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 <quentin.monnet@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/tools/bpf/bpftool/json_writer.h b/tools/bpf/bpftool/json_writer.h
index 1516aaf..0fa2fb1 100644
--- a/tools/bpf/bpftool/json_writer.h
+++ b/tools/bpf/bpftool/json_writer.h
@@ -17,6 +17,7 @@
 
 #include <stdbool.h>
 #include <stdint.h>
+#include <stdarg.h>
 
 /* Opaque class structure */
 typedef struct json_writer json_writer_t;
@@ -33,6 +34,7 @@ void jsonw_pretty(json_writer_t *self, bool on);
 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);