scripts/gdb/symbols: Fix BPF debug on older GDB

The GDB python script for BPF uses the recently added '.bytes' method [0],
which is only available with GDB 14+ and otherwise leads to failures:

  (gdb) lx-symbols
  loading vmlinux
  scanning for modules in /home/kodidev/linux
  loading @0xbf008000: .../tools/testing/selftests/bpf/bpf_testmod.ko
  loading @0xbf000000: .../kernel/bpf/preload/bpf_preload.ko
  Traceback (most recent call last):
    File "/home/kodidev/linux/scripts/gdb/linux/symbols.py", line 321, in invoke
      self.bpf_ksym_monitor = bpf.KsymMonitor(self.add_bpf_ksym,
    File "/home/kodidev/linux/scripts/gdb/linux/bpf.py", line 67, in __init__
      self.notify_initial()
    File "/home/kodidev/linux/scripts/gdb/linux/bpf.py", line 71, in notify_initial
      self.add(ksym)
    File "/home/kodidev/linux/scripts/gdb/linux/symbols.py", line 217, in add_bpf_ksym
      name = bpf.get_ksym_name(ksym)
    File "/home/kodidev/linux/scripts/gdb/linux/bpf.py", line 19, in get_ksym_name
      name = ksym["name"].bytes
  AttributeError: 'gdb.Value' object has no attribute 'bytes'
  Error occurred in Python: 'gdb.Value' object has no attribute 'bytes'

Implement '.bytes' method equivalents to make wonderful BPF debugging work
on less recent systems (e.g. GDB 12.1 on Ubuntu 22 LTS):

  (gdb) lx-symbols
  loading vmlinux
  scanning for modules in /home/kodidev/linux
  loading @0xbf008000: .../tools/testing/selftests/bpf/bpf_testmod.ko
  loading @0xbf000000: .../kernel/bpf/preload/bpf_preload.ko
  loading @0xbf00ea0c: bpf_prog_1e1c76c33a07abcc_dump_bpf_map
  loading @0xbf010630: bpf_prog_bee9db790ebbd5a6_dump_bpf_prog
  loading @0xbf01e70c: bpf_prog_24c071e52e49653a___tld_fetch_key
  loading @0xbf01c4c8: bpf_prog_89487142fd0ba34f_task_main
  (gdb) list bpf_prog_89487142fd0ba34f_task_main
  30              struct tld_object tld_obj;
  31              struct test_tld_struct *struct_p;
  32              struct task_struct *task;
  33              int err, *int_p;
  34
  35              task = bpf_get_current_task_btf();
  36              err = tld_object_init(task, &tld_obj);
  37              if (err)
  38                      return 1;

Link 0: https://sourceware.org/bugzilla/show_bug.cgi?id=13267
Fixes: XXXXXXXXXX ("scripts/gdb/symbols: make BPF debug info available to GDB")
Signed-off-by: Tony Ambardar <[email protected]>

Author: guidosarducci

scripts/gdb/linux/bpf.py

@@ -16,7 +16,7 @@
 
 
 def get_ksym_name(ksym):
-    name = ksym["name"].bytes
+    name = bytes(ksym["name"].string(), 'utf-8')
     end = name.find(b"\x00")
     if end != -1:
         name = name[:end]
@@ -210,9 +210,10 @@ def generate_debug_obj(ksym, prog):
     name = get_ksym_name(ksym)
     # Avoid read_memory(); it throws bogus gdb.MemoryError in some contexts.
     start = ksym["start"]
+    length = int(ksym["end"]) - int(start)
     code = start.cast(gdb.lookup_type("unsigned char")
-                      .array(int(ksym["end"]) - int(start))
-                      .pointer()).dereference().bytes
+                      .array(length)
+                      .pointer()).dereference()
     linfo_iter = LInfoIter(prog)
 
     result = tempfile.NamedTemporaryFile(suffix=".o", mode="wb")
@@ -227,7 +228,8 @@ def generate_debug_obj(ksym, prog):
             src.write(".globl {}\n".format(name))
             src.write(".type {},@function\n".format(name))
             src.write("{}:\n".format(name))
-            for code_off, code_byte in enumerate(code):
+            for code_off in range(length):
+                code_byte = code[code_off]
                 if linfo_iter.get_code_off() == code_off:
                     fileno, file_name = linfo_iter.get_fileno()
                     if file_name is not None:
@@ -237,8 +239,8 @@ def generate_debug_obj(ksym, prog):
                     src.write(".loc {} {} {}\n".format(fileno, line, col))
                     src.write("0:\n")
                     linfo_iter.advance()
-                src.write(".byte {}\n".format(code_byte))
-            src.write(".size {},{}\n".format(name, len(code)))
+                src.write(".byte {}\n".format(hex(code_byte)))
+            src.write(".size {},{}\n".format(name, length))
             src.flush()
 
             try: