/* bpf_jit_comp.c: BPF JIT compiler
 *
 * Copyright 2011 Matt Evans <matt@ozlabs.org>, IBM Corporation
 *
 * Based on the x86 BPF compiler, by Eric Dumazet (eric.dumazet@gmail.com)
 * Ported to ppc32 by Denis Kirjanov <kda@linux-powerpc.org>
 *
 * 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/moduleloader.h>
#include <asm/cacheflush.h>
#include <linux/netdevice.h>
#include <linux/filter.h>
#include <linux/if_vlan.h>

#include "bpf_jit32.h"

static inline void bpf_flush_icache(void *start, void *end)
{
        smp_wmb();
        flush_icache_range((unsigned long)start, (unsigned long)end);
}

static void bpf_jit_build_prologue(struct bpf_prog *fp, u32 *image,
                                   struct codegen_context *ctx)
{
        int i;
        const struct sock_filter *filter = fp->insns;

        if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) {
                /* Make stackframe */
                if (ctx->seen & SEEN_DATAREF) {
                        /* If we call any helpers (for loads), save LR */
                        EMIT(PPC_INST_MFLR | __PPC_RT(R0));
                        PPC_BPF_STL(0, 1, PPC_LR_STKOFF);

                        /* Back up non-volatile regs. */
                        PPC_BPF_STL(r_D, 1, -(REG_SZ*(32-r_D)));
                        PPC_BPF_STL(r_HL, 1, -(REG_SZ*(32-r_HL)));
                }
                if (ctx->seen & SEEN_MEM) {
                        /*
                         * Conditionally save regs r15-r31 as some will be used
                         * for M[] data.
                         */
                        for (i = r_M; i < (r_M+16); i++) {
                                if (ctx->seen & (1 << (i-r_M)))
                                        PPC_BPF_STL(i, 1, -(REG_SZ*(32-i)));
                        }
                }
                PPC_BPF_STLU(1, 1, -BPF_PPC_STACKFRAME);
        }

        if (ctx->seen & SEEN_DATAREF) {
                /*
                 * If this filter needs to access skb data,
                 * prepare r_D and r_HL:
                 *  r_HL = skb->len - skb->data_len
                 *  r_D  = skb->data
                 */
                PPC_LWZ_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff,
                                                         data_len));
                PPC_LWZ_OFFS(r_HL, r_skb, offsetof(struct sk_buff, len));
                PPC_SUB(r_HL, r_HL, r_scratch1);
                PPC_LL_OFFS(r_D, r_skb, offsetof(struct sk_buff, data));
        }

        if (ctx->seen & SEEN_XREG) {
                /*
                 * TODO: Could also detect whether first instr. sets X and
                 * avoid this (as below, with A).
                 */
                PPC_LI(r_X, 0);
        }

        /* make sure we dont leak kernel information to user */
        if (bpf_needs_clear_a(&filter[0]))
                PPC_LI(r_A, 0);
}

static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
{
        int i;

        if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) {
                PPC_ADDI(1, 1, BPF_PPC_STACKFRAME);
                if (ctx->seen & SEEN_DATAREF) {
                        PPC_BPF_LL(0, 1, PPC_LR_STKOFF);
                        PPC_MTLR(0);
                        PPC_BPF_LL(r_D, 1, -(REG_SZ*(32-r_D)));
                        PPC_BPF_LL(r_HL, 1, -(REG_SZ*(32-r_HL)));
                }
                if (ctx->seen & SEEN_MEM) {
                        /* Restore any saved non-vol registers */
                        for (i = r_M; i < (r_M+16); i++) {
                                if (ctx->seen & (1 << (i-r_M)))
                                        PPC_BPF_LL(i, 1, -(REG_SZ*(32-i)));
                        }
                }
        }
        /* The RETs have left a return value in R3. */

        PPC_BLR();
}

#define CHOOSE_LOAD_FUNC(K, func) \
        ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)

/* Assemble the body code between the prologue & epilogue. */
static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
                              struct codegen_context *ctx,
                              unsigned int *addrs)
{
        const struct sock_filter *filter = fp->insns;
        int flen = fp->len;
        u8 *func;
        unsigned int true_cond;
        int i;

