使用 GDB 除錯 C API 擴充套件和 CPython 內部¶
本文件解釋了 Python GDB 擴充套件 python-gdb.py 如何與 GDB 偵錯程式一起使用，以除錯 CPython 擴充套件和 CPython 直譯器本身。
在除錯諸如崩潰或死鎖之類的低階問題時，GDB 之類的低階偵錯程式對於診斷和糾正問題很有用。預設情況下，GDB（或其任何前端）不支援特定於 CPython 直譯器的高階資訊。
python-gdb.py 擴充套件向 GDB 添加了 CPython 直譯器資訊。該擴充套件有助於自省當前正在執行的 Python 函式的堆疊。給定由 PyObject* 指標表示的 Python 物件，該擴充套件會顯示物件的型別和值。
正在開發 CPython 擴充套件或修改 C 語言編寫的 CPython 部分的開發人員可以使用本文件來學習如何將 python-gdb.py 擴充套件與 GDB 一起使用。
備註
本文件假設您熟悉 GDB 和 CPython C API 的基礎知識。它整合了來自 devguide 和 Python wiki 的指導。
先決條件¶
您需要具備
GDB 7 或更高版本。（對於早期版本的 GDB，請參閱 Python 3.11 或更早版本的原始碼中的
Misc/gdbinit。）適用於 Python 和您正在除錯的任何擴充套件的 GDB 相容除錯資訊。
python-gdb.py擴充套件。
該擴充套件是隨 Python 一起構建的，但可能單獨分發或根本不分發。下面，我們提供了一些常見系統的提示作為示例。請注意，即使說明與您的系統匹配，它們也可能已過時。
使用從原始碼構建的 Python 進行設定¶
當您從原始碼構建 CPython 時，應該可以獲得除錯資訊，並且構建應該在您的儲存庫的根目錄中新增一個 python-gdb.py 檔案。
要啟用支援，您必須將包含 python-gdb.py 的目錄新增到 GDB 的“自動載入安全路徑”。如果您沒有這樣做，最新版本的 GDB 將會列印一條警告，其中包含如何執行此操作的說明。
備註
如果您沒有看到您的 GDB 版本的說明，請將其放入您的配置檔案（~/.gdbinit 或 ~/.config/gdb/gdbinit）中。
add-auto-load-safe-path /path/to/cpython
您還可以新增多個路徑，用 : 分隔。
為來自 Linux 發行版的 Python 進行設定¶
大多數 Linux 系統在名為 python-debuginfo、python-dbg 或類似名稱的包中提供系統 Python 的除錯資訊。例如
Fedora
sudo dnf install gdb sudo dnf debuginfo-install python3
Ubuntu
sudo apt install gdb python3-dbg
在一些最新的 Linux 系統上，GDB 可以使用 debuginfod 自動下載除錯符號。但是，這不會安裝 python-gdb.py 擴充套件；您通常確實需要單獨安裝除錯資訊包。
使用除錯構建和開發模式¶
為了更方便除錯，您可能需要
使用 Python 的除錯構建。（從原始碼構建時，使用
configure --with-pydebug。在 Linux 發行版上，安裝並執行python-debug或python-dbg等軟體包，如果可用的話。）使用執行時開發模式（
-X dev）。
兩者都啟用額外的斷言並停用某些最佳化。有時這會隱藏您正在嘗試查詢的錯誤，但在大多數情況下，它們會使過程更容易。
使用 python-gdb 擴充套件¶
載入擴充套件後，它提供兩個主要功能：Python 值的美觀印表機和附加命令。
美觀印表機¶
啟用此擴充套件後，GDB 回溯（已截斷）如下所示
#0 0x000000000041a6b1 in PyObject_Malloc (nbytes=Cannot access memory at address 0x7fffff7fefe8
) at Objects/obmalloc.c:748
#1 0x000000000041b7c0 in _PyObject_DebugMallocApi (id=111 'o', nbytes=24) at Objects/obmalloc.c:1445
#2 0x000000000041b717 in _PyObject_DebugMalloc (nbytes=24) at Objects/obmalloc.c:1412
#3 0x000000000044060a in _PyUnicode_New (length=11) at Objects/unicodeobject.c:346
#4 0x00000000004466aa in PyUnicodeUCS2_DecodeUTF8Stateful (s=0x5c2b8d "__lltrace__", size=11, errors=0x0, consumed=
0x0) at Objects/unicodeobject.c:2531
#5 0x0000000000446647 in PyUnicodeUCS2_DecodeUTF8 (s=0x5c2b8d "__lltrace__", size=11, errors=0x0)
at Objects/unicodeobject.c:2495
#6 0x0000000000440d1b in PyUnicodeUCS2_FromStringAndSize (u=0x5c2b8d "__lltrace__", size=11)
at Objects/unicodeobject.c:551
