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LD_DEBUG 环境变量 (2012)
The LD_DEBUG environment variable (2012)

原始链接: https://bnikolic.co.uk/blog/linux-ld-debug.html

开发包含许多共享库的复杂系统时，常会因为加载了错误的库版本而导致难以排查的错误。虽然 `strace` 等传统工具提供了一定的参考，但在 Linux 上调试此类问题的最有效方法是使用 `LD_DEBUG` 环境变量。 通过在运行程序前设置 `LD_DEBUG`，动态链接器将提供有关库搜索路径、符号绑定和版本依赖关系的详细诊断信息。用户可以通过运行 `LD_DEBUG=help ` 查看可用选项。对于更复杂的分析，可以使用 `LD_DEBUG_OUTPUT` 将输出重定向到文件。 除了 `LD_DEBUG`，其他有用的诊断工具还包括： * **`ldd`**：解析库依赖关系。 * **`objdump`**：检查所需的库。 * **`patchelf`**：修改可执行文件的搜索顺序（rpath）。 * **`LD_PRELOAD`**：便于动态库替换。 虽然 `LD_DEBUG` 是 Linux 专有的，但通过 `gflags.exe` 启用“Show Loader Snaps”并使用 `WinDbg` 调试，也可以在 Windows 上实现类似的效果。这些技术对于解决链接冲突和优化动态加载性能具有极高的价值。

这篇 Hacker News 帖子讨论了 `LD_DEBUG` 及其他动态链接器环境变量在排查 Linux 库加载问题时的作用。 用户分享了一些实际案例，例如使用 `LD_DEBUG` 来诊断因不必要的库导出而导致文件无法正常卸载的问题。讨论还强调了 `LD_AUDIT` 是一种功能强大但鲜为人知的库活动审计替代方案，并提供了关于如何将其用于安全和调试目的的资源。 贡献者们一致认为，虽然一些环境变量在 `ld.so` 的帮助文档（man page）中有详细说明，但其他一些变量仍然鲜为人知。为了发现未记录的选项，参与者建议查阅 `ld.so` 源代码中的 `getenv` 调用。总的来说，该帖子为 Linux 动态加载器中可用的底层诊断工具提供了一个参考。
相关文章
原文

Originally published 23 April 2012, updated 10 September 2019 (add link to troubleshooting tool), updated 18 October 2019 (moved to Jekyll), updated 3 April 2023 with links to other tools

Development of large systems using many shared (dynamically) loaded libraries can sometimes lead to some frustrating bugs that are difficult to diagnose. These bugs often arise because there a few different versions of libraries on the system and the “wrong” version gets loaded instead of the one the developer used wanted.

Note You may also find of use my online tool for diagnosing linker problems on Linux implemented as an expert system. It is being expanded at the time of writing this but probably useful already.

I used to often debug these problems reasonably efficiently using the strace command (man strace) and checking which libraries are getting accessed. However, there is a much more efficient but perhaps not very well known way of debugging shared library loading problems: the LD_DEBUG environment variable.

If the LD_DEBUG variable is set then the Linux dynamic linker will dump debug information which can be used to resolve most loading problems very quickly. To see the available options just run any program with the variable set to help, i.e.:

LD_DEBUG=help cat
Valid options for the LD_DEBUG environment variable are:

  libs        display library search paths
  reloc       display relocation processing
  files       display progress for input file
  symbols     display symbol table processing
  bindings    display information about symbol binding
  versions    display version dependencies
  all         all previous options combined
  statistics  display relocation statistics
  unused      determined unused DSOs
  help        display this help message and exit

To direct the debugging output into a file instead of standard output
a filename can be specified using the LD_DEBUG_OUTPUT environment
variable.

Note There are many other useful tools to deal with linking issues:

  1. The strace program provides insight into all system calls, including searching, opening dynamic libraries
  2. The ldd program resolves dynamic library dependencies
  3. The objdump -x YOURFILE | grep NEEDED command lists the records in the program or library showing which other libraries are needed
  4. The patchelf program makes it easy to change the rpath of an ELF executable, changing the built-in search order
  5. The LD_PRELOAD environment allows easy substitution of dynamic libraries

Need further advice? With over 20 years of experience we are uniquely placed to help – contact us at [email protected]

Note This variable is available Linux only. On MS Windows similar information can be obtained by enabling “Show Loader Snaps” (https://abitofscotland.wordpress.com/2019/12/20/dll-load-failure/) using the gflags.exe program to enable this and then using windbg to view the log. For example:

