用 python gdb 客製化 backtrace 的結果 (2)

幫之前寫的指令 bt 加上參數 -s, 使用 -s 時, 會一併記錄 backtrace 每個 frame 附近的原始碼。

以下是一個範例輸出:

(gdb) bt -s
#0   A::hello at b.cpp:8
  | class A
  | {
  | public:
  |   void hello(int n)
  |   {
->|     std::cout << n << std::endl;
  |   }
  |
  |   void foo(int n)
  |   {

#1   A::bar at b.cpp:18
  |     bar(n + 1);
  |   }
  |
  |   void bar(int n)
  |   {
->|     hello(n + 10);
  |   }
  | };
  |
  | int main(void) {

#2   A::foo at b.cpp:13
  |     std::cout << n << std::endl;
  |   }
  |
  |   void foo(int n)
  |   {
->|     bar(n + 1);
  |   }
  |
  |   void bar(int n)
  |   {

#3   main at b.cpp:24
  |   }
  | };
  |
  | int main(void) {
  |   A a;
->|   a.foo(5);
  |   return 0;
  | }

修改後的 python script 如下:

	import gdb
	def read_source_code(filename, target_line, num_lines):
	with open(filename, 'r') as fr:
	target_line -= 1
	lines = [' | ' + line[:-1] for line in fr]
	lines[target_line] = '->| ' + lines[target_line][4:]
	offset = num_lines / 2
	return lines[target_line - offset : target_line + offset]
	class ShorternBacktraceCommand(gdb.Command):
	'''Show a backtrace without argument info in each frame.'''
	def __init__(self):
	super(ShorternBacktraceCommand, self).__init__ ("bt",
	gdb.COMMAND_SUPPORT,
	gdb.COMPLETE_NONE)
	def invoke(self, arg, from_tty):
	# Parse arguments.
	show_source = False
	num = 0;
	args = arg.split()
	for s in args:
	if s == '-s':
	show_source = True
	else:
	try:
	num = int(s)
	except Exception, e:
	pass
	# Extract frame info.
	frames = []
	f = gdb.newest_frame()
	fn = 0
	while f is not None:
	symtab_and_line = gdb.Frame.find_sal(f)
	frame_name = gdb.Frame.name(f)
	if frame_name:
	outs = (
	fn,
	frame_name,
	symtab_and_line.symtab.filename,
	symtab_and_line.line,
	)
	else:
	outs = (fn, '??', 'unknown', 0)
	head = '#%-2d %s at %s:%s' % outs
	codes = None
	if show_source and frame_name:
	codes = read_source_code(symtab_and_line.symtab.fullname(),
	symtab_and_line.line,
	10)
	frames.append((head, codes))
	f = gdb.Frame.older(f)
	fn += 1
	# Hold the subset.
	if num > 0:
	frames = frames[:num]
	elif num < 0:
	frames = frames[len(frames) + num:]
	# Print the result.
	for head, codes in frames:
	print head
	if codes:
	for line in codes:
	print line
	print
	ShorternBacktraceCommand()

view raw backtrace.py hosted with ❤ by GitHub

作法大致和 《用 python gdb 客製化 backtrace 的結果》一樣, 只是改取檔案的 fullname, 再自己讀出相關的原始碼。這部份用 python 實作, 相當地輕鬆寫意。