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RE: [avr-gcc-list] Re: [patch #6004] "main-as-normal" patches for GCC

From: Weddington, Eric
Subject: RE: [avr-gcc-list] Re: [patch #6004] "main-as-normal" patches for GCC
Date: Thu, 26 Feb 2009 09:47:08 -0700


> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Bob Paddock
> Sent: Thursday, February 26, 2009 6:50 AM
> Subject: Re: [avr-gcc-list] Re: [patch #6004] 
> "main-as-normal" patches for GCC
> > The OS_main and OS_task attributes are mainly used for 
> RTOSes, for the
> > main() function and task functions respectively. However, 
> OS_main can be
> > useful in an application's main() function that does not 
> have an RTOS,
> > as it will reduce the code size slightly.
> Is there any workable combination of OS_main and the noreturn 
> attribute,
> that would prevent the compiler from inserting the _exit function?
> In the ideal case six bytes would be saved.


The whole exit stuff is spread across two projects.

The avr-libc startup (gcrt1.S) code contains the reference to exit:

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

And exit is defined in libgcc here:

#ifdef L_exit
        .section .fini9,"ax",@progbits
        .global _exit
        .func   _exit
        .weak   exit

        /* Code from .fini8 ... .fini1 sections inserted by ld script.  */

        .section .fini0,"ax",@progbits
        rjmp    __stop_program
#endif /* defined (L_exit) */

So to be able to optimize this out, some changes would have to be done in gcc, 
libgcc, and avr-libc....

But I think it's a good idea.

Eric Weddington

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