        /* Start of epilogue code */
        unsigned int exit_addr = addrs[flen];

        for (i = 0; i < flen; i++) {
                unsigned int K = filter[i].k;
                u16 code = bpf_anc_helper(&filter[i]);

                /*
                 * addrs[] maps a BPF bytecode address into a real offset from
                 * the start of the body code.
                 */
                addrs[i] = ctx->idx * 4;

                switch (code) {
                        /*** ALU ops ***/
                case BPF_ALU | BPF_ADD | BPF_X: /* A += X; */
                        ctx->seen |= SEEN_XREG;
                        PPC_ADD(r_A, r_A, r_X);
                        break;
                case BPF_ALU | BPF_ADD | BPF_K: /* A += K; */
                        if (!K)
                                break;
                        PPC_ADDI(r_A, r_A, IMM_L(K));
                        if (K >= 32768)
                                PPC_ADDIS(r_A, r_A, IMM_HA(K));
                        break;
                case BPF_ALU | BPF_SUB | BPF_X: /* A -= X; */
                        ctx->seen |= SEEN_XREG;
                        PPC_SUB(r_A, r_A, r_X);
                        break;
                case BPF_ALU | BPF_SUB | BPF_K: /* A -= K */
                        if (!K)
                                break;
                        PPC_ADDI(r_A, r_A, IMM_L(-K));
                        if (K >= 32768)
                                PPC_ADDIS(r_A, r_A, IMM_HA(-K));
                        break;
                case BPF_ALU | BPF_MUL | BPF_X: /* A *= X; */
                        ctx->seen |= SEEN_XREG;
                        PPC_MULW(r_A, r_A, r_X);
                        break;
                case BPF_ALU | BPF_MUL | BPF_K: /* A *= K */
                        if (K < 32768)
                                PPC_MULI(r_A, r_A, K);
                        else {
                                PPC_LI32(r_scratch1, K);
                                PPC_MULW(r_A, r_A, r_scratch1);
                        }
                        break;
                case BPF_ALU | BPF_MOD | BPF_X: /* A %= X; */
                case BPF_ALU | BPF_DIV | BPF_X: /* A /= X; */
                        ctx->seen |= SEEN_XREG;
                        PPC_CMPWI(r_X, 0);
                        if (ctx->pc_ret0 != -1) {
                                PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
                        } else {
                                PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
                                PPC_LI(r_ret, 0);
                                PPC_JMP(exit_addr);
                        }
                        if (code == (BPF_ALU | BPF_MOD | BPF_X)) {
                                PPC_DIVWU(r_scratch1, r_A, r_X);
                                PPC_MULW(r_scratch1, r_X, r_scratch1);
                                PPC_SUB(r_A, r_A, r_scratch1);
                        } else {
                                PPC_DIVWU(r_A, r_A, r_X);
                        }
                        break;
                case BPF_ALU | BPF_MOD | BPF_K: /* A %= K; */
                        PPC_LI32(r_scratch2, K);
                        PPC_DIVWU(r_scratch1, r_A, r_scratch2);
                        PPC_MULW(r_scratch1, r_scratch2, r_scratch1);
                        PPC_SUB(r_A, r_A, r_scratch1);
                        break;
                case BPF_ALU | BPF_DIV | BPF_K: /* A /= K */
                        if (K == 1)
                                break;
                        PPC_LI32(r_scratch1, K);
                        PPC_DIVWU(r_A, r_A, r_scratch1);
                        break;
                case BPF_ALU | BPF_AND | BPF_X:
                        ctx->seen |= SEEN_XREG;
                        PPC_AND(r_A, r_A, r_X);
                        break;
                case BPF_ALU | BPF_AND | BPF_K:
                        if (!IMM_H(K))
                                PPC_ANDI(r_A, r_A, K);
                        else {
                                PPC_LI32(r_scratch1, K);
                                PPC_AND(r_A, r_A, r_scratch1);
                        }
                        break;
                case BPF_ALU | BPF_OR | BPF_X:
                        ctx->seen |= SEEN_XREG;
                        PPC_OR(r_A, r_A, r_X);
                        break;
                case BPF_ALU | BPF_OR | BPF_K:
                        if (IMM_L(K))
                                PPC_ORI(r_A, r_A, IMM_L(K));
                        if (K >= 65536)
                                PPC_ORIS(r_A, r_A, IMM_H(K));
                        break;
                case BPF_ANC | SKF_AD_ALU_XOR_X:
                case BPF_ALU | BPF_XOR | BPF_X: /* A ^= X */
                        ctx->seen |= SEEN_XREG;
                        PPC_XOR(r_A, r_A, r_X);
                        break;
                case BPF_ALU | BPF_XOR | BPF_K: /* A ^= K */
                        if (IMM_L(K))
                                PPC_XORI(r_A, r_A, IMM_L(K));
                        if (K >= 65536)
                                PPC_XORIS(r_A, r_A, IMM_H(K));
                        break;
                case BPF_ALU | BPF_LSH | BPF_X: /* A <<= X; */
                        ctx->seen |= SEEN_XREG;
                        PPC_SLW(r_A, r_A, r_X);
                        break;
                case BPF_ALU | BPF_LSH | BPF_K:
                        if (K == 0)
                                break;
                        else
                                PPC_SLWI(r_A, r_A, K);
                        break;
                case BPF_ALU | BPF_RSH | BPF_X: /* A >>= X; */
                        ctx->seen |= SEEN_XREG;
                        PPC_SRW(r_A, r_A, r_X);
                        break;
                case BPF_ALU | BPF_RSH | BPF_K: /* A >>= K; */
                        if (K == 0)
                                break;
                        else
                                PPC_SRWI(r_A, r_A, K);
                        break;
                case BPF_ALU | BPF_NEG:
                        PPC_NEG(r_A, r_A);
                        break;
                case BPF_RET | BPF_K:
                        PPC_LI32(r_ret, K);
                        if (!K) {
                                if (ctx->pc_ret0 == -1)
                                        ctx->pc_ret0 = i;
                        }
                        /*
                         * If this isn't the very last instruction, branch to
                         * the epilogue if we've stuff to clean up.  Otherwise,
                         * if there's nothing to tidy, just return.  If we /are/
                         * the last instruction, we're about to fall through to
                         * the epilogue to return.
                         */
                        if (i != flen - 1) {
                                /*
                                 * Note: 'seen' is properly valid only on pass
                                 * #2.  Both parts of this conditional are the
                                 * same instruction size though, meaning the
                                 * first pass will still correctly determine the
                                 * code size/addresses.
                                 */
                                if (ctx->seen)
                                        PPC_JMP(exit_addr);
                                else
                                        PPC_BLR();
                        }
                        break;
                case BPF_RET | BPF_A:
                        PPC_MR(r_ret, r_A);
                        if (i != flen - 1) {
                                if (ctx->seen)
                                        PPC_JMP(exit_addr);
                                else
                                        PPC_BLR();
                        }
                        break;
                case BPF_MISC | BPF_TAX: /* X = A */
                        PPC_MR(r_X, r_A);
                        break;
                case BPF_MISC | BPF_TXA: /* A = X */
                        ctx->seen |= SEEN_XREG;
                        PPC_MR(r_A, r_X);
                        break;

