70 lines · c
1// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)2 3#include <bpf/bpf.h>4#include "disasm.h"5 6struct print_insn_context {7 char scratch[16];8 char *buf;9 size_t sz;10};11 12static void print_insn_cb(void *private_data, const char *fmt, ...)13{14 struct print_insn_context *ctx = private_data;15 va_list args;16 17 va_start(args, fmt);18 vsnprintf(ctx->buf, ctx->sz, fmt, args);19 va_end(args);20}21 22static const char *print_call_cb(void *private_data, const struct bpf_insn *insn)23{24 struct print_insn_context *ctx = private_data;25 26 /* For pseudo calls verifier.c:jit_subprogs() hides original27 * imm to insn->off and changes insn->imm to be an index of28 * the subprog instead.29 */30 if (insn->src_reg == BPF_PSEUDO_CALL) {31 snprintf(ctx->scratch, sizeof(ctx->scratch), "%+d", insn->off);32 return ctx->scratch;33 }34 35 return NULL;36}37 38struct bpf_insn *disasm_insn(struct bpf_insn *insn, char *buf, size_t buf_sz)39{40 struct print_insn_context ctx = {41 .buf = buf,42 .sz = buf_sz,43 };44 struct bpf_insn_cbs cbs = {45 .cb_print = print_insn_cb,46 .cb_call = print_call_cb,47 .private_data = &ctx,48 };49 char *tmp, *pfx_end, *sfx_start;50 bool double_insn;51 int len;52 53 print_bpf_insn(&cbs, insn, true);54 /* We share code with kernel BPF disassembler, it adds '(FF) ' prefix55 * for each instruction (FF stands for instruction `code` byte).56 * Remove the prefix inplace, and also simplify call instructions.57 * E.g.: "(85) call foo#10" -> "call foo".58 * Also remove newline in the end (the 'max(strlen(buf) - 1, 0)' thing).59 */60 pfx_end = buf + 5;61 sfx_start = buf + max((int)strlen(buf) - 1, 0);62 if (strncmp(pfx_end, "call ", 5) == 0 && (tmp = strrchr(buf, '#')))63 sfx_start = tmp;64 len = sfx_start - pfx_end;65 memmove(buf, pfx_end, len);66 buf[len] = 0;67 double_insn = insn->code == (BPF_LD | BPF_IMM | BPF_DW);68 return insn + (double_insn ? 2 : 1);69}70