#7 0x0000000000440d94 in PyUnicodeUCS2_FromString (u=0x5c2b8d "__lltrace__") at Objects/unicodeobject.c:569
#8 0x0000000000584abd in PyDict_GetItemString (v=
{'Yuck': <type at remote 0xad4730>, '__builtins__': <module at remote 0x7ffff7fd5ee8>, '__file__': 'Lib/test/crashers/nasty_eq_vs_dict.py', '__package__': None, 'y': <Yuck(i=0) at remote 0xaacd80>, 'dict': {0: 0, 1: 1, 2: 2, 3: 3}, '__cached__': None, '__name__': '__main__', 'z': <Yuck(i=0) at remote 0xaace60>, '__doc__': None}, key=
0x5c2b8d "__lltrace__") at Objects/dictobject.c:2171
請注意，PyDict_GetItemString 的字典引數顯示為其 repr()，而不是不透明的 PyObject * 指標。
該擴充套件透過為 PyObject * 型別的值提供自定義列印例程來工作。如果您需要訪問物件的低階詳細資訊，請將該值轉換為相應型別的指標。例如
(gdb) p globals
$1 = {'__builtins__': <module at remote 0x7ffff7fb1868>, '__name__':
'__main__', 'ctypes': <module at remote 0x7ffff7f14360>, '__doc__': None,
'__package__': None}
(gdb) p *(PyDictObject*)globals
$2 = {ob_refcnt = 3, ob_type = 0x3dbdf85820, ma_fill = 5, ma_used = 5,
ma_mask = 7, ma_table = 0x63d0f8, ma_lookup = 0x3dbdc7ea70
<lookdict_string>, ma_smalltable = {{me_hash = 7065186196740147912,
me_key = '__builtins__', me_value = <module at remote 0x7ffff7fb1868>},
{me_hash = -368181376027291943, me_key = '__name__',
me_value ='__main__'}, {me_hash = 0, me_key = 0x0, me_value = 0x0},
{me_hash = 0, me_key = 0x0, me_value = 0x0},
{me_hash = -9177857982131165996, me_key = 'ctypes',
me_value = <module at remote 0x7ffff7f14360>},
{me_hash = -8518757509529533123, me_key = '__doc__', me_value = None},
{me_hash = 0, me_key = 0x0, me_value = 0x0}, {
me_hash = 6614918939584953775, me_key = '__package__', me_value = None}}}
請注意，美觀印表機實際上不呼叫 repr()。對於基本型別，它們會嘗試與其結果緊密匹配。
一個可能令人困惑的領域是，某些型別的自定義印表機看起來很像 GDB 的標準型別內建印表機。例如，Python int (PyLongObject*) 的美觀印表機給出的表示形式與常規機器級整數的表示形式無法區分
(gdb) p some_machine_integer
$3 = 42
(gdb) p some_python_integer
$4 = 42
透過轉換為 PyLongObject* 可以顯示內部結構
(gdb) p *(PyLongObject*)some_python_integer
$5 = {ob_base = {ob_base = {ob_refcnt = 8, ob_type = 0x3dad39f5e0}, ob_size = 1},
ob_digit = {42}}
使用 str 型別也會出現類似的混淆，其輸出看起來很像 gdb 的 char * 內建印表機
(gdb) p ptr_to_python_str
$6 = '__builtins__'
str 例項的美觀印表機預設為使用單引號（Python 的字串 repr 也如此），而 char * 值的標準印表機使用雙引號幷包含十六進位制地址
(gdb) p ptr_to_char_star
$7 = 0x6d72c0 "hello world"
同樣，透過轉換為 PyUnicodeObject* 可以顯示實現細節
(gdb) p *(PyUnicodeObject*)$6
$8 = {ob_base = {ob_refcnt = 33, ob_type = 0x3dad3a95a0}, length = 12,
str = 0x7ffff2128500, hash = 7065186196740147912, state = 1, defenc = 0x0}