                        /*** Constant loads/M[] access ***/
                case BPF_LD | BPF_IMM: /* A = K */
                        PPC_LI32(r_A, K);
                        break;
                case BPF_LDX | BPF_IMM: /* X = K */
                        PPC_LI32(r_X, K);
                        break;
                case BPF_LD | BPF_MEM: /* A = mem[K] */
                        PPC_MR(r_A, r_M + (K & 0xf));
                        ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
                        break;
                case BPF_LDX | BPF_MEM: /* X = mem[K] */
                        PPC_MR(r_X, r_M + (K & 0xf));
                        ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
                        break;
                case BPF_ST: /* mem[K] = A */
                        PPC_MR(r_M + (K & 0xf), r_A);
                        ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
                        break;
                case BPF_STX: /* mem[K] = X */
                        PPC_MR(r_M + (K & 0xf), r_X);
                        ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf));
                        break;
                case BPF_LD | BPF_W | BPF_LEN: /*       A = skb->len; */
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
                        PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len));
                        break;
                case BPF_LDX | BPF_W | BPF_ABS: /* A = *((u32 *)(seccomp_data + K)); */
                        PPC_LWZ_OFFS(r_A, r_skb, K);
                        break;
                case BPF_LDX | BPF_W | BPF_LEN: /* X = skb->len; */
                        PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len));
                        break;