  1. Install Windows SDK for gflags and windbg winget install Microsoft.WindowsSDK.10.0.19041 (or download from Microsoft website )
  2. Enable ShowLoaderSnaps for an executable. Example: to enable for notepad.exe for example do in Powershell &"C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\gflags.exe" /i notepad.exe +sls
  3. Execute notepad.exe under WinDbg app. Detailed DLL loading log will be displayed

And here is an example run on my laptop:

 LD_DEBUG=all cat
 28504:	
 28504:	file=libc.so.6 [0];  needed by cat [0]
 28504:	find library=libc.so.6 [0]; searching
 28504:	 search path=/home/bnikolic/s/lib/tls/x86_64:/home/bnikolic/s/lib/tls:/home/bnikolic/s/lib/x86_64:/home/bnikolic/s/lib:tls/x86_64:tls:x86_64::/home/bnikolic/d/p/R-2.14.1bin/lib/R/lib/tls/x86_64:/home/bnikolic/d/p/R-2.14.1bin/lib/R/lib/tls:/home/bnikolic/d/p/R-2.14.1bin/lib/R/lib/x86_64:/home/bnikolic/d/p/R-2.14.1bin/lib/R/lib		(LD_LIBRARY_PATH)
 28504:	  trying file=/home/bnikolic/s/lib/tls/x86_64/libc.so.6
 28504:	  trying file=/home/bnikolic/s/lib/tls/libc.so.6
 28504:	  trying file=/home/bnikolic/s/lib/x86_64/libc.so.6
 28504:	  trying file=/home/bnikolic/s/lib/libc.so.6
 28504:	  trying file=tls/x86_64/libc.so.6
 28504:	  trying file=tls/libc.so.6
 28504:	  trying file=x86_64/libc.so.6
 28504:	  trying file=libc.so.6
 28504:	  trying file=/home/bnikolic/d/p/R-2.14.1bin/lib/R/lib/tls/x86_64/libc.so.6
 28504:	  trying file=/home/bnikolic/d/p/R-2.14.1bin/lib/R/lib/tls/libc.so.6
 28504:	  trying file=/home/bnikolic/d/p/R-2.14.1bin/lib/R/lib/x86_64/libc.so.6
 28504:	  trying file=/home/bnikolic/d/p/R-2.14.1bin/lib/R/lib/libc.so.6
 28504:	 search cache=/etc/ld.so.cache
 28504:	  trying file=/lib/x86_64-linux-gnu/libc.so.6
 28504:	
 28504:	file=libc.so.6 [0];  generating link map
 28504:	  dynamic: 0x00007fc38e525b40  base: 0x00007fc38e18c000   size: 0x00000000003a0368
 28504:	    entry: 0x00007fc38e1ad420  phdr: 0x00007fc38e18c040  phnum:                 10
 28504:	
 28504:	checking for version `GLIBC_2.4' in file /lib/x86_64-linux-gnu/libc.so.6 [0] required by file cat [0]
 28504:	checking for version `GLIBC_2.3' in file /lib/x86_64-linux-gnu/libc.so.6 [0] required by file cat [0]
 28504:	checking for version `GLIBC_2.3.4' in file /lib/x86_64-linux-gnu/libc.so.6 [0] required by file cat [0]
 28504:	checking for version `GLIBC_2.2.5' in file /lib/x86_64-linux-gnu/libc.so.6 [0] required by file cat [0]
 28504:	checking for version `GLIBC_2.3' in file /lib64/ld-linux-x86-64.so.2 [0] required by file /lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	checking for version `GLIBC_PRIVATE' in file /lib64/ld-linux-x86-64.so.2 [0] required by file /lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	
 28504:	relocation processing: /lib/x86_64-linux-gnu/libc.so.6 (lazy)
 28504:	symbol=_res;  lookup in file=cat [0]
 28504:	symbol=_res;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_res' [GLIBC_2.2.5]
 28504:	symbol=_IO_file_close;  lookup in file=cat [0]
 28504:	symbol=_IO_file_close;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_IO_file_close' [GLIBC_2.2.5]
 28504:	symbol=stderr;  lookup in file=cat [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to cat [0]: normal symbol `stderr' [GLIBC_2.2.5]
 28504:	symbol=error_one_per_line;  lookup in file=cat [0]
 28504:	symbol=error_one_per_line;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `error_one_per_line' [GLIBC_2.2.5]
 28504:	symbol=__malloc_initialize_hook;  lookup in file=cat [0]
 28504:	symbol=__malloc_initialize_hook;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__malloc_initialize_hook' [GLIBC_2.2.5]
 28504:	symbol=__morecore;  lookup in file=cat [0]
 28504:	symbol=__morecore;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__morecore' [GLIBC_2.2.5]
 28504:	symbol=__key_encryptsession_pk_LOCAL;  lookup in file=cat [0]
 28504:	symbol=__key_encryptsession_pk_LOCAL;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__key_encryptsession_pk_LOCAL' [GLIBC_2.2.5]
 28504:	symbol=__progname_full;  lookup in file=cat [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to cat [0]: normal symbol `__progname_full' [GLIBC_2.2.5]
 28504:	symbol=__ctype32_tolower;  lookup in file=cat [0]
