1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Minimal BPF assembler
4  *
5  * Instead of libpcap high-level filter expressions, it can be quite
6  * useful to define filters in low-level BPF assembler (that is kept
7  * close to Steven McCanne and Van Jacobson's original BPF paper).
8  * In particular for BPF JIT implementors, JIT security auditors, or
9  * just for defining BPF expressions that contain extensions which are
10  * not supported by compilers.
11  *
12  * How to get into it:
13  *
14  * 1) read Documentation/networking/filter.rst
15  * 2) Run `bpf_asm [-c] <filter-prog file>` to translate into binary
16  *    blob that is loadable with xt_bpf, cls_bpf et al. Note: -c will
17  *    pretty print a C-like construct.
18  *
19  * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
20  */
21 
22 #include <stdbool.h>
23 #include <stdio.h>
24 #include <string.h>
25 
26 extern void bpf_asm_compile(FILE *fp, bool cstyle);
27 
main(int argc,char ** argv)28 int main(int argc, char **argv)
29 {
30 	FILE *fp = stdin;
31 	bool cstyle = false;
32 	int i;
33 
34 	for (i = 1; i < argc; i++) {
35 		if (!strncmp("-c", argv[i], 2)) {
36 			cstyle = true;
37 			continue;
38 		}
39 
40 		fp = fopen(argv[i], "r");
41 		if (!fp) {
42 			fp = stdin;
43 			continue;
44 		}
45 
46 		break;
47 	}
48 
49 	bpf_asm_compile(fp, cstyle);
50 
51 	return 0;
52 }
53