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

[Georg-Johann Lay]

Marcin S schrieb:
> 2011/6/11 Georg-Johann Lay <address@hidden>:
> > 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
>
> Hi, It's atmega128, so r20 still is a main suspect.
>
> > Note that these calls will be indirect, so searching for symbol
> > will not help.
>
> Umm, then I'm afraid I dont know how to check it.
>
> Btw. I tried to confirm this thinking by building 4.6.1 avr-gcc but i
> think its buggy atm (dwarf2 bug) and i am unable to build any

Yes, that's PR48459: DWARF is unusable in current 4.6 and 4.7, so using 
DWARF or configuring with --with-dwarf2 will abort.

If you build the compiler on your own, you can simply copy 
./gcc/config/avr/libgcc.S
from 4.6 or 4.7 into your 4.5 sources. Or you can build 4.6 without 
dwarf and copy the generated libgcc.a's in respective places in your 
installed compiler (no matter if win32 or linux).

> project with it. I'll wait till it will be usable and let You know.
>
> Marcin.