bpf_jit_comp.c

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/* bpf_jit_comp.c: BPF JIT compiler for PPC64
 *
 * Copyright 2011 Matt Evans <[email protected]>, IBM Corporation
 *
 * Based on the x86 BPF compiler, by Eric Dumazet ([email protected])
 *
 * 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 "bpf_jit.h"

#ifndef __BIG_ENDIAN
/* There are endianness assumptions herein. */
#error "Little-endian PPC not supported in BPF compiler"
#endif

int bpf_jit_enable __read_mostly;


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 sk_filter *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_STD(0, 1, 16);

            /* Back up non-volatile regs. */
            PPC_STD(r_D, 1, -(8*(32-r_D)));
            PPC_STD(r_HL, 1, -(8*(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_STD(i, 1, -(8*(32-i)));
            }
        }
        EMIT(PPC_INST_STDU | __PPC_RS(R1) | __PPC_RA(R1) |
             (-BPF_PPC_STACKFRAME & 0xfffc));
    }

    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_LD_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);
    }

    switch (filter[0].code) {
    case BPF_S_RET_K:
    case BPF_S_LD_W_LEN:
    case BPF_S_ANC_PROTOCOL:
    case BPF_S_ANC_IFINDEX:
    case BPF_S_ANC_MARK:
    case BPF_S_ANC_RXHASH:
    case BPF_S_ANC_CPU:
    case BPF_S_ANC_QUEUE:
    case BPF_S_LD_W_ABS:
    case BPF_S_LD_H_ABS:
    case BPF_S_LD_B_ABS:
        /* first instruction sets A register (or is RET 'constant') */
        break;
    default:
        /* make sure we dont leak kernel information to user */
        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_LD(0, 1, 16);
            PPC_MTLR(0);
            PPC_LD(r_D, 1, -(8*(32-r_D)));
            PPC_LD(r_HL, 1, -(8*(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_LD(i, 1, -(8*(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 sk_filter *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;

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

        switch (filter[i].code) {
            /*** ALU ops ***/
        case BPF_S_ALU_ADD_X: /* A += X; */
            ctx->seen |= SEEN_XREG;
            PPC_ADD(r_A, r_A, r_X);
            break;
        case BPF_S_ALU_ADD_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_S_ALU_SUB_X: /* A -= X; */
            ctx->seen |= SEEN_XREG;
            PPC_SUB(r_A, r_A, r_X);
            break;
        case BPF_S_ALU_SUB_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_S_ALU_MUL_X: /* A *= X; */
            ctx->seen |= SEEN_XREG;
            PPC_MUL(r_A, r_A, r_X);
            break;
        case BPF_S_ALU_MUL_K: /* A *= K */
            if (K < 32768)
                PPC_MULI(r_A, r_A, K);
            else {
                PPC_LI32(r_scratch1, K);
                PPC_MUL(r_A, r_A, r_scratch1);
            }
            break;
        case BPF_S_ALU_DIV_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 {
                /*
                 * Exit, returning 0; first pass hits here
                 * (longer worst-case code size).
                 */
                PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
                PPC_LI(r_ret, 0);
                PPC_JMP(exit_addr);
            }
            PPC_DIVWU(r_A, r_A, r_X);
            break;
        case BPF_S_ALU_DIV_K: /* A = reciprocal_divide(A, K); */
            PPC_LI32(r_scratch1, K);
            /* Top 32 bits of 64bit result -> A */
            PPC_MULHWU(r_A, r_A, r_scratch1);
            break;
        case BPF_S_ALU_AND_X:
            ctx->seen |= SEEN_XREG;
            PPC_AND(r_A, r_A, r_X);
            break;
        case BPF_S_ALU_AND_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_S_ALU_OR_X:
            ctx->seen |= SEEN_XREG;
            PPC_OR(r_A, r_A, r_X);
            break;
        case BPF_S_ALU_OR_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_S_ALU_LSH_X: /* A <<= X; */
            ctx->seen |= SEEN_XREG;
            PPC_SLW(r_A, r_A, r_X);
            break;
        case BPF_S_ALU_LSH_K:
            if (K == 0)
                break;
            else
                PPC_SLWI(r_A, r_A, K);
            break;
        case BPF_S_ALU_RSH_X: /* A >>= X; */
            ctx->seen |= SEEN_XREG;
            PPC_SRW(r_A, r_A, r_X);
            break;
        case BPF_S_ALU_RSH_K: /* A >>= K; */
            if (K == 0)
                break;
            else
                PPC_SRWI(r_A, r_A, K);
            break;
        case BPF_S_ALU_NEG:
            PPC_NEG(r_A, r_A);
            break;
        case BPF_S_RET_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_S_RET_A:
            PPC_MR(r_ret, r_A);
            if (i != flen - 1) {
                if (ctx->seen)
                    PPC_JMP(exit_addr);
                else
                    PPC_BLR();
            }
            break;
        case BPF_S_MISC_TAX: /* X = A */
            PPC_MR(r_X, r_A);
            break;
        case BPF_S_MISC_TXA: /* A = X */
            ctx->seen |= SEEN_XREG;
            PPC_MR(r_A, r_X);
            break;

