Re: [avr-gcc-list] Put text string after interrupt vectors

[Dave Hylands]

Hi Lars,

> Is there a way to tell gcc (or ld) to put the signature at 0x20? If not,
> is there at least a way to guarantee, that the signature is "anywhere
> near the beginning" of the flash memory?

The secret lies in the linker script files. An example of such a file
can be found in WinAVR/avr/lib/ldscript/avr5.x

You'll see something like the following:

  .text :
  {
    *(.vectors)
     __ctors_start = . ;
     *(.ctors)
     __ctors_end = . ;
     __dtors_start = . ;
     *(.dtors)
     __dtors_end = . ;
    *(.progmem.gcc*)
    *(.progmem*)
    . = ALIGN(2);
    *(.init0)  /* Start here after reset.  */
    *(.init1)
    *(.init2)  /* Clear __zero_reg__, set up stack pointer.  */
    *(.init3)
    *(.init4)  /* Initialize data and BSS.  */
    *(.init5)
    *(.init6)  /* C++ constructors.  */
    *(.init7)
    *(.init8)
    *(.init9)  /* Call main().  */
    *(.text)
    . = ALIGN(2);
    *(.text.*)
    . = ALIGN(2);
    *(.fini9)  /* _exit() starts here.  */
    *(.fini8)
    *(.fini7)
    *(.fini6)  /* C++ destructors.  */
    *(.fini5)
    *(.fini4)
    *(.fini3)
    *(.fini2)
    *(.fini1)
    *(.fini0)  /* Infinite loop after program termination.  */
     _etext = . ;
  }  > text

So if you're not use C++, then the .ctors and .dtors will be empty.
Anything in a section that starts with .progmem will go next. So you
could name your section:

.progmem.signature

and it would go pretty early in the file. If you make your section
named .vectors then it will go after the real vectors.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/