 28504:	symbol=__ctype32_tolower;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__ctype32_tolower' [GLIBC_2.2.5]
 28504:	symbol=__key_gendes_LOCAL;  lookup in file=cat [0]
 28504:	symbol=__key_gendes_LOCAL;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__key_gendes_LOCAL' [GLIBC_2.2.5]
 28504:	symbol=_environ;  lookup in file=cat [0]
 28504:	symbol=_environ;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_environ' [GLIBC_2.2.5]
 28504:	symbol=_rtld_global;  lookup in file=cat [0]
 28504:	symbol=_rtld_global;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	symbol=_rtld_global;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib64/ld-linux-x86-64.so.2 [0]: normal symbol `_rtld_global' [GLIBC_PRIVATE]
 28504:	symbol=__progname;  lookup in file=cat [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to cat [0]: normal symbol `__progname' [GLIBC_2.2.5]
 28504:	symbol=argp_err_exit_status;  lookup in file=cat [0]
 28504:	symbol=argp_err_exit_status;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `argp_err_exit_status' [GLIBC_2.2.5]
 28504:	symbol=mallwatch;  lookup in file=cat [0]
 28504:	symbol=mallwatch;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `mallwatch' [GLIBC_2.2.5]
 28504:	symbol=__rcmd_errstr;  lookup in file=cat [0]
 28504:	symbol=__rcmd_errstr;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__rcmd_errstr' [GLIBC_2.2.5]
 28504:	symbol=svcauthdes_stats;  lookup in file=cat [0]
 28504:	symbol=svcauthdes_stats;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `svcauthdes_stats' [GLIBC_2.2.5]
 28504:	symbol=__libc_enable_secure;  lookup in file=cat [0]
 28504:	symbol=__libc_enable_secure;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	symbol=__libc_enable_secure;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib64/ld-linux-x86-64.so.2 [0]: normal symbol `__libc_enable_secure' [GLIBC_PRIVATE]
 28504:	symbol=_res_hconf;  lookup in file=cat [0]
 28504:	symbol=_res_hconf;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_res_hconf' [GLIBC_2.2.5]
 28504:	symbol=malloc;  lookup in file=cat [0]
 28504:	symbol=malloc;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `malloc' [GLIBC_2.2.5]
 28504:	symbol=getdate_err;  lookup in file=cat [0]
 28504:	symbol=getdate_err;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `getdate_err' [GLIBC_2.2.5]
 28504:	symbol=__tzname;  lookup in file=cat [0]
 28504:	symbol=__tzname;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__tzname' [GLIBC_2.2.5]
 28504:	symbol=__timezone;  lookup in file=cat [0]
 28504:	symbol=__timezone;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__timezone' [GLIBC_2.2.5]
 28504:	symbol=_rtld_global_ro;  lookup in file=cat [0]
 28504:	symbol=_rtld_global_ro;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	symbol=_rtld_global_ro;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib64/ld-linux-x86-64.so.2 [0]: normal symbol `_rtld_global_ro' [GLIBC_PRIVATE]
 28504:	symbol=optarg;  lookup in file=cat [0]
 28504:	symbol=optarg;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `optarg' [GLIBC_2.2.5]
 28504:	symbol=__ctype_tolower;  lookup in file=cat [0]
 28504:	symbol=__ctype_tolower;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__ctype_tolower' [GLIBC_2.2.5]
 28504:	symbol=__ctype_toupper;  lookup in file=cat [0]
 28504:	symbol=__ctype_toupper;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__ctype_toupper' [GLIBC_2.2.5]
 28504:	symbol=svc_max_pollfd;  lookup in file=cat [0]
 28504:	symbol=svc_max_pollfd;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `svc_max_pollfd' [GLIBC_2.2.5]
 28504:	symbol=__ctype_b;  lookup in file=cat [0]
 28504:	symbol=__ctype_b;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__ctype_b' [GLIBC_2.2.5]
 28504:	symbol=argp_program_version_hook;  lookup in file=cat [0]
 28504:	symbol=argp_program_version_hook;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `argp_program_version_hook' [GLIBC_2.2.5]
 28504:	symbol=__after_morecore_hook;  lookup in file=cat [0]
 28504:	symbol=__after_morecore_hook;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__after_morecore_hook' [GLIBC_2.2.5]
 28504:	symbol=__environ;  lookup in file=cat [0]
 28504:	symbol=__environ;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__environ' [GLIBC_2.2.5]
