Considering the following piece of code : extern int var; void foo(int & param) { (void) param; } int main(void) { foo(*(&var)); return 0; } Compiled this way : $ g++ -Os -o test.o -c test.cpp $ g++ test.o But when I remove the -Os flag, there is an undefined reference to var. What kind… Read More Optimization flag removing undefined reference to extern variable