tools: bpftool: add JSON output for `bpftool prog dump xlated *` command

Add a new printing function to dump translated eBPF instructions as
JSON. As for plain output, opcodes are printed only on request (when
`opcodes` is provided on the command line).

The disassembled output is generated by the same code that is used by
the kernel verifier.

Example output:

$ bpftool --json --pretty prog dump xlated id 1
[{
"disasm": "(bf) r6 = r1"
},{
"disasm": "(61) r7 = *(u32 *)(r6 +16)"
},{
"disasm": "(95) exit"
}
]

$ bpftool --json --pretty prog dump xlated id 1 opcodes
[{
"disasm": "(bf) r6 = r1",
"opcodes": {
"code": "0xbf",
"src_reg": "0x1",
"dst_reg": "0x6",
"off": ["0x00","0x00"
],
"imm": ["0x00","0x00","0x00","0x00"
]
}
},{
"disasm": "(61) r7 = *(u32 *)(r6 +16)",
"opcodes": {
"code": "0x61",
"src_reg": "0x6",
"dst_reg": "0x7",
"off": ["0x10","0x00"
],
"imm": ["0x00","0x00","0x00","0x00"
]
}
},{
"disasm": "(95) exit",
"opcodes": {
"code": "0x95",
"src_reg": "0x0",
"dst_reg": "0x0",
"off": ["0x00","0x00"
],
"imm": ["0x00","0x00","0x00","0x00"
]
}
}
]

Signed-off-by: Quentin Monnet <[e-mail]>
Acked-by: Daniel Borkmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/bpf/bpftool/common.c

···
 	fclose(fdi);
 	return NULL;
 }
+
+void print_hex_data_json(uint8_t *data, size_t len)
+{
+	unsigned int i;
+
+	jsonw_start_array(json_wtr);
+	for (i = 0; i < len; i++)
+		jsonw_printf(json_wtr, "\"0x%02hhx\"", data[i]);
+	jsonw_end_array(json_wtr);
+}

tools/bpf/bpftool/json_writer.c

···
 		putc(' ', self->out);
 }
 
+void jsonw_vprintf_enquote(json_writer_t *self, const char *fmt, va_list ap)
+{
+	jsonw_eor(self);
+	putc('"', self->out);
+	vfprintf(self->out, fmt, ap);
+	putc('"', self->out);
+}
+
 void jsonw_printf(json_writer_t *self, const char *fmt, ...)
 {
 	va_list ap;

tools/bpf/bpftool/json_writer.h

···
 
 #include <stdbool.h>
 #include <stdint.h>
+#include <stdarg.h>
 
 /* Opaque class structure */
 typedef struct json_writer json_writer_t;
···
 void jsonw_name(json_writer_t *self, const char *name);
 
 /* Add value  */
+void jsonw_vprintf_enquote(json_writer_t *self, const char *fmt, va_list ap);
 void jsonw_printf(json_writer_t *self, const char *fmt, ...);
 void jsonw_string(json_writer_t *self, const char *value);
 void jsonw_bool(json_writer_t *self, bool value);

tools/bpf/bpftool/main.h

···
 int prog_parse_fd(int *argc, char ***argv);
 
 void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes);
+void print_hex_data_json(uint8_t *data, size_t len);
 
 #endif

tools/bpf/bpftool/prog.c

···
 	va_end(args);
 }
 
-static void dump_xlated(void *buf, unsigned int len, bool opcodes)
+static void dump_xlated_plain(void *buf, unsigned int len, bool opcodes)
 {
 	struct bpf_insn *insn = buf;
 	bool double_insn = false;
···
 			printf("\n");
 		}
 	}
+}
+
+static void print_insn_json(struct bpf_verifier_env *env, const char *fmt, ...)
+{
+	unsigned int l = strlen(fmt);
+	char chomped_fmt[l];
+	va_list args;
+
+	va_start(args, fmt);
+	if (l > 0) {
+		strncpy(chomped_fmt, fmt, l - 1);
+		chomped_fmt[l - 1] = '\0';
+	}
+	jsonw_vprintf_enquote(json_wtr, chomped_fmt, args);
+	va_end(args);
+}
+
+static void dump_xlated_json(void *buf, unsigned int len, bool opcodes)
+{
+	struct bpf_insn *insn = buf;
+	bool double_insn = false;
+	unsigned int i;
+
+	jsonw_start_array(json_wtr);
+	for (i = 0; i < len / sizeof(*insn); i++) {
+		if (double_insn) {
+			double_insn = false;
+			continue;
+		}
+		double_insn = insn[i].code == (BPF_LD | BPF_IMM | BPF_DW);
+
+		jsonw_start_object(json_wtr);
+		jsonw_name(json_wtr, "disasm");
+		print_bpf_insn(print_insn_json, NULL, insn + i, true);
+
+		if (opcodes) {
+			jsonw_name(json_wtr, "opcodes");
+			jsonw_start_object(json_wtr);
+
+			jsonw_name(json_wtr, "code");
+			jsonw_printf(json_wtr, "\"0x%02hhx\"", insn[i].code);
+
+			jsonw_name(json_wtr, "src_reg");
+			jsonw_printf(json_wtr, "\"0x%hhx\"", insn[i].src_reg);
+
+			jsonw_name(json_wtr, "dst_reg");
+			jsonw_printf(json_wtr, "\"0x%hhx\"", insn[i].dst_reg);
+
+			jsonw_name(json_wtr, "off");
+			print_hex_data_json((uint8_t *)(&insn[i].off), 2);
+
+			jsonw_name(json_wtr, "imm");
+			if (double_insn && i < len - 1)
+				print_hex_data_json((uint8_t *)(&insn[i].imm),
+						    12);
+			else
+				print_hex_data_json((uint8_t *)(&insn[i].imm),
+						    4);
+			jsonw_end_object(json_wtr);
+		}
+		jsonw_end_object(json_wtr);
+	}
+	jsonw_end_array(json_wtr);
 }
 
 static int do_dump(int argc, char **argv)
···
 		if (member_len == &info.jited_prog_len)
 			disasm_print_insn(buf, *member_len, opcodes);
 		else
-			dump_xlated(buf, *member_len, opcodes);
+			if (json_output)
+				dump_xlated_json(buf, *member_len, opcodes);
+			else
+				dump_xlated_plain(buf, *member_len, opcodes);
 	}
 
 	free(buf);