tools: bpftool: generate .dot graph from CFG information

This patch let bpftool print .dot graph file into stdout.

This graph is generated by the following steps:

  - iterate through the function list.
  - generate basic-block(BB) definition for each BB in the function.
  - draw out edges to connect BBs.

This patch is the initial support, the layout and decoration of the .dot
graph could be improved.

Also, it will be useful if we could visualize some performance data from
static analysis.

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>

tools/bpf/bpftool/cfg.c

@@ -41,6 +41,7 @@
 
 #include "cfg.h"
 #include "main.h"
+#include "xlated_dumper.h"
 
 struct cfg {
 	struct list_head funcs;
@@ -408,6 +409,96 @@ static void cfg_destroy(struct cfg *cfg)
 	}
 }
 
+static void draw_bb_node(struct func_node *func, struct bb_node *bb)
+{
+	const char *shape;
+
+	if (bb->idx == ENTRY_BLOCK_INDEX || bb->idx == EXIT_BLOCK_INDEX)
+		shape = "Mdiamond";
+	else
+		shape = "record";
+
+	printf("\tfn_%d_bb_%d [shape=%s,style=filled,label=\"",
+	       func->idx, bb->idx, shape);
+
+	if (bb->idx == ENTRY_BLOCK_INDEX) {
+		printf("ENTRY");
+	} else if (bb->idx == EXIT_BLOCK_INDEX) {
+		printf("EXIT");
+	} else {
+		unsigned int start_idx;
+		struct dump_data dd = {};
+
+		printf("{");
+		kernel_syms_load(&dd);
+		start_idx = bb->head - func->start;
+		dump_xlated_for_graph(&dd, bb->head, bb->tail, start_idx);
+		kernel_syms_destroy(&dd);
+		printf("}");
+	}
+
+	printf("\"];\n\n");
+}
+
+static void draw_bb_succ_edges(struct func_node *func, struct bb_node *bb)
+{
+	const char *style = "\"solid,bold\"";
+	const char *color = "black";
+	int func_idx = func->idx;
+	struct edge_node *e;
+	int weight = 10;
+
+	if (list_empty(&bb->e_succs))
+		return;
+
+	list_for_each_entry(e, &bb->e_succs, l) {
+		printf("\tfn_%d_bb_%d:s -> fn_%d_bb_%d:n [style=%s, color=%s, weight=%d, constraint=true",
+		       func_idx, e->src->idx, func_idx, e->dst->idx,
+		       style, color, weight);
+		printf("];\n");
+	}
+}
+
+static void func_output_bb_def(struct func_node *func)
+{
+	struct bb_node *bb;
+
+	list_for_each_entry(bb, &func->bbs, l) {
+		draw_bb_node(func, bb);
+	}
+}
+
+static void func_output_edges(struct func_node *func)
+{
+	int func_idx = func->idx;
+	struct bb_node *bb;
+
+	list_for_each_entry(bb, &func->bbs, l) {
+		draw_bb_succ_edges(func, bb);
+	}
+
+	/* Add an invisible edge from ENTRY to EXIT, this is to
+	 * improve the graph layout.
+	 */
+	printf("\tfn_%d_bb_%d:s -> fn_%d_bb_%d:n [style=\"invis\", constraint=true];\n",
+	       func_idx, ENTRY_BLOCK_INDEX, func_idx, EXIT_BLOCK_INDEX);
+}
+
+static void cfg_dump(struct cfg *cfg)
+{
+	struct func_node *func;
+
+	printf("digraph \"DOT graph for eBPF program\" {\n");
+	list_for_each_entry(func, &cfg->funcs, l) {
+		printf("subgraph \"cluster_%d\" {\n\tstyle=\"dashed\";\n\tcolor=\"black\";\n\tlabel=\"func_%d ()\";\n",
+		       func->idx, func->idx);
+		func_output_bb_def(func);
+		func_output_edges(func);
+		printf("}\n");
+	}
+	printf("}\n");
+}
+
 void dump_xlated_cfg(void *buf, unsigned int len)
 {
 	struct bpf_insn *insn = buf;
@@ -417,5 +508,7 @@ void dump_xlated_cfg(void *buf, unsigned int len)
 	if (cfg_build(&cfg, insn, len))
 		return;
 
+	cfg_dump(&cfg);
+
 	cfg_destroy(&cfg);
 }

tools/bpf/bpftool/xlated_dumper.c

@@ -123,6 +123,37 @@ static void print_insn(struct bpf_verifier_env *env, const char *fmt, ...)
 	va_end(args);
 }
 
+static void
+print_insn_for_graph(struct bpf_verifier_env *env, const char *fmt, ...)
+{
+	char buf[64], *p;
+	va_list args;
+
+	va_start(args, fmt);
+	vsnprintf(buf, sizeof(buf), fmt, args);
+	va_end(args);
+
+	p = buf;
+	while (*p != '\0') {
+		if (*p == '\n') {
+			memmove(p + 3, p, strlen(buf) + 1 - (p - buf));
+			/* Align each instruction dump row left. */
+			*p++ = '\\';
+			*p++ = 'l';
+			/* Output multiline concatenation. */
+			*p++ = '\\';
+		} else if (*p == '<' || *p == '>' || *p == '|' || *p == '&') {
+			memmove(p + 1, p, strlen(buf) + 1 - (p - buf));
+			/* Escape special character. */
+			*p++ = '\\';
+		}
+
+		p++;
+	}
+
+	printf("%s", buf);
+}
+
 static void print_insn_json(struct bpf_verifier_env *env, const char *fmt, ...)
 {
 	unsigned int l = strlen(fmt);
@@ -284,3 +315,24 @@ void dump_xlated_plain(struct dump_data *dd, void *buf, unsigned int len,
 		}
 	}
 }
+
+void dump_xlated_for_graph(struct dump_data *dd, void *buf_start, void *buf_end,
+			   unsigned int start_idx)
+{
+	const struct bpf_insn_cbs cbs = {
+		.cb_print	= print_insn_for_graph,
+		.cb_call	= print_call,
+		.cb_imm		= print_imm,
+		.private_data	= dd,
+	};
+	struct bpf_insn *insn_start = buf_start;
+	struct bpf_insn *insn_end = buf_end;
+	struct bpf_insn *cur = insn_start;
+
+	for (; cur <= insn_end; cur++) {
+		printf("% 4d: ", (int)(cur - insn_start + start_idx));
+		print_bpf_insn(&cbs, NULL, cur, true);
+		if (cur != insn_end)
+			printf(" | ");
+	}
+}

tools/bpf/bpftool/xlated_dumper.h

@@ -58,5 +58,7 @@ void dump_xlated_json(struct dump_data *dd, void *buf, unsigned int len,
 		      bool opcodes);
 void dump_xlated_plain(struct dump_data *dd, void *buf, unsigned int len,
 		       bool opcodes);
+void dump_xlated_for_graph(struct dump_data *dd, void *buf, void *buf_end,
+			   unsigned int start_index);
 
 #endif