Understanding C runtime environment (ARM) - where to start

Question

I\'am embedded developer working with ARM Cortex-M devices mainly. Recently I\'ve switched to Linux and decided to learn more about the build/assemble/link process, how to write

Answer 1

The modules you are referring to (ctr0.o, crti.o, _init, __libc_init_array, _exit) are prebuilt libraries/object files/functions by IAR and/or Keil. As you are saying they are needed to get the environment initialized (global variables initialization, interrupt vector table, etc.) before running your main() function.

At some point in those libraries/object files there will be a function in C or assembly like this:

void startup(void)
{ 
    ... init code ...

    main();

    while(1);   // or _exit()
}

You may look into these examples that build the startup code from scratch:

http://www.embedded.com/design/mcus-processors-and-socs/4007119/Building-Bare-Metal-ARM-Systems-with-GNU-Part-1--Getting-Started

https://github.com/payne92/bare-metal-arm