bpftool: Support printing opcodes and source file references in CFG

Add support for displaying opcodes or/and file references (filepath,
line and column numbers) when dumping the control flow graphs of loaded
BPF programs with bpftool.

The filepaths in the records are absolute. To avoid blocks on the graph
to get too wide, we truncate them when they get too long (but we always
keep the entire file name). In the unlikely case where the resulting
file name is ambiguous, it remains possible to get the full path with a
regular dump (no CFG).

Signed-off-by: Quentin Monnet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

tools/bpf/bpftool/btf_dumper.c

@@ -842,15 +842,64 @@ static void dotlabel_puts(const char *s)
  }
 }
 
+static const char *shorten_path(const char *path)
+{
+ const unsigned int MAX_PATH_LEN = 32;
+ size_t len = strlen(path);
+ const char *shortpath;
+
+ if (len <= MAX_PATH_LEN)
+ return path;
+
+ /* Search for last '/' under the MAX_PATH_LEN limit */
+ shortpath = strchr(path + len - MAX_PATH_LEN, '/');
+ if (shortpath) {
+ if (shortpath < path + strlen("..."))
+ /* We removed a very short prefix, e.g. "/w", and we'll
+ * make the path longer by prefixing with the ellipsis.
+ * Not worth it, keep initial path.
+ */
+ return path;
+ return shortpath;
+ }
+
+ /* File base name length is > MAX_PATH_LEN, search for last '/' */
+ shortpath = strrchr(path, '/');
+ if (shortpath)
+ return shortpath;
+
+ return path;
+}
+
 void btf_dump_linfo_dotlabel(const struct btf *btf,
- const struct bpf_line_info *linfo)
+ const struct bpf_line_info *linfo, bool linum)
 {
  const char *line = btf__name_by_offset(btf, linfo->line_off);
 
  if (!line || !strlen(line))
  return;
  line = ltrim(line);
 
+ if (linum) {
+ const char *file = btf__name_by_offset(btf, linfo->file_name_off);
+ const char *shortfile;
+
+ /* More forgiving on file because linum option is
+ * expected to provide more info than the already
+ * available src line.
+ */
+ if (!file)
+ shortfile = "";
+ else
+ shortfile = shorten_path(file);
+
+ printf("; [%s", shortfile > file ? "..." : "");
+ dotlabel_puts(shortfile);
+ printf(" line:%u col:%u]\\l\\\n",
+ BPF_LINE_INFO_LINE_NUM(linfo->line_col),
+ BPF_LINE_INFO_LINE_COL(linfo->line_col));
+ }
+
  printf("; ");
  dotlabel_puts(line);
  printf("\\l\\\n");

tools/bpf/bpftool/cfg.c

@@ -381,7 +381,8 @@ static void cfg_destroy(struct cfg *cfg)
 }
 
 static void
-draw_bb_node(struct func_node *func, struct bb_node *bb, struct dump_data *dd)
+draw_bb_node(struct func_node *func, struct bb_node *bb, struct dump_data *dd,
+ bool opcodes, bool linum)
 {
  const char *shape;
 
@@ -401,7 +402,8 @@ draw_bb_node(struct func_node *func, struct bb_node *bb, struct dump_data *dd)
  unsigned int start_idx;
  printf("{\\\n");
  start_idx = bb->head - func->start;
- dump_xlated_for_graph(dd, bb->head, bb->tail, start_idx);
+ dump_xlated_for_graph(dd, bb->head, bb->tail, start_idx,
+ opcodes, linum);
  printf("}");
  }
 
@@ -427,12 +429,14 @@ static void draw_bb_succ_edges(struct func_node *func, struct bb_node *bb)
  }
 }
 
-static void func_output_bb_def(struct func_node *func, struct dump_data *dd)
+static void
+func_output_bb_def(struct func_node *func, struct dump_data *dd,
+ bool opcodes, bool linum)
 {
  struct bb_node *bb;
 
  list_for_each_entry(bb, &func->bbs, l) {
- draw_bb_node(func, bb, dd);
+ draw_bb_node(func, bb, dd, opcodes, linum);
  }
 }
 
@@ -452,22 +456,24 @@ static void func_output_edges(struct func_node *func)
  func_idx, ENTRY_BLOCK_INDEX, func_idx, EXIT_BLOCK_INDEX);
 }
 
