(ctx);
                        }
                        break;
                case BPF_MISC | BPF_TAX:
                        /* X = A */
                        ctx->flags |= SEEN_X | SEEN_A;
                        emit_jit_reg_move(r_X, r_A, ctx);
                        break;
                case BPF_MISC | BPF_TXA:
                        /* A = X */
                        ctx->flags |= SEEN_A | SEEN_X;
                        emit_jit_reg_move(r_A, r_X, ctx);
                        break;
                /* AUX */
                case BPF_ANC | SKF_AD_PROTOCOL:
                        /* A = ntohs(skb->protocol */
                        ctx->flags |= SEEN_SKB | SEEN_OFF | SEEN_A;
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
                                                  protocol) != 2);
                        off = offsetof(struct sk_buff, protocol);
                        emit_half_load(r_A, r_skb, off, ctx);
#ifdef CONFIG_CPU_LITTLE_ENDIAN
                        /* This needs little endian fixup */
                        if (cpu_has_wsbh) {
                                /* R2 and later have the wsbh instruction */
                                emit_wsbh(r_A, r_A, ctx);
                        } else {
                                /* Get first byte */
                                emit_andi(r_tmp_imm, r_A, 0xff, ctx);
                                /* Shift it */
                                emit_sll(r_tmp, r_tmp_imm, 8, ctx);
                                /* Get second byte */
                                emit_srl(r_tmp_imm, r_A, 8, ctx);
                                emit_andi(r_tmp_imm, r_tmp_imm, 0xff, ctx);
                                /* Put everyting together in r_A */
                                emit_or(r_A, r_tmp, r_tmp_imm, ctx);
                        }
#endif
                        break;
                case BPF_ANC | SKF_AD_CPU:
                        ctx->flags |= SEEN_A | SEEN_OFF;
                        /* A = current_thread_info()->cpu */
                        BUILD_BUG_ON(FIELD_SIZEOF(struct thread_info,
                                                  cpu) != 4);
                        off = offsetof(struct thread_info, cpu);
                        /* $28/gp points to the thread_info struct */
                        emit_load(r_A, 28, off, ctx);
                        break;
                case BPF_ANC | SKF_AD_IFINDEX:
                        /* A = skb->dev->ifindex */
                        ctx->flags |= SEEN_SKB | SEEN_A | SEEN_S0;
                        off = offsetof(struct sk_buff, dev);
                        /* Load *dev pointer */
                        emit_load_ptr(r_s0, r_skb, off, ctx);
                        /* error (0) in the delay slot */
                        emit_bcond(MIPS_COND_EQ, r_s0, r_zero,
                                   b_imm(prog->len, ctx), ctx);
                        emit_reg_move(r_ret, r_zero, ctx);
                        BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
                                                  ifindex) != 4);
                        off = offsetof(struct net_device, ifindex);
                        emit_load(r_A, r_s0, off, ctx);
                        break;
                case BPF_ANC | SKF_AD_MARK:
                        ctx->flags |= SEEN_SKB | SEEN_A;
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
                        off = offsetof(struct sk_buff, mark);
                        emit_load(r_A, r_skb, off, ctx);
                        break;
                case BPF_ANC | SKF_AD_RXHASH:
                        ctx->flags |= SEEN_SKB | SEEN_A;
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4);
                        off = offsetof(struct sk_buff, hash);
                        emit_load(r_A, r_skb, off, ctx);
                        break;
                case BPF_ANC | SKF_AD_VLAN_TAG:
                case BPF_ANC | SKF_AD_VLAN_TAG_PRESENT:
                        ctx->flags |= SEEN_SKB | SEEN_S0 | SEEN_A;
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
                                                  vlan_tci) != 2);
                        off = offsetof(struct sk_buff, vlan_tci);
                        emit_half_load(r_s0, r_skb, off, ctx);
                        if (code == (BPF_ANC | SKF_AD_VLAN_TAG)) {
                                emit_andi(r_A, r_s0, (u16)~VLAN_TAG_PRESENT, ctx);
                        } else {
                                emit_andi(r_A, r_s0, VLAN_TAG_PRESENT, ctx);
                                /* return 1 if present */
                                emit_sltu(r_A, r_zero, r_A, ctx);
                        }
                        break;
                case BPF_ANC | SKF_AD_PKTTYPE:
                        ctx->flags |= SEEN_SKB;

                        emit_load_byte(r_tmp, r_skb, PKT_TYPE_OFFSET(), ctx);
                        /* Keep only the last 3 bits */
                        emit_andi(r_A, r_tmp, PKT_TYPE_MAX, ctx);
#ifdef __BIG_ENDIAN_BITFIELD
                        /* Get the actual packet type to the lower 3 bits */
                        emit_srl(r_A, r_A, 5, ctx);
#endif
                        break;
                case BPF_ANC | SKF_AD_QUEUE:
                        ctx->flags |= SEEN_SKB | SEEN_A;
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
                                                  queue_mapping) != 2);
                        BUILD_BUG_ON(offsetof(struct sk_buff,
                                              queue_mapping) > 0xff);
                        off = offsetof(struct sk_buff, queue_mapping);
                        emit_half_load(r_A, r_skb, off, ctx);
                        break;
                default:
                        pr_debug("%s: Unhandled opcode: 0x%02x\n", __FILE__,
                                 inst->code);
                        return -1;
                }
        }

        /* compute offsets only during the first pass */
        if (ctx->target == NULL)
                ctx->offsets[i] = ctx->idx * 4;

        return 0;
}

int bpf_jit_enable __read_mostly;

void bpf_jit_compile(struct bpf_prog *fp)
{
        struct jit_ctx ctx;
        unsigned int alloc_size, tmp_idx;

        if (!bpf_jit_enable)
                return;

        memset(&ctx, 0, sizeof(ctx));

        ctx.offsets = kcalloc(fp->len, sizeof(*ctx.offsets), GFP_KERNEL);
        if (ctx.offsets == NULL)
                return;

        ctx.skf = fp;

        if (build_body(&ctx))
                goto out;

        tmp_idx = ctx.idx;
        build_prologue(&ctx);
        ctx.prologue_bytes = (ctx.idx - tmp_idx) * 4;
        /* just to complete the ctx.idx count */
        build_epilogue(&ctx);

        alloc_size = 4 * ctx.idx;
        ctx.target = module_alloc(alloc_size);
        if (ctx.target == NULL)
                goto out;

        /* Clean it */
        memset(ctx.target, 0, alloc_size);

        ctx.idx = 0;

        /* Generate the actual JIT code */
        build_prologue(&ctx);
        build_body(&ctx);
        build_epilogue(&ctx);

        /* Update the icache */
        flush_icache_range((ptr)ctx.target, (ptr)(ctx.target + ctx.idx));

        if (bpf_jit_enable > 1)
                /* Dump JIT code */
                bpf_jit_dump(fp->len, alloc_size, 2, ctx.target);

        fp->bpf_func = (void *)ctx.target;
        fp->jited = true;

out:
        kfree(ctx.offsets);
}

void bpf_jit_free(struct bpf_prog *fp)
{
        if (fp->jited)
                module_memfree(fp->bpf_func);

        bpf_prog_unlock_free(fp);
}