py-list¶
該擴充套件添加了一個
py-list命令，該命令列出選定執行緒中當前幀的 Python 原始碼（如果有）。當前行用“>”標記(gdb) py-list 901 if options.profile: 902 options.profile = False 903 profile_me() 904 return 905 >906 u = UI() 907 if not u.quit: 908 try: 909 gtk.main() 910 except KeyboardInterrupt: 911 # properly quit on a keyboard interrupt...使用
py-list START在 Python 原始碼中的不同行號處列出，使用py-list START,END列出 Python 原始碼中的特定行範圍。
py-up 和 py-down¶
py-up和py-down命令類似於 GDB 的常規up和down命令，但嘗試在 CPython 幀級別而不是 C 幀級別移動。GDB 並非總能讀取相關幀資訊，這取決於 CPython 編譯時的最佳化級別。在內部，這些命令會查詢正在執行預設幀評估函式（即 CPython 核心位元組碼直譯器迴圈）的 C 幀，並查詢相關
PyFrameObject *的值。它們會發出線程內的幀號（在 C 級別）。
例如:
(gdb) py-up #37 Frame 0x9420b04, for file /usr/lib/python2.6/site-packages/ gnome_sudoku/main.py, line 906, in start_game () u = UI() (gdb) py-up #40 Frame 0x948e82c, for file /usr/lib/python2.6/site-packages/ gnome_sudoku/gnome_sudoku.py, line 22, in start_game(main=<module at remote 0xb771b7f4>) main.start_game() (gdb) py-up Unable to find an older python frame所以我們處在 Python 棧的頂部。
幀號與 GDB 標準
backtrace命令顯示的幀號相對應。該命令會跳過不執行 Python 程式碼的 C 幀。回到下面
(gdb) py-down #37 Frame 0x9420b04, for file /usr/lib/python2.6/site-packages/gnome_sudoku/main.py, line 906, in start_game () u = UI() (gdb) py-down #34 (unable to read python frame information) (gdb) py-down #23 (unable to read python frame information) (gdb) py-down #19 (unable to read python frame information) (gdb) py-down #14 Frame 0x99262ac, for file /usr/lib/python2.6/site-packages/gnome_sudoku/game_selector.py, line 201, in run_swallowed_dialog (self=<NewOrSavedGameSelector(new_game_model=<gtk.ListStore at remote 0x98fab44>, puzzle=None, saved_games=[{'gsd.auto_fills': 0, 'tracking': {}, 'trackers': {}, 'notes': [], 'saved_at': 1270084485, 'game': '7 8 0 0 0 0 0 5 6 0 0 9 0 8 0 1 0 0 0 4 6 0 0 0 0 7 0 6 5 0 0 0 4 7 9 2 0 0 0 9 0 1 0 0 0 3 9 7 6 0 0 0 1 8 0 6 0 0 0 0 2 8 0 0 0 5 0 4 0 6 0 0 2 1 0 0 0 0 0 4 5\n7 8 0 0 0 0 0 5 6 0 0 9 0 8 0 1 0 0 0 4 6 0 0 0 0 7 0 6 5 1 8 3 4 7 9 2 0 0 0 9 0 1 0 0 0 3 9 7 6 0 0 0 1 8 0 6 0 0 0 0 2 8 0 0 0 5 0 4 0 6 0 0 2 1 0 0 0 0 0 4 5', 'gsd.impossible_hints': 0, 'timer.__absolute_start_time__': <float at remote 0x984b474>, 'gsd.hints': 0, 'timer.active_time': <float at remote 0x984b494>, 'timer.total_time': <float at remote 0x984b464>}], dialog=<gtk.Dialog at remote 0x98faaa4>, saved_game_model=<gtk.ListStore at remote 0x98fad24>, sudoku_maker=<SudokuMaker(terminated=False, played=[], batch_siz...