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«GDB» отладчик пропускает точку останова Жутко

2017-02-02 3 views
2

Здесь есть короткий фрагмент моего кода:«GDB» отладчик пропускает точку останова Жутко

//l2tp_inspector.cc 
14 else if (f_info->key.proto == UDP_PROTO) { 
15  if (size >= 4) { 
16  uint32_t l2tp_part; 
17  l2tp_part = *((uint32_t*)(data)); 
18 
19  if ((l2tp_part & 0xFFFF0000) == 0xC802 &&                             
20   (l2tp_part & 0x0000FFFF) == size) { 
21   f_info->protocol_id = Bina::Protocols::UDP_L2TP; 
22   f_info->application_id = Bina::Applications::UNKNOWN; 
23   return PROTOCOL_ACCEPTED_FINALIZED; 
24  } 
25  } 
26  return REJECTED; 
27 }

После компиляции кода и использования gdb отладчика с точками разрыва на линии 17, 18 и 19, мы имеем следующий вывод:

[email protected]:~/prj$ gdb prj-loader 

GNU gdb (Ubuntu 7.11.90.20161005-0ubuntu1) 7.11.90.20161005-git 
This GDB was configured as "x86_64-linux-gnu". 

(gdb) b l2tp_inspector.cc:17 
No source file named l2tp_inspector.cc. 
Make breakpoint pending on future shared library load? (y or [n]) y 
Breakpoint 1 (l2tp_inspector.cc:17) pending. 

(gdb) b l2tp_inspector.cc:18 
No source file named l2tp_inspector.cc. 
Make breakpoint pending on future shared library load? (y or [n]) y 
Breakpoint 2 (l2tp_inspector.cc:18) pending. 

(gdb) b l2tp_inspector.cc:19 
No source file named l2tp_inspector.cc. 
Make breakpoint pending on future shared library load? (y or [n]) y 
Breakpoint 3 (l2tp_inspector.cc:19) pending. 

(gdb) r 
Starting program: ~/prj/prj-loader 
[Thread debugging using libthread_db enabled] 
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". 
[2017-02-02 08:44:52.267622] [0x00007ffff7fc9780] [info] New id registered TCP with id 0 
[2017-02-02 08:44:52.267899] [0x00007ffff7fc9780] [info] New id registered TCP_PAYLOAD with id 1 
[2017-02-02 08:44:52.267991] [0x00007ffff7fc9780] [info] New id registered UDP with id 2 
[2017-02-02 08:44:52.268025] [0x00007ffff7fc9780] [info] New id registered UDP_PAYLOAD with id 3 
[2017-02-02 08:44:52.268169] [0x00007ffff7fc9780] [info] Already registered id TCP with id 0 
[2017-02-02 08:44:52.268201] [0x00007ffff7fc9780] [info] Already registered id TCP_PAYLOAD with id 1 
[2017-02-02 08:44:52.268285] [0x00007ffff7fc9780] [info] Already registered id UDP with id 2 
[2017-02-02 08:44:52.268380] [0x00007ffff7fc9780] [info] Already registered id UDP_PAYLOAD with id 3 
[2017-02-02 08:44:52.268519] [0x00007ffff7fc9780] [info] New id registered IPV4 with id 4 
[2017-02-02 08:44:52.268553] [0x00007ffff7fc9780] [info] New id registered IPV4FRAG with id 5 
[2017-02-02 08:44:52.268632] [0x00007ffff7fc9780] [info] Already registered id TCP with id 0 
[2017-02-02 08:44:52.268715] [0x00007ffff7fc9780] [info] Already registered id TCP_PAYLOAD with id 1 
[2017-02-02 08:44:52.268795] [0x00007ffff7fc9780] [info] Already registered id UDP with id 2 
[2017-02-02 08:44:52.268877] [0x00007ffff7fc9780] [info] Already registered id UDP_PAYLOAD with id 3 
[2017-02-02 08:44:52.268972] [0x00007ffff7fc9780] [info] Already registered id TCP with id 0 
[2017-02-02 08:44:52.269066] [0x00007ffff7fc9780] [info] Already registered id TCP_PAYLOAD with id 1 
[2017-02-02 08:44:52.269149] [0x00007ffff7fc9780] [info] Already registered id UDP with id 2 
[2017-02-02 08:44:52.269229] [0x00007ffff7fc9780] [info] Already registered id UDP_PAYLOAD with id 3 
[2017-02-02 08:44:52.269370] [0x00007ffff7fc9780] [info] Already registered id TCP with id 0 
[2017-02-02 08:44:52.269401] [0x00007ffff7fc9780] [info] Already registered id TCP_PAYLOAD with id 1 
[2017-02-02 08:44:52.269481] [0x00007ffff7fc9780] [info] Already registered id UDP with id 2 
[2017-02-02 08:44:52.269561] [0x00007ffff7fc9780] [info] Already registered id UDP_PAYLOAD with id 3 
[2017-02-02 08:44:52.269643] [0x00007ffff7fc9780] [info] Already registered id IPV4 with id 4 
[2017-02-02 08:44:52.269723] [0x00007ffff7fc9780] [info] Already registered id IPV4FRAG with id 5 
[2017-02-02 08:44:52.269807] [0x00007ffff7fc9780] [info] New id registered ETHERNET with id 6 