-static void cfg_dump(struct cfg *cfg, struct dump_data *dd)
+static void
+cfg_dump(struct cfg *cfg, struct dump_data *dd, bool opcodes, bool linum)
 {
  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, dd);
+ func_output_bb_def(func, dd, opcodes, linum);
  func_output_edges(func);
  printf("}\n");
  }
  printf("}\n");
 }
 
-void dump_xlated_cfg(struct dump_data *dd, void *buf, unsigned int len)
+void dump_xlated_cfg(struct dump_data *dd, void *buf, unsigned int len,
+ bool opcodes, bool linum)
 {
  struct bpf_insn *insn = buf;
  struct cfg cfg;
@@ -476,7 +482,7 @@ void dump_xlated_cfg(struct dump_data *dd, void *buf, unsigned int len)
  if (cfg_build(&cfg, insn, len))
  return;
 
- cfg_dump(&cfg, dd);
+ cfg_dump(&cfg, dd, opcodes, linum);
 
  cfg_destroy(&cfg);
 }

tools/bpf/bpftool/cfg.h

@@ -6,6 +6,7 @@
 
 #include "xlated_dumper.h"
 
-void dump_xlated_cfg(struct dump_data *dd, void *buf, unsigned int len);
+void dump_xlated_cfg(struct dump_data *dd, void *buf, unsigned int len,
+ bool opcodes, bool linum);
 
 #endif /* __BPF_TOOL_CFG_H */

tools/bpf/bpftool/main.h

@@ -230,7 +230,7 @@ void btf_dump_linfo_plain(const struct btf *btf,
 void btf_dump_linfo_json(const struct btf *btf,
  const struct bpf_line_info *linfo, bool linum);
 void btf_dump_linfo_dotlabel(const struct btf *btf,
- const struct bpf_line_info *linfo);
+ const struct bpf_line_info *linfo, bool linum);
 
 struct nlattr;
 struct ifinfomsg;

tools/bpf/bpftool/prog.c

@@ -852,7 +852,7 @@ prog_dump(struct bpf_prog_info *info, enum dump_mode mode,
  if (json_output)
  dump_xlated_json(&dd, buf, member_len, opcodes, linum);
  else if (visual)
- dump_xlated_cfg(&dd, buf, member_len);
+ dump_xlated_cfg(&dd, buf, member_len, opcodes, linum);
  else
  dump_xlated_plain(&dd, buf, member_len, opcodes, linum);
  kernel_syms_destroy(&dd);

tools/bpf/bpftool/xlated_dumper.c

@@ -361,7 +361,8 @@ 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)
+ unsigned int start_idx,
+ bool opcodes, bool linum)
 {
  const struct bpf_insn_cbs cbs = {
  .cb_print = print_insn_for_graph,
@@ -405,14 +406,24 @@ void dump_xlated_for_graph(struct dump_data *dd, void *buf_start, void *buf_end,
 
  linfo = bpf_prog_linfo__lfind(prog_linfo, insn_off, 0);
  if (linfo && linfo != last_linfo) {
- btf_dump_linfo_dotlabel(btf, linfo);
+ btf_dump_linfo_dotlabel(btf, linfo, linum);
  last_linfo = linfo;
  }
  }
 
  printf("%d: ", insn_off);
  print_bpf_insn(&cbs, cur, true);
 
+ if (opcodes) {
+ printf("\\ \\ \\ \\ ");
+ fprint_hex(stdout, cur, 8, " ");
+ if (double_insn && cur <= insn_end - 1) {
+ printf(" ");
+ fprint_hex(stdout, cur + 1, 8, " ");
+ }
+ printf("\\l\\\n");
+ }
+
  if (cur != insn_end)
  printf("| ");
  }

tools/bpf/bpftool/xlated_dumper.h

@@ -34,6 +34,7 @@ void dump_xlated_json(struct dump_data *dd, void *buf, unsigned int len,
 void dump_xlated_plain(struct dump_data *dd, void *buf, unsigned int len,
  bool opcodes, bool linum);
 void dump_xlated_for_graph(struct dump_data *dd, void *buf, void *buf_end,
- unsigned int start_index);
+ unsigned int start_index,
+ bool opcodes, bool linum);
 
 #endif