            /*** Constant loads/M[] access ***/
        case BPF_S_LD_IMM: /* A = K */
            PPC_LI32(r_A, K);
            break;
        case BPF_S_LDX_IMM: /* X = K */
            PPC_LI32(r_X, K);
            break;
        case BPF_S_LD_MEM: /* A = mem[K] */
            PPC_MR(r_A, r_M + (K & 0xf));
            ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
            break;
        case BPF_S_LDX_MEM: /* X = mem[K] */
            PPC_MR(r_X, r_M + (K & 0xf));
            ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
            break;
        case BPF_S_ST: /* mem[K] = A */
            PPC_MR(r_M + (K & 0xf), r_A);
            ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
            break;
        case BPF_S_STX: /* mem[K] = X */
            PPC_MR(r_M + (K & 0xf), r_X);
            ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf));
            break;
        case BPF_S_LD_W_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_S_LDX_W_LEN: /* X = skb->len; */
            PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len));
            break;

            /*** Ancillary info loads ***/

            /* None of the BPF_S_ANC* codes appear to be passed by
             * sk_chk_filter().  The interpreter and the x86 BPF
             * compiler implement them so we do too -- they may be
             * planted in future.
             */
        case BPF_S_ANC_PROTOCOL: /* A = ntohs(skb->protocol); */
            BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
                          protocol) != 2);
            PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
                              protocol));
            /* ntohs is a NOP with BE loads. */
            break;
        case BPF_S_ANC_IFINDEX:
            PPC_LD_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);
            }
            BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
                          ifindex) != 4);
            PPC_LWZ_OFFS(r_A, r_scratch1,
                     offsetof(struct net_device, ifindex));
            break;
        case BPF_S_ANC_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_S_ANC_RXHASH:
            BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, rxhash) != 4);
            PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
                              rxhash));
            break;
        case BPF_S_ANC_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_S_ANC_CPU:
#ifdef CONFIG_SMP
            /*
             * PACA ptr is r13:
             * raw_smp_processor_id() = local_paca->paca_index
             */
            BUILD_BUG_ON(FIELD_SIZEOF(struct paca_struct,
                          paca_index) != 2);
            PPC_LHZ_OFFS(r_A, 13,
                     offsetof(struct paca_struct, paca_index));
#else
            PPC_LI(r_A, 0);
#endif
            break;

            /*** Absolute loads from packet header/data ***/
        case BPF_S_LD_W_ABS:
            func = CHOOSE_LOAD_FUNC(K, sk_load_word);
            goto common_load;
        case BPF_S_LD_H_ABS:
            func = CHOOSE_LOAD_FUNC(K, sk_load_half);
            goto common_load;
        case BPF_S_LD_B_ABS:
            func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
        common_load:
            /* Load from [K]. */
            ctx->seen |= SEEN_DATAREF;
            PPC_LI64(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_S_LD_W_IND:
            func = sk_load_word;
            goto common_load_ind;
        case BPF_S_LD_H_IND:
            func = sk_load_half;
            goto common_load_ind;
        case BPF_S_LD_B_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_LI64(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_S_LDX_B_MSH:
            func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh);
            goto common_load;
            break;

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

        case BPF_S_JMP_JGT_K:
        case BPF_S_JMP_JGT_X:
            true_cond = COND_GT;
            goto cond_branch;
        case BPF_S_JMP_JGE_K:
        case BPF_S_JMP_JGE_X:
            true_cond = COND_GE;
            goto cond_branch;
        case BPF_S_JMP_JEQ_K:
        case BPF_S_JMP_JEQ_X:
            true_cond = COND_EQ;
            goto cond_branch;
        case BPF_S_JMP_JSET_K:
        case BPF_S_JMP_JSET_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 (filter[i].code) {
            case BPF_S_JMP_JGT_X:
            case BPF_S_JMP_JGE_X:
            case BPF_S_JMP_JEQ_X:
                ctx->seen |= SEEN_XREG;
                PPC_CMPLW(r_A, r_X);
                break;
            case BPF_S_JMP_JSET_X:
                ctx->seen |= SEEN_XREG;
                PPC_AND_DOT(r_scratch1, r_A, r_X);
                break;
            case BPF_S_JMP_JEQ_K:
            case BPF_S_JMP_JGT_K:
            case BPF_S_JMP_JGE_K:
                if (K < 32768)
                    PPC_CMPLWI(r_A, K);
                else {
                    PPC_LI32(r_scratch1, K);
                    PPC_CMPLW(r_A, r_scratch1);
                }
                break;
            case BPF_S_JMP_JSET_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 sk_filter *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(max_t(unsigned int, alloclen,
                   sizeof(struct work_struct)));
    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)
        pr_info("flen=%d proglen=%u pass=%d image=%p\n",
               flen, proglen, pass, image);

    if (image) {
        if (bpf_jit_enable > 1)
            print_hex_dump(KERN_ERR, "JIT code: ",
                       DUMP_PREFIX_ADDRESS,
                       16, 1, code_base,
                       proglen, false);

        bpf_flush_icache(code_base, code_base + (proglen/4));
        /* Function descriptor nastiness: Address + TOC */
        ((u64 *)image)[0] = (u64)code_base;
        ((u64 *)image)[1] = local_paca->kernel_toc;
        fp->bpf_func = (void *)image;
    }
out:
    kfree(addrs);
    return;
}

static void jit_free_defer(struct work_struct *arg)
{
    module_free(NULL, arg);
}

/* run from softirq, we must use a work_struct to call
 * module_free() from process context
 */
void bpf_jit_free(struct sk_filter *fp)
{
    if (fp->bpf_func != sk_run_filter) {
        struct work_struct *work = (struct work_struct *)fp->bpf_func;

        INIT_WORK(work, jit_free_defer);
        schedule_work(work);
    }
}