> By letting the linker run arbitrary code before main

As I know C++ allows running arbitrary code before main too - for constructors of global variables. Does it bring security risks too?

It does not, it's actually arbitrary code running during the dynamic loading process, i.e. before _start.

	▲	Panzerschrek 3 hours ago \| parent [-]
		But what if I have a C++ dynamic library? Does it call constructors for global variables before _start function in the main program starts?