What is -soname, in shared libraries?
gcc -shared -Wl,-soname,libmylib.so.1 \ -o libmylib.so.1.0.1 mylib.o –lc 1 Answer
An soname (‘shared object name’) is a label used when declaring shared library dependencies. Each executable contains a list of shared libraries that it needs in order to execute. Shared libraries can similarly declare dependencies on other shared libraries. This can be done using pathnames, but if the required library has an soname then that will be used in preference.
Typically the pathname of a library will change whenever a new version is installed, whereas the soname should change only when the new version is incompatible with its predecessors to the extent that it cannot be used their place. It follows that when dependencies are declared using sonames, the library used at runtime need not be an exact match for the one present at build time:
- For a given library with a given soname, only the most recent version need be installed.
- Where there is a need for two versions of the same library to be installed alongside each other, they can be distinguished because they have different sonames.
It is the degree of binary compatibility which determines whether the soname should change. For example, new functions can be added without breaking backward compatibility, but you cannot normally change the prototype of an existing function, nor do anything that could change the layout of a data structure. You should also consider changes made to the high-level behaviour of the library, as these can have an equally significant effect on backwards compatibility.