 28504:	symbol=__ctype32_b;  lookup in file=cat [0]
 28504:	symbol=__ctype32_b;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__ctype32_b' [GLIBC_2.2.5]
 28504:	symbol=__curbrk;  lookup in file=cat [0]
 28504:	symbol=__curbrk;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__curbrk' [GLIBC_2.2.5]
 28504:	symbol=argp_program_version;  lookup in file=cat [0]
 28504:	symbol=argp_program_version;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `argp_program_version' [GLIBC_2.2.5]
 28504:	symbol=__daylight;  lookup in file=cat [0]
 28504:	symbol=__daylight;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__daylight' [GLIBC_2.2.5]
 28504:	symbol=__memalign_hook;  lookup in file=cat [0]
 28504:	symbol=__memalign_hook;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__memalign_hook' [GLIBC_2.2.5]
 28504:	symbol=__malloc_hook;  lookup in file=cat [0]
 28504:	symbol=__malloc_hook;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__malloc_hook' [GLIBC_2.2.5]
 28504:	symbol=__free_hook;  lookup in file=cat [0]
 28504:	symbol=__free_hook;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__free_hook' [GLIBC_2.2.5]
 28504:	symbol=svc_pollfd;  lookup in file=cat [0]
 28504:	symbol=svc_pollfd;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `svc_pollfd' [GLIBC_2.2.5]
 28504:	symbol=_nl_domain_bindings;  lookup in file=cat [0]
 28504:	symbol=_nl_domain_bindings;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_nl_domain_bindings' [GLIBC_2.2.5]
 28504:	symbol=_nl_msg_cat_cntr;  lookup in file=cat [0]
 28504:	symbol=_nl_msg_cat_cntr;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_nl_msg_cat_cntr' [GLIBC_2.2.5]
 28504:	symbol=argp_program_bug_address;  lookup in file=cat [0]
 28504:	symbol=argp_program_bug_address;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `argp_program_bug_address' [GLIBC_2.2.5]
 28504:	symbol=__key_decryptsession_pk_LOCAL;  lookup in file=cat [0]
 28504:	symbol=__key_decryptsession_pk_LOCAL;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__key_decryptsession_pk_LOCAL' [GLIBC_2.2.5]
 28504:	symbol=h_errlist;  lookup in file=cat [0]
 28504:	symbol=h_errlist;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `h_errlist' [GLIBC_2.2.5]
 28504:	symbol=program_invocation_short_name;  lookup in file=cat [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to cat [0]: normal symbol `program_invocation_short_name' [GLIBC_2.2.5]
 28504:	symbol=optind;  lookup in file=cat [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to cat [0]: normal symbol `optind' [GLIBC_2.2.5]
 28504:	symbol=_dl_starting_up;  lookup in file=cat [0]
 28504:	symbol=_dl_starting_up;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	symbol=_dl_starting_up;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 28504:	symbol=stdout;  lookup in file=cat [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to cat [0]: normal symbol `stdout' [GLIBC_2.2.5]
 28504:	symbol=obstack_alloc_failed_handler;  lookup in file=cat [0]
 28504:	symbol=obstack_alloc_failed_handler;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `obstack_alloc_failed_handler' [GLIBC_2.2.5]
 28504:	symbol=error_print_progname;  lookup in file=cat [0]
 28504:	symbol=error_print_progname;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `error_print_progname' [GLIBC_2.2.5]
 28504:	symbol=optopt;  lookup in file=cat [0]
 28504:	symbol=optopt;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `optopt' [GLIBC_2.2.5]
 28504:	symbol=_IO_funlockfile;  lookup in file=cat [0]
 28504:	symbol=_IO_funlockfile;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_IO_funlockfile' [GLIBC_2.2.5]
 28504:	symbol=obstack_exit_failure;  lookup in file=cat [0]
 28504:	symbol=obstack_exit_failure;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `obstack_exit_failure' [GLIBC_2.2.5]
 28504:	symbol=error_message_count;  lookup in file=cat [0]
 28504:	symbol=error_message_count;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `error_message_count' [GLIBC_2.2.5]
 28504:	symbol=svc_fdset;  lookup in file=cat [0]
 28504:	symbol=svc_fdset;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `svc_fdset' [GLIBC_2.2.5]