(truncated) swallower.run_dialog(self.dialog) (gdb) py-down #11 Frame 0x9aead74, for file /usr/lib/python2.6/site-packages/gnome_sudoku/dialog_swallower.py, line 48, in run_dialog (self=<SwappableArea(running=<gtk.Dialog at remote 0x98faaa4>, main_page=0) at remote 0x98fa6e4>, d=<gtk.Dialog at remote 0x98faaa4>) gtk.main() (gdb) py-down #8 (unable to read python frame information) (gdb) py-down Unable to find a newer python frame我們處於 Python 棧的底部。
請注意，在 Python 3.12 及更高版本中，同一個 C 棧幀可以用於多個 Python 棧幀。這意味著
py-up和py-down可能會一次移動多個 Python 幀。例如(gdb) py-up #6 Frame 0x7ffff7fb62b0, for file /tmp/rec.py, line 5, in recursive_function (n=0) time.sleep(5) #6 Frame 0x7ffff7fb6240, for file /tmp/rec.py, line 7, in recursive_function (n=1) recursive_function(n-1) #6 Frame 0x7ffff7fb61d0, for file /tmp/rec.py, line 7, in recursive_function (n=2) recursive_function(n-1) #6 Frame 0x7ffff7fb6160, for file /tmp/rec.py, line 7, in recursive_function (n=3) recursive_function(n-1) #6 Frame 0x7ffff7fb60f0, for file /tmp/rec.py, line 7, in recursive_function (n=4) recursive_function(n-1) #6 Frame 0x7ffff7fb6080, for file /tmp/rec.py, line 7, in recursive_function (n=5) recursive_function(n-1) #6 Frame 0x7ffff7fb6020, for file /tmp/rec.py, line 9, in <module> () recursive_function(5) (gdb) py-up Unable to find an older python frame
py-bt¶
py-bt命令嘗試顯示當前執行緒的 Python 級別回溯。例如:
(gdb) py-bt #8 (unable to read python frame information) #11 Frame 0x9aead74, for file /usr/lib/python2.6/site-packages/gnome_sudoku/dialog_swallower.py, line 48, in run_dialog (self=<SwappableArea(running=<gtk.Dialog at remote 0x98faaa4>, main_page=0) at remote 0x98fa6e4>, d=<gtk.Dialog at remote 0x98faaa4>) gtk.main() #14 Frame 0x99262ac, for file /usr/lib/python2.6/site-packages/gnome_sudoku/game_selector.py, line 201, in run_swallowed_dialog (self=<NewOrSavedGameSelector(new_game_model=<gtk.ListStore at remote 0x98fab44>, puzzle=None, saved_games=[{'gsd.auto_fills': 0, 'tracking': {}, 'trackers': {}, 'notes': [], 'saved_at': 1270084485, 'game': '7 8 0 0 0 0 0 5 6 0 0 9 0 8 0 1 0 0 0 4 6 0 0 0 0 7 0 6 5 0 0 0 4 7 9 2 0 0 0 9 0 1 0 0 0 3 9 7 6 0 0 0 1 8 0 6 0 0 0 0 2 8 0 0 0 5 0 4 0 6 0 0 2 1 0 0 0 0 0 4 5\n7 8 0 0 0 0 0 5 6 0 0 9 0 8 0 1 0 0 0 4 6 0 0 0 0 7 0 6 5 1 8 3 4 7 9 2 0 0 0 9 0 1 0 0 0 3 9 7 6 0 0 0 1 8 0 6 0 0 0 0 2 8 0 0 0 5 0 4 0 6 0 0 2 1 0 0 0 0 0 4 5', 'gsd.impossible_hints': 0, 'timer.