如何在运行时调试共享库？

Question

谁能告诉我如何对共享库进行运行时调试？

我需要在运行时调试共享库中的一个函数，但另一个程序会调用它。如何使用共享库执行类似dbx的操作？

我在AIX上使用dbx。我想做的是gdb比dbx好吗？

Answer 1

您只需要使用可执行文件调用gdb（无论是您的文件还是第三方文件都没有关系）。这是一个示例，其中我调试 ls 命令并在（共享） c库中
设置断点。此示例使用了gdb 6.8，它支持延迟（挂起）断点，这使此操作变得容易：

gdb /bin/ls
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu"...
(no debugging symbols found)
(gdb) b write
Function "write" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (write) pending.
(gdb) r
Starting program: /bin/ls
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
[Thread debugging using libthread_db enabled]
(no debugging symbols found)
(no debugging symbols found)
[New Thread 0x7f98d2d23780 (LWP 7029)]
[Switching to Thread 0x7f98d2d23780 (LWP 7029)]

Breakpoint 1, 0x00007f98d2264bb0 in write () from /lib/libc.so.6
(gdb)

如您所见，gdb自动管理可执行文件使用的所有线程。您不必为那里的线程做任何特殊的事情。断点将在任何线程中工作。

或者，如果要将调试器附加到已经运行的应用程序（我在此处以 tail -f / tmp / ttt 为例）：

ps ux | grep tail
lothar    8496  0.0  0.0   9352   804 pts/3    S+   12:38   0:00 tail -f /tmp/ttt
lothar    8510  0.0  0.0   5164   840 pts/4    S+   12:39   0:00 grep tail

gdb
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu"...
(no debugging symbols found)
(gdb) attach 8496
Attaching to program: /usr/bin/tail, process 8496
Reading symbols from /lib/librt.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib/librt.so.1
Reading symbols from /lib/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib/libpthread.so.0...(no debugging symbols found)...done.
[Thread debugging using libthread_db enabled]
[New Thread 0x7f24853f56e0 (LWP 8496)]
Loaded symbols for /lib/libpthread.so.0
Reading symbols from /lib/ld-linux-x86-64.so.2...
(no debugging symbols found)...done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
(no debugging symbols found)
0x00007f2484d2bb50 in nanosleep () from /lib/libc.so.6
(gdb) b write
Breakpoint 1 at 0x7f2484d57bb0
(gdb) c
Continuing.
[Switching to Thread 0x7f24853f56e0 (LWP 8496)]

Breakpoint 1, 0x00007f2484d57bb0 in write () from /lib/libc.so.6
(gdb)