 28504:	symbol=program_invocation_name;  lookup in file=cat [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to cat [0]: normal symbol `program_invocation_name' [GLIBC_2.2.5]
 28504:	symbol=loc1;  lookup in file=cat [0]
 28504:	symbol=loc1;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `loc1' [GLIBC_2.2.5]
 28504:	symbol=free;  lookup in file=cat [0]
 28504:	symbol=free;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `free' [GLIBC_2.2.5]
 28504:	symbol=loc2;  lookup in file=cat [0]
 28504:	symbol=loc2;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `loc2' [GLIBC_2.2.5]
 28504:	symbol=__fpu_control;  lookup in file=cat [0]
 28504:	symbol=__fpu_control;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__fpu_control' [GLIBC_2.2.5]
 28504:	symbol=re_syntax_options;  lookup in file=cat [0]
 28504:	symbol=re_syntax_options;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `re_syntax_options' [GLIBC_2.2.5]
 28504:	symbol=stdin;  lookup in file=cat [0]
 28504:	symbol=stdin;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `stdin' [GLIBC_2.2.5]
 28504:	symbol=__check_rhosts_file;  lookup in file=cat [0]
 28504:	symbol=__check_rhosts_file;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__check_rhosts_file' [GLIBC_2.2.5]
 28504:	symbol=opterr;  lookup in file=cat [0]
 28504:	symbol=opterr;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `opterr' [GLIBC_2.2.5]
 28504:	symbol=__ctype32_toupper;  lookup in file=cat [0]
 28504:	symbol=__ctype32_toupper;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__ctype32_toupper' [GLIBC_2.2.5]
 28504:	symbol=__realloc_hook;  lookup in file=cat [0]
 28504:	symbol=__realloc_hook;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__realloc_hook' [GLIBC_2.2.5]
 28504:	symbol=_dl_argv;  lookup in file=cat [0]
 28504:	symbol=_dl_argv;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	symbol=_dl_argv;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib64/ld-linux-x86-64.so.2 [0]: normal symbol `_dl_argv' [GLIBC_PRIVATE]
 28504:	symbol=rpc_createerr;  lookup in file=cat [0]
 28504:	symbol=rpc_createerr;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `rpc_createerr' [GLIBC_2.2.5]
 28504:	symbol=_IO_2_1_stderr_;  lookup in file=cat [0]
 28504:	symbol=_IO_2_1_stderr_;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_IO_2_1_stderr_' [GLIBC_2.2.5]
 28504:	symbol=_IO_2_1_stdout_;  lookup in file=cat [0]
 28504:	symbol=_IO_2_1_stdout_;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_IO_2_1_stdout_' [GLIBC_2.2.5]
 28504:	symbol=_IO_2_1_stdin_;  lookup in file=cat [0]
 28504:	symbol=_IO_2_1_stdin_;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `_IO_2_1_stdin_' [GLIBC_2.2.5]
 28504:	
 28504:	relocation processing: cat (lazy)
 28504:	symbol=__gmon_start__;  lookup in file=cat [0]
 28504:	symbol=__gmon_start__;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	symbol=__gmon_start__;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 28504:	symbol=__progname;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__progname' [GLIBC_2.2.5]
 28504:	symbol=__progname_full;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__progname_full' [GLIBC_2.2.5]
 28504:	symbol=optind;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `optind' [GLIBC_2.2.5]
 28504:	symbol=stderr;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `stderr' [GLIBC_2.2.5]
 28504:	symbol=stdout;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `stdout' [GLIBC_2.2.5]
 28504:	
 28504:	relocation processing: /lib64/ld-linux-x86-64.so.2
 28504:	symbol=_r_debug;  lookup in file=cat [0]
 28504:	symbol=_r_debug;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	symbol=_r_debug;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 28504:	binding file /lib64/ld-linux-x86-64.so.2 [0] to /lib64/ld-linux-x86-64.so.2 [0]: normal symbol `_r_debug' [GLIBC_2.2.5]
 28504:	symbol=free;  lookup in file=cat [0]
 28504:	symbol=free;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib64/ld-linux-x86-64.so.2 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `free' [GLIBC_2.2.5]
 28504:	symbol=__libc_memalign;  lookup in file=cat [0]
 28504:	symbol=__libc_memalign;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib64/ld-linux-x86-64.so.2 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__libc_memalign' [GLIBC_2.2.5]