__absolute_start_time__': <float at remote 0x984b474>, 'gsd.hints': 0, 'timer.active_time': <float at remote 0x984b494>, 'timer.total_time': <float at remote 0x984b464>}], dialog=<gtk.Dialog at remote 0x98faaa4>, saved_game_model=<gtk.ListStore at remote 0x98fad24>, sudoku_maker=<SudokuMaker(terminated=False, played=[], batch_siz...(truncated) swallower.run_dialog(self.dialog) #19 (unable to read python frame information) #23 (unable to read python frame information) #34 (unable to read python frame information) #37 Frame 0x9420b04, for file /usr/lib/python2.6/site-packages/gnome_sudoku/main.py, line 906, in start_game () u = UI() #40 Frame 0x948e82c, for file /usr/lib/python2.6/site-packages/gnome_sudoku/gnome_sudoku.py, line 22, in start_game (main=<module at remote 0xb771b7f4>) main.start_game()幀號與 GDB 標準
backtrace命令顯示的幀號相對應。
py-print¶
py-print命令查詢一個 Python 名稱並嘗試列印它。它首先在當前執行緒的區域性變數中查詢，然後是全域性變數，最後是內建變數(gdb) py-print self local 'self' = <SwappableArea(running=<gtk.Dialog at remote 0x98faaa4>, main_page=0) at remote 0x98fa6e4> (gdb) py-print __name__ global '__name__' = 'gnome_sudoku.dialog_swallower' (gdb) py-print len builtin 'len' = <built-in function len> (gdb) py-print scarlet_pimpernel 'scarlet_pimpernel' not found如果當前的 C 幀對應於多個 Python 幀，則
py-print只考慮第一個。
py-locals¶
py-locals命令查詢選定執行緒中當前 Python 幀中的所有 Python 區域性變數，並列印它們的表示形式(gdb) py-locals self = <SwappableArea(running=<gtk.Dialog at remote 0x98faaa4>, main_page=0) at remote 0x98fa6e4> d = <gtk.Dialog at remote 0x98faaa4>如果當前的 C 幀對應於多個 Python 幀，則會顯示所有這些幀的區域性變數
(gdb) py-locals Locals for recursive_function n = 0 Locals for recursive_function n = 1 Locals for recursive_function n = 2 Locals for recursive_function n = 3 Locals for recursive_function n = 4 Locals for recursive_function n = 5 Locals for <module>
與 GDB 命令一起使用¶
擴充套件命令補充了 GDB 的內建命令。例如，您可以使用 py-bt 顯示的幀號與 frame 命令一起使用，以進入所選執行緒中的特定幀，如下所示
(gdb) py-bt
(output snipped)
#68 Frame 0xaa4560, for file Lib/test/regrtest.py, line 1548, in <module> ()
main()
(gdb) frame 68
#68 0x00000000004cd1e6 in PyEval_EvalFrameEx (f=Frame 0xaa4560, for file Lib/test/regrtest.py, line 1548, in <module> (), throwflag=0) at Python/ceval.c:2665
2665 x = call_function(&sp, oparg);
(gdb) py-list
1543 # Run the tests in a context manager that temporary changes the CWD to a
1544 # temporary and writable directory. If it's not possible to create or
1545 # change the CWD, the original CWD will be used. The original CWD is
1546 # available from test_support.SAVEDCWD.
