Solution to conflicts between symbols with the same name under Linux

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Solution to the problem of conflicting symbols with the same name under Linux

I encountered the following annoying problem at work recently:

There are three modules aa, bb, and cc under Linux. The basic situation is as follows:

cc Compile and connect to get cc. so dynamic library, cc has the following interface:

cc_fun 
{ 
…… 
do();//调用名为do的cc模块内部函数 
…… 
}

bb compile and connect to get bb.a static library, in bb It has the following interface:

bb_fun 
{ 
…… 
handle = dlopen(cc.so, RTLD_LAZY);//加载cc.so 
pccfun = dlsym(handle, “cc_fun”);//获取cc_fun函数指针 
(*pccfun)();//调用cc_fun函数，此时应该会调用cc模块中的do()函数 
do();//调用名为do的bb模块内部函数（与cc模块中的do()函数同名，实现却不相同） 
…… 
}

aa After compilation, connect bb.a through the -lbb link option to obtain the aa executable program, and call the interface function bb_fun( of bb.a ):

main 
{ 
…… 
bb_fun()；//调用bb_fun函数 
…… 
}

During work, it was found that aa behaves abnormally at runtime, and there are always memory leaks and functional abnormalities. Through locating, it is found that the problem is concentrated in the same name on the do() function. Through the output printing, it was found that the two calls to the do() function in the program both called the do() function in the bb module, while the do() function in the cc module was never called, resulting in abnormal program behavior and memory leaks.

After many verifications, I learned that because the symbol tables in each library in the Linux program will eventually be loaded into the global symbol table where the program is located, at this time, if there is a symbol with the same name, only the first one loaded can be called. Symbols, that is to say, symbols with the same name loaded later will be overwritten by the previous ones. The do() function in the cc module is overwritten by the do() function in the bb module, so it cannot be called.

No more nonsense. . .

After trying many unsatisfactory methods, the final solution is as follows:

1. Add -Wl, -Bsymbolic -Wl, to the cc makefile. --version-script, the connection option of version, means to use the script in the version file to specify which functions it exports.

2.version file is implemented as follows:

VERS{ 
global: 
cc_fun; 
local: *; 
};

means that the cc module is specified to only export the interface function cc_fun, and the other functions are set to local and not exported. .

Save the file in the directory where the makefile is located.

3. Recompile and connect the three modules, and the problem is solved.

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