Liunx下解决动态链接库符号未定义问题

Liunx下解决动态链接库符号未定义问题

标签（空格分隔）： 技术

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nm

作用

列出二进制程序中的负号的值，符号类型和符号名称等

用法

• -A 显示对象文件名称
• -C 显示程序中的原始名称
• -D 打印动态负号
• -u 打印那些未定义的符号

符号类型

符号类型	涵义
A	该符号的值在以后的链接中不再改变
B	未初始化的全局变量
D	初始化的全局变量
T	表示全局非静态函数
U	未定义符号

ldd

作用

查看elf文件一脸的 so 动态链接库

参考

ldd命令浅析

gcc

用法

–undefined symbols = method

ignore-all

Do not report any unresolved symbols. 

report-all

Report all unresolved symbols. This is the default. 

ignore-in-object-files

Report unresolved symbols that are contained in shared libraries, but ignore them if they come from regular object files. 

ignore-in-shared-libs

Report unresolved symbols that come from regular object files, but ignore them if they come from shared libraries. This can be useful when creating a dynamic binary and it is known that all the shared libraries that it should be referencing are included on the linker's command line.

-z

Report unresolved symbol references from regular object files. This is done even if the linker is creating a non-symbolic shared library. The switch --[no-]allow-shlib-undefined controls the behaviour for reporting unresolved references found in shared libraries being linked in.

–allow-shlib-undefined/–no-allow-shlib-undefined

Allows or disallows undefined symbols in shared libraries. This switch is similar to --no-undefined except that it determines the behaviour when the undefined symbols are in a shared library rather than a regular object file. It does not affect how undefined symbols in regular object files are handled.

The default behaviour is to report errors for any undefined symbols referenced in shared libraries if the linker is being used to create an executable, but to allow them if the linker is being used to create a shared library.

The reasons for allowing undefined symbol references in shared libraries specified at link time are that:

A shared library specified at link time may not be the same as the one that is available at load time, so the symbol might actually be resolvable at load time.

There are some operating systems, eg BeOS and HPPA, where undefined symbols in shared libraries are normal.

The BeOS kernel for example patches shared libraries at load time to select whichever function is most appropriate for the current architecture. This is used, for example, to dynamically select an appropriate memset function.