Re: [avr-gcc-list] strange c++ obiect initialization problems (full code included)

[Georg-Johann Lay]

Marcin S schrieb:
> 2011/6/9 Georg-Johann Lay <address@hidden>:
>
> > Marcin S schrieb:
> >
> > > Hello there,
> > >
> > > from time to time i have a strange problems when initializing
> > > class objects in file range by their respective constructors, i
> > > noted that problem occurs only when that constructors takes
> > > pointers to other global objects, tables or something else.
> > >
> > > Whats the problem? in best scenario object pointer are wrongly
> > > set and pointing to some random locations, at worst my program
> > > does not start at all (event with my main() func empty) it just
> > > hangs
> > >
> > > here is link to my code 
> > > http://dl.dropbox.com/u/6883398/Lays.tar.bz2 its and eclipse
> > > project, simple "make" in project directory should work too. Note
> > > that archive contains already compiled program in "Release"
> > > directory, this compilation does not work at all! (worst case
> > > scenario described above).
> > >
> > > As I wrote this program incrementaly it stopped working after i
> > > added 2 objects inits in layouts.cpp
> > >
> > > CLayPGMString
> > > minTag(minTagData,strMin,true,CLayPGMString::XSMALL); 
> > > CLayPGMString
> > > maxTag(maxTagData,strMax,true,CLayPGMString::XSMALL);
> > >
> > > strMin and strMax params are pointers to strings in PROGMEM, if i
> > >  replace it with zeros like
> > >
> > > CLayPGMString minTag(minTagData,0,true,CLayPGMString::XSMALL); 
> > > CLayPGMString maxTag(maxTagData,0,true,CLayPGMString::XSMALL);
> > >
> > > program starts again.
> > >
> > > Other important thing noted is, when I initialise those objects
> > > in file range with their default, empty constructors and then set
> > > needed pointers at run time (for example right after main()
> > > function) everything works too. I ran out of ideas what could be
> > > wrong, maybe wrong code, I'm open to any suggestions.
> > >
> > > I'm using avr-gcc-4.5.2 on gentoo linux, also checked on stable
> > > 4.4 and it behaves exactly the same way.
> > >
> > > Marcin
> >
> > Do you see r20 used in one of the functions? Reminds me of 
> > http://gcc.gnu.org/PR45263 which is not yet backported to avr-gcc <
> > 4.6
> >
> > Johann
>
> Hej Johann,
>
> I'm not sure if i checked it correctly, I've opened .lss file 
> corresponding to my program and yes, there are some r20 operations in
>  this function.
>
> Excuse me my lack of knowledge of low lvl stuff, but You think this 
> might cause the problem?

That depends on the hardware you use. The problem will not occur on 
devices <= 64 kib flash. Look at the code again. In the startup code 
that runs before main you might see use of r20 around calls to you 
function. Note that these calls will be indirect, so searching for 
symbol will not help. Using r20 that way in startup can cause problems 
because is is callee-used register and the callee can clobber it, 
leaving its content in a mess in startup code.

> Marcin

Johann