Need help in figuring out the flow of RTEMS codes

[Richi Dubey]

Hii,

I had a small doubt about all the source code/procedures that a code
goes through. Where can I read more about it? For instance, when I am
debugging smpschededf02.exe with gdb, It starts  with
bsps/sparc/shared/start/start.S, line 107(Why did it start with
start.s?) and the last line of this file is:

 mov     %g0, %o0                ! command line
        call    SYM(boot_card)          ! does not return
         sub     %sp, 0x60, %sp         ! room for boot_card to save args

After this it starts executing bsps/shared/start/bootcard.c: line 53 .
How did this happen? Is it because of call? If yes, why was sub
executed(in gdb) before executing code from bootcard.c?

I hope I am not trying to going too deep into this. I just want to
have a overall picture of how a code gets executed. This is necessary
for writing your own code in RTEMS, right?