                        /*** Ancillary info loads ***/
                case BPF_ANC | SKF_AD_PROTOCOL: /* A = ntohs(skb->protocol); */
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
                                                  protocol) != 2);
                        PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff,
                                                            protocol));
                        break;
                case BPF_ANC | SKF_AD_IFINDEX:
                case BPF_ANC | SKF_AD_HATYPE:
                        BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
                                                ifindex) != 4);
                        BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
                                                type) != 2);
                        PPC_LL_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff,
                                                                dev));
                        PPC_CMPDI(r_scratch1, 0);
                        if (ctx->pc_ret0 != -1) {
                                PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
                        } else {
                                /* Exit, returning 0; first pass hits here. */
                                PPC_BCC_SHORT(COND_NE, ctx->idx * 4 + 12);
                                PPC_LI(r_ret, 0);
                                PPC_JMP(exit_addr);
                        }
                        if (code == (BPF_ANC | SKF_AD_IFINDEX)) {
                                PPC_LWZ_OFFS(r_A, r_scratch1,
                                     offsetof(struct net_device, ifindex));
                        } else {
                                PPC_LHZ_OFFS(r_A, r_scratch1,
                                     offsetof(struct net_device, type));
                        }

                        break;
                case BPF_ANC | SKF_AD_MARK:
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
                        PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
                                                          mark));
                        break;
                case BPF_ANC | SKF_AD_RXHASH:
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4);
                        PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
                                                          hash));
                        break;
                case BPF_ANC | SKF_AD_VLAN_TAG:
                case BPF_ANC | SKF_AD_VLAN_TAG_PRESENT:
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2);
                        BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000);

                        PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
                                                          vlan_tci));
                        if (code == (BPF_ANC | SKF_AD_VLAN_TAG)) {
                                PPC_ANDI(r_A, r_A, ~VLAN_TAG_PRESENT);
                        } else {
                                PPC_ANDI(r_A, r_A, VLAN_TAG_PRESENT);
                                PPC_SRWI(r_A, r_A, 12);
                        }
                        break;
                case BPF_ANC | SKF_AD_QUEUE:
                        BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
                                                  queue_mapping) != 2);
                        PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
                                                          queue_mapping));
                        break;
                case BPF_ANC | SKF_AD_PKTTYPE:
                        PPC_LBZ_OFFS(r_A, r_skb, PKT_TYPE_OFFSET());
                        PPC_ANDI(r_A, r_A, PKT_TYPE_MAX);
                        PPC_SRWI(r_A, r_A, 5);
                        break;
                case BPF_ANC | SKF_AD_CPU:
                        PPC_BPF_LOAD_CPU(r_A);
                        break;
                        /*** Absolute loads from packet header/data ***/
                case BPF_LD | BPF_W | BPF_ABS:
                        func = CHOOSE_LOAD_FUNC(K, sk_load_word);
                        goto common_load;
                case BPF_LD | BPF_H | BPF_ABS:
                        func = CHOOSE_LOAD_FUNC(K, sk_load_half);
                        goto common_load;
                case BPF_LD | BPF_B | BPF_ABS:
                        func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
                common_load:
                        /* Load from [K]. */
                        ctx->seen |= SEEN_DATAREF;
                        PPC_FUNC_ADDR(r_scratch1, func);
                        PPC_MTLR(r_scratch1);
                        PPC_LI32(r_addr, K);
                        PPC_BLRL();
                        /*
                         * Helper returns 'lt' condition on error, and an
                         * appropriate return value in r3
                         */
                        PPC_BCC(COND_LT, exit_addr);
                        break;

                        /*** Indirect loads from packet header/data ***/
                case BPF_LD | BPF_W | BPF_IND:
                        func = sk_load_word;
                        goto common_load_ind;
                case BPF_LD | BPF_H | BPF_IND:
                        func = sk_load_half;
                        goto common_load_ind;
                case BPF_LD | BPF_B | BPF_IND:
                        func = sk_load_byte;
                common_load_ind:
                        /*
                         * Load from [X + K].  Negative offsets are tested for
                         * in the helper functions.
                         */
                        ctx->seen |= SEEN_DATAREF | SEEN_XREG;
                        PPC_FUNC_ADDR(r_scratch1, func);
                        PPC_MTLR(r_scratch1);
                        PPC_ADDI(r_addr, r_X, IMM_L(K));
                        if (K >= 32768)
                                PPC_ADDIS(r_addr, r_addr, IMM_HA(K));
                        PPC_BLRL();
                        /* If error, cr0.LT set */
                        PPC_BCC(COND_LT, exit_addr);
                        break;

                case BPF_LDX | BPF_B | BPF_MSH:
                        func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh);
                        goto common_load;
                        break;

