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arm64: bpf: implement bpf_tail_call() helper
Add support for JMP_CALL_X (tail call) introduced by commit 04fd61ab36
("bpf: allow bpf programs to tail-call other bpf programs").
bpf_tail_call() arguments:
ctx - context pointer passed to next program
array - pointer to map which type is BPF_MAP_TYPE_PROG_ARRAY
index - index inside array that selects specific program to run
In this implementation arm64 JIT jumps into callee program after prologue,
so callee program reuses the same stack. For tail_call_cnt, we use the
callee-saved R26 (which was already saved/restored but previously unused
by JIT).
With this patch a tail call generates the following code on arm64:
if (index >= array->map.max_entries)
goto out;
34: mov x10, #0x10 // #16
38: ldr w10, [x1,x10]
3c: cmp w2, w10
40: b.ge 0x0000000000000074
if (tail_call_cnt > MAX_TAIL_CALL_CNT)
goto out;
tail_call_cnt++;
44: mov x10, #0x20 // #32
48: cmp x26, x10
4c: b.gt 0x0000000000000074
50: add x26, x26, #0x1
prog = array->ptrs[index];
if (prog == NULL)
goto out;
54: mov x10, #0x68 // #104
58: ldr x10, [x1,x10]
5c: ldr x11, [x10,x2]
60: cbz x11, 0x0000000000000074
goto *(prog->bpf_func + prologue_size);
64: mov x10, #0x20 // #32
68: ldr x10, [x11,x10]
6c: add x10, x10, #0x20
70: br x10
74:
Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Zi Shen Lim
David S. Miller
parent
002245cc64
commit
ddb55992b0
@ -1,7 +1,7 @@
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/*
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* BPF JIT compiler for ARM64
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*
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* Copyright (C) 2014-2015 Zi Shen Lim <zlim.lnx@gmail.com>
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* Copyright (C) 2014-2016 Zi Shen Lim <zlim.lnx@gmail.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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@ -55,6 +55,7 @@
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#define A64_BL(imm26) A64_BRANCH((imm26) << 2, LINK)
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/* Unconditional branch (register) */
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#define A64_BR(Rn) aarch64_insn_gen_branch_reg(Rn, AARCH64_INSN_BRANCH_NOLINK)
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#define A64_BLR(Rn) aarch64_insn_gen_branch_reg(Rn, AARCH64_INSN_BRANCH_LINK)
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#define A64_RET(Rn) aarch64_insn_gen_branch_reg(Rn, AARCH64_INSN_BRANCH_RETURN)
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@ -18,6 +18,7 @@
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#define pr_fmt(fmt) "bpf_jit: " fmt
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#include <linux/bpf.h>
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#include <linux/filter.h>
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#include <linux/printk.h>
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#include <linux/skbuff.h>
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@ -33,6 +34,7 @@ int bpf_jit_enable __read_mostly;
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#define TMP_REG_1 (MAX_BPF_JIT_REG + 0)
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#define TMP_REG_2 (MAX_BPF_JIT_REG + 1)
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#define TCALL_CNT (MAX_BPF_JIT_REG + 2)
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/* Map BPF registers to A64 registers */
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static const int bpf2a64[] = {
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@ -54,6 +56,8 @@ static const int bpf2a64[] = {
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/* temporary registers for internal BPF JIT */
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[TMP_REG_1] = A64_R(10),
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[TMP_REG_2] = A64_R(11),
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/* tail_call_cnt */
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[TCALL_CNT] = A64_R(26),
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/* temporary register for blinding constants */
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[BPF_REG_AX] = A64_R(9),
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};
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@ -146,13 +150,18 @@ static inline int epilogue_offset(const struct jit_ctx *ctx)
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#define STACK_SIZE STACK_ALIGN(_STACK_SIZE)
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static void build_prologue(struct jit_ctx *ctx)
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#define PROLOGUE_OFFSET 8
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static int build_prologue(struct jit_ctx *ctx)
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{
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const u8 r6 = bpf2a64[BPF_REG_6];
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const u8 r7 = bpf2a64[BPF_REG_7];
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const u8 r8 = bpf2a64[BPF_REG_8];
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const u8 r9 = bpf2a64[BPF_REG_9];
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const u8 fp = bpf2a64[BPF_REG_FP];
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const u8 tcc = bpf2a64[TCALL_CNT];
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const int idx0 = ctx->idx;
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int cur_offset;
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/*
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* BPF prog stack layout
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@ -162,8 +171,6 @@ static void build_prologue(struct jit_ctx *ctx)
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* |FP/LR|
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* current A64_FP => -16:+-----+
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* | ... | callee saved registers
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* +-----+
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* | | x25/x26
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* BPF fp register => -64:+-----+ <= (BPF_FP)
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* | |
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* | ... | BPF prog stack
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@ -183,18 +190,90 @@ static void build_prologue(struct jit_ctx *ctx)
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emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx);
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emit(A64_MOV(1, A64_FP, A64_SP), ctx);
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/* Save callee-saved register */
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/* Save callee-saved registers */
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emit(A64_PUSH(r6, r7, A64_SP), ctx);
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emit(A64_PUSH(r8, r9, A64_SP), ctx);
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emit(A64_PUSH(fp, tcc, A64_SP), ctx);
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/* Save fp (x25) and x26. SP requires 16 bytes alignment */
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emit(A64_PUSH(fp, A64_R(26), A64_SP), ctx);
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/* Set up BPF prog stack base register (x25) */
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/* Set up BPF prog stack base register */