Breakpoint 1, inspect (f_info=0x7fffffffce50, data=0x555555be439a "\310\002", size=106, [email protected]: 0x0) 
    at ../src/modules/prj-lib/src/proto-inspectors/l2tp_inspector.cc:17 
17  l2tp_part = *((uint32_t*)(data)); 

(gdb) s 
Breakpoint 2, inspect (f_info=0x7fffffffce50, data=0x555555be439a "\310\002", size=106, [email protected]: 0x0) 
    at ../src/modules/prj-lib/src/proto-inspectors/l2tp_inspector.cc:26 
26  return REJECTED;

Как вы видите выше, в то время как я положил перерыв на линии 19, gdb не останавливается на этой линии, и пропустить его к строке 26, почему?

Когда я заменяю 0xC802 с 0xC8020000 в строке 19, то он работает отлично gdb не пропускает линии 19 больше:

//l2tp_inspector.cc 
14 else if (f_info->key.proto == UDP_PROTO) { 
15  if (size >= 4) { 
16  uint32_t l2tp_part; 
17  l2tp_part = *((uint32_t*)(data)); 
18 
19  if ((l2tp_part & 0xFFFF0000) == 0xC8020000 &&                             
20   (l2tp_part & 0x0000FFFF) == size) { 
21   f_info->protocol_id = Bina::Protocols::UDP_L2TP; 
22   f_info->application_id = Bina::Applications::UNKNOWN; 
23   return PROTOCOL_ACCEPTED_FINALIZED; 
24  } 
25  } 
26  return REJECTED; 
27 }

выход ввп:

[email protected]:~/prj$ gdb prj-loader 
GNU gdb (Ubuntu 7.11.90.20161005-0ubuntu1) 7.11.90.20161005-git 
This GDB was configured as "x86_64-linux-gnu". 

(gdb) b l2tp_inspector.cc:17 
No source file named l2tp_inspector.cc. 
Make breakpoint pending on future shared library load? (y or [n]) y 
Breakpoint 1 (l2tp_inspector.cc:17) pending. 

(gdb) b l2tp_inspector.cc:18 
No source file named l2tp_inspector.cc. 
Make breakpoint pending on future shared library load? (y or [n]) y 
Breakpoint 2 (l2tp_inspector.cc:18) pending. 

(gdb) b l2tp_inspector.cc:19 
No source file named l2tp_inspector.cc. 
Make breakpoint pending on future shared library load? (y or [n]) y 
Breakpoint 3 (l2tp_inspector.cc:19) pending. 

