embedded - How can I use crt0.o to setup .bss and .data in my bare metal C program? -

embedded - How can I use crt0.o to setup .bss and .data in my bare metal C program? -

i wrote bare metal c programme running on stm32f4. it's nil fancy, usual led-blinky-program. in project have written initialization routines clearing .bss section , initializing .data section myself.

this wasn't complicated. in linker script, instructed linker create symbols marking start , end of .data , .bss section.

.data 0x20001000 : align(4) { __etext = loadaddr(.data); __data_start__ = addr(.data) ; *(.data*) ; __data_end__ = addr(.data) + sizeof(.data) ; } >ram at>rom .bss : align(4) { __bss_start__ = addr(.bss) ; *(.bss*) ; __bss_end__ = addr(.bss) + sizeof(.bss) ; } >ram

then using these symbols in code:

extern unsigned int __etext; extern unsigned int __data_start__; extern unsigned int __data_end__; extern unsigned int __bss_start__; extern unsigned int __bss_end__; void reset_handler() { unsigned int * src; unsigned int * dest; src = &__etext; dest = &__data_start__; /* re-create .data */ while (dest < &__data_end__) *(dest++) = *(src++); /* 0 bss. */ (dest = &__bss_start__; dest < &__bss_end__; dest++) *dest = 0; }

now utilize crt0 purpose of setting-up .bss , .data. (i heard setting things main purpose of crt0.)

how can that? basic principle of defining symbols in linker script , using in code same?

tl;dr

how can utilize crt0 setup .bss , .data section?

in general, in linker command file/script...

the posted script has few problems.

suggest similar following. (use actual origin , length parameters) (note .text, .data, .bss not sections created. there many more , should listed appropriately )

you should @ http://www.math.utah.edu/docs/info/ld_3.html#sec18 details , examples linker command files

/* simple memory layout */ /* there separate memory items */ /* each memory mapped peripheral */ /* external ram, etc etc etc */ memory { rom : origin = 0, length = 256k ram : origin = 0x40000000, length = 4m } sections { rom :0 (noload) block(4) { } ram : { .text : block(4) { .textstart = .; *(.text) .textend = .; } .bss : block(4) { .bssstart = .; *(.bss) .bssend = .; } .data : block(4) { .datastart = .; *(.data) .dataend = .; } } }

c embedded crt bare-metal cortex-m