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>

1 files changed, 8 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/json_writer.c b/tools/bpf/bpftool/json_writer.c
index 6b77d288cce2..c6eef76322ae 100644
--- a/tools/bpf/bpftool/json_writer.c
+++ b/tools/bpf/bpftool/json_writer.c
@@ -156,6 +156,14 @@ void jsonw_name(json_writer_t *self, const char *name)
                 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;