RE: [avr-libc-dev] OPTIMIZE_SPEED for avr5?

[Eric Weddington]

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Ned Konz
> Sent: Tuesday, March 06, 2007 12:37 PM
> To: Joerg Wunsch; address@hidden
> Subject: Re: [avr-libc-dev] OPTIMIZE_SPEED for avr5?
> 
> Joerg Wunsch wrote:
> > As David Brown wrote:
> >
> >   
> >> Size is the main priority when you are low on flash space -
> >> otherwise, it is irrelevant.  If your chosen AVR has 16k 
> flash, then
> >> it does not matter if the program code takes 2k or 15.9k of that
> >> flash.  In particular, for smaller devices, program space 
> will be at
> >> a premium, while for the larger devices, much of the flash will
> >> often be things like tables or other data that is of fixed size.
> >>     
> >
> > The issue here is, to the best of my knowledge, we don't have access
> > to the -O level when linking, so we cannot operate depending on the
> > user's wishes.  We thus have to decide for *one* implementation that
> > goes into the library.
> >
> >   
> if we could get to the -O level when compiling,

That's the problem that Joerg is talking about.

How do these library functions get used? Currently a user creates a makefile
with a call to gcc (avr-gcc) that will link object code modules. This
includes a flag to tell the linker to link to a specifically named library.
GCC then calls the linker (ld) directly to do the actual linking. Where in
this process does the linker know, or even care, what optimization setting
was used to compile the source code to object code? All the compiling was
done in previous, multiple steps in the makefile. Even if the linker could
somehow determine the optimization settings of the object module, each
object code module could even have different compiler optimization settings.
There is no way to automatically determine what library functions should be
included. It is only the end-user that can make that decision. And the only
way for the end-user to make that decision is to have them explicitly tell
the linker exactly what type of library that should be linked in to the
final application.

Eric