Re: [avr-gcc-list] Using Named Address spaces.

[Thomas, George]

From: Erik Christiansen 
Sent: Monday, March 18, 2013 2:58 PM

> George, your question on back-filling flash[1-4] with arbitrary .text is
> possibly more completely answered if we also look at some limitations
> faced by ld.
>
> Firstly, ld does not know that flash[1-4] are unoccupied, while it is
> linking input sections according to the active script. Data and code
> arrive willy-nilly, in whatever link order the user throws at ld. Until
> linking is complete, any of flash[1-4] might at any time be populated by
> a late xxx.o file. What information could ld use to decide to clobber
> flash[1-4] with arbitrary .hightext?
>
> Please note that the linker script _does_ populate any unutilised flashN
> pages _above_ the last populated flashN page. It is only the deliberate
> gap use-case which reserves memory.
>
> Secondly, even if we did implement some way to promise to ld that
> flash[1-4] would not be used for flashN, there remains the problem that
> ld cannot flow code around memory holes. That feature has been requested
> before, as in:
>
> http://sourceware.org/ml/binutils/2012-01/msg00183.html
>
> The reply to that post effectively rules out a backwards memory use
> interpretation in our holey use case.
>
> That only leaves memory reservation as a real-world purpose for
> populating a high flashN, with lower flashN vacant, AFAICT.
>

I understand the issues in the implementation but I was just curious. Thanks 
for the detailed response.

In such a situation,

result from avr-size  should have to be taken with a pinch of salt. As avr-size 
is not aware of the paged structure of flash.

Should this information be made available to avr-size ?

IMO If its available, the user may be able to understand how much space is 
available for code if an information like sizeofcontinuousblock is provided by 
avr-size.