                        /*** Jump and branches ***/
                case BPF_JMP | BPF_JA:
                        if (K != 0)
                                PPC_JMP(addrs[i + 1 + K]);
                        break;

                case BPF_JMP | BPF_JGT | BPF_K:
                case BPF_JMP | BPF_JGT | BPF_X:
                        true_cond = COND_GT;
                        goto cond_branch;
                case BPF_JMP | BPF_JGE | BPF_K:
                case BPF_JMP | BPF_JGE | BPF_X:
                        true_cond = COND_GE;
                        goto cond_branch;
                case BPF_JMP | BPF_JEQ | BPF_K:
                case BPF_JMP | BPF_JEQ | BPF_X:
                        true_cond = COND_EQ;
                        goto cond_branch;
                case BPF_JMP | BPF_JSET | BPF_K:
                case BPF_JMP | BPF_JSET | BPF_X:
                        true_cond = COND_NE;
                        /* Fall through */
                cond_branch:
                        /* same targets, can avoid doing the test :) */
                        if (filter[i].jt == filter[i].jf) {
                                if (filter[i].jt > 0)
                                        PPC_JMP(addrs[i + 1 + filter[i].jt]);
                                break;
                        }

                        switch (code) {
                        case BPF_JMP | BPF_JGT | BPF_X:
                        case BPF_JMP | BPF_JGE | BPF_X:
                        case BPF_JMP | BPF_JEQ | BPF_X:
                                ctx->seen |= SEEN_XREG;
                                PPC_CMPLW(r_A, r_X);
                                break;
                        case BPF_JMP | BPF_JSET | BPF_X:
                                ctx->seen |= SEEN_XREG;
                                PPC_AND_DOT(r_scratch1, r_A, r_X);
                                break;
                        case BPF_JMP | BPF_JEQ | BPF_K:
                        case BPF_JMP | BPF_JGT | BPF_K:
                        case BPF_JMP | BPF_JGE | BPF_K:
                                if (K < 32768)
                                        PPC_CMPLWI(r_A, K);
                                else {
                                        PPC_LI32(r_scratch1, K);
                                        PPC_CMPLW(r_A, r_scratch1);
                                }
                                break;
                        case BPF_JMP | BPF_JSET | BPF_K:
                                if (K < 32768)
                                        /* PPC_ANDI is /only/ dot-form */
                                        PPC_ANDI(r_scratch1, r_A, K);
                                else {
                                        PPC_LI32(r_scratch1, K);
                                        PPC_AND_DOT(r_scratch1, r_A,
                                                    r_scratch1);
                                }
                                break;
                        }
                        /* Sometimes branches are constructed "backward", with
                         * the false path being the branch and true path being
                         * a fallthrough to the next instruction.
                         */
                        if (filter[i].jt == 0)
                                /* Swap the sense of the branch */
                                PPC_BCC(true_cond ^ COND_CMP_TRUE,
                                        addrs[i + 1 + filter[i].jf]);
                        else {
                                PPC_BCC(true_cond, addrs[i + 1 + filter[i].jt]);
                                if (filter[i].jf != 0)
                                        PPC_JMP(addrs[i + 1 + filter[i].jf]);
                        }
                        break;
                default:
                        /* The filter contains something cruel & unusual.
                         * We don't handle it, but also there shouldn't be
                         * anything missing from our list.
                         */
                        if (printk_ratelimit())
                                pr_err("BPF filter opcode %04x (@%d) unsupported\n",
                                       filter[i].code, i);
                        return -ENOTSUPP;
                }

        }
        /* Set end-of-body-code address for exit. */
        addrs[i] = ctx->idx * 4;

        return 0;
}

void bpf_jit_compile(struct bpf_prog *fp)
{
        unsigned int proglen;
        unsigned int alloclen;
        u32 *image = NULL;
        u32 *code_base;
        unsigned int *addrs;
        struct codegen_context cgctx;
        int pass;
        int flen = fp->len;

        if (!bpf_jit_enable)
                return;

        addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL);
        if (addrs == NULL)
                return;

