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

i wrote bare metal c program running on stm32f4. it's nothing 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__;      /* copy .data */     while (dest < &__data_end__)         *(dest++) = *(src++);      /* 0 bss.  */     (dest = &__bss_start__; dest < &__bss_end__; dest++)         *dest = 0; } 

now use 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?

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tl;dr

how can use 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 = .;         }     } }