tools: bpftool: new command-line option and documentation for 'visual'

This patch adds new command-line option for visualizing the xlated eBPF
sequence.

Documentations are updated accordingly.

Usage:

  bpftool prog dump xlated id 2 visual
Reviewed-by: NQuentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: NJiong Wang <jiong.wang@netronome.com>
Acked-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/Documentation/bpftool-prog.rst

@@ -21,7 +21,7 @@ MAP COMMANDS
 =============
 
 |	**bpftool** **prog { show | list }** [*PROG*]
-|	**bpftool** **prog dump xlated** *PROG* [{**file** *FILE* | **opcodes**}]
+|	**bpftool** **prog dump xlated** *PROG* [{**file** *FILE* | **opcodes** | **visual**}]
 |	**bpftool** **prog dump jited**  *PROG* [{**file** *FILE* | **opcodes**}]
 |	**bpftool** **prog pin** *PROG* *FILE*
 |	**bpftool** **prog load** *OBJ* *FILE*
@@ -39,12 +39,18 @@ DESCRIPTION
 		  Output will start with program ID followed by program type and
 		  zero or more named attributes (depending on kernel version).
 
-	**bpftool prog dump xlated** *PROG* [{ **file** *FILE* | **opcodes** }]
-		  Dump eBPF instructions of the program from the kernel.
-		  If *FILE* is specified image will be written to a file,
-		  otherwise it will be disassembled and printed to stdout.
+	**bpftool prog dump xlated** *PROG* [{ **file** *FILE* | **opcodes** | **visual** }]
+		  Dump eBPF instructions of the program from the kernel. By
+		  default, eBPF will be disassembled and printed to standard
+		  output in human-readable format. In this case, **opcodes**
+		  controls if raw opcodes should be printed as well.
 
-		  **opcodes** controls if raw opcodes will be printed.
+		  If **file** is specified, the binary image will instead be
+		  written to *FILE*.
+
+		  If **visual** is specified, control flow graph (CFG) will be
+		  built instead, and eBPF instructions will be presented with
+		  CFG in DOT format, on standard output.
 
 	**bpftool prog dump jited**  *PROG* [{ **file** *FILE* | **opcodes** }]
 		  Dump jited image (host machine code) of the program.

tools/bpf/bpftool/prog.c

@@ -47,6 +47,7 @@
 #include <bpf.h>
 #include <libbpf.h>
 
+#include "cfg.h"
 #include "main.h"
 #include "xlated_dumper.h"
 
@@ -415,6 +416,7 @@ static int do_dump(int argc, char **argv)
 	unsigned int buf_size;
 	char *filepath = NULL;
 	bool opcodes = false;
+	bool visual = false;
 	unsigned char *buf;
 	__u32 *member_len;
 	__u64 *member_ptr;
@@ -453,6 +455,9 @@ static int do_dump(int argc, char **argv)
 	} else if (is_prefix(*argv, "opcodes")) {
 		opcodes = true;
 		NEXT_ARG();
+	} else if (is_prefix(*argv, "visual")) {
+		visual = true;
+		NEXT_ARG();
 	}
 
 	if (argc) {
@@ -536,6 +541,11 @@ static int do_dump(int argc, char **argv)
 		}
 
 		disasm_print_insn(buf, *member_len, opcodes, name);
+	} else if (visual) {
+		if (json_output)
+			jsonw_null(json_wtr);
+		else
+			dump_xlated_cfg(buf, *member_len);
 	} else {
 		kernel_syms_load(&dd);
 		if (json_output)
@@ -596,7 +606,7 @@ static int do_help(int argc, char **argv)
 
 	fprintf(stderr,
 		"Usage: %s %s { show | list } [PROG]\n"
-		"       %s %s dump xlated PROG [{ file FILE | opcodes }]\n"
+		"       %s %s dump xlated PROG [{ file FILE | opcodes | visual }]\n"
 		"       %s %s dump jited  PROG [{ file FILE | opcodes }]\n"
 		"       %s %s pin   PROG FILE\n"
 		"       %s %s load  OBJ  FILE\n"