/*
   * Minimal BPF assembler
   *
   * Instead of libpcap high-level filter expressions, it can be quite
   * useful to define filters in low-level BPF assembler (that is kept
   * close to Steven McCanne and Van Jacobson's original BPF paper).
   * In particular for BPF JIT implementors, JIT security auditors, or
   * just for defining BPF expressions that contain extensions which are
   * not supported by compilers.
   *
   * How to get into it:
   *
   * 1) read Documentation/networking/filter.txt
   * 2) Run `bpf_asm [-c] <filter-prog file>` to translate into binary
   *    blob that is loadable with xt_bpf, cls_bpf et al. Note: -c will
   *    pretty print a C-like construct.
   *
   * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
   * Licensed under the GNU General Public License, version 2.0 (GPLv2)
   */
  
  #include <stdbool.h>
  #include <stdio.h>
  #include <string.h>
  
  extern void bpf_asm_compile(FILE *fp, bool cstyle);
  
  int main(int argc, char **argv)
  {
  	FILE *fp = stdin;
  	bool cstyle = false;
  	int i;
  
  	for (i = 1; i < argc; i++) {
  		if (!strncmp("-c", argv[i], 2)) {
  			cstyle = true;
  			continue;
  		}
  
  		fp = fopen(argv[i], "r");
  		if (!fp) {
  			fp = stdin;
  			continue;
  		}
  
  		break;
  	}
  
  	bpf_asm_compile(fp, cstyle);
  
  	return 0;
  }