linux - 如何跟踪动态加载的库

Question

我们的系统有一个开源库。棘手的是我们有两个库的副本，一个是我们自己修改的，另一个是原始的。两个副本都在源代码树中，但定制的副本应在运行时调用，而原始副本则在构建时用于其他目的。

现在我怀疑在我们的系统升级过程中，自定义项被隐藏在原始系统中了。由于系统的复杂性，修改源代码以添加一些跟踪是可行的，但很困难。我想如果我可以 objdump 顶级库来获得线索。

以下是更多详细信息:

1) The customization one and the original one have the same source file names 
2) Their library names are same
3) The customization is some implementation change at deep within; so it is 
   invisible from outside
4) The 2 libraries are at different sub directory trees

因为它是动态链接的，所以我实际上怀疑 objdump 能否告诉我任何区别。但如有任何建议，我们将不胜感激!

Answer 1

我认为 ldd 应该简单地告诉你这一点，作为预测而不是作为跟踪。例如 ls 命令:

# ldd $(which ls)
    linux-vdso.so.1 (0x00000333f2a54000)
    libselinux.so.1 => /lib64/libselinux.so.1 (0x00000333f2610000)
    libcap.so.2 => /lib64/libcap.so.2 (0x00000333f2408000)
    libacl.so.1 => /lib64/libacl.so.1 (0x00000333f21f8000)
    libc.so.6 => /lib64/libc.so.6 (0x00000333f1e48000)
    libdl.so.2 => /lib64/libdl.so.2 (0x00000333f1c40000)
    libpcre.so.1 => /usr/lib64/libpcre.so.1 (0x00000333f19d8000)
    libpthread.so.0 => /lib64/libpthread.so.0 (0x00000333f17b8000)
    /lib64/ld-linux-x86-64.so.2 (0x00000333f2838000)
    libattr.so.1 => /lib64/libattr.so.1 (0x00000333f15b0000)

为了进行跟踪，您可以在提示模式下滥用 apparmor 之类的东西。

或者使用 gdb，GNU 调试器。运行“ls”命令的示例:

# gdb ls
GNU gdb (GDB; openSUSE 13.1) 7.6.50.20130731-cvs
Copyright (C) 2013 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-suse-linux".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://bugs.opensuse.org/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".
..
Reading symbols from /usr/bin/ls...Missing separate debuginfo for /usr/bin/ls
Try: zypper install -C "debuginfo(build-id)=eb844a5c20c70a59fc693cd1061f851fb7d046f4"
(no debugging symbols found)...done.
(gdb) start
Function "main" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Temporary breakpoint 1 (main) pending.
Starting program: /usr/bin/ls 
warning: Cannot call inferior functions, Linux kernel PaX protection forbids return to non-executable pages!
Missing separate debuginfo for /lib64/ld-linux-x86-64.so.2
Try: zypper install -C "debuginfo(build-id)=afa98667969782208459e394f8c8f87ac7510710"
bak  core   learning.log       learning.mode  lr   old          test.log   testpolicy        testpolicy.large
c    learn  learning.log.uniq  ll             lrw  paxtest.log  test2.log  testpolicy.gradm  testpolicy.large.gradm
[Inferior 1 (process 25609) exited normally]
(gdb) info sharedlibrary
From                To                  Syms Read   Shared Object Library
0x00000342a0556ae0  0x00000342a056ee10  Yes (*)     /lib64/ld-linux-x86-64.so.2
(*): Shared library is missing debugging information.
(gdb)