First Stage Initialization Files - 2024.1 English

crt0.o

This initialization file is used for programs which are to be executed in standalone mode, without the use of any bootloader or debugging stub. This CRT populates the reset, interrupt, exception, and hardware exception vectors and invokes the second stage startup routine _crtinit. On returning from _crtinit, it ends the program by infinitely looping in the _exit label.

crt1.o

This initialization file is used when the application is debugged in a software-intrusive manner. It populates all the vectors except the breakpoint and reset vectors and transfers control to the second-stage _crtinit startup routine.

crt2.o

This initialization file is used when the executable is loaded using a bootloader. It populates all the vectors except the reset vector and transfers control to the second-stage _crtinit startup routine. On returning from _crtinit, it ends the program by infinitely looping at the _exit label. Because the reset vector is not populated, on a processor reset, control is transferred to the bootloader, which can reload and restart the program.

crt3.o

This initialization file is employed when the executable does not use any vectors and wishes to reduce code size. It populates only the reset vector and transfers control to the second stage _crtinit startup routine. On returning from _crtinit, it ends the program by infinitely looping at the _exit label. Because the other vectors are not populated, the GNU linking mechanism does not pull in any of the interrupt and exception handling related routines, thus saving code space.