        /*
         * There are multiple assembly passes as the generated code will change
         * size as it settles down, figuring out the max branch offsets/exit
         * paths required.
         *
         * The range of standard conditional branches is +/- 32Kbytes.  Since
         * BPF_MAXINSNS = 4096, we can only jump from (worst case) start to
         * finish with 8 bytes/instruction.  Not feasible, so long jumps are
         * used, distinct from short branches.
         *
         * Current:
         *
         * For now, both branch types assemble to 2 words (short branches padded
         * with a NOP); this is less efficient, but assembly will always complete
         * after exactly 3 passes:
         *
         * First pass: No code buffer; Program is "faux-generated" -- no code
         * emitted but maximum size of output determined (and addrs[] filled
         * in).  Also, we note whether we use M[], whether we use skb data, etc.
         * All generation choices assumed to be 'worst-case', e.g. branches all
         * far (2 instructions), return path code reduction not available, etc.
         *
         * Second pass: Code buffer allocated with size determined previously.
         * Prologue generated to support features we have seen used.  Exit paths
         * determined and addrs[] is filled in again, as code may be slightly
         * smaller as a result.
         *
         * Third pass: Code generated 'for real', and branch destinations
         * determined from now-accurate addrs[] map.
         *
         * Ideal:
         *
         * If we optimise this, near branches will be shorter.  On the
         * first assembly pass, we should err on the side of caution and
         * generate the biggest code.  On subsequent passes, branches will be
         * generated short or long and code size will reduce.  With smaller
         * code, more branches may fall into the short category, and code will
         * reduce more.
         *
         * Finally, if we see one pass generate code the same size as the
         * previous pass we have converged and should now generate code for
         * real.  Allocating at the end will also save the memory that would
         * otherwise be wasted by the (small) current code shrinkage.
         * Preferably, we should do a small number of passes (e.g. 5) and if we
         * haven't converged by then, get impatient and force code to generate
         * as-is, even if the odd branch would be left long.  The chances of a
         * long jump are tiny with all but the most enormous of BPF filter
         * inputs, so we should usually converge on the third pass.
         */

        cgctx.idx = 0;
        cgctx.seen = 0;
        cgctx.pc_ret0 = -1;
        /* Scouting faux-generate pass 0 */
        if (bpf_jit_build_body(fp, 0, &cgctx, addrs))
                /* We hit something illegal or unsupported. */
                goto out;

        /*
         * Pretend to build prologue, given the features we've seen.  This will
         * update ctgtx.idx as it pretends to output instructions, then we can
         * calculate total size from idx.
         */
        bpf_jit_build_prologue(fp, 0, &cgctx);
        bpf_jit_build_epilogue(0, &cgctx);

        proglen = cgctx.idx * 4;
        alloclen = proglen + FUNCTION_DESCR_SIZE;
        image = module_alloc(alloclen);
        if (!image)
                goto out;

        code_base = image + (FUNCTION_DESCR_SIZE/4);

        /* Code generation passes 1-2 */
        for (pass = 1; pass < 3; pass++) {
                /* Now build the prologue, body code & epilogue for real. */
                cgctx.idx = 0;
                bpf_jit_build_prologue(fp, code_base, &cgctx);
                bpf_jit_build_body(fp, code_base, &cgctx, addrs);
                bpf_jit_build_epilogue(code_base, &cgctx);

                if (bpf_jit_enable > 1)
                        pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass,
                                proglen - (cgctx.idx * 4), cgctx.seen);
        }

        if (bpf_jit_enable > 1)
                /* Note that we output the base address of the code_base
                 * rather than image, since opcodes are in code_base.
                 */
                bpf_jit_dump(flen, proglen, pass, code_base);

        bpf_flush_icache(code_base, code_base + (proglen/4));

#ifdef CONFIG_PPC64
        /* Function descriptor nastiness: Address + TOC */
        ((u64 *)image)[0] = (u64)code_base;
        ((u64 *)image)[1] = local_paca->kernel_toc;
#endif

        fp->bpf_func = (void *)image;
        fp->jited = 1;

out:
        kfree(addrs);
        return;
}

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

        bpf_prog_unlock_free(fp);
}