[avr-libc-dev] Request: gcrt1.S with empty section .init9

[Marko Mäkelä]

I am trying to move from assembler to C programming on the AVR while 
avoiding unnecessary overhead. I see that crt1/gcrt1.S contains the 
following code:

        .section .init9,"ax",@progbits
#ifdef __AVR_ASM_ONLY__
        XJMP    main
#else   /* !__AVR_ASM_ONLY__ */
        XCALL   main
        XJMP    exit
#endif  /* __AVR_ASM_ONLY__ */

The above references to main() and exit() are needed for complying with 
the C standard. However, I would tend to believe that normally programs 
written for bare metal (such as the AVR) never terminate. Such programs 
do not need an exit() function or even a call or jump to main().

Would it be possible to introduce a (necessarily non-standard) option 
that allows the .init9 section of the runtime libary to be omitted?  
Then, the user could declare their infinite main loop something like 
this:

__attribute__((naked)) __attribute__((section(".init9")))
static
void
mainloop (void)
{
        for (;;) do_my_stuff ();
}

This would save 3 instructions and some RAM (call main/ret, jump exit).

I am aware of the linker options -nostartfiles -nostdlib, but I do want 
the interrupt table and the sections .init0 through .init8.

Perhaps .linkonce or some clever use of .weak could help here? Or 
perhaps an alternative crt.o file could be provided for a minimal 
startup?

I would have tried to patch gcrt1.S myself, but I am having trouble 
setting up the build environment.

Best regards,

        Marko