xref: /linux/tools/bpf/bpftool/jit_disasm.c (revision fa84cf094ef9667e2b91c104b0a788fd1896f482)
1 /*
2  * Based on:
3  *
4  * Minimal BPF JIT image disassembler
5  *
6  * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
7  * debugging or verification purposes.
8  *
9  * Copyright 2013 Daniel Borkmann <daniel@iogearbox.net>
10  * Licensed under the GNU General Public License, version 2.0 (GPLv2)
11  */
12 
13 #include <stdarg.h>
14 #include <stdint.h>
15 #include <stdio.h>
16 #include <stdlib.h>
17 #include <assert.h>
18 #include <unistd.h>
19 #include <string.h>
20 #include <bfd.h>
21 #include <dis-asm.h>
22 #include <sys/types.h>
23 #include <sys/stat.h>
24 #include <limits.h>
25 
26 #include "json_writer.h"
27 #include "main.h"
28 
29 static void get_exec_path(char *tpath, size_t size)
30 {
31 	ssize_t len;
32 	char *path;
33 
34 	snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
35 	tpath[size - 1] = 0;
36 
37 	path = strdup(tpath);
38 	assert(path);
39 
40 	len = readlink(path, tpath, size - 1);
41 	assert(len > 0);
42 	tpath[len] = 0;
43 
44 	free(path);
45 }
46 
47 static int oper_count;
48 static int fprintf_json(void *out, const char *fmt, ...)
49 {
50 	va_list ap;
51 	char *s;
52 
53 	va_start(ap, fmt);
54 	if (!oper_count) {
55 		int i;
56 
57 		s = va_arg(ap, char *);
58 
59 		/* Strip trailing spaces */
60 		i = strlen(s) - 1;
61 		while (s[i] == ' ')
62 			s[i--] = '\0';
63 
64 		jsonw_string_field(json_wtr, "operation", s);
65 		jsonw_name(json_wtr, "operands");
66 		jsonw_start_array(json_wtr);
67 		oper_count++;
68 	} else if (!strcmp(fmt, ",")) {
69 		   /* Skip */
70 	} else {
71 		s = va_arg(ap, char *);
72 		jsonw_string(json_wtr, s);
73 		oper_count++;
74 	}
75 	va_end(ap);
76 	return 0;
77 }
78 
79 void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
80 		       const char *arch)
81 {
82 	disassembler_ftype disassemble;
83 	struct disassemble_info info;
84 	int count, i, pc = 0;
85 	char tpath[PATH_MAX];
86 	bfd *bfdf;
87 
88 	if (!len)
89 		return;
90 
91 	memset(tpath, 0, sizeof(tpath));
92 	get_exec_path(tpath, sizeof(tpath));
93 
94 	bfdf = bfd_openr(tpath, NULL);
95 	assert(bfdf);
96 	assert(bfd_check_format(bfdf, bfd_object));
97 
98 	if (json_output)
99 		init_disassemble_info(&info, stdout,
100 				      (fprintf_ftype) fprintf_json);
101 	else
102 		init_disassemble_info(&info, stdout,
103 				      (fprintf_ftype) fprintf);
104 
105 	/* Update architecture info for offload. */
106 	if (arch) {
107 		const bfd_arch_info_type *inf = bfd_scan_arch(arch);
108 
109 		if (inf) {
110 			bfdf->arch_info = inf;
111 		} else {
112 			p_err("No libfd support for %s", arch);
113 			return;
114 		}
115 	}
116 
117 	info.arch = bfd_get_arch(bfdf);
118 	info.mach = bfd_get_mach(bfdf);
119 	info.buffer = image;
120 	info.buffer_length = len;
121 
122 	disassemble_init_for_target(&info);
123 
124 #ifdef DISASM_FOUR_ARGS_SIGNATURE
125 	disassemble = disassembler(info.arch,
126 				   bfd_big_endian(bfdf),
127 				   info.mach,
128 				   bfdf);
129 #else
130 	disassemble = disassembler(bfdf);
131 #endif
132 	assert(disassemble);
133 
134 	if (json_output)
135 		jsonw_start_array(json_wtr);
136 	do {
137 		if (json_output) {
138 			jsonw_start_object(json_wtr);
139 			oper_count = 0;
140 			jsonw_name(json_wtr, "pc");
141 			jsonw_printf(json_wtr, "\"0x%x\"", pc);
142 		} else {
143 			printf("%4x:\t", pc);
144 		}
145 
146 		count = disassemble(pc, &info);
147 		if (json_output) {
148 			/* Operand array, was started in fprintf_json. Before
149 			 * that, make sure we have a _null_ value if no operand
150 			 * other than operation code was present.
151 			 */
152 			if (oper_count == 1)
153 				jsonw_null(json_wtr);
154 			jsonw_end_array(json_wtr);
155 		}
156 
157 		if (opcodes) {
158 			if (json_output) {
159 				jsonw_name(json_wtr, "opcodes");
160 				jsonw_start_array(json_wtr);
161 				for (i = 0; i < count; ++i)
162 					jsonw_printf(json_wtr, "\"0x%02hhx\"",
163 						     (uint8_t)image[pc + i]);
164 				jsonw_end_array(json_wtr);
165 			} else {
166 				printf("\n\t");
167 				for (i = 0; i < count; ++i)
168 					printf("%02x ",
169 					       (uint8_t)image[pc + i]);
170 			}
171 		}
172 		if (json_output)
173 			jsonw_end_object(json_wtr);
174 		else
175 			printf("\n");
176 
177 		pc += count;
178 	} while (count > 0 && pc < len);
179 	if (json_output)
180 		jsonw_end_array(json_wtr);
181 
182 	bfd_close(bfdf);
183 }
184