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: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
index e4ceee7..67ca6c6 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
@@ -21,7 +21,7 @@
 =============
 
 |	**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 @@
 		  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.