Re: Binutils/ld: linker script does not work for AVR mega 0 series (avrxmega3)

[Nick Clifton]

Hi Konrad,

> the linker fails on trying to arrange data/bss segments even with very few 
> small variables. E.g.:

Please could you file a bug report for this problem here:

  https://sourceware.org/bugzilla/enter_bug.cgi?product=binutils


> avr-g++ -Os -Wl,--gc-sections -B 
> ~/tronic/atmel-compiler-packs/mega/gcc/dev/atmega3208 -mmcu=atmega3208 -o 
> fw.elf dimmer.o dmx.o input.o ledout.o pwm.o
> <...>/lib/gcc/avr/12.2.0/../../../../avr/bin/ld: address 0x803004 of fw.elf 
> section `.bss' is not within region `data'

If you can include these object files as an aid for reproducing the problem, 
that would be appreciated.


> I narrowed the problem down to the Linker script avrxmega3.xn - it somehow messes up the data segment in the MEMORY section at the top. I was able to get it to link by 
> changing that line:
>
> -  data   (rw!x) : ORIGIN = 0x802000, LENGTH = __DATA_REGION_LENGTH__
> +  data   (rw!x) : ORIGIN = 0x802000, LENGTH = 0x10000
>
> The fixed origin seems very dubious to me and I wasn't able to debug 
> __DATA_REGION_LENGTH__.

It is defined earlier on in script:

  __DATA_REGION_LENGTH__ = DEFINED(__DATA_REGION_LENGTH__) ? 
__DATA_REGION_LENGTH__ : 0xffa0;

In terms of source code, it is defined in ld/scripttempl/avr.sc as:

  __DATA_REGION_LENGTH__ = DEFINED(__DATA_REGION_LENGTH__) ? 
__DATA_REGION_LENGTH__ : $DATA_LENGTH;

and DATA_LENGTH is defined in the ld/emulparams/avr*.sh files.



> I consider my fix "an ugly hack". The linker script in Arduino looks more 
> elegant and also works:
>
> __DATA_REGION_ORIGIN__ = DEFINED(__DATA_REGION_ORIGIN__) ? 
> __DATA_REGION_ORIGIN__ : 0x802000;
> //...
> data   (rw!x) : ORIGIN = __DATA_REGION_ORIGIN__, LENGTH = __DATA_REGION_LENGTH__

Actually this reasonable, and would provide some more utility to users.

Currently the avr.sc file (mentioned above) has this code:

   data   (rw!x) : ORIGIN = $DATA_ORIGIN, LENGTH = __DATA_REGION_LENGTH__

and the definition of DATA_ORIGIN can be found in ld/emulparams/avrxmega3.sh:

  DATA_ORIGIN=0x802000

I am not intimately familiar with the AVR architecture variants, so I do not
know if this is a reasonable value...

Cheers
  Nick