1547 with test_support.temp_cwd(TESTCWD, quiet=True):
>1548 main()
info threads 命令會為您提供程序中執行緒的列表，您可以使用 thread 命令選擇另一個執行緒
(gdb) info threads
105 Thread 0x7fffefa18710 (LWP 10260) sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:86
104 Thread 0x7fffdf5fe710 (LWP 10259) sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:86
* 1 Thread 0x7ffff7fe2700 (LWP 10145) 0x00000038e46d73e3 in select () at ../sysdeps/unix/syscall-template.S:82
您可以使用 thread apply all COMMAND 或（簡寫為 t a a COMMAND）在所有執行緒上執行命令。結合 py-bt，這讓您可以在 Python 級別檢視每個執行緒正在做什麼
(gdb) t a a py-bt
Thread 105 (Thread 0x7fffefa18710 (LWP 10260)):
#5 Frame 0x7fffd00019d0, for file /home/david/coding/python-svn/Lib/threading.py, line 155, in _acquire_restore (self=<_RLock(_Verbose__verbose=False, _RLock__owner=140737354016512, _RLock__block=<thread.lock at remote 0x858770>, _RLock__count=1) at remote 0xd7ff40>, count_owner=(1, 140737213728528), count=1, owner=140737213728528)
self.__block.acquire()
#8 Frame 0x7fffac001640, for file /home/david/coding/python-svn/Lib/threading.py, line 269, in wait (self=<_Condition(_Condition__lock=<_RLock(_Verbose__verbose=False, _RLock__owner=140737354016512, _RLock__block=<thread.lock at remote 0x858770>, _RLock__count=1) at remote 0xd7ff40>, acquire=<instancemethod at remote 0xd80260>, _is_owned=<instancemethod at remote 0xd80160>, _release_save=<instancemethod at remote 0xd803e0>, release=<instancemethod at remote 0xd802e0>, _acquire_restore=<instancemethod at remote 0xd7ee60>, _Verbose__verbose=False, _Condition__waiters=[]) at remote 0xd7fd10>, timeout=None, waiter=<thread.lock at remote 0x858a90>, saved_state=(1, 140737213728528))
self._acquire_restore(saved_state)
#12 Frame 0x7fffb8001a10, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 348, in f ()
cond.wait()
#16 Frame 0x7fffb8001c40, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 37, in task (tid=140737213728528)
f()
Thread 104 (Thread 0x7fffdf5fe710 (LWP 10259)):
#5 Frame 0x7fffe4001580, for file /home/david/coding/python-svn/Lib/threading.py, line 155, in _acquire_restore (self=<_RLock(_Verbose__verbose=False, _RLock__owner=140737354016512, _RLock__block=<thread.lock at remote 0x858770>, _RLock__count=1) at remote 0xd7ff40>, count_owner=(1, 140736940992272), count=1, owner=140736940992272)
self.__block.acquire()
#8 Frame 0x7fffc8002090, for file /home/david/coding/python-svn/Lib/threading.py, line 269, in wait (self=<_Condition(_Condition__lock=<_RLock(_Verbose__verbose=False, _RLock__owner=140737354016512, _RLock__block=<thread.lock at remote 0x858770>, _RLock__count=1) at remote 0xd7ff40>, acquire=<instancemethod at remote 0xd80260>, _is_owned=<instancemethod at remote 0xd80160>, _release_save=<instancemethod at remote 0xd803e0>, release=<instancemethod at remote 0xd802e0>, _acquire_restore=<instancemethod at remote 0xd7ee60>, _Verbose__verbose=False, _Condition__waiters=[]) at remote 0xd7fd10>, timeout=None, waiter=<thread.lock at remote 0x858860>, saved_state=(1, 140736940992272))
self._acquire_restore(saved_state)
#12 Frame 0x7fffac001c90, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 348, in f ()
cond.wait()
#16 Frame 0x7fffac0011c0, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 37, in task (tid=140736940992272)
f()
Thread 1 (Thread 0x7ffff7fe2700 (LWP 10145)):
#5 Frame 0xcb5380, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 16, in _wait ()
time.sleep(0.01)
#8 Frame 0x7fffd00024a0, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 378, in _check_notify (self=<ConditionTests(_testMethodName='test_notify', _resultForDoCleanups=<TestResult(_original_stdout=<cStringIO.StringO at remote 0xc191e0>, skipped=[], _mirrorOutput=False, testsRun=39, buffer=False, _original_stderr=<file at remote 0x7ffff7fc6340>, _stdout_buffer=<cStringIO.StringO at remote 0xc9c7f8>, _stderr_buffer=<cStringIO.StringO at remote 0xc9c790>, _moduleSetUpFailed=False, expectedFailures=[], errors=[], _previousTestClass=<type at remote 0x928310>, unexpectedSuccesses=[], failures=[], shouldStop=False, failfast=False) at remote 0xc185a0>, _threads=(0,), _cleanups=[], _type_equality_funcs={<type at remote 0x7eba00>: <instancemethod at remote 0xd750e0>, <type at remote 0x7e7820>: <instancemethod at remote 0xd75160>, <type at remote 0x7e30e0>: <instancemethod at remote 0xd75060>, <type at remote 0x7e7d20>: <instancemethod at remote 0xd751e0>, <type at remote 0x7f19e0...(truncated)
_wait()