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

Reuse the json_writer API introduced in an earlier commit to make
bpftool able to generate JSON output on `bpftool prog show *` commands.
A new printing function is created to be passed as an argument to the
disassembler.

Similarly to plain output, opcodes are printed on request.

Outputs from sample programs have been successfully tested against a
JSON validator.

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

tools/bpf/bpftool/jit_disasm.c

···
  * Licensed under the GNU General Public License, version 2.0 (GPLv2)
  */
 
+#include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
···
 #include <dis-asm.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+
+#include "json_writer.h"
+#include "main.h"
 
 static void get_exec_path(char *tpath, size_t size)
 {
···
 	tpath[len] = 0;
 
 	free(path);
+}
+
+static int oper_count;
+static int fprintf_json(void *out, const char *fmt, ...)
+{
+	va_list ap;
+	char *s;
+
+	va_start(ap, fmt);
+	if (!oper_count) {
+		int i;
+
+		s = va_arg(ap, char *);
+
+		/* Strip trailing spaces */
+		i = strlen(s) - 1;
+		while (s[i] == ' ')
+			s[i--] = '\0';
+
+		jsonw_string_field(json_wtr, "operation", s);
+		jsonw_name(json_wtr, "operands");
+		jsonw_start_array(json_wtr);
+		oper_count++;
+	} else if (!strcmp(fmt, ",")) {
+		   /* Skip */
+	} else {
+		s = va_arg(ap, char *);
+		jsonw_string(json_wtr, s);
+		oper_count++;
+	}
+	va_end(ap);
+	return 0;
 }
 
 void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes)
···
 	assert(bfdf);
 	assert(bfd_check_format(bfdf, bfd_object));
 
-	init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
+	if (json_output)
+		init_disassemble_info(&info, stdout,
+				      (fprintf_ftype) fprintf_json);
+	else
+		init_disassemble_info(&info, stdout,
+				      (fprintf_ftype) fprintf);
 	info.arch = bfd_get_arch(bfdf);
 	info.mach = bfd_get_mach(bfdf);
 	info.buffer = image;
···
 	disassemble = disassembler(bfdf);
 	assert(disassemble);
 
+	if (json_output)
+		jsonw_start_array(json_wtr);
 	do {
-		printf("%4x:\t", pc);
+		if (json_output) {
+			jsonw_start_object(json_wtr);
+			oper_count = 0;
+			jsonw_name(json_wtr, "pc");
+			jsonw_printf(json_wtr, "\"0x%x\"", pc);
+		} else {
+			printf("%4x:\t", pc);
+		}
 
 		count = disassemble(pc, &info);
+		if (json_output) {
+			/* Operand array, was started in fprintf_json. Before
+			 * that, make sure we have a _null_ value if no operand
+			 * other than operation code was present.
+			 */
+			if (oper_count == 1)
+				jsonw_null(json_wtr);
+			jsonw_end_array(json_wtr);
+		}
 
 		if (opcodes) {
-			printf("\n\t");
-			for (i = 0; i < count; ++i)
-				printf("%02x ", (uint8_t) image[pc + i]);
+			if (json_output) {
+				jsonw_name(json_wtr, "opcodes");
+				jsonw_start_array(json_wtr);
+				for (i = 0; i < count; ++i)
+					jsonw_printf(json_wtr, "\"0x%02hhx\"",
+						     (uint8_t)image[pc + i]);
+				jsonw_end_array(json_wtr);
+			} else {
+				printf("\n\t");
+				for (i = 0; i < count; ++i)
+					printf("%02x ",
+					       (uint8_t)image[pc + i]);
+			}
 		}
-		printf("\n");
+		if (json_output)
+			jsonw_end_object(json_wtr);
+		else
+			printf("\n");
 
 		pc += count;
 	} while (count > 0 && pc < len);
+	if (json_output)
+		jsonw_end_array(json_wtr);
 
 	bfd_close(bfdf);
 }