tools: bpftool: partition basic-block for each function in the CFG

This patch partition basic-block for each function in the CFG. The
algorithm is simple, we identify basic-block head in a first traversal,
then second traversal to identify the tail.

We could build extended basic-block (EBB) in next steps. EBB could make the
graph more readable when the eBPF sequence is big.
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

@@ -49,17 +49,32 @@ struct cfg {
 
 struct func_node {
 	struct list_head l;
+	struct list_head bbs;
 	struct bpf_insn *start;
 	struct bpf_insn *end;
 	int idx;
+	int bb_num;
+};
+
+struct bb_node {
+	struct list_head l;
+	struct bpf_insn *head;
+	struct bpf_insn *tail;
+	int idx;
 };
 
 #define func_prev(func)		list_prev_entry(func, l)
 #define func_next(func)		list_next_entry(func, l)
+#define bb_prev(bb)		list_prev_entry(bb, l)
+#define bb_next(bb)		list_next_entry(bb, l)
 #define cfg_first_func(cfg)	\
 	list_first_entry(&cfg->funcs, struct func_node, l)
 #define cfg_last_func(cfg)	\
 	list_last_entry(&cfg->funcs, struct func_node, l)
+#define func_first_bb(func)	\
+	list_first_entry(&func->bbs, struct bb_node, l)
+#define func_last_bb(func)	\
+	list_last_entry(&func->bbs, struct bb_node, l)
 
 static struct func_node *cfg_append_func(struct cfg *cfg, struct bpf_insn *insn)
 {
@@ -86,6 +101,30 @@ static struct func_node *cfg_append_func(struct cfg *cfg, struct bpf_insn *insn)
 	return new_func;
 }
 
+static struct bb_node *func_append_bb(struct func_node *func,
+				      struct bpf_insn *insn)
+{
+	struct bb_node *new_bb, *bb;
+
+	list_for_each_entry(bb, &func->bbs, l) {
+		if (bb->head == insn)
+			return bb;
+		else if (bb->head > insn)
+			break;
+	}
+
+	bb = bb_prev(bb);
+	new_bb = calloc(1, sizeof(*new_bb));
+	if (!new_bb) {
+		p_err("OOM when allocating BB node");
+		return NULL;
+	}
+	new_bb->head = insn;
+	list_add(&new_bb->l, &bb->l);
+
+	return new_bb;
+}
+
 static bool cfg_partition_funcs(struct cfg *cfg, struct bpf_insn *cur,
 				struct bpf_insn *end)
 {
@@ -115,13 +154,83 @@ static bool cfg_partition_funcs(struct cfg *cfg, struct bpf_insn *cur,
 	return false;
 }
 
+static bool func_partition_bb_head(struct func_node *func)
+{
+	struct bpf_insn *cur, *end;
+	struct bb_node *bb;
+
+	cur = func->start;
+	end = func->end;
+	INIT_LIST_HEAD(&func->bbs);
+	bb = func_append_bb(func, cur);
+	if (!bb)
+		return true;
+
+	for (; cur <= end; cur++) {
+		if (BPF_CLASS(cur->code) == BPF_JMP) {
+			u8 opcode = BPF_OP(cur->code);
+
+			if (opcode == BPF_EXIT || opcode == BPF_CALL)
+				continue;
+
+			bb = func_append_bb(func, cur + cur->off + 1);
+			if (!bb)
+				return true;
+
+			if (opcode != BPF_JA) {
+				bb = func_append_bb(func, cur + 1);
+				if (!bb)
+					return true;
+			}
+		}
+	}
+
+	return false;
+}
+
+static void func_partition_bb_tail(struct func_node *func)
+{
+	struct bb_node *bb, *last;
+	unsigned int bb_idx = 0;
+
+	last = func_last_bb(func);
+	last->tail = func->end;
+	bb = func_first_bb(func);
+	list_for_each_entry_from(bb, &last->l, l) {
+		bb->tail = bb_next(bb)->head - 1;
+		bb->idx = bb_idx++;
+	}
+
+	last->idx = bb_idx++;
+	func->bb_num = bb_idx;
+}
+
+static bool func_partition_bb(struct func_node *func)
+{
+	if (func_partition_bb_head(func))
+		return true;
+
+	func_partition_bb_tail(func);
+
+	return false;
+}
+
 static bool cfg_build(struct cfg *cfg, struct bpf_insn *insn, unsigned int len)
 {
 	int cnt = len / sizeof(*insn);
+	struct func_node *func;
 
 	INIT_LIST_HEAD(&cfg->funcs);
 
-	return cfg_partition_funcs(cfg, insn, insn + cnt);
+	if (cfg_partition_funcs(cfg, insn, insn + cnt))
+		return true;
+
+	list_for_each_entry(func, &cfg->funcs, l) {
+		if (func_partition_bb(func))
+			return true;
+	}
+
+	return false;
 }
 
 static void cfg_destroy(struct cfg *cfg)
@@ -129,6 +238,13 @@ static void cfg_destroy(struct cfg *cfg)
 	struct func_node *func, *func2;
 
 	list_for_each_entry_safe(func, func2, &cfg->funcs, l) {
+		struct bb_node *bb, *bb2;
+
+		list_for_each_entry_safe(bb, bb2, &func->bbs, l) {
+			list_del(&bb->l);
+			free(bb);
+		}
+
 		list_del(&func->l);
 		free(func);
 	}