(gdb) r 
Starting program: ~/prj/prj-loader 
[Thread debugging using libthread_db enabled] 
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". 
[2017-02-02 08:53:07.201600] [0x00007ffff7fc9780] [info] New id registered TCP with id 0 
[2017-02-02 08:53:07.201677] [0x00007ffff7fc9780] [info] New id registered TCP_PAYLOAD with id 1 
[2017-02-02 08:53:07.201711] [0x00007ffff7fc9780] [info] New id registered UDP with id 2 
[2017-02-02 08:53:07.201728] [0x00007ffff7fc9780] [info] New id registered UDP_PAYLOAD with id 3 
[2017-02-02 08:53:07.201757] [0x00007ffff7fc9780] [info] Already registered id TCP with id 0 
[2017-02-02 08:53:07.201773] [0x00007ffff7fc9780] [info] Already registered id TCP_PAYLOAD with id 1 
[2017-02-02 08:53:07.201817] [0x00007ffff7fc9780] [info] Already registered id UDP with id 2 
[2017-02-02 08:53:07.201832] [0x00007ffff7fc9780] [info] Already registered id UDP_PAYLOAD with id 3 
[2017-02-02 08:53:07.201853] [0x00007ffff7fc9780] [info] New id registered IPV4 with id 4 
[2017-02-02 08:53:07.201871] [0x00007ffff7fc9780] [info] New id registered IPV4FRAG with id 5 
[2017-02-02 08:53:07.201888] [0x00007ffff7fc9780] [info] Already registered id TCP with id 0 
[2017-02-02 08:53:07.201903] [0x00007ffff7fc9780] [info] Already registered id TCP_PAYLOAD with id 1 
[2017-02-02 08:53:07.201933] [0x00007ffff7fc9780] [info] Already registered id UDP with id 2 
[2017-02-02 08:53:07.201951] [0x00007ffff7fc9780] [info] Already registered id UDP_PAYLOAD with id 3 
[2017-02-02 08:53:07.201968] [0x00007ffff7fc9780] [info] Already registered id TCP with id 0 
[2017-02-02 08:53:07.201983] [0x00007ffff7fc9780] [info] Already registered id TCP_PAYLOAD with id 1 
[2017-02-02 08:53:07.201998] [0x00007ffff7fc9780] [info] Already registered id UDP with id 2 
[2017-02-02 08:53:07.202023] [0x00007ffff7fc9780] [info] Already registered id UDP_PAYLOAD with id 3 
[2017-02-02 08:53:07.202048] [0x00007ffff7fc9780] [info] Already registered id TCP with id 0 
[2017-02-02 08:53:07.202067] [0x00007ffff7fc9780] [info] Already registered id TCP_PAYLOAD with id 1 
[2017-02-02 08:53:07.202083] [0x00007ffff7fc9780] [info] Already registered id UDP with id 2 
[2017-02-02 08:53:07.202099] [0x00007ffff7fc9780] [info] Already registered id UDP_PAYLOAD with id 3 
[2017-02-02 08:53:07.202114] [0x00007ffff7fc9780] [info] Already registered id IPV4 with id 4 
[2017-02-02 08:53:07.202133] [0x00007ffff7fc9780] [info] Already registered id IPV4FRAG with id 5 
[2017-02-02 08:53:07.202150] [0x00007ffff7fc9780] [info] New id registered ETHERNET with id 6 

Breakpoint 1, inspect (f_info=0x7fffffffce50, data=0x555555be439a "\310\002", size=106, [email protected]: 0x0) 
    at ../src/modules/prj-lib/src/proto-inspectors/l2tp_inspector.cc:17 
17  l2tp_part = *((uint32_t*)(data)); 

(gdb) s 
Breakpoint 2, inspect (f_info=0x7fffffffce50, data=0x555555be439a "\310\002", size=106, [email protected]: 0x0) 
    at ../src/modules/prj-lib/src/proto-inspectors/l2tp_inspector.cc:19 
19  if ((l2tp_part & 0xFFFF0000) == 0xC8020000 && 

(gdb) s 
26  return REJECTED;

Почему DBG пропущена строка 19 в первом фрагменте, но он останавливается на нем во втором фрагменте? Почти все одно и то же, и единственное различие - это значение.

источник

2017-02-02 Abraham

+0

короткое замыкание? Означает ли он значение '(l2tp_part & 0x0000FFFF) == size)' to false и пропускает другое выражение, в котором находится точка останова? –

+0

HInt: поставьте оператор печати внутри тела оператора if и запустите снова. –

+2

Возможный дубликат [gdb перескакивает через линии] (http://stackoverflow.com/questions/8064911/gdb-is-jumping-over-lines) – kaylum

ответ

3

Наверное, я понял.

Короткий ответ:

Compiler Оптимизация удалить, если условие с блоком целиком!

Длинный ответ:

Результат (l2tp_part & 0xFFFF0000) == 0xC802 в состоянии if всегда false! Поскольку мы сравниваем 4-байтовый номер, который имеет 2-наименее значимые байты, равные 0x0000, с 2-байтным ненулевым числом. Другими словами, мы сравниваем 0xXXXX0000 с 0x0000C802 и, очевидно, они ни в коем случае не равны. Таким образом, все условие всегда является ложным, а когда блок if избыточен, компилятор удаляет его. Поэтому отладчик не может останавливаться на этой линии.

источник

2017-02-02 06:08:08 Abraham

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