分析结果中的 _init 是什么

Question

I've seen a strange function (_init) in my profile results :

In the parent function there is a uint64_t initialization and some math operations (sum, multiply, ...).

What is this _init function? Is it related to that uint64_t init?

Edit: I am using gcc version 8.3.0

Answer 1

_init is a function that gets called when a shared library is loaded. In our example, it will depend on what library you are linking against (running ldd against the binary should give you some hints).

As a side-note, the _init and _fini functions are obsolete now and should be replaced by __attribute__ ((constructor)) and __attribute__ ((destructor)) . To quote from thedocumentation 5.2.1 :

5.2.1. Special functions _init and _fini (OBSOLETE/DANGEROUS)

Historically there have been two special functions, _init and _fini that can be used to control constructors and destructors. However, they are obsolete, and their use can lead to unpredicatable results. Your libraries should not use these; use the function attributes constructor and destructor above instead.

If you must work with old systems or code that used _init or _fini, here's how they worked. Two special functions were defined for initializing and finalizing a module: _init and _fini. If a function ``_init'' is exported in a library, then it is called when the library is first opened (via dlopen() or simply as a shared library). In a C program, this just means that you defined some function named _init. There is a corresponding function called _fini, which is called whenever a client finishes using the library (via a call dlclose() that brings its reference count to zero, or on normal exit of the program). The C prototypes for these functions are:

 void _init(void); void _fini(void);