 28504:	symbol=malloc;  lookup in file=cat [0]
 28504:	symbol=malloc;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib64/ld-linux-x86-64.so.2 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `malloc' [GLIBC_2.2.5]
 28504:	symbol=__tls_get_addr;  lookup in file=cat [0]
 28504:	symbol=__tls_get_addr;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	symbol=__tls_get_addr;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 28504:	binding file /lib64/ld-linux-x86-64.so.2 [0] to /lib64/ld-linux-x86-64.so.2 [0]: normal symbol `__tls_get_addr' [GLIBC_2.3]
 28504:	symbol=calloc;  lookup in file=cat [0]
 28504:	symbol=calloc;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib64/ld-linux-x86-64.so.2 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `calloc' [GLIBC_2.2.5]
 28504:	symbol=realloc;  lookup in file=cat [0]
 28504:	symbol=realloc;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib64/ld-linux-x86-64.so.2 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `realloc' [GLIBC_2.2.5]
 28504:	symbol=free;  lookup in file=cat [0]
 28504:	symbol=free;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib64/ld-linux-x86-64.so.2 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `free' [GLIBC_2.2.5]
 28504:	
 28504:	calling init: /lib64/ld-linux-x86-64.so.2
 28504:	
 28504:	
 28504:	calling init: /lib/x86_64-linux-gnu/libc.so.6
 28504:	
 28504:	symbol=gettimeofday;  lookup in file=cat [0]
 28504:	binding file cat [0] to cat [0]: normal symbol `gettimeofday' [LINUX_2.6]
 28504:	symbol=clock_gettime;  lookup in file=cat [0]
 28504:	binding file cat [0] to cat [0]: normal symbol `clock_gettime' [LINUX_2.6]
 28504:	symbol=__libc_start_main;  lookup in file=cat [0]
 28504:	symbol=__libc_start_main;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__libc_start_main' [GLIBC_2.2.5]
 28504:	
 28504:	initialize program: cat
 28504:	
 28504:	
 28504:	transferring control: cat
 28504:	
 28504:	symbol=getpagesize;  lookup in file=cat [0]
 28504:	symbol=getpagesize;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `getpagesize' [GLIBC_2.2.5]
 28504:	symbol=strrchr;  lookup in file=cat [0]
 28504:	symbol=strrchr;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `strrchr' [GLIBC_2.2.5]
 28504:	symbol=setlocale;  lookup in file=cat [0]
 28504:	symbol=setlocale;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `setlocale' [GLIBC_2.2.5]
 28504:	symbol=malloc;  lookup in file=cat [0]
 28504:	symbol=malloc;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `malloc' [GLIBC_2.2.5]
 28504:	symbol=free;  lookup in file=cat [0]
 28504:	symbol=free;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file /lib/x86_64-linux-gnu/libc.so.6 [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `free' [GLIBC_2.2.5]
 28504:	symbol=bindtextdomain;  lookup in file=cat [0]
 28504:	symbol=bindtextdomain;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `bindtextdomain' [GLIBC_2.2.5]
 28504:	symbol=textdomain;  lookup in file=cat [0]
 28504:	symbol=textdomain;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `textdomain' [GLIBC_2.2.5]
 28504:	symbol=__cxa_atexit;  lookup in file=cat [0]
 28504:	symbol=__cxa_atexit;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__cxa_atexit' [GLIBC_2.2.5]
 28504:	symbol=getopt_long;  lookup in file=cat [0]
 28504:	symbol=getopt_long;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `getopt_long' [GLIBC_2.2.5]
 28504:	symbol=__fxstat;  lookup in file=cat [0]
 28504:	symbol=__fxstat;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `__fxstat' [GLIBC_2.2.5]
 28504:	symbol=malloc;  lookup in file=cat [0]
 28504:	symbol=malloc;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `malloc' [GLIBC_2.2.5]
 28504:	symbol=read;  lookup in file=cat [0]
 28504:	symbol=read;  lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0]
 28504:	binding file cat [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `read' [GLIBC_2.2.5]

The output of the command is also very useful for tracking performance problems for excessive dynamic loading etc. So it is a very simple but extremely useful tool for debugging linux ld problems!

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