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emit(A64_MOV(1, fp, A64_SP), ctx);
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/* Initialize tail_call_cnt */
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emit(A64_MOVZ(1, tcc, 0, 0), ctx);
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/* Set up function call stack */
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emit(A64_SUB_I(1, A64_SP, A64_SP, STACK_SIZE), ctx);
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cur_offset = ctx->idx - idx0;
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if (cur_offset != PROLOGUE_OFFSET) {
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pr_err_once("PROLOGUE_OFFSET = %d, expected %d!\n",
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cur_offset, PROLOGUE_OFFSET);
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return -1;
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}
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return 0;
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}
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static int out_offset = -1; /* initialized on the first pass of build_body() */
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static int emit_bpf_tail_call(struct jit_ctx *ctx)
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{
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/* bpf_tail_call(void *prog_ctx, struct bpf_array *array, u64 index) */
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const u8 r2 = bpf2a64[BPF_REG_2];
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const u8 r3 = bpf2a64[BPF_REG_3];
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const u8 tmp = bpf2a64[TMP_REG_1];
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const u8 prg = bpf2a64[TMP_REG_2];
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const u8 tcc = bpf2a64[TCALL_CNT];
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const int idx0 = ctx->idx;
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#define cur_offset (ctx->idx - idx0)
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#define jmp_offset (out_offset - (cur_offset))
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size_t off;
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/* if (index >= array->map.max_entries)
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* goto out;
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*/
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off = offsetof(struct bpf_array, map.max_entries);
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emit_a64_mov_i64(tmp, off, ctx);
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emit(A64_LDR32(tmp, r2, tmp), ctx);
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emit(A64_CMP(0, r3, tmp), ctx);
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emit(A64_B_(A64_COND_GE, jmp_offset), ctx);
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/* if (tail_call_cnt > MAX_TAIL_CALL_CNT)
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* goto out;
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* tail_call_cnt++;
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*/
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emit_a64_mov_i64(tmp, MAX_TAIL_CALL_CNT, ctx);
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emit(A64_CMP(1, tcc, tmp), ctx);
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emit(A64_B_(A64_COND_GT, jmp_offset), ctx);
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emit(A64_ADD_I(1, tcc, tcc, 1), ctx);
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/* prog = array->ptrs[index];
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* if (prog == NULL)
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* goto out;
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*/
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off = offsetof(struct bpf_array, ptrs);
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emit_a64_mov_i64(tmp, off, ctx);
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emit(A64_LDR64(tmp, r2, tmp), ctx);
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emit(A64_LDR64(prg, tmp, r3), ctx);
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emit(A64_CBZ(1, prg, jmp_offset), ctx);
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/* goto *(prog->bpf_func + prologue_size); */
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off = offsetof(struct bpf_prog, bpf_func);
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emit_a64_mov_i64(tmp, off, ctx);
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emit(A64_LDR64(tmp, prg, tmp), ctx);
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emit(A64_ADD_I(1, tmp, tmp, sizeof(u32) * PROLOGUE_OFFSET), ctx);
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emit(A64_BR(tmp), ctx);
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/* out: */
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if (out_offset == -1)
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out_offset = cur_offset;
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if (cur_offset != out_offset) {
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pr_err_once("tail_call out_offset = %d, expected %d!\n",
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cur_offset, out_offset);
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return -1;
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}
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return 0;
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#undef cur_offset
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#undef jmp_offset
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}
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static void build_epilogue(struct jit_ctx *ctx)
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@ -506,6 +585,11 @@ emit_cond_jmp:
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emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx);
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break;
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}
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/* tail call */
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case BPF_JMP | BPF_CALL | BPF_X:
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if (emit_bpf_tail_call(ctx))
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return -EFAULT;
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break;
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/* function return */
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case BPF_JMP | BPF_EXIT:
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/* Optimization: when last instruction is EXIT,
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@ -780,7 +864,10 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
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goto out_off;
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}
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build_prologue(&ctx);
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if (build_prologue(&ctx)) {
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prog = orig_prog;
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goto out_off;
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}
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ctx.epilogue_offset = ctx.idx;
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build_epilogue(&ctx);
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