I am trying to write a bootloader that fits within a 4Kbyte space and I'm trying to keep the essential code as small as possible.
However, with the standard default setup from the CMSDK Cortex M0 enviroment, even with a empty main(), I notice that it has already taken up almost 2.5Kbytes
Looking further into the compiled code, I noticed that crt0.o uses some functions which are taking up space some of them below ( dumped from *nm)
20000430 00000004 D _impure_ptr 3000022a 00000004 T main 30000438 00000010 T atexit 30000324 00000018 t register_fini 30000230 00000020 T exit 30000448 00000034 T __libc_fini_array 30000198 00000044 T Reset_Handler 30000250 00000048 T __libc_init_array 30000298 0000008c T memset 30000000 000000c0 T __isr_vector 3000047c 000000d4 T __register_exitproc 3000033c 000000fc T __call_exitprocs
What does crt0.o do anyways and I thought all the necessary copy-downs from Flash to RAM are already defined in startup_CMSDK_CM0.s.
Can I exclude calling this file and go straight to startup_CMSDK_CM0.s?
Also looking at the linker script sections.ld there are references to crt and ctors. Can I exclude those as well?
/* .ctors */ *crtbegin.o(.ctors) *crtbegin?.o(.ctors) *(EXCLUDE_FILE(*crtend?.o *crtend.o) .ctors) *(SORT(.ctors.*)) *(.ctors) /* .dtors */ *crtbegin.o(.dtors) *crtbegin?.o(.dtors) *(EXCLUDE_FILE(*crtend?.o *crtend.o) .dtors) *(SORT(.dtors.*)) *(.dtors) *(.rodata*)
Just starting out with programming on Cortex M0 